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Vella, Ryan, Matthew Forrest, Jos Lelieveld e Holger Tost. "Isoprene and monoterpene simulations using the chemistry–climate model EMAC (v2.55) with interactive vegetation from LPJ-GUESS (v4.0)". Geoscientific Model Development 16, n. 3 (3 febbraio 2023): 885–906. http://dx.doi.org/10.5194/gmd-16-885-2023.
Testo completoAbstract (sommario):
Abstract. Earth system models (ESMs) integrate previously separate models of the ocean, atmosphere and vegetation into one comprehensive modelling system enabling the investigation of interactions between different components of the Earth system. Global isoprene and monoterpene emissions from terrestrial vegetation, which represent the most important source of volatile organic compounds (VOCs) in the Earth system, need to be included in global and regional chemical transport models given their major chemical impacts on the atmosphere. Due to the feedback of vegetation activity involving interactions with weather and climate, a coupled modelling system between vegetation and atmospheric chemistry is recommended to address the fate of biogenic volatile organic compounds (BVOCs). In this work, further development in linking LPJ-GUESS, a global dynamic vegetation model, to the atmospheric-chemistry-enabled atmosphere–ocean general circulation model EMAC is presented. New parameterisations are included to calculate the foliar density and leaf area density (LAD) distribution from LPJ-GUESS information. The new vegetation parameters are combined with existing LPJ-GUESS output (i.e. leaf area index and cover fractions) and used in empirically based BVOC modules in EMAC. Estimates of terrestrial BVOC emissions from EMAC's submodels ONEMIS and MEGAN are evaluated using (1) prescribed climatological vegetation boundary conditions at the land–atmosphere interface and (2) dynamic vegetation states calculated in LPJ-GUESS (replacing the “offline” vegetation inputs). LPJ-GUESS-driven global emission estimates for isoprene and monoterpenes from the submodel ONEMIS were 546 and 102 Tg yr−1, respectively. MEGAN determines 657 and 55 Tg of isoprene and monoterpene emissions annually. The new vegetation-sensitive BVOC fluxes in EMAC are in good agreement with emissions from the semi-process-based module in LPJ-GUESS. The new coupled system is used to evaluate the temperature and vegetation sensitivity of BVOC fluxes in doubling CO2 scenarios. This work provides evidence that the new coupled model yields suitable estimates for global BVOC emissions that are responsive to vegetation dynamics. It is concluded that the proposed model set-up is useful for studying land–biosphere–atmosphere interactions in the Earth system.
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Yoshioka, H. "Vegetation Isoline Equations for an Atmosphere–Canopy–Soil System". IEEE Transactions on Geoscience and Remote Sensing 42, n. 1 (gennaio 2004): 166–75. http://dx.doi.org/10.1109/tgrs.2003.817793.
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Port, U., e M. Claussen. "Stability of the vegetation–atmosphere system in the early Eocene climate". Climate of the Past Discussions 11, n. 3 (5 maggio 2015): 1551–78. http://dx.doi.org/10.5194/cpd-11-1551-2015.
Testo completoAbstract (sommario):
Abstract. We explore the stability of the atmosphere–vegetation system in the warm, almost ice-free early Eocene climate and in the interglacial, pre-industrial climate by analysing the dependence of the system on the initial vegetation cover. The Earth system model of the Max Planck Institute for Meteorology is initialised with either dense forests or bare deserts on all continents. Starting with desert continents, an extended desert remains in Central Asia in early Eocene climate. Starting with dense forest coverage, this desert is much smaller because the initially dense vegetation cover enhances water recycling in Central Asia relative to the simulation with initial deserts. With a smaller Asian desert, the Asian monsoon is stronger than in the case with a larger desert. The stronger Asian monsoon shifts the global tropical circulation leading to coastal subtropical deserts in North and South America which are significantly larger than with a large Asian desert. This result indicates a global teleconnection of the vegetation cover in several regions. In present-day climate, a bi-stability of the atmosphere–vegetation system is found for Northern Africa only. A global teleconnection of bi-stabilities in several regions is absent highlighting that the stability of the vegetation–atmosphere system depends on climatic and tectonic boundary conditions.
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Kleidon, A., K. Fraedrich e C. Low. "Multiple steady-states in the terrestrial atmosphere-biosphere system: a result of a discrete vegetation classification?" Biogeosciences 4, n. 5 (28 agosto 2007): 707–14. http://dx.doi.org/10.5194/bg-4-707-2007.
Testo completoAbstract (sommario):
Abstract. Multiple steady states in the atmosphere-biosphere system can arise as a consequence of interactions and positive feedbacks. While atmospheric conditions affect vegetation productivity in terms of available light, water, and heat, different levels of vegetation productivity can result in differing energy- and water partitioning at the land surface, thereby leading to different atmospheric conditions. Here we investigate the emergence of multiple steady states in the terrestrial atmosphere-biosphere system and focus on the role of how vegetation is represented in the model: (i) in terms of a few, discrete vegetation classes, or (ii) a continuous representation. We then conduct sensitivity simulations with respect to initial conditions and to the number of discrete vegetation classes in order to investigate the emergence of multiple steady states. We find that multiple steady states occur in our model only if vegetation is represented by a few vegetation classes. With an increased number of classes, the difference between the number of multiple steady states diminishes, and disappears completely in our model when vegetation is represented by 8 classes or more. Despite the convergence of the multiple steady states into a single one, the resulting climate-vegetation state is nevertheless less productive when compared to the emerging state associated with the continuous vegetation parameterization. We conclude from these results that the representation of vegetation in terms of a few, discrete vegetation classes can result (a) in an artificial emergence of multiple steady states and (b) in a underestimation of vegetation productivity. Both of these aspects are important limitations to be considered when global vegetation-atmosphere models are to be applied to topics of global change.
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Kleidon, A., K. Fraedrich e C. Low. "Multiple steady-states in the terrestrial atmosphere-biosphere system: a result of a discrete vegetation classification?" Biogeosciences Discussions 4, n. 1 (22 febbraio 2007): 687–705. http://dx.doi.org/10.5194/bgd-4-687-2007.
Testo completoAbstract (sommario):
Abstract. Multiple steady states in the atmosphere-biosphere system can arise as a consequence of interactions and positive feedbacks. While atmospheric conditions affect vegetation productivity in terms of available light, water, and heat, different levels of vegetation productivity can result in differing energy- and water partitioning at the land surface, thereby leading to different atmospheric conditions. Here we investigate the emergence of multiple steady states in the terrestrial atmosphere-biosphere system and focus on the role of how vegetation is represented in the model: (i) in terms of a few, discrete vegetation classes, or (ii) a continuous representation. We then conduct sensitivity simulations with respect to initial conditions and to the number of discrete vegetation classes in order to investigate the emergence of multiple steady states. We find that multiple steady states occur in our model only if vegetation is represented by a few vegetation classes. With an increased number of classes, the difference between the number of multiple steady states diminishes, and disappears completely in our model when vegetation is represented by 8 classes or more. Despite the convergence of the multiple steady states into a single one, the resulting climate-vegetation state is nevertheless less productive when compared to the emerging state associated with the continuous vegetation parameterization. We conclude from these results that the representation of vegetation in terms of a few, discrete vegetation classes can result (a) in an artificial emergence of multiple steady states and (b) in a underestimation of vegetation productivity. Both of these aspects are important limitations to be considered when global vegetation-atmosphere models are to be applied to topics of global change.
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Wang, Fuyao, Michael Notaro, Zhengyu Liu e Guangshan Chen. "Observed Local and Remote Influences of Vegetation on the Atmosphere across North America Using a Model-Validated Statistical Technique That First Excludes Oceanic Forcings*". Journal of Climate 27, n. 1 (1 gennaio 2014): 362–82. http://dx.doi.org/10.1175/jcli-d-13-00080.1.
Testo completoAbstract (sommario):
Abstract The observed local and nonlocal influences of vegetation on the atmosphere across North America are quantified after first removing the oceanic impact. The interaction between vegetation and the atmosphere is dominated by forcing from the atmosphere, making it difficult to extract the forcing from vegetation. Furthermore, the atmosphere is not only influenced by vegetation but also the oceans, so in order to extract the vegetation impact, the oceanic forcing must first be excluded. This study identified significant vegetation impact in two climatically and ecologically unique regions: the North American monsoon region (NAMR) and the North American boreal forest (NABF). A multivariate statistical method, a generalized equilibrium feedback assessment, is applied to extract vegetation influence on the atmosphere. The statistical method is validated using a dynamical experiment for the NAMR in a fully coupled climate model, the Community Climate System Model, version 3.5 (CCSM3.5). The observed influence of NAMR vegetation on the atmosphere peaks in June–August and is primarily attributed to both roughness and hydrological feedbacks. Elevated vegetation amount increases evapotranspiration and surface roughness, which leads to a local decline in sea level pressure and generates an atmospheric teleconnection response. This atmospheric response leads to moister and cooler (drier and warmer) conditions over the western and central United States (Gulf states). The observed influence of the NABF on the atmosphere peaks in March–May, related to a thermal feedback. Enhanced vegetation greenness increases the air temperature locally. The atmosphere tends to form a positive Pacific–North American (PNA)-like pattern, and this anomalous atmospheric circulation and associated moisture advection lead to moister (drier) conditions in the western (eastern) United States.
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Yang, Peiqi, Wout Verhoef e Christiaan van der van der Tol. "Unified Four-Stream Radiative Transfer Theory in the Optical-Thermal Domain with Consideration of Fluorescence for Multi-Layer Vegetation Canopies". Remote Sensing 12, n. 23 (28 novembre 2020): 3914. http://dx.doi.org/10.3390/rs12233914.
Testo completoAbstract (sommario):
Vegetation radiative transfer models (RTMs) are important tools to understand biosphere-atmosphere interactions. The four-stream theory has been successfully applied to solve the radiative transfer problems in homogeneous canopies for both incident solar radiation, thermal and fluorescence emission since 1984. In this note, we describe the development of a unified radiative transfer theory for optical scattering, thermal and fluorescence emission in multi-layer vegetation canopy, and provide a detailed mathematical derivation for the fluxes inside and leaving the canopy. This theory can be used to develop vegetation models for remote sensing applications and plant physiological processes, such as photosynthesis and transpiration. It can also be used to solve the radiative transfer problems in soil-water, soil-water-atmosphere, or soil-vegetation-atmosphere ensembles, besides the soil-vegetation system presented in the note.
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Calvet, Jean-Christophe, Patricia de Rosnay e Stephen G. Penny. "Editorial for the Special Issue “Assimilation of Remote Sensing Data into Earth System Models”". Remote Sensing 11, n. 18 (19 settembre 2019): 2177. http://dx.doi.org/10.3390/rs11182177.
Testo completoAbstract (sommario):
This Special Issue is a collection of papers reporting research on various aspects of coupled data assimilation in Earth system models. It includes contributions presenting recent progress in ocean–atmosphere, land–atmosphere, and soil–vegetation data assimilation.
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Dekker, S. C., H. J. de Boer, V. Brovkin, K. Fraedrich, M. J. Wassen e M. Rietkerk. "Biogeophysical feedbacks trigger shifts in the modelled vegetation-atmosphere system at multiple scales". Biogeosciences 7, n. 4 (12 aprile 2010): 1237–45. http://dx.doi.org/10.5194/bg-7-1237-2010.
Testo completoAbstract (sommario):
Abstract. Terrestrial vegetation influences climate by modifying the radiative-, momentum-, and hydrologic-balance. This paper contributes to the ongoing debate on the question whether positive biogeophysical feedbacks between vegetation and climate may lead to multiple equilibria in vegetation and climate and consequent abrupt regime shifts. Several modelling studies argue that vegetation-climate feedbacks at local to regional scales could be strong enough to establish multiple states in the climate system. An Earth Model of Intermediate Complexity, PlaSim, is used to investigate the resilience of the climate system to vegetation disturbance at regional to global scales. We hypothesize that by starting with two extreme initialisations of biomass, positive vegetation-climate feedbacks will keep the vegetation-atmosphere system within different attraction domains. Indeed, model integrations starting from different initial biomass distributions diverged to clearly distinct climate-vegetation states in terms of abiotic (precipitation and temperature) and biotic (biomass) variables. Moreover, we found that between these states there are several other steady states which depend on the scale of perturbation. From here global susceptibility maps were made showing regions of low and high resilience. The model results suggest that mainly the boreal and monsoon regions have low resiliences, i.e. instable biomass equilibria, with positive vegetation-climate feedbacks in which the biomass induced by a perturbation is further enforced. The perturbation did not only influence single vegetation-climate cell interactions but also caused changes in spatial patterns of atmospheric circulation due to neighbouring cells constituting in spatial vegetation-climate feedbacks. Large perturbations could trigger an abrupt shift of the system towards another steady state. Although the model setup used in our simulation is rather simple, our results stress that the coupling of feedbacks at multiple scales in vegetation-climate models is essential and urgent to understand the system dynamics for improved projections of ecosystem responses to anthropogenic changes in climate forcing.
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Milcu, Alexandru, Martin Lukac, Jens-Arne Subke, Pete Manning, Andreas Heinemeyer, Dennis Wildman, Robert Anderson e Phil Ineson. "Biotic carbon feedbacks in a materially closed soil–vegetation–atmosphere system". Nature Climate Change 2, n. 4 (11 marzo 2012): 281–84. http://dx.doi.org/10.1038/nclimate1448.
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Delire, Christine, Nathalie de Noblet-Ducoudré, Adriana Sima e Isabelle Gouirand. "Vegetation Dynamics Enhancing Long-Term Climate Variability Confirmed by Two Models". Journal of Climate 24, n. 9 (1 maggio 2011): 2238–57. http://dx.doi.org/10.1175/2010jcli3664.1.
Testo completoAbstract (sommario):
Abstract Two different coupled climate–vegetation models, the Community Climate Model version 3 coupled to the Integrated Biosphere Simulator (CCM3–IBIS) and the Laboratoire de Météorologie Dynamique’s climate model coupled to the Organizing Carbon and Hydrology in Dynamic Ecosystems model (LMDz–ORCHIDEE), are used to study the effects of vegetation dynamics on climate variability. Two sets of simulations of the preindustrial climate are performed using fixed climatological sea surface temperatures: one set taking into account vegetation cover dynamics and the other keeping the vegetation cover fixed. Spectral analysis of the simulated precipitation and temperature over land shows that for both models the interactions between vegetation dynamics and the atmosphere enhance the low-frequency variability of the biosphere–atmosphere system at time scales ranging from a few years to a century. Despite differences in the magnitude of the signal between the two models, this confirms that vegetation dynamics introduces a long-term memory into the climate system by slowly modifying the physical characteristics of the land surface (albedo, roughness evapotranspiration). Unrealistic modeled feedbacks between the vegetation and the atmosphere would cast doubts on this result. The simulated feedback processes in the models used in this work are compared to the observed using a recently developed statistical approach. The models simulate feedbacks of the right sign and order of magnitude over large regions of the globe: positive temperature feedback in the mid- to high latitudes, negative feedback in semiarid regions, and positive precipitation feedback in semiarid regions. The models disagree in the tropics, where there is no statistical significance in the observations. The realistic modeled vegetation–atmosphere feedback gives us confidence that the vegetation dynamics enhancement of the long-term climate variability is not a model artifact.
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Liston, Glen E., e Christopher A. Hiemstra. "Representing Grass– and Shrub–Snow–Atmosphere Interactions in Climate System Models". Journal of Climate 24, n. 8 (15 aprile 2011): 2061–79. http://dx.doi.org/10.1175/2010jcli4028.1.
Testo completoAbstract (sommario):
Abstract A vegetation-protruding-above-snow parameterization for earth system models was developed to improve energy budget calculations of interactions among vegetation, snow, and the atmosphere in nonforested areas. These areas include shrublands, grasslands, and croplands, which represent 68% of the seasonally snow-covered Northern Hemisphere land surface (excluding Greenland). Snow depth observations throughout nonforested areas suggest that mid- to late-winter snowpack depths are often comparable or lower than the vegetation heights. As a consequence, vegetation protruding above the snow cover has an important impact on snow-season surface energy budgets. The protruding vegetation parameterization uses disparate energy balances for snow-covered and protruding vegetation fractions of each model grid cell, and fractionally weights these fluxes to define grid-average quantities. SnowModel, a spatially distributed snow-evolution modeling system, was used to test and assess the parameterization. Simulations were conducted during the winters of 2005/06 and 2006/07 for conditions of 1) no protruding vegetation (the control) and 2) with protruding vegetation. The spatial domain covered Colorado, Wyoming, and portions of the surrounding states; 81% of this area is nonforested. The surface net radiation, energy, and moisture fluxes displayed considerable differences when protruding vegetation was included. For shrubs, the net radiation, sensible, and latent fluxes changed by an average of 12.7, 6.9, and −22.7 W m−2, respectively. For grass and crops, these fluxes changed by an average of 6.9, −0.8, and −7.9 W m−2, respectively. Daily averaged flux changes were as much as 5 times these seasonal averages. As such, the new parameterization represents a major change in surface flux calculations over more simplistic and less physically realistic approaches.
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Claussen, Martin, Victor Brovkin, Andrey Ganopolski, Claudia Kubatzki e Vladimir Petoukhov. "Modelling global terrestrial vegetation–climate interaction". Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 353, n. 1365 (29 gennaio 1998): 53–63. http://dx.doi.org/10.1098/rstb.1998.0190.
Testo completoAbstract (sommario):
By coupling an atmospheric general circulation model asynchronously with an equilibrium vegetation model, manifold equilibrium solutions of the atmosphere–biosphere system have been explored. It is found that under present–day conditions of the Earth's orbital parameters and sea–surface temperatures, two stable equilibria of vegetation patterns are possible: one corresponding to present–day sparse vegetation in the Sahel, the second solution yielding savannah which extends far into the south–western part of the Sahara. A similar picture is obtained for conditions during the last glacial maximum (21 000 years before present (BP)). For the mid–Holocene (6000 years BP), however, the model finds only one solution: the green Sahara. We suggest that this intransitive behaviour of the atmosphere–biosphere is related to a westward shift of the Hadley–Walker circulation. A conceptual model of atmosphere–vegetation dynamics is used to interpret the bifurcation as well as its change in terms of stability theory.
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Chylek, P., J. Li, M. K. Dubey, M. Wang e G. Lesins. "Observed and model simulated 20th century Arctic temperature variability: Canadian Earth System Model CanESM2". Atmospheric Chemistry and Physics Discussions 11, n. 8 (15 agosto 2011): 22893–907. http://dx.doi.org/10.5194/acpd-11-22893-2011.
Testo completoAbstract (sommario):
Abstract. We present simulations of the 20th century Arctic temperature anomaly from the second generation Canadian Earth System Model (CanESM2). The new model couples together an atmosphere-ocean general circulation model, a land-vegetation model and terrestrial and oceanic interactive carbon cycle. It simulates well the observed 20th century Arctic temperature variability that includes the early and late 20th century warming periods and the intervening 1940–1970 period of substantial cooling. The addition of the land-vegetation model and the terrestrial and oceanic interactive carbon cycle to the coupled atmosphere-ocean model improves the agreement with observations from 1900–1970, however, it increases the overestimate of the post 1970 warming. In contrast the older generation coupled atmosphere-ocean general circulation models Canadian CanCM3 and NCAR/LANL CCSM3, used in the IPCC 2007 climate change assessment report, overestimate the rate of the 20th century Arctic warming by factor of two to three and they are unable to reproduce the observed 20th century Arctic climate variability.
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Curdt, Constanze, Dirk Hoffmeister, Guido Waldhoff, Christian Jekel e Georg Bareth. "Scientific Research Data Management for Soil-Vegetation-Atmosphere Data – The TR32DB". International Journal of Digital Curation 7, n. 2 (23 ottobre 2012): 68–80. http://dx.doi.org/10.2218/ijdc.v7i2.208.
Testo completoAbstract (sommario):
The implementation of a scientific research data management system is an important task within long-term, interdisciplinary research projects. Besides sustainable storage of data, including accurate descriptions with metadata, easy and secure exchange and provision of data is necessary, as well as backup and visualisation. The design of such a system poses challenges and problems that need to be solved.This paper describes the practical experiences gained by the implementation of a scientific research data management system, established in a large, interdisciplinary research project with focus on Soil-Vegetation-Atmosphere Data.
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CLAUSSEN, MARTIN. "On multiple solutions of the atmosphere-vegetation system in present-day climate". Global Change Biology 4, n. 5 (giugno 1998): 549–59. http://dx.doi.org/10.1046/j.1365-2486.1998.00122.x.
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Claussen, Martin. "On multiple solutions of the atmosphere–vegetation system in present‐day climate". Global Change Biology 4, n. 5 (giugno 1998): 549–59. http://dx.doi.org/10.1046/j.1365-2486.1998.t01-1-00122.x.
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Wang, Weile, Bruce T. Anderson, Dara Entekhabi, Dong Huang, Yin Su, Robert K. Kaufmann e Ranga B. Myneni. "Intraseasonal Interactions between Temperature and Vegetation over the Boreal Forests". Earth Interactions 11, n. 18 (1 dicembre 2007): 1–30. http://dx.doi.org/10.1175/ei219.1.
Testo completoAbstract (sommario):
Abstract This paper uses statistical and analytical techniques to investigate intraseasonal interactions between temperature and vegetation [surrogated by the normalized difference vegetation index (NDVI)] over the boreal forests. Results indicate that interactions between the two fields may be approximated as a coupled second-order system, in which the variability of NDVI and temperature of the current month is significantly regulated by lagged NDVI anomalies from the preceding two months. In particular, the influence from the one-month lagged NDVI anomalies upon both temperature and vegetation variability is generally positive, but the influence from the second-month lagged NDVI anomalies is often negative. Such regulations lead to an intrinsic oscillatory variability of vegetation at growing-season time scales across the study domain. The regulation of temperature variability by NDVI anomalies is most significant over interior Asia (Siberia), suggesting strong vegetation–atmosphere couplings over these regions. Physical mechanisms for these statistical results are investigated further with a stochastic model. The model suggests that the oscillatory variability of the temperature–NDVI system may reflect the dynamic adjustments between the two fields as they maintain a thermal balance within the soil and lower boundary layer of the atmosphere; the particular role vegetation plays in this scenario is mainly to dissipate heat and therefore reduce surface temperatures.
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Wilhelm, C., D. Rechid e D. Jacob. "Interactive coupling of regional atmosphere with biosphere in the new generation regional climate system model REMO-iMOVE". Geoscientific Model Development 7, n. 3 (6 giugno 2014): 1093–114. http://dx.doi.org/10.5194/gmd-7-1093-2014.
Testo completoAbstract (sommario):
Abstract. The main objective of this study is the coupling of the regional climate model REMO with a new land surface scheme including dynamic vegetation phenology, and the evaluation of the new model version called REMO with interactive MOsaic-based VEgetation: REMO-iMOVE. First, we focus on the documentation of the technical aspects of the new model constituents and the coupling mechanism. The representation of vegetation in iMOVE is based on plant functional types (PFTs). Their geographical distribution is prescribed to the model which can be derived from different land surface data sets. Here, the PFT distribution is derived from the GLOBCOVER 2000 data set which is available on 1 km × 1 km horizontal resolution. Plant physiological processes like photosynthesis, respiration and transpiration are incorporated into the model. The vegetation modules are fully coupled to atmosphere and soil. In this way, plant physiological activity is directly driven by atmospheric and soil conditions at the model time step (two minutes to some seconds). In turn, the vegetation processes and properties influence the exchange of substances, energy and momentum between land and atmosphere. With the new coupled regional model system, dynamic feedbacks between vegetation, soil and atmosphere are represented at regional to local scale. In the evaluation part, we compare simulation results of REMO-iMOVE and of the reference version REMO2009 to multiple observation data sets of temperature, precipitation, latent heat flux, leaf area index and net primary production, in order to investigate the sensitivity of the regional model to the new land surface scheme and to evaluate the performance of both model versions. Simulations for the regional model domain Europe on a horizontal resolution of 0.44° had been carried out for the time period 1995–2005, forced with ECMWF ERA-Interim reanalyses data as lateral boundary conditions. REMO-iMOVE is able to simulate the European climate with the same quality as the parent model REMO2009. Differences in near-surface climate parameters can be restricted to some regions and are mainly related to the new representation of vegetation phenology. The seasonal and interannual variations in growth and senescence of vegetation are captured by the model. The net primary productivity lies in the range of observed values for most European regions. This study reveals the need for implementing vertical soil water dynamics in order to differentiate the access of plants to water due to different rooting depths. This gets especially important if the model will be used in dynamic vegetation studies.
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Brovkin, Victor, Martin Claussen, Vladimir Petoukhov e Andrey Ganopolski. "On the stability of the atmosphere-vegetation system in the Sahara/Sahel region". Journal of Geophysical Research: Atmospheres 103, n. D24 (1 dicembre 1998): 31613–24. http://dx.doi.org/10.1029/1998jd200006.
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Zeng, Xiaodong, Aihui Wang, Qingcun Zeng, Robert E. Dickinson, Xubin Zeng e Samuel S. P. Shen. "Intermediately complex models for the hydrological interactions in the atmosphere-vegetation-soil system". Advances in Atmospheric Sciences 23, n. 1 (gennaio 2006): 127–40. http://dx.doi.org/10.1007/s00376-006-0013-6.
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Devaraju, N., L. Cao, G. Bala, K. Caldeira e R. Nemani. "A model investigation of vegetation-atmosphere interactions on a millennial timescale". Biogeosciences 8, n. 12 (15 dicembre 2011): 3677–86. http://dx.doi.org/10.5194/bg-8-3677-2011.
Testo completoAbstract (sommario):
Abstract. A terrestrial biosphere model with dynamic vegetation capability, Integrated Biosphere Simulator (IBIS2), coupled to the NCAR Community Atmosphere Model (CAM2) is used to investigate the multiple climate-forest equilibrium states of the climate system. A 1000-year control simulation and another 1000-year land cover change simulation that consisted of global deforestation for 100 years followed by re-growth of forests for the subsequent 900 years were performed. After several centuries of interactive climate-vegetation dynamics, the land cover change simulation converged to essentially the same climate state as the control simulation. However, the climate system takes about a millennium to reach the control forest state. In the absence of deep ocean feedbacks in our model, the millennial time scale for converging to the original climate state is dictated by long time scales of the vegetation dynamics in the northern high latitudes. Our idealized modeling study suggests that the equilibrium state reached after complete global deforestation followed by re-growth of forests is unlikely to be distinguishable from the control climate. The real world, however, could have multiple climate-forest states since our modeling study is unlikely to have represented all the essential ecological processes (e.g. altered fire regimes, seed sources and seedling establishment dynamics) for the re-establishment of major biomes.
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Devaraju, N., L. Cao, G. Bala, K. Caldeira e R. Nemani. "A model investigation of vegetation-atmosphere interactions on a millennial timescale". Biogeosciences Discussions 8, n. 4 (29 agosto 2011): 8761–80. http://dx.doi.org/10.5194/bgd-8-8761-2011.
Testo completoAbstract (sommario):
Abstract. A terrestrial biosphere model with dynamic vegetation capability, Integrated Biosphere Simulator (IBIS), coupled to the NCAR Community Atmosphere Model (CAM2) is used to investigate the multiple climate-forest equilibrium states of the climate system. A 1000-yr control simulation and another 1000-yr land cover change simulation that consisted of global deforestation for 100 yr followed by re-growth of forests for the subsequent 900 yr were performed. After several centuries of interactive climate-vegetation dynamics, the land cover change simulation converged to essentially the same climate state as the control simulation. However, the climate system takes about a millennium to reach the control forest state. In the absence of deep ocean feedbacks in our model, the millennial time scale for converging to the original climate state is dictated by long time scales of the terrestrial carbon stocks, biomass and soil carbon. Our idealized modeling study suggests that the equilibrium state reached after complete global deforestation followed by re-growth of forests is unlikely to be distinguishable from the control climate. The real world, however, could have multiple climate-forest states since our modeling study is unlikely to have represented all the essential ecological processes (e.g. altered fire regimes, seed sources and seedling establishment dynamics) for the re-establishment of major biomes.
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Laguë, Marysa M., Gordon B. Bonan e Abigail L. S. Swann. "Separating the Impact of Individual Land Surface Properties on the Terrestrial Surface Energy Budget in both the Coupled and Uncoupled Land–Atmosphere System". Journal of Climate 32, n. 18 (12 agosto 2019): 5725–44. http://dx.doi.org/10.1175/jcli-d-18-0812.1.
Testo completoAbstract (sommario):
Abstract Changes in the land surface can drive large responses in the atmosphere on local, regional, and global scales. Surface properties control the partitioning of energy within the surface energy budget to fluxes of shortwave and longwave radiation, sensible and latent heat, and ground heat storage. Changes in surface energy fluxes can impact the atmosphere across scales through changes in temperature, cloud cover, and large-scale atmospheric circulation. We test the sensitivity of the atmosphere to global changes in three land surface properties: albedo, evaporative resistance, and surface roughness. We show the impact of changing these surface properties differs drastically between simulations run with an offline land model, compared to coupled land–atmosphere simulations that allow for atmospheric feedbacks associated with land–atmosphere coupling. Atmospheric feedbacks play a critical role in defining the temperature response to changes in albedo and evaporative resistance, particularly in the extratropics. More than 50% of the surface temperature response to changing albedo comes from atmospheric feedbacks in over 80% of land areas. In some regions, cloud feedbacks in response to increased evaporative resistance result in nearly 1 K of additional surface warming. In contrast, the magnitude of surface temperature responses to changes in vegetation height are comparable between offline and coupled simulations. We improve our fundamental understanding of how and why changes in vegetation cover drive responses in the atmosphere, and develop understanding of the role of individual land surface properties in controlling climate across spatial scales—critical to understanding the effects of land-use change on Earth’s climate.
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Dekker, S. C., H. J. de Boer, V. Brovkin, K. Fraedrich, M. J. Wassen e M. Rietkerk. "Biogeophysical feedbacks trigger shifts in the modelled climate system at multiple scales". Biogeosciences Discussions 6, n. 6 (25 novembre 2009): 10983–1004. http://dx.doi.org/10.5194/bgd-6-10983-2009.
Testo completoAbstract (sommario):
Abstract. Terrestrial vegetation influences climate by modifying the radiative-, momentum-, and hydrologic-balance. This paper contributes to the ongoing debate on the question whether positive biogeophysical feedbacks between vegetation and climate may lead to multiple equilibria in vegetation and climate and consequent abrupt regime shifts. Several modelling studies argue that vegetation-climate feedbacks at local to regional scales could be strong enough to establish multiple states in the climate system. An Earth Model of Intermediate Complexity, PlaSim, is used to investigate the resilience of the climate system to vegetation disturbance at regional to global scales. We hypothesize that by starting with two extreme initialisations of biomass, positive vegetation-climate feedbacks will keep the vegetation-atmosphere system within different attraction domains. Indeed, model integrations starting from different initial biomass distributions diverged to clearly distinct climate-vegetation states in terms of abiotic (precipitation and temperature) and biotic (biomass) variables. Moreover, we found that between these states there are several other steady states which depend on the scale of perturbation. From here global susceptibility maps were made showing regions of low and high resilience. The model results suggest that mainly the boreal and monsoon regions have low resiliences, i.e. instable biomass equilibria, with positive vegetation-climate feedbacks in which the biomass induced by a perturbation is further enforced. The perturbation did not only influence single vegetation-climate cell interactions but also caused changes in spatial patterns of atmospheric circulation due to neighbouring cells constituting in spatial vegetation-climate feedbacks. Large perturbations could trigger an abrupt shift of the system towards another steady state. Although the model setup used in our simulation is rather simple, our results stress that the coupling of feedbacks at multiple scales in vegetation-climate models is essential and urgent to understand the system dynamics for improved projections of ecosystem responses to anthropogenic changes in climate forcing.
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Subin, Z. M., W. J. Riley, J. Jin, D. S. Christianson, M. S. Torn e L. M. Kueppers. "Ecosystem Feedbacks to Climate Change in California: Development, Testing, and Analysis Using a Coupled Regional Atmosphere and Land Surface Model (WRF3–CLM3.5)". Earth Interactions 15, n. 15 (1 maggio 2011): 1–38. http://dx.doi.org/10.1175/2010ei331.1.
Testo completoAbstract (sommario):
Abstract A regional atmosphere model [Weather Research and Forecasting model version 3 (WRF3)] and a land surface model [Community Land Model, version 3.5 (CLM3.5)] were coupled to study the interactions between the atmosphere and possible future California land-cover changes. The impact was evaluated on California’s climate of changes in natural vegetation under climate change and of intentional afforestation. The ability of WRF3 to simulate California’s climate was assessed by comparing simulations by WRF3–CLM3.5 and WRF3–Noah to observations from 1982 to 1991. Using WRF3–CLM3.5, the authors performed six 13-yr experiments using historical and future large-scale climate boundary conditions from the Geophysical Fluid Dynamics Laboratory Climate Model version 2.1 (GFDL CM2.1). The land-cover scenarios included historical and future natural vegetation from the Mapped Atmosphere-Plant-Soil System-Century 1 (MC1) dynamic vegetation model, in addition to a future 8-million-ha California afforestation scenario. Natural vegetation changes alone caused summer daily-mean 2-m air temperature changes of −0.7° to +1°C in regions without persistent snow cover, depending on the location and the type of vegetation change. Vegetation temperature changes were much larger than the 2-m air temperature changes because of the finescale spatial heterogeneity of the imposed vegetation change. Up to 30% of the magnitude of the summer daily-mean 2-m air temperature increase and 70% of the magnitude of the 1600 local time (LT) vegetation temperature increase projected under future climate change were attributable to the climate-driven shift in land cover. The authors projected that afforestation could cause local 0.2°–1.2°C reductions in summer daily-mean 2-m air temperature and 2.0°–3.7°C reductions in 1600 LT vegetation temperature for snow-free regions, primarily because of increased evapotranspiration. Because some of these temperature changes are of comparable magnitude to those projected under climate change this century, projections of climate and vegetation change in this region need to consider these climate–vegetation interactions.
27
Quevedo, D. I., e F. Francés. "A conceptual dynamic vegetation-soil model for arid and semiarid zones". Hydrology and Earth System Sciences Discussions 4, n. 5 (25 settembre 2007): 3469–99. http://dx.doi.org/10.5194/hessd-4-3469-2007.
Testo completoAbstract (sommario):
Abstract. Plant ecosystems in arid and semiarid zones show high complexity from the point of view of water resources, since they depend on water availability to carry out their vital processes. In these climates, water stress is the main factor controlling vegetation development. The available water in the system results from a water balance where the soil, vegetation and the atmosphere are the key issues; but it is the vegetation which modulates (to a great extent) the total balance of water and the mechanisms of the feedback between soil and atmosphere, being the knowledge about soil moisture quite relevant for assessing available water and, as a consequence, for growth and plants maintenance and the final water balance in the system. A conceptual dynamic vegetation-soil model (CDVSM) for arid and semiarid zones was developed. This model based in a tank type conceptualization represents in a suitable way, for Mediterranean climate, the vegetation responses to soil moisture fluctuations. Two tanks interconnected were considered using the water balance equation and the appropriate dynamic equation for all considered fluxes. The first one corresponds to the interception process done by the vegetation. The second one models the upper soil moisture determination. In this tank parameters are based on soil and vegetation properties. The transpiration of the vegetation is a function of the soil moisture, the vegetation type and the biomass. Once all water state variables are evaluated at each time step, the modifications in the biomass are made as a function of transpiration rate and water stress. Simulations for monoculture of Quercus Coccifera L. were carried out. Results shows that CDVSM is able to represent the vegetation dynamic, reflecting how the monoculture is stabilized around 0.7 of relative biomass, with adaptation to the soil moisture fluctuations in the long term. The model shows the vegetation adaptation to the variability of the climatic conditions, demonstrating how either in the presence or shortage of water, the vegetation regulates its biomass as well as its rate of transpiration trying to minimize the total water stress.
28
Kuchment, L. S., V. N. Demidov e Z. P. Startseva. "Coupled modeling of the hydrological and carbon cycles in the soil–vegetation–atmosphere system". Journal of Hydrology 323, n. 1-4 (maggio 2006): 4–21. http://dx.doi.org/10.1016/j.jhydrol.2005.08.011.
Testo completo
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Zeng, Ning, Katrina Hales e J. David Neelin. "Nonlinear Dynamics in a Coupled Vegetation–Atmosphere System and Implications for Desert–Forest Gradient". Journal of Climate 15, n. 23 (dicembre 2002): 3474–87. http://dx.doi.org/10.1175/1520-0442(2002)015<3474:ndiacv>2.0.co;2.
Testo completo
30
Zhang, Yuan, Devaraju Narayanappa, Philippe Ciais, Wei Li, Daniel Goll, Nicolas Vuichard, Martin G. De Kauwe, Laurent Li e Fabienne Maignan. "Evaluating the vegetation–atmosphere coupling strength of ORCHIDEE land surface model (v7266)". Geoscientific Model Development 15, n. 24 (20 dicembre 2022): 9111–25. http://dx.doi.org/10.5194/gmd-15-9111-2022.
Testo completoAbstract (sommario):
Abstract. Plant transpiration dominates terrestrial latent heat fluxes (LE) and plays a central role in regulating the water cycle and land surface energy budget. However, Earth system models (ESMs) currently disagree strongly on the amount of transpiration, and thus LE, leading to large uncertainties in simulating future climate. Therefore, it is crucial to correctly represent the mechanisms controlling the transpiration in models. At the leaf scale, transpiration is controlled by stomatal regulation, and at the canopy scale, through turbulence, which is a function of canopy structure and wind. The coupling of vegetation to the atmosphere can be characterized by the coefficient Ω. A value of Ω→0 implies a strong coupling of vegetation and the atmosphere, leaving a dominant role to stomatal conductance in regulating water (H2O) and carbon dioxide (CO2) fluxes, while Ω→1 implies a complete decoupling of leaves from the atmosphere, i.e., the transfer of H2O and CO2 is limited by aerodynamic transport. In this study, we investigated how well the land surface model (LSM) Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) (v7266) simulates the coupling of vegetation to the atmosphere by using empirical daily estimates of Ω derived from flux measurements from 90 FLUXNET sites. Our results show that ORCHIDEE generally captures the Ω in forest vegetation types (0.27 ± 0.12) compared with observation (0.26 ± 0.09) but underestimates Ω in grasslands (GRA) and croplands (CRO) (0.25 ± 0.15 for model, 0.33 ± 0.17 for observation). The good model performance in forests is due to compensation of biases in surface conductance (Gs) and aerodynamic conductance (Ga). Calibration of key parameters controlling the dependence of the stomatal conductance to the water vapor deficit (VPD) improves the simulated Gs and Ω estimates in grasslands and croplands (0.28 ± 0.20). To assess the underlying controls of Ω, we applied random forest (RF) models to both simulated and observation-based Ω. We found that large observed Ω are associated with periods of low wind speed, high temperature and low VPD; it is also related to sites with large leaf area index (LAI) and/or short vegetation. The RF models applied to ORCHIDEE output generally agree with this pattern. However, we found that the ORCHIDEE underestimated the sensitivity of Ω to VPD when the VPD is high, overestimated the impact of the LAI on Ω, and did not correctly simulate the temperature dependence of Ω when temperature is high. Our results highlight the importance of observational constraints on simulating the vegetation–atmosphere coupling strength, which can help to improve predictive accuracy of water fluxes in Earth system models.
31
Badger, A. M., e P. A. Dirmeyer. "Climate response to Amazon forest replacement by heterogeneous crop cover". Hydrology and Earth System Sciences Discussions 12, n. 1 (22 gennaio 2015): 879–910. http://dx.doi.org/10.5194/hessd-12-879-2015.
Testo completoAbstract (sommario):
Abstract. Previous modeling studies with atmospheric general circulation models and basic land surface schemes to balance energy and water budgets have shown that by removing the natural vegetation over the Amazon, the region's climate becomes warmer and drier. In this study we use a fully coupled Earth System Model and replace tropical forests by a distribution of six common tropical crops with variable planting dates, physiological parameters and irrigation. There is still general agreement with previous studies as areal averages show a warmer (+1.4 K) and drier (−0.35 mm day−1) climate. Using an interactive crop model with a realistic crop distribution shows that regions of vegetation change experience different responses dependent upon the initial tree coverage and whether the replacement vegetation is irrigated, with seasonal changes synchronized to the cropping season. Areas with initial tree coverage greater than 80% show an increase in coupling with atmosphere after deforestation, suggesting land use change could heighten sensitivity to climate anomalies, while irrigation acts to dampen coupling with atmosphere.
32
Bagley, Justin E., Ankur R. Desai, Paul C. West e Jonathan A. Foley. "A Simple, Minimal Parameter Model for Predicting the Influence of Changing Land Cover on the Land–Atmosphere System+". Earth Interactions 15, n. 29 (1 ottobre 2011): 1–32. http://dx.doi.org/10.1175/2011ei394.1.
Testo completoAbstract (sommario):
Abstract The impacts of changing land cover on the soil–vegetation–atmosphere system are numerous. With the fraction of land used for farming and grazing expected to increase, extensive alterations to land cover such as replacing forests with cropland will continue. Therefore, quantifying the impact of global land-cover scenarios on the biosphere is critical. The Predicting Ecosystem Goods and Services Using Scenarios boundary layer (PegBL) model is a new global soil–vegetation–boundary layer model designed to quantify these impacts and act as a complementary tool to computationally expensive general circulation models and large-eddy simulations. PegBL provides high spatial resolution and inexpensive first-order estimates of land-cover change on the surface energy balance and atmospheric boundary layer with limited input requirements. The model uses a climatological-data-driven land surface model that contains only the physics necessary to accurately reproduce observed seasonal cycles of fluxes and state variables for natural and agricultural ecosystems. A bulk boundary layer model was coupled to the land model to estimate the impacts of changing land cover on the lower atmosphere. The model most realistically simulated surface–atmosphere dynamics and impacts of land-cover change at tropical rain forest and northern boreal forest sites. Further, simple indices to measure the potential impact of land-cover change on boundary layer climate were defined and shown to be dependent on boundary layer dynamics and geographically similar to results from previous studies, which highlighted the impacts of land-cover change on the atmosphere in the tropics and boreal forest.
33
Matsui, Toshihisa, Venkataraman Lakshmi e Eric E. Small. "The Effects of Satellite-Derived Vegetation Cover Variability on Simulated Land–Atmosphere Interactions in the NAMS". Journal of Climate 18, n. 1 (1 gennaio 2005): 21–40. http://dx.doi.org/10.1175/jcli3254.1.
Testo completoAbstract (sommario):
Abstract Substantial evolution of Normalized Difference Vegetation Index (NVDI)-derived vegetation cover (Fg) exists in the southwestern United States and Mexico. The intraseasonal and wet-/dry-year fluctuations of Fg are linked to observed precipitation in the North American monsoon system (NAMS). The manner in which the spatial and temporal variability of Fg influences the land–atmosphere energy and moisture fluxes, and associated likelihood of moist convection in the NAMS regions, is examined. For this, the regional climate model (RCM) is employed, with three different Fg boundary conditions to examine the influence of intraseasonal and wet-/dry-year vegetation variability. Results show that a strong link exists between evaporative fraction (EF), surface temperature, and relative humidity in the boundary layer (BL), which is consistent with a positive soil moisture feedback. However, contrary to expectations, higher Fg does not consistently enhance EF across the NAMS region. This is because the low soil moisture values simulated by the land surface model (LSM) yield high canopy resistance values throughout the monsoon season. As a result, the experiment with the lowest Fg yields the greatest EF and precipitation in the NAMS region, and also modulates regional atmospheric circulation that steers the track of tropical cyclones. In conclusion, the simulated influence of vegetation on land–atmosphere exchanges depends strongly on the canopy stress index parameterized in the LSM. Therefore, a reliable dataset, at appropriate scales, is needed to calibrate transpiration schemes and to assess simulated and realistic vegetation–atmosphere interactions in the NAMS region.
34
Martin, G. M., e R. C. Levine. "The influence of dynamic vegetation on the present-day simulation and future projections of the South Asian summer monsoon in the HadGEM2 family". Earth System Dynamics 3, n. 2 (28 novembre 2012): 245–61. http://dx.doi.org/10.5194/esd-3-245-2012.
Testo completoAbstract (sommario):
Abstract. Various studies have shown the importance of Earth System feedbacks in the climate system and the necessity of including these in models used for making climate change projections. The HadGEM2 family of Met Office Unified Model configurations combines model components which facilitate the representation of many different processes within the climate system, including atmosphere, ocean and sea ice, and Earth System components including the terrestrial and oceanic carbon cycle and tropospheric chemistry. We examine the climatology of the Asian summer monsoon in present-day simulations and in idealised climate change experiments. Members of the HadGEM2 family are used, with a common physical framework (one of which includes tropospheric chemistry and an interactive terrestrial and oceanic carbon cycle), to investigate whether such components affect the way in which the monsoon changes. We focus particularly on the role of interactive vegetation in the simulations from these model configurations. Using an atmosphere-only HadGEM2 configuration, we investigate how the changes in land cover which result from the interaction between the dynamic vegetation and the model systematic rainfall biases affect the Asian summer monsoon, both in the present-day and in future climate projections. We demonstrate that the response of the dynamic vegetation to biases in regional climate, such as lack of rainfall over tropical dust-producing regions, can affect both the present-day simulation and the response to climate change forcing scenarios.
35
Groner, Vivienne P., Thomas Raddatz, Christian H. Reick e Martin Claussen. "Plant functional diversity affects climate–vegetation interaction". Biogeosciences 15, n. 7 (4 aprile 2018): 1947–68. http://dx.doi.org/10.5194/bg-15-1947-2018.
Testo completoAbstract (sommario):
Abstract. We present how variations in plant functional diversity affect climate–vegetation interaction towards the end of the African Humid Period (AHP) in coupled land–atmosphere simulations using the Max Planck Institute Earth system model (MPI-ESM). In experiments with AHP boundary conditions, the extent of the “green” Sahara varies considerably with changes in plant functional diversity. Differences in vegetation cover extent and plant functional type (PFT) composition translate into significantly different land surface parameters, water cycling, and surface energy budgets. These changes have not only regional consequences but considerably alter large-scale atmospheric circulation patterns and the position of the tropical rain belt. Towards the end of the AHP, simulations with the standard PFT set in MPI-ESM depict a gradual decrease of precipitation and vegetation cover over time, while simulations with modified PFT composition show either a sharp decline of both variables or an even slower retreat. Thus, not the quantitative but the qualitative PFT composition determines climate–vegetation interaction and the climate–vegetation system response to external forcing. The sensitivity of simulated system states to changes in PFT composition raises the question how realistically Earth system models can actually represent climate–vegetation interaction, considering the poor representation of plant diversity in the current generation of land surface models.
36
Hong, Seungbum, Venkat Lakshmi e Eric E. Small. "Relationship between Vegetation Biophysical Properties and Surface Temperature Using Multisensor Satellite Data". Journal of Climate 20, n. 22 (15 novembre 2007): 5593–606. http://dx.doi.org/10.1175/2007jcli1294.1.
Testo completoAbstract (sommario):
Abstract Vegetation is an important factor in global climatic variability and plays a key role in the complex interactions between the land surface and the atmosphere. This study focuses on the spatial and temporal variability of vegetation and its relationship with land–atmosphere interactions. The authors have analyzed the vegetation water content (VegWC) from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E), the leaf area index (LAI), the normalized difference vegetation index (NDVI), the land surface temperature (Ts), and the Moderate Resolution Imaging Spectroradiometer (MODIS). Three regions, which have climatically differing characteristics, have been selected: the North America Monsoon System (NAMS) region, the Southern Great Plains (SGP) region, and the Little River Watershed in Tifton, Georgia. Temporal analyses were performed by comparing satellite observations from 2003 and 2004. The introduction of the normalized vegetation water content (NVegWC) derived as the ratio of VegWC and LAI corresponding to the amount of water in individual leaves has been estimated and this yields significant correlation with NDVI and Ts. The analysis of the NVegWC–NDVI relationship in the above listed three regions displays a negative exponential relation, and the Ts–NDVI relationship (TvX relationship) is inversely proportional. The correlation between these variables is higher in arid areas such as the NAMS region, and becomes less correlated in the more humid and more vegetated regions such as the area of eastern Georgia. A land-cover map is used to examine the influence of vegetation types on the vegetation biophysical and surface temperature relationships. The regional distribution of vegetation reflects the relationship between the vegetation biological characteristics of water and the growing environment.
37
Chug, Divyansh, e Francina Dominguez. "Isolating the Observed Influence of Vegetation Variability on the Climate of La Plata River Basin". Journal of Climate 32, n. 14 (24 giugno 2019): 4473–90. http://dx.doi.org/10.1175/jcli-d-18-0677.1.
Testo completoAbstract (sommario):
AbstractThis work aims to isolate and quantify the local and remote biogeophysical influences of slowly varying vegetation variability on the climate of La Plata basin (LPB) in the austral spring season (September–November) using observational records. Past studies have shown strong land–atmosphere coupling in LPB during this season. The analysis uses a 34-yr record (1981–2014) of the modified enhanced vegetation index (EVI2) from the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Vegetation Index and Phenology dataset and the third-generation normalized difference vegetation index (NDVI) from Global Inventory Modeling and Mapping Studies. The dominant patterns of vegetation index variability in space and time are assessed using empirical orthogonal function/principal component analysis over the LPB. The dominant mode in the austral spring is a vegetation dipole, with greening (browning) or positive (negative) vegetation index anomalies in the northeastern (southwestern) part of the basin. Using the stepwise generalized equilibrium feedback assessment (SGEFA), the effect of the vegetation variability on the atmosphere is then isolated. The dominant mode of LPB vegetation variability in austral spring is related to warmer temperatures in the southwest LPB and enhanced precipitation over the central and southern parts of the basin. A mechanism is proposed for the increase in latent heat flux and cooler temperatures in the northeastern LPB due to greening, and the increase in sensible heat flux, warmer temperatures, and decrease in surface pressure in southwestern LPB due to browning. The geostrophic response to this induced pressure gradient leads to anomalous northerly enhancement of moisture-laden winds, deeper penetration of moisture into LPB, and increased precipitation over the central and southern parts of the basin.
38
Martin, G. M., e R. C. Levine. "The influence of dynamic vegetation on the present-day simulation and future projections of the South Asian summer monsoon in the HadGEM2 family". Earth System Dynamics Discussions 3, n. 2 (3 agosto 2012): 759–99. http://dx.doi.org/10.5194/esdd-3-759-2012.
Testo completoAbstract (sommario):
Abstract. Various studies have shown the importance of Earth System feedbacks in the climate system and the necessity of including these in models used for making climate change projections. The HadGEM2 family of Met Office Unified Model configurations combines model components which facilitate the representation of many different processes within the climate system, including atmosphere, ocean and sea ice, and Earth System components including the terrestrial and oceanic carbon cycle and tropospheric chemistry. We examine the climatology of the Asian summer monsoon in present-day simulations and in idealised climate change experiments in which a quadrupling of CO2 is applied as a step change. Members of the HadGEM2 family are used, with a common physical framework, one of which includes tropospheric chemistry and an interactive terrestrial and oceanic carbon cycle, to investigate whether such components affect the way in which the monsoon changes. We focus particularly on the role of interactive vegetation in the simulations from these model configurations. Using an atmosphere-only HadGEM2 configuration, we investigate how the changes in land cover which result from the interaction between the dynamic vegetation and the model systematic rainfall biases affect the Asian summer monsoon, both in the present-day and in future climate projections. We demonstrate that the response of the dynamic vegetation to biases in regional climate, such as lack of rainfall over tropical dust-producing regions, can affect both the present-day simulation and the response to climate change forcing scenarios.
39
Badger, A. M., e P. A. Dirmeyer. "Climate response to Amazon forest replacement by heterogeneous crop cover". Hydrology and Earth System Sciences 19, n. 11 (16 novembre 2015): 4547–57. http://dx.doi.org/10.5194/hess-19-4547-2015.
Testo completoAbstract (sommario):
Abstract. Previous modeling studies with atmospheric general circulation models and basic land surface schemes to balance energy and water budgets have shown that by removing the natural vegetation over the Amazon, the region's climate becomes warmer and drier. In this study we use a fully coupled Earth system model and replace tropical forests by a distribution of six common tropical crops with variable planting dates, physiological parameters and irrigation. There is still general agreement with previous studies as areal averages show a warmer (+1.4 K) and drier (−0.35 mm day−1) climate. Using an interactive crop model with a realistic crop distribution shows that regions of vegetation change experience different responses dependent upon the initial tree coverage and whether the replacement vegetation is irrigated, with seasonal changes synchronized to the cropping season. Areas with initial tree coverage greater than 80 % show an increase in coupling with the atmosphere after deforestation, suggesting land use change could heighten sensitivity to climate anomalies, while irrigation acts to dampen coupling with the atmosphere.
40
Teixeira, João C., Gerd A. Folberth, Fiona M. O'Connor, Nadine Unger e Apostolos Voulgarakis. "Coupling interactive fire with atmospheric composition and climate in the UK Earth System Model". Geoscientific Model Development 14, n. 10 (28 ottobre 2021): 6515–39. http://dx.doi.org/10.5194/gmd-14-6515-2021.
Testo completoAbstract (sommario):
Abstract. Fire constitutes a key process in the Earth system (ES), being driven by climate as well as affecting the climate by changing atmospheric composition and impacting the terrestrial carbon cycle. However, studies on the effects of fires on atmospheric composition, radiative forcing and climate have been limited to date, as the current generation of ES models (ESMs) does not include fully atmosphere–composition–vegetation coupled fires feedbacks. The aim of this work is to develop and evaluate a fully coupled fire–composition–climate ES model. For this, the INteractive Fires and Emissions algoRithm for Natural envirOnments (INFERNO) fire model is coupled to the atmosphere-only configuration of the UK's Earth System Model (UKESM1). This fire–atmosphere interaction through atmospheric chemistry and aerosols allows for fire emissions to influence radiation, clouds and generally weather, which can consequently influence the meteorological drivers of fire. Additionally, INFERNO is updated based on recent developments in the literature to improve the representation of human and/or economic factors in the anthropogenic ignition and suppression of fire. This work presents an assessment of the effects of interactive fire coupling on atmospheric composition and climate compared to the standard UKESM1 configuration that uses prescribed fire emissions. Results show a similar performance when using the fire–atmosphere coupling (the “online” version of the model) when compared to the offline UKESM1 that uses prescribed fire. The model can reproduce observed present-day global fire emissions of carbon monoxide (CO) and aerosols, despite underestimating the global average burnt area. However, at a regional scale, there is an overestimation of fire emissions over Africa due to the misrepresentation of the underlying vegetation types and an underestimation over equatorial Asia due to a lack of representation of peat fires. Despite this, comparing model results with observations of CO column mixing ratio and aerosol optical depth (AOD) show that the fire–atmosphere coupled configuration has a similar performance when compared to UKESM1. In fact, including the interactive biomass burning emissions improves the interannual CO atmospheric column variability and consequently its seasonality over the main biomass burning regions – Africa and South America. Similarly, for aerosols, the AOD results broadly agree with the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic Network (AERONET) observations.
41
Imbach, Pablo, Luis Molina, Bruno Locatelli, Olivier Roupsard, Gil Mahé, Ronald Neilson, Lenin Corrales, Marko Scholze e Philippe Ciais. "Modeling Potential Equilibrium States of Vegetation and Terrestrial Water Cycle of Mesoamerica under Climate Change Scenarios*". Journal of Hydrometeorology 13, n. 2 (1 aprile 2012): 665–80. http://dx.doi.org/10.1175/jhm-d-11-023.1.
Testo completoAbstract (sommario):
Abstract The likelihood and magnitude of the impacts of climate change on potential vegetation and the water cycle in Mesoamerica is evaluated. Mesoamerica is a global biodiversity hotspot with highly diverse topographic and climatic conditions and is among the tropical regions with the highest expected changes in precipitation and temperature under future climate scenarios. The biogeographic soil–vegetation–atmosphere model Mapped Atmosphere Plant Soil System (MAPSS) was used for simulating the integrated changes in leaf area index (LAI), vegetation types (grass, shrubs, and trees), evapotranspiration, and runoff at the end of the twenty-first century. Uncertainty was estimated as the likelihood of changes in vegetation and water cycle under three ensembles of model runs, one for each of the groups of greenhouse gas emission scenarios (low, intermediate, and high emissions), for a total of 136 runs generated with 23 general circulation models (GCMs). LAI is likely to decrease over 77%–89% of the region, depending on climate scenario groups, showing that potential vegetation will likely shift from humid to dry types. Accounting for potential effects of CO2 on water use efficiency significantly decreased impacts on LAI. Runoff will decrease across the region even in areas where precipitation increases (even under increased water use efficiency), as temperature change will increase evapotranspiration. Higher emission scenarios show lower uncertainty (higher likelihood) in modeled impacts. Although the projection spread is high for future precipitation, the impacts of climate change on vegetation and water cycle are predicted with relatively low uncertainty.
42
Zhang, W., C. Jansson, P. A. Miller, B. Smith e P. Samuelsson. "Biogeophysical feedbacks enhance Arctic terrestrial carbon sink in regional Earth system dynamics". Biogeosciences Discussions 11, n. 5 (12 maggio 2014): 6715–54. http://dx.doi.org/10.5194/bgd-11-6715-2014.
Testo completoAbstract (sommario):
Abstract. Continued warming of the Arctic will likely accelerate terrestrial carbon (C) cycling by increasing both uptake and release of C. There are still large uncertainties in modelling Arctic terrestrial ecosystems as a source or sink of C. Most modelling studies assessing or projecting the future fate of C exchange with the atmosphere are based an either stand-alone process-based models or coupled climate–C cycle general circulation models, in either case disregarding biogeophysical feedbacks of land surface changes to the atmosphere. To understand how biogeophysical feedbacks will impact on both climate and C budget over Arctic terrestrial ecosystems, we apply the regional Earth system model RCA-GUESS over the CORDEX-Arctic domain. The model is forced with lateral boundary conditions from an GCMs CMIP5 climate projection under the RCP 8.5 scenario. We perform two simulations with or without interactive vegetation dynamics respectively to assess the impacts of biogeophysical feedbacks. Both simulations indicate that Arctic terrestrial ecosystems will continue to sequester C with an increased uptake rate until 2060s–2070s, after which the C budget will return to a weak C sink as increased soil respiration and biomass burning outpaces increased net primary productivity. The additional C sinks arising from biogeophysical feedbacks are considerable, around 8.5 Gt C, accounting for 22% of the total C sinks, of which 83.5% are located in areas of Arctic tundra. Two opposing feedback mechanisms, mediated by albedo and evapotranspiration changes respectively, contribute to this response. Albedo feedback dominates over winter and spring season, amplifying the near-surface warming by up to 1.35 K in spring, while evapotranspiration feedback dominates over summer exerting the evaporative cooling by up to 0.81 K. Such feedbacks stimulate vegetation growth with an earlier onset of growing-season, leading to compositional changes in woody plants and vegetation redistribution.
43
Wang, Yunfei, Yijian Zeng, Lianyu Yu, Peiqi Yang, Christiaan Van der Tol, Qiang Yu, Xiaoliang Lü, Huanjie Cai e Zhongbo Su. "Integrated modeling of canopy photosynthesis, fluorescence, and the transfer of energy, mass, and momentum in the soil–plant–atmosphere continuum (STEMMUS–SCOPE v1.0.0)". Geoscientific Model Development 14, n. 3 (11 marzo 2021): 1379–407. http://dx.doi.org/10.5194/gmd-14-1379-2021.
Testo completoAbstract (sommario):
Abstract. Root water uptake by plants is a vital process that influences terrestrial energy, water, and carbon exchanges. At the soil, vegetation, and atmosphere interfaces, root water uptake and solar radiation predominantly regulate the dynamics and health of vegetation growth, which can be remotely monitored by satellites, using the soil–plant relationship proxy – solar-induced chlorophyll fluorescence. However, most current canopy photosynthesis and fluorescence models do not account for root water uptake, which compromises their applications under water-stressed conditions. To address this limitation, this study integrated photosynthesis, fluorescence emission, and transfer of energy, mass, and momentum in the soil–plant–atmosphere continuum system, via a simplified 1D root growth model and a resistance scheme linking soil, roots, leaves, and the atmosphere. The coupled model was evaluated with field measurements of maize and grass canopies. The results indicated that the simulation of land surface fluxes was significantly improved by the coupled model, especially when the canopy experienced moderate water stress. This finding highlights the importance of enhanced soil heat and moisture transfer, as well as dynamic root growth, on simulating ecosystem functioning.
44
Wu, Minchao, Guy Schurgers, Markku Rummukainen, Benjamin Smith, Patrick Samuelsson, Christer Jansson, Joe Siltberg e Wilhelm May. "Vegetation–climate feedbacks modulate rainfall patterns in Africa under future climate change". Earth System Dynamics 7, n. 3 (26 luglio 2016): 627–47. http://dx.doi.org/10.5194/esd-7-627-2016.
Testo completoAbstract (sommario):
Abstract. Africa has been undergoing significant changes in climate and vegetation in recent decades, and continued changes may be expected over this century. Vegetation cover and composition impose important influences on the regional climate in Africa. Climate-driven changes in vegetation structure and the distribution of forests versus savannah and grassland may feed back to climate via shifts in the surface energy balance, hydrological cycle and resultant effects on surface pressure and larger-scale atmospheric circulation. We used a regional Earth system model incorporating interactive vegetation–atmosphere coupling to investigate the potential role of vegetation-mediated biophysical feedbacks on climate dynamics in Africa in an RCP8.5-based future climate scenario. The model was applied at high resolution (0.44 × 0.44°) for the CORDEX-Africa domain with boundary conditions from the CanESM2 general circulation model. We found that increased tree cover and leaf-area index (LAI) associated with a CO2 and climate-driven increase in net primary productivity, particularly over subtropical savannah areas, not only imposed important local effect on the regional climate by altering surface energy fluxes but also resulted in remote effects over central Africa by modulating the land–ocean temperature contrast, Atlantic Walker circulation and moisture inflow feeding the central African tropical rainforest region with precipitation. The vegetation-mediated feedbacks were in general negative with respect to temperature, dampening the warming trend simulated in the absence of feedbacks, and positive with respect to precipitation, enhancing rainfall reduction over the rainforest areas. Our results highlight the importance of accounting for vegetation–atmosphere interactions in climate projections for tropical and subtropical Africa.
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Woodward, Stephanie, Alistair A. Sellar, Yongming Tang, Marc Stringer, Andrew Yool, Eddy Robertson e Andy Wiltshire. "The simulation of mineral dust in the United Kingdom Earth System Model UKESM1". Atmospheric Chemistry and Physics 22, n. 22 (15 novembre 2022): 14503–28. http://dx.doi.org/10.5194/acp-22-14503-2022.
Testo completoAbstract (sommario):
Abstract. Mineral dust plays an important role in Earth system models and is linked to many components, including atmospheric wind speed, precipitation and radiation, surface vegetation cover and soil properties and oceanic biogeochemical systems. In this paper, the dust scheme in the first configuration of the United Kingdom Earth System Model UKESM1 is described, and simulations of dust and its radiative effects are presented and compared with results from the parallel coupled atmosphere–ocean general circulation model (GCM) HadGEM3-GC3.1. Not only changes in the driving model fields but also changes in the dust size distribution are shown to lead to considerable differences to the present-day dust simulations and to projected future changes. UKESM1 simulations produce a present-day, top-of-the-atmosphere (ToA) dust direct radiative effect (DRE – defined as the change in downward net flux directly due to the presence of dust) of 0.086 W m−2 from a dust load of 19.5 Tg. Under climate change pathways these values decrease considerably. In the 2081–2100 mean of the Shared Socioeconomic Pathway SSP5–8.45 ToA DRE reaches 0.048 W m−2 from a load of 15.1 Tg. In contrast, in HadGEM3-GC3.1 the present-day values of −0.296 W m−2 and 15.0 Tg are almost unchanged at −0.289 W m−2 and 14.5 Tg in the 2081–2100 mean. The primary mechanism causing the differences in future dust projections is shown to be the vegetation response, which dominates over the direct effects of warming in our models. Though there are considerable uncertainties associated with any such estimates, the results presented demonstrate both the importance of the size distribution for dust modelling and also the necessity of including Earth system processes such as interactive vegetation in dust simulations for climate change studies.
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Quevedo, D. I., e F. Francés. "A conceptual dynamic vegetation-soil model for arid and semiarid zones". Hydrology and Earth System Sciences 12, n. 5 (10 settembre 2008): 1175–87. http://dx.doi.org/10.5194/hess-12-1175-2008.
Testo completoAbstract (sommario):
Abstract. Plant ecosystems in arid and semiarid climates show high complexity, since they depend on water availability to carry out their vital processes. In these climates, water stress is the main factor controlling vegetation development and its dynamic evolution. The available water-soil content results from the water balance in the system, where the key issues are the soil, the vegetation and the atmosphere. However, it is the vegetation, which modulates, to a great extent, the water fluxes and the feedback mechanisms between soil and atmosphere. Thus, soil moisture content is most relevant for plant growth maintenance and final water balance assessment. A conceptual dynamic vegetation-soil model (called HORAS) for arid and semi-arid zones has been developed. This conceptual model, based on a series of connected tanks, represents in a way suitable for a Mediterranean climate, the vegetation response to soil moisture fluctuations and the actual leaf biomass influence on soil water availability and evapotranspiration. Two tanks were considered using at each of them the water balance and the appropriate dynamic equation for all considered fluxes. The first one corresponds to the interception process, whereas the second one models the evolution of moisture by the upper soil. The model parameters were based on soil and vegetation properties, but reduced their numbers. Simulations for dominant species, Quercus coccifera L., were carried out to calibrate and validate the model. Our results show that HORAS succeeded in representing the vegetation dynamics and, on the one hand, reflects how following a fire this monoculture stabilizes after 9 years. On the other hand, the model shows the adaptation of the vegetation to the variability of climatic and soil conditions, demonstrating that in the presence or shortage of water, the vegetation regulates its leaf biomass as well as its rate of transpiration in an attempt to minimize total water stress.
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Dunne, John P., Jasmin G. John, Elena Shevliakova, Ronald J. Stouffer, John P. Krasting, Sergey L. Malyshev, P. C. D. Milly et al. "GFDL’s ESM2 Global Coupled Climate–Carbon Earth System Models. Part II: Carbon System Formulation and Baseline Simulation Characteristics*". Journal of Climate 26, n. 7 (1 aprile 2013): 2247–67. http://dx.doi.org/10.1175/jcli-d-12-00150.1.
Testo completoAbstract (sommario):
Abstract The authors describe carbon system formulation and simulation characteristics of two new global coupled carbon–climate Earth System Models (ESM), ESM2M and ESM2G. These models demonstrate good climate fidelity as described in part I of this study while incorporating explicit and consistent carbon dynamics. The two models differ almost exclusively in the physical ocean component; ESM2M uses the Modular Ocean Model version 4.1 with vertical pressure layers, whereas ESM2G uses generalized ocean layer dynamics with a bulk mixed layer and interior isopycnal layers. On land, both ESMs include a revised land model to simulate competitive vegetation distributions and functioning, including carbon cycling among vegetation, soil, and atmosphere. In the ocean, both models include new biogeochemical algorithms including phytoplankton functional group dynamics with flexible stoichiometry. Preindustrial simulations are spun up to give stable, realistic carbon cycle means and variability. Significant differences in simulation characteristics of these two models are described. Because of differences in oceanic ventilation rates, ESM2M has a stronger biological carbon pump but weaker northward implied atmospheric CO2 transport than ESM2G. The major advantages of ESM2G over ESM2M are improved representation of surface chlorophyll in the Atlantic and Indian Oceans and thermocline nutrients and oxygen in the North Pacific. Improved tree mortality parameters in ESM2G produced more realistic carbon accumulation in vegetation pools. The major advantages of ESM2M over ESM2G are reduced nutrient and oxygen biases in the southern and tropical oceans.
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Drüke, Markus, Werner von Bloh, Stefan Petri, Boris Sakschewski, Sibyll Schaphoff, Matthias Forkel, Willem Huiskamp, Georg Feulner e Kirsten Thonicke. "CM2Mc-LPJmL v1.0: biophysical coupling of a process-based dynamic vegetation model with managed land to a general circulation model". Geoscientific Model Development 14, n. 6 (1 luglio 2021): 4117–41. http://dx.doi.org/10.5194/gmd-14-4117-2021.
Testo completoAbstract (sommario):
Abstract. The terrestrial biosphere is exposed to land-use and climate change, which not only affects vegetation dynamics but also changes land–atmosphere feedbacks. Specifically, changes in land cover affect biophysical feedbacks of water and energy, thereby contributing to climate change. In this study, we couple the well-established and comprehensively validated dynamic global vegetation model LPJmL5 (Lund–Potsdam–Jena managed Land) to the coupled climate model CM2Mc, the latter of which is based on the atmosphere model AM2 and the ocean model MOM5 (Modular Ocean Model 5), and name it CM2Mc-LPJmL. In CM2Mc, we replace the simple land-surface model LaD (Land Dynamics; where vegetation is static and prescribed) with LPJmL5, and we fully couple the water and energy cycles using the Geophysical Fluid Dynamics Laboratory (GFDL) Flexible Modeling System (FMS). Several improvements to LPJmL5 were implemented to allow a fully functional biophysical coupling. These include a sub-daily cycle for calculating energy and water fluxes, conductance of the soil evaporation and plant interception, canopy-layer humidity, and the surface energy balance in order to calculate the surface and canopy-layer temperature within LPJmL5. Exchanging LaD with LPJmL5 and, therefore, switching from a static and prescribed vegetation to a dynamic vegetation allows us to model important biospheric processes, including fire, mortality, permafrost, hydrological cycling and the impacts of managed land (crop growth and irrigation). Our results show that CM2Mc-LPJmL has similar temperature and precipitation biases to the original CM2Mc model with LaD. The performance of LPJmL5 in the coupled system compared to Earth observation data and to LPJmL offline simulation results is within acceptable error margins. The historical global mean temperature evolution of our model setup is within the range of CMIP5 (Coupled Model Intercomparison Project Phase 5) models. The comparison of model runs with and without land-use change shows a partially warmer and drier climate state across the global land surface. CM2Mc-LPJmL opens new opportunities to investigate important biophysical vegetation–climate feedbacks with a state-of-the-art and process-based dynamic vegetation model.
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Kerkhoven, E., e T. Y. Gan. "Differences in the Potential Hydrologic Impact of Climate Change to the Athabasca and Fraser River Basins of Canada with and without Considering Shifts in Vegetation Patterns Induced by Climate Change". Journal of Hydrometeorology 14, n. 3 (1 giugno 2013): 963–76. http://dx.doi.org/10.1175/jhm-d-12-011.1.
Testo completoAbstract (sommario):
Abstract The research objectives are to estimate differences between the potential impact of climatic change to the Athabasca River basin (ARB) and Fraser River basin (FRB) of Canada with and without considering shifts in vegetation patterns induced by climate change and how much the difference will depend on vegetation types and climate. The hydrologic effects of vegetation shifts on ARB and FRB were estimated by applying the Mapped Atmosphere–Plant–Soil System (MAPSS) simulated results based on the Intergovernmental Panel on Climate Change’s First and Second Assessment Report general circulation model (GCM) scenarios to the modified Interaction Soil–Biosphere–Atmosphere (MISBA) scheme. According to MAPSS, vegetation shifts in mountainous regions of FRB are expected to be dominated by conifer/broadleaf competition, while in ARB, climate projections of MAPSS predicted a southern expansion of the boreal forest. Because of differences in sublimation, there is a tendency for more snow to accumulate in open grassland than forests. Furthermore, changes to simulated mean annual maximum snowpack, runoff, and basin area covered by grassland are positively correlated to each other. Generally, a 4% increase in snow water equivalent (SWE) results in a 1% increase in mean annual runoff. These relationships hold true in both basins over a wide range of GCM-projected climate conditions and vegetation responses, suggesting that most changes in mean annual flow can be attributed to changes in SWE. Because of the different modeling approaches between MAPSS and MISBA, it seems that the treatment of these processes in vegetation and hydrologic models should be similar before conclusions can be drawn from various stand-alone simulations. Ideally, a land surface scheme should be coupled with a vegetation model in future studies.
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Brunsell, N. A., S. J. Schymanski e A. Kleidon. "Quantifying the thermodynamic entropy budget of the land surface: is this useful?" Earth System Dynamics 2, n. 1 (20 giugno 2011): 87–103. http://dx.doi.org/10.5194/esd-2-87-2011.
Testo completoAbstract (sommario):
Abstract. As a system is moved away from a state of thermodynamic equilibrium, spatial and temporal heterogeneity is induced. A possible methodology to assess these impacts is to examine the thermodynamic entropy budget and assess the role of entropy production and transfer between the surface and the atmosphere. Here, we adopted this thermodynamic framework to examine the implications of changing vegetation fractional cover on land surface energy exchange processes using the NOAH land surface model and eddy covariance observations. Simulations that varied the relative fraction of vegetation were used to calculate the resultant entropy budget as a function of fraction of vegetation. Results showed that increasing vegetation fraction increases entropy production by the land surface while decreasing the overall entropy budget (the rate of change in entropy at the surface). This is accomplished largely via simultaneous increase in the entropy production associated with the absorption of solar radiation and a decline in the Bowen ratio (ratio of sensible to latent heat flux), which leads to increasing the entropy export associated with the latent heat flux during the daylight hours and dominated by entropy transfer associated with sensible heat and soil heat fluxes during the nighttime hours. Eddy covariance observations also show that the entropy production has a consistent sensitivity to land cover, while the overall entropy budget appears most related to the net radiation at the surface, however with a large variance. This implies that quantifying the thermodynamic entropy budget and entropy production is a useful metric for assessing biosphere-atmosphere-hydrosphere system interactions.