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1
Delon, C., C. Galy-Lacaux, A. Boone, C. Liousse, D. Serça, M. Adon, B. Diop, et al. "Atmospheric nitrogen budget in Sahelian dry savannas." Atmospheric Chemistry and Physics Discussions 9, no. 3 (June 30, 2009): 14189–233. http://dx.doi.org/10.5194/acpd-9-14189-2009.
Повний текст джерелаАнотація:
Abstract. The atmospheric nitrogen budget depends on emission and deposition fluxes both as reduced and oxidized nitrogen compounds. In this study, a first attempt at estimating the Sahel nitrogen budget for the year 2006 is made, through measurements and simulations at three stations from the IDAF network situated in dry savanna ecosystems. Dry deposition fluxes are estimated from measurements of NO2, HNO3 and NH3 gaseous concentrations, and wet deposition fluxes are calculated from NH4+ and NO3− concentrations in samples of rain. Emission fluxes are estimated including biogenic emission of NO from soils (an Artificial Neural Network module has been inserted into the ISBA-SURFEX surface model), emission of NOx and NH3 from domestic fires and biomass burning, and volatilization of NH3 from animal excreta. This study uses original and unique data from remote and hardly-ever-explored regions. The monthly evolution of oxidized N compounds shows that deposition increases at the beginning of the rainy season because of large emissions of biogenic NO (pulse events). Emission of oxidized compounds is dominated by biogenic emission from soils (domestic fires and biomass burning account for 27% at the most, depending on the station), whereas emission of NH3 is dominated by the process of volatilization. Deposition fluxes are dominated by gaseous dry deposition processes (58% of the total), for both oxidized and reduced compounds. The average deposition flux in dry savanna ecosystems ranges from 8.6 to 10.9 kgN ha−1 yr−1, with 30% attributed to oxidized compounds, and the other 70% attributed to NHx. The average emission flux ranges from 7.8 to 9.7 kgN ha−1 yr−1, dominated by NH3 volatilization (67%) and biogenic emission from soils (24%). The annual budget is then balanced, with emission fluxes on the same order of magnitude as deposition fluxes. When scaled up to the Sahelian region (10° N:20° N, 15° W:10° E), the estimates of total emission range from 3.6 to 4.5 TgN yr−1 and total deposition ranges from 3.9 to 5 TgN yr−1. The N budget gives a net deposition flux ranging from 0.2 to 0.6 TgN yr−1. If scaled up to the global scale (in the tropical band), it is possible to calculate a total budget of oxidized and reduced N compounds for dry savannas, with a global nitrogen deposition flux ranging from 11.1 to 14.1 TgN yr−1, and a global emission flux ranging from 10.1 to 12.5 TgN yr−1. These ecosystems contribute a significant amount (around 12%) to the global nitrogen budget.
2
Frison, P. L., G. Mercier, G. Faye, E. Mougin, P. Hiernaux, C. Lardeux, and J. P. Rudant. "Analysis of L- and C-Band SAR Image Time Series Over a Sahelian Area." IEEE Geoscience and Remote Sensing Letters 10, no. 5 (September 2013): 1016–20. http://dx.doi.org/10.1109/lgrs.2012.2227931.
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3
Sy, Abdoulaye, Christophe Duroure, Jean-Luc Baray, Yahya Gour, Joël Van Baelen, and Bouya Diop. "Space-Time Variability of the Rainfall over Sahel: Observation of a Latitudinal Sharp Transition of the Statistical Properties." Atmosphere 9, no. 12 (December 7, 2018): 482. http://dx.doi.org/10.3390/atmos9120482.
Повний текст джерелаАнотація:
The rain statistics of 0–45° N area including equatorial, Sahelian, and mid-latitude regions, are studied using the probability distributions of the duration of rainy and dry events. Long time daily data set from ground measurements and satellite observations of rain fields are used. This technique highlights a sharp latitudinal transition of the statistics between equatorial and all other regions (Sahel, mid-latitude). The probability distribution of the 8° S to 8° N latitude band shows a large-scale organization with a slow decreasing (power law decrease) distributions for the time and space size of rain events. This observation is in agreement with a scaling, or macro turbulent, behavior of the equatorial regions rain fields. For the Sahelian and mid-latitude regions, our observations are clearly not in agreement with this behavior. They show that the largest rain systems have a limited time and space size (well described with a decreasing exponential distribution). For these non-equatorial regions it is possible to define a local characteristic duration and a characteristic horizontal size of the large rain events. These characteristics time and space scales of observed mesoscale convective systems could be a sensible indicator for the detection of the possible trend of rain distribution properties due to anthropogenic influence.
4
Magagi, R. D., Y. H. Kerr, and J. C. Meunier. "Results of combining L- and C-band passive microwave airborne data over the Sahelian area." IEEE Transactions on Geoscience and Remote Sensing 38, no. 4 (July 2000): 1997–2008. http://dx.doi.org/10.1109/36.851781.
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Alcoba, M., M. Gosset, M. Kacou, F. Cazenave, and E. Fontaine. "Characterization of Hydrometeors in Sahelian Convective Systems with an X-Band Radar and Comparison with In Situ Measurements. Part II: A Simple Brightband Method to Infer the Density of Icy Hydrometeors." Journal of Applied Meteorology and Climatology 55, no. 2 (February 2016): 251–63. http://dx.doi.org/10.1175/jamc-d-15-0014.1.
Повний текст джерелаАнотація:
AbstractA simple scheme that is based on the shape and intensity of the radar bright band is used to infer the density of hydrometeors just above the freezing level in Sahelian mesoscale convective systems (MCS). Four MCS jointly observed by a ground-based X-band radar and by an instrumented aircraft as part of the Megha-Tropiques algorithm-validation campaign during August 2010 in Niamey, Niger, are analyzed. The instrumented aircraft (with a 94-GHz radar and various optical probes on board) provided mass–diameter laws for the particles sampled during the flights. The mass–diameter laws derived from the ground-radar vertical profile of reflectivity (VPR) for each flight are compared with those derived from the airborne measurements. The density laws derived by both methods are consistent and encourage further use of the simple VPR scheme to quantify hydrometeor density laws and their variability for various analyses (microphysical processes and icy-hydrometeor scattering and radiative properties).
6
Rowell, David P., Rory G. J. Fitzpatrick, Lawrence S. Jackson, and Grace Redmond. "Understanding Intermodel Variability in Future Projections of a Sahelian Storm Proxy and Southern Saharan Warming." Journal of Climate 34, no. 2 (January 2021): 509–25. http://dx.doi.org/10.1175/jcli-d-20-0382.1.
Повний текст джерелаАнотація:
AbstractProjected changes in the intensity of severe rain events over the North African Sahel—falling from large mesoscale convective systems—cannot be directly assessed from global climate models due to their inadequate resolution and parameterization of convection. Instead, the large-scale atmospheric drivers of these storms must be analyzed. Here we study changes in meridional lower-tropospheric temperature gradient across the Sahel (ΔTGrad), which affect storm development via zonal vertical wind shear and Saharan air layer characteristics. Projected changes in ΔTGrad vary substantially among models, adversely affecting planning decisions that need to be resilient to adverse risks, such as increased flooding. This study seeks to understand the causes of these projection uncertainties and finds three key drivers. The first is intermodel variability in remote warming, which has strongest impact on the eastern Sahel, decaying toward the west. Second, and most important, a warming–advection–circulation feedback in a narrow band along the southern Sahara varies in strength between models. Third, variations in southern Saharan evaporative anomalies weakly affect ΔTGrad, although for an outlier model these are sufficiently substantive to reduce warming here to below that of the global mean. Together these uncertain mechanisms lead to uncertain southern Saharan/northern Sahelian warming, causing the bulk of large intermodel variations in ΔTGrad. In the southern Sahel, a local negative feedback limits the contribution to uncertainties in ΔTGrad. This new knowledge of ΔTGrad projection uncertainties provides understanding that can be used, in combination with further research, to constrain projections of severe Sahelian storm activity.
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Louf, Valentin, Olivier Pujol, and Henri Sauvageot. "The Seasonal and Diurnal Cycles of Refractivity and Anomalous Propagation in the Sahelian Area from Microwave Radiometric Profiling." Journal of Atmospheric and Oceanic Technology 33, no. 10 (October 2016): 2095–112. http://dx.doi.org/10.1175/jtech-d-14-00208.1.
Повний текст джерелаАнотація:
AbstractThe Sahelian zone of West Africa is a semiarid area where strong amplitude of the seasonal and diurnal cycles of water vapor and temperature is observed. One year of continuous observation of vertical profiles of water vapor and temperature gathered from Niamey, Niger, with a profiling microwave radiometer is used to analyze the climatology of refractivity and microwave propagation regimes in the low troposphere. Seasonal and diurnal cycles of refractivity and ground-based radar anomalous propagation are emphasized. It is shown that the combined effect of water vapor and temperature vertical gradients is responsible for strong seasonal and diurnal cycles of the ducting propagation regime. Statistics of propagation regimes are given. The probability density functions of the refractivity gradient are found lognormally distributed. Three months of C-band radar data simultaneous with the profiling microwave radiometer observations have also been collected. Relations between the vertical refractivity gradient and the ground-based radar anomalous propagation echoes (APE) are illustrated and discussed. APE spatial distributions are found strongly related to the main features of the orography and topography inside the radar-observed area. Contingency tests show that the probability for APE to be linked to ducting is higher than 95%. In addition, this paper suggests that observing the refractivity vertical profiles from a microwave radiometer profiler located close to a meteorological radar provides information on whether anomalous propagation has to be considered as a potential cause of spurious signal in the measured reflectivity field.
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Samasse, Kaboro, Niall P. Hanan, Julius Y. Anchang, and Yacouba Diallo. "A High-Resolution Cropland Map for the West African Sahel Based on High-Density Training Data, Google Earth Engine, and Locally Optimized Machine Learning." Remote Sensing 12, no. 9 (May 1, 2020): 1436. http://dx.doi.org/10.3390/rs12091436.
Повний текст джерелаАнотація:
The West African Sahel Cropland map (WASC30) is a new 30-m cropland extent product for the nominal year of 2015. We used the computing resources provided by Google Earth Engine (GEE) to fit and apply Random Forest models for cropland detection in each of 189 grid cells (composed of 100 km2, hence a total of ~1.9 × 106 km2) across five countries of the West African Sahel (Burkina Faso, Mauritania, Mali, Niger, and Senegal). Landsat-8 surface reflectance (Bands 2–7) and vegetation indices (NDVI, EVI, SAVI, and MSAVI), organized to include dry-season and growing-season band reflectances and vegetation indices for the years 2013–2015, were used as predictors. Training data were derived from an independent, high-resolution, visually interpreted sample dataset that classifies sample points across West Africa using a 2-km grid (~380,000 points were used in this study, with 50% used for model training and 50% used for model validation). Analysis of the new cropland dataset indicates a summed cropland area of ~316 × 103 km2 across the 5 countries, primarily in rainfed cropland (309 × 103 km2), with irrigated cropland area (7 × 103 km2) representing 2% of the total cropland area. At regional scale, the cropland dataset has an overall accuracy of 90.1% and a cropland class (rainfed and irrigated) user’s accuracy of 79%. At bioclimatic zones scale, results show that land proportion occupied by rainfed agriculture increases with annual precipitation up to 1000 mm. The Sudanian zone (600–1200 mm) has the highest proportion of land in agriculture (24%), followed by the Sahelian (200–600 mm) and the Guinean (1200 +) zones for 15% and 4%, respectively. The new West African Sahel dataset is made freely available for applications requiring improved cropland area information for agricultural monitoring and food security applications.
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Cazenave, F., M. Gosset, M. Kacou, M. Alcoba, E. Fontaine, C. Duroure, and B. Dolan. "Characterization of Hydrometeors in Sahelian Convective Systems with an X-Band Radar and Comparison with In Situ Measurements. Part I: Sensitivity of Polarimetric Radar Particle Identification Retrieval and Case Study Evaluation." Journal of Applied Meteorology and Climatology 55, no. 2 (February 2016): 231–49. http://dx.doi.org/10.1175/jamc-d-15-0013.1.
Повний текст джерелаАнотація:
AbstractThe particle identification scheme developed by Dolan and Rutledge for X-band polarimetric radar is tested for the first time in Africa and compared with in situ measurements. The data were acquired during the Megha-Tropiques mission algorithm-validation campaign that occurred in Niger in 2010. The radar classification is compared with the in situ observations gathered by an instrumented aircraft for the 13 August 2010 squall-line case. An original approach has been developed for the radar–in situ comparison: it consists of simulating synthetic radar variables from the microphysical-probe information and comparing the two datasets in a common “radar space.” The consistency between the two types of observation is good considering the differences in sampling illustrated in the paper. The time evolution of the hydrometeor types and their relative proportion in the convective and stratiform regions are analyzed. The farther away from the convection one looks, the more aggregation dominates, riming diminishes, and hydrometeors are less dense. Particle identification based on the polarimetric radar will be applied to a 5-yr African dataset in the future.
10
Thouret, V., M. Saunois, A. Minga, A. Mariscal, B. Sauvage, A. Solete, D. Agbangla, et al. "Two years of Ozone radio soundings over Cotonou as part of AMMA: overview." Atmospheric Chemistry and Physics Discussions 9, no. 3 (May 5, 2009): 11221–68. http://dx.doi.org/10.5194/acpd-9-11221-2009.
Повний текст джерелаАнотація:
Abstract. As part of the African Monsoon Multidisciplinary Analysis (AMMA) program, a total of 98 ozone vertical profiles over Cotonou, Benin, have been measured during a 26 month period (December 2004–January 2007). These regular measurements broadly document the seasonal and inter annual variability of ozone in both the troposphere and the lower stratosphere over West Africa for the first time. This data set is complementary to the MOZAIC observations made from Lagos between 0 and 12 km during the period 1998–2004. Both data sets highlight the unique way in which West Africa is impacted by two biomass burning seasons: in December–February (dry season) due to burning in the Sahelian band and in June–August (wet season) due to burning in southern Africa. High inter annual variabilities between Cotonou and Lagos data sets and within each data set are observed and are found to be a major characteristic of this region. In particular, the dry and wet seasons are discussed in order to set the data of the Special Observing Periods (SOPs) into a climatological context. Compared to other dry and wet seasons, the dry and wet season campaigns took place in rather high ozoneenvironments. During the sampled wet seasons, southern intrusions of biomass burning were particularly frequent with concentrations up to 120 ppbv of ozone in the lower troposphere. An insight into the ozone distribution in the upper troposphere and the lower stratosphere (up to 26 km) is given. The first tropospheric columns of ozone based on in-situ data in this region are assessed. They compare well with satellite products on seasonal and inter annual time-scales, provided that the layer below 850 Pa where the remote instrument is less sensitive to ozone, is removed.
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Thouret, V., M. Saunois, A. Minga, A. Mariscal, B. Sauvage, A. Solete, D. Agbangla, et al. "An overview of two years of ozone radio soundings over Cotonou as part of AMMA." Atmospheric Chemistry and Physics 9, no. 16 (August 28, 2009): 6157–74. http://dx.doi.org/10.5194/acp-9-6157-2009.
Повний текст джерелаАнотація:
Abstract. As part of the African Monsoon Multidisciplinary Analysis (AMMA) program, a total of 98 ozone vertical profiles over Cotonou, Benin, have been measured during a 26 month period (December 2004–January 2007). These regular measurements broadly document the seasonal and interannual variability of ozone in both the troposphere and the lower stratosphere over West Africa for the first time. This data set is complementary to the MOZAIC observations made from Lagos between 0 and 12 km during the period 1998–2004. Both data sets highlight the unique way in which West Africa is impacted by two biomass burning seasons: in December–February (dry season) due to burning in the Sahelian band and in June-August (wet season) due to burning in southern Africa. High interannual variabilities between Cotonou and Lagos data sets and within each data set are observed and are found to be a major characteristic of this region. In particular, the dry and wet seasons are discussed in order to set the data of the Special Observing Periods (SOPs) into a climatological context. Compared to other dry and wet seasons, the 2006 dry and wet season campaigns took place in rather high ozone environments. During the sampled wet seasons, southern intrusions of biomass burning were particularly frequent with concentrations up to 120 ppbv of ozone in the lower troposphere. An insight into the ozone distribution in the upper troposphere and the lower stratosphere (up to 26 km) is given. The first tropospheric columns of ozone based on in-situ data over West Africa are assessed. They compare well with satellite products on seasonal and interannual time-scales, provided that the layer below 850 hPa where the remote instrument is less sensitive to ozone, is removed.
12
Rodríguez, S., E. Cuevas, J. M. Prospero, A. Alastuey, X. Querol, J. López-Solano, M. I. García, and S. Alonso-Pérez. "Modulation of Saharan dust export by the North African dipole." Atmospheric Chemistry and Physics 15, no. 13 (July 10, 2015): 7471–86. http://dx.doi.org/10.5194/acp-15-7471-2015.
Повний текст джерелаАнотація:
Abstract. We have studied the relationship between the long-term interannual variability in large-scale meteorology in western North Africa – the largest and most active dust source worldwide – and Saharan dust export in summer, when enhanced dust mobilization in the hyper-arid Sahara results in maximum dust impacts throughout the North Atlantic. We address this issue by analyzing 28 years (1987–2014) of summer averaged dust concentrations at the high-altitude Izaña observatory (~ 2400 m a.s.l.) on Tenerife, and satellite and meteorological reanalysis data. The summer meteorological scenario in North Africa (aloft 850 hPa) is characterized by a high over the the subtropical Sahara and a low over the tropics linked to the monsoon. We measured the variability of this high–low dipole-like pattern in terms of the North African dipole intensity (NAFDI): the difference of geopotential height anomalies averaged over the subtropics (30–32° N, Morocco) and the tropics (10–13° N, Bamako region) close to the Atlantic coast (at 5–8° W). We focused on the 700 hPa standard level due to dust export off the coast of North Africa tending to occur between 1 and 5 km a.s.l. Variability in the NAFDI is associated with displacements of the North African anticyclone over the Sahara and this has implications for wind and dust export. The correlations we found between the 1987–2014 summer mean of NAFDI with dust at Izaña, satellite dust observations and meteorological re-analysis data indicate that increases in the NAFDI (i) result in higher wind speeds at the north of the Inter-Tropical Convergence Zone that are associated with enhanced dust export over the subtropical North Atlantic, (ii) influence the long-term variability of the size distribution of exported dust particles (increasing the load of coarse dust) and (iii) are associated with enhanced rains in the tropical and northern shifts of the tropical rain band that may affect the southern Sahel. Interannual variability in NAFDI is also connected to spatial distribution of dust over the North Atlantic; high NAFDI summers are associated with major dust export (linked to winds) in the subtropics and minor dust loads in the tropics (linked to higher rainfall), and vice versa. The evolution of the summer NAFDI values since 1950 to the present day shows connections to climatic variability (through the Sahelian drought, ENSO (El Niño–Southern Oscillation) and winds) that have implications for dust export paths. Efforts to anticipate how dust export may evolve in future decades will require a better understanding of how the large-scale meteorological systems represented by the NAFD will evolve.
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Diawara, Mamadou Oumar, Pierre Hiernaux, Sory Sissoko, Eric Mougin, Alassane Ba, Nogmana Soumaguel, and Hawa Salif Diakité. "Sensibilité de la production herbacée aux aléas de la distribution des pluies au Sahel (Agoufou, Mali): une approche par modélisation." International Journal of Biological and Chemical Sciences 14, no. 4 (August 17, 2020): 1341–53. http://dx.doi.org/10.4314/ijbcs.v14i4.14.
Повний текст джерелаАнотація:
La forte variation du régime des pluies au Sahel est reconnue par tous. La phénologie de la strate herbacée dominée par des plantes annuelles suit ce cycle annuel en faisant alterner une courte saison de croissance et une longue saison morte. Le Gourma situé dans la bande sahélienne au Mali est une zone pastorale soumise à cette variabilité temporelle des ressources pastorales (eau et fourrage) liée au régime de la mousson Ouest africaine, et aux fortes variations interannuelles de la pluviosité. Cette étude a pour objectif d’évaluer la sensibilité de la production de la strate herbacée aux variations de la distribution intra-saisonnière des pluies au Sahel à travers le cas du site pastoral d’Agoufou. Les simulations ont été effectuées avec le modèle STEP (Sahelian Transpiration Evaporation and Production model). Les analyses reposent sur de simples permutations des pluies journalières enregistrées sur le site en 2010, réalisées de façon aléatoire sans modifier le total saisonnier ni les cumuls journaliers. Les résultats montrent que la relation entre le cumul des pluies saisonnières et les phytomasses herbacées mesurées en fin de saison masque des chutes de production intra-saisonnière liées aux stress hydriques, notamment au cours de la période de croissance rapide qui affectent la production saisonnière. Le modèle pourrait servir dans un système intégré d’alertes précoces pour anticiper les pénuries de fourrage fréquentes dans cette région.Mots clés : Production primaire, strate herbacée, variation pluviométrique, stress hydrique, modèle STEP.
English Title: Sensitivity of herbaceous vegetation production to the variability of rainfall distribution in the Sahel (Agoufou, Mali): a modeling approachThe strong spatial and temporal variability of rainfall patterns in the Sahel is accepted by everybody. The phenology of the herbaceous layer dominated by annual plants follows this rhythm by alternating a short growing period with a long dormancy period. The Gourma region located in the Sahelian belt in Mali is a pastoral area subject to this temporal variability of resources (water and forage) linked to the rains regime. This study aims to assess the sensitivity of the herbaceous vegetation production to the variation of the intra-seasonal rainfall distribution in the Sahel through the case of the Agoufou rangeland site. The simulations were performed with the STEP model (Sahelian Transpiration Evaporation and Production model). The analyses were based on simple changes of rainfall height recorded on the site in 2010, carried out randomly without changing the seasonal total or the daily totals. The results show that the relationship between rainfall totals and the fall of the herbaceous mass conceal intra-seasonal production related to water stress especially during the period of so-called main growth can affect the seasonal production. The model could be used in an integrated early warning system to anticipate frequent forage shortages in this region.Keywords: Primary production, herbaceous layer, rainfall variation, water deficit, STEP model.
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Ngandam Mfondoum, A. H., P. G. Gbetkom, R. Cooper, S. Hakdaoui, and M. B. Mansour Badamassi. "EXTRACTING BUILT-UP FEATURES IN COMPLEX BIOPHYSICAL ENVIRONMENTS BY USING A LANDSAT BANDS RATIO." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLIV-M-2-2020 (November 17, 2020): 79–85. http://dx.doi.org/10.5194/isprs-archives-xliv-m-2-2020-79-2020.
Повний текст джерелаАнотація:
Abstract. This paper addresses the remote sensing challenging field of urban mixed pixels on a medium spatial resolution satellite data. The tentatively named Normalized Difference Built-up and Surroundings Unmixing Index (NDBSUI) is proposed by using Landsat-8 Operational Land Imager (OLI) bands. It uses the Shortwave Infrared 2 (SWIR2) as the main wavelength, the SWIR1 with the red wavelengths, for the built-up extraction. A ratio is computed based on the normalization process and the application is made on six cities with different urban and environmental characteristics. The built-up of the experimental site of Yaoundé is extracted with an overall accuracy of 95.51% and a kappa coefficient of 0.90. The NDBSUI is validated over five other sites, chosen according to Cameroon’s bioclimatic zoning. The results are satisfactory for the cities of Yokadouma and Kumba in the bimodal and monomodal rainfall zones, where overall accuracies are up to 98.9% and 97.5%, with kappa coefficients of 0.88 and 0.94 respectively, although these values are close to those of three other indices. However, in the cities of Foumban, Ngaoundéré and Garoua, representing the western highlands, the high Guinea savannah and the Sudano-sahelian zones where built-up is more confused with soil features, overall accuracies of 97.06%, 95.29% and 74.86%, corresponding to 0.918, 0.89 and 0.42 kappa coefficients were recorded. Difference of accuracy with EBBI, NDBI and UI are up to 31.66%, confirming the NDBSUI efficiency to automate built-up extraction and unmixing from surrounding noises with less biases.
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Traoré, Hamidou, Albert Barro, Djibril Yonli, Zachary Stewart, and Vara Prasad. "Water Conservation Methods and Cropping Systems for Increased Productivity and Economic Resilience in Burkina Faso." Water 12, no. 4 (March 30, 2020): 976. http://dx.doi.org/10.3390/w12040976.
Повний текст джерелаАнотація:
Resilience of smallholder farmers in their ability to bounce-back and overcome shocks, such as drought, is critical to ensure a pathway out of hunger and poverty. Efficient water conservation methods that increase rainwater capture and reduce soil erosion such as stone lines and grass bands are two technologies that have been proposed to increase the resilience in Sudano–Sahelian farming systems. In Burkina Faso, we show that stone lines, grass bands, and crop rotation are effective resilience strategies individually and in combination. During years when rainfall is well-distributed over time, differences are minimal between fields with water conservation methods and fields without. However, when there are periods of prolonged drought, water conservation methods are effective for increasing soil water, yield, revenue, and resilience. During drought conditions, sorghum (Sorghum bicolor (L.) Moench) grain yield and revenue with stone lines and grass bands were over 50% greater than that of the control, by an average of 450 kg ha−1, which amounted to an increase of 58,500 West African CFA franc (CFA) ha−1 (i.e., 98 USD ha−1). The results also suggest that the combination of water conservation method and crop rotation additionally improves cropping system productivity and revenue. Growing cowpea (Vigna unguiculata (L.) Walp.) in rotation with sorghum production provided more options for farmers to increase their income and access to nutrition. This study also sheds light on the limited productivity gains due to improved crop varieties. The local sorghum landrace, Nongomsoba, and the local cowpea variety in rotation resulted in the highest yields as compared to the improved varieties of Sariaso 14 sorghum and KVX 396-4-4 cowpea. Under similar low input/degraded conditions, improved crop varieties likely are not a suitable resilience strategy alone. We conclude that during erratic rainy seasons with frequent periods of drought (i.e., water stress) in rain-fed conditions in Burkina Faso, stone lines or grass bands in combination with sorghum and cowpea rotation are effective practices for increasing resilience of smallholder farmers to maintain crop productivity and revenue. With future and present increases in climate variability due to climate change, stone lines, grass bands, and crop rotation will have growing importance as resilience strategies to buffer crop productivity and revenue during periods of drought.
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Söhne, Nathalie, Jean-Pierre Chaboureau, and Françoise Guichard. "Verification of Cloud Cover Forecast with Satellite Observation over West Africa." Monthly Weather Review 136, no. 11 (November 1, 2008): 4421–34. http://dx.doi.org/10.1175/2008mwr2432.1.
Повний текст джерелаАнотація:
Abstract The 3-hourly brightness temperatures (BTs) at 10.8 μm from the Meteosat Second Generation (MSG) satellite were used to document the cloud system variability over West Africa in the summer of 2006 and to evaluate the quality of the Méso-NH model forecasts of cloud cover in the African Monsoon Multidisciplinary Analysis (AMMA) framework. Cloud systems were observed over the Guinean and Sahelian bands with more frequent occurrence and patchier structures in the afternoon. Some intraseasonal variations of the number of cloud systems were found, partly related to the intermittency of the African easterly wave (AEW) activity. Compared to the MSG observations, the Méso-NH model reproduces the overall variation of the BT at 10.8 μm well at D + 1 forecast. The model captures the BT diurnal cycle under conditions of clear-sky and high-cloud cover, but misses the lowest BT values associated with deep convection. Forecasted cloud systems are more numerous and smaller, hence patchier, than those observed. These results suggest some deficiencies in the model’s convection and cloud parameterization schemes. The use of meteorological scores further documents the skill of the model to predict cloud systems. Beyond some systematic differences between simulations and observations, analysis also suggests that the model high-cloud forecast is improved under specific synoptic forcing conditions related to AEW activity. This indicates that room exists for improving the skills of weather forecasting over West Africa.
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Abdou, Laouali, Abdoulaye Diouf, Maman Maarouhi Inoussa, Boubacar Moussa Mamoudou, Salamatou Abdourahamane Illiassou, and Ali Mahamane. "Modeling the Geographic Distribution of Prosopis africana (G. and Perr.) Taub. in Niger." Environment and Natural Resources Research 6, no. 2 (May 29, 2016): 136. http://dx.doi.org/10.5539/enrr.v6n2p136.
Повний текст джерелаАнотація:
<p class="1Body"><em>Prosopis africana </em>is a species of great socio-economic importance, threatened with extinction from its natural habitat in Niger due to overexploitation. The main objective of this study is to determine the potential geographic distribution of <em>P. africana</em> in Niger. Climatic and botanical data has been collected and used to model the distribution, on the basis of principle of maximum entropy (MAXENT) using MAXENT 3.3.3k, DIVA-GIS 7.5, and ArcGIS 10.0. programs. Rainfall and temperature are the most significant variables in the distribution of <em>P. africana</em> in Niger. Thus the southern band of the country (from the sudanian zone to the sahelio-soudanian zone), the wettest, is the area conducive to the development of <em>P.</em> <em>africana </em>(128,692.32 km<sup>2</sup> in total, 10.16% of the territory). Given the extent of this area revealed by this study, a reforestation policy implementation of <em>P. africana</em> would allow to restore its stands in Niger.</p>
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Pinna, Thibault, N. Py, L. Aigle, S. Travers, P. Pasquier, and N. Cazes. "Retrospective analysis of tranexamic acid administration in French war-wounded between October 2016 and September 2020." BMJ Military Health, January 30, 2023, e002321. http://dx.doi.org/10.1136/military-2022-002321.
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IntroductionSince 2013, the French Army Health Service, in agreement with international experts, has recommended the administration of 1 g of tranexamic acid (TXA) in trauma patients in haemorrhagic shock or at risk of bleeding within 3 hours of the trauma.MethodsThe aim of this analysis was to describe the administration of TXA in French military personnel wounded during military operations in the Sahelo-Sahelian band between October 2016 and September 2020. Data were collected from forward health records and hospital data from the French hospital where the casualty was finally evacuated. Underuse of TXA was defined as the lack of administration in casualties who had received a blood transfusion with one or more of red blood cells, low-titre whole blood or French lyophilised plasma within the first 24 hours of injury and overuse as its administration in the non-transfused casualty.ResultsOf the 76 patients included, 75 were men with an average age of 28 years. Five patients died during their management. 19 patients received TXA (25%) and 16 patients were transfused (21%). Underuse of TXA occurred in 3 of the 16 patients (18.8%) transfused. Overuse occurred in 6 of 60 (10%) non-transfused patients.ConclusionThe analysis found an important underuse of TXA (almost 20%) and highlighted the need for optimising the prehospital clinical practice guidelines to aid prehospital medical practitioners more accurately in administering TXA to casualties that will require blood products.
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Mint Abdelaziz, Selouka, Leila Medraoui, Mohammed Alami, Ouafae Pakhrou, Meryem Makkaoui, Ali Ould Mohamed Salem Boukhary, and Abdelkarim Filali-Maltouf. "Inter simple sequence repeat markers to assess genetic diversity of the desert date (Balanites aegyptiaca Del.) for Sahelian ecosystem restoration." Scientific Reports 10, no. 1 (September 11, 2020). http://dx.doi.org/10.1038/s41598-020-71835-9.
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Abstract Drought and desertification are the major environmental constraints facing the Sahelian agro-ecosystems for decades. Assessing genetic diversity of native tree species is critical to assist ecosystems restoration efforts. Here we describe genetic diversity and structure of seven Balanites aegyptiaca L. natural populations distributed across the Sahelian-Saharan zone of Mauritania using 16 polymorphic ISSR primers. These generated 505 polymorphic bands. Polymorphism information content (PIC) varied from (0.13–0.29) with an average 0.23, marker index (MI) averaged 7.3 (range 3.3–10.3) and resolving power (RP) ranged from (4.53–14.6) with an average 9.9. The number of observed alleles (Na) ranged from (0.62–1.39), Effective number of alleles (Ne) varied from (1.26–1.37), Shannon’s information index (I) ranged from (0.25–0.36). AMOVA analysis showed that 80% of the genetic variation was fined within populations, which is supported by a low level of genetic differentiation between population (GST = 0.21) and an overall estimate of gene flow among populations (Nm = 1.9). The dendrogram based on Jaccard's similarity coefficient and the structure analysis divided the seven populations into two main clusters in which two populations from the Saharan zone were grouped. Our results provide baseline data for genetic conservation programs of this Sahelian neglected crop and with an important econ-ecological role.
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Lo, Adama, Abdoul Aziz Diouf, Ibrahima Diedhiou, Cyrille Djitamagne Edouard Bassène, Louise Leroux, Torbern Tagesson, Rasmus Fensholt, et al. "Dry season forage assessment across senegalese rangelands using earth observation data." Frontiers in Environmental Science 10 (September 29, 2022). http://dx.doi.org/10.3389/fenvs.2022.931299.
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Strengthening of feed security in the Sahel is urgently needed given the climate change and growing human population. A prerequisite to this is sustainable use of rangeland forage resources for livestock. Many studies have focused on the assessment of rangeland resources during the rainy season, while only a few have focused on the dry season which is the longest and most demanding period for livestock in Sahelian rangelands. The objective of this study is to develop remote sensing-based models for estimating dry season forage vegetation mass. To that end, 29 vegetation indices calculated from each of the MODIS-MCD43A4 (500 m), Landsat-8 (30 m), and Sentinel-2 (10 m) satellite products were used and tested against in situ data collected during three field-measurement campaigns in 2021 at eleven monitoring sites across Senegalese rangelands. Four statistical models were tested, namely, random forest, gradient boosting machines, and simple linear and multiple linear regressions. The two main vegetation mass variables modeled from remote sensing imagery were the standing herbaceous and litter dry mass (BH) and total forage dry mass (BT) with a dry mass of woody plant leaves added to BH. Overall, Sentinel-2 data provided the best performance for the assessment of BH with multiple linear regression (R2 = 0.74; RMSE = 378 kg DM/ha) using NDI5 (Normalized Difference Index5), GRCI (Green Residue Cover Index), SRI (Simple Ratio Index), TCARI (Transformed Chlorophyll Absorption in Reflectance Index), and DFI (Dead Fuel Index) indices. For BT, the best model was also obtained from Sentinel-2 data, including RVI3 (Ratio Vegetation Index3) (R2 = 0.78; RMSE = 496 kg DM/ha). Results showed the suitability of combining the red, green, blue, NIR, SWIR1, and SWIR2 bands in monitoring forage availability during the dry season. Our study revealed that the spectral richness of the optical sensor systems Sentinel-2, Landsat-8, and MODIS-MCD43A4 allowed for accurate assessments of dry-season forage mass of semi-arid rangelands. Adding to this, the high spatial and temporal resolution of Sentinel-2 satellite imagery makes this a promising data source for timely monitoring. These findings can support the monitoring of the animal feed balance in Sahelian countries and contribute to enhancing the resilience of pastoralism toward feed shortage through early warning systems.