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1
Diba, Ibrahima, Moctar Camara, Alioune Sarr, and Arona Diedhiou. "Potential Impacts of Land Cover Change on the Interannual Variability of Rainfall and Surface Temperature over West Africa." Atmosphere 9, no. 10 (September 28, 2018): 376. http://dx.doi.org/10.3390/atmos9100376.
Анотація:
We used the Abdu Salam International Centre for Theoretical Physics (ICTP) Regional Climate Model version 4.5 (RegCM4.5), to investigate the potential impacts of land cover change of the Sahel–Sahara interface on the West African climate over an interannual timescale from 1990 to 2009. A simulation at 50 km grid spacing is performed with the standard version of the RegCM4.5 model (control run), followed by three vegetation change experiments at the Sahel-Sahara interface (15° N and 20° N): forest, tall grass, and short grass savanna. The impacts of land cover change are assessed by analyzing the difference between the altered runs and the control one in different sub-domains (western Sahel, central Sahel, eastern Sahel, and Guinea). Results show that the presence of forest, tall grass, and short grass savanna at the Sahel–Sahara interface tends to decrease the mean summer surface temperature in the whole domain. Nevertheless, this decrease is more pronounced over the Central Sahel when considering the forest experiment. This temperature decrease is associated with a weakening (strengthening) of the sensible (latent) heat flux in the whole domain. An analysis of the radiation field is performed to better explain the changes noted in the latent heat flux, the sensible heat flux, and the surface temperature. When considering the rainfall signal, the analysis shows that the afforestation options tend to alter the precipitation in the considered sub-domains substantially by increasing it in the whole Sahel region, with strong interannual variability. This rainfall increase is associated with an increase of the atmospheric moisture. Finally, we investigated the impacts of the afforestation options on some features of the rainfall events, and on the atmospheric dynamics during wet and dry years. All afforestation options tend to increase the frequency of the number of rainy days in regions located south of 18° N during both periods. Nevertheless, this increase is stronger over the Central and Eastern Sahel during wet years in the forest case. All afforestation experiments induce an increase (decrease) of the low-levels monsoon flux in the Eastern Sahel (western Sahel) during both periods. At the mid-levels, the three afforestation options tend to move northward and to decrease the intensity of the African Easterly Jet (AEJ) south of 13° N during wet and dry years.The intensity of the AEJ is weaker during the wet period. The vegetation change experiments also affect the Tropical Easterly Jet (TEJ), especially during wet years, by increasing its intensity over the southern Sahel. The analysis of the activity of African Easterly Waves (AEWs) patterns exhibits a decrease of the intensity of these disturbances over the Sahel during both periods. This may be due to the weakening of the meridional temperature contrast between the continent and the Gulf of Guinea due to the Sahel–Sahara surface temperature cooling induced by the afforestation. In summary, this study shows that during both periods, the increase of the atmospheric moisture due to the afforestation is associated with favorable AEJ/TEJ configurations (weaker and northward position of the AEJ; stronger TEJ) which in turn may create a stronger convection and then, an increase in the Sahel rainfall. This Sahel rainfall increase is associated with a strengthening of the intense and heavy rainfall events which may impact diversely local populations.
2
Vircoulon, Thierry. "Quand le Sahel central rencontre l’Afrique centrale, réflexions sur le conflit centrafricain." Hérodote N°179, no. 4 (2020): 56. http://dx.doi.org/10.3917/her.179.0056.
3
Monerie, Paul-Arthur, Emilia Sanchez-Gomez, Marco Gaetani, Elsa Mohino, and Buwen Dong. "Future evolution of the Sahel precipitation zonal contrast in CESM1." Climate Dynamics 55, no. 9-10 (August 17, 2020): 2801–21. http://dx.doi.org/10.1007/s00382-020-05417-w.
Анотація:
Abstract The main focus of this study is the zonal contrast of the Sahel precipitation shown in the CMIP5 climate projections: precipitation decreases over the western Sahel (i.e., Senegal and western Mali) and increases over the central Sahel (i.e., eastern Mali, Burkina Faso and Niger). This zonal contrast in future precipitation change is a robust model response to climate change but suffers from a lack of an explanation. To this aim, we study the impact of current and future climate change on Sahel precipitation by using the Large Ensemble of the Community Earth System Model version 1 (CESM1). In CESM1, global warming leads to a strengthening of the zonal contrast, as shown by the difference between the 2060–2099 period (under a high emission scenario) and the 1960–1999 period (under the historical forcing). The zonal contrast is associated with dynamic shifts in the atmospheric circulation. We show that, in absence of a forced response, that is, when only accounting for internal climate variability, the zonal contrast is associated with the Pacific and the tropical Atlantic oceans variability. However, future patterns in sea surface temperature (SST) anomalies are not necessary to explaining the projected strengthening of the zonal contrast. The mechanisms underlying the simulated changes are elucidated by analysing a set of CMIP5 idealised simulations. We show the increase in precipitation over the central Sahel to be mostly associated with the surface warming over northern Africa, which favour the displacement of the monsoon cell northwards. Over the western Sahel, the decrease in Sahel precipitation is associated with a southward shift of the monsoon circulation, and is mostly due to the warming of the SST. These two mechanisms allow explaining the zonal contrast in precipitation change.
4
Schewe, Jacob, and Anders Levermann. "Non-linear intensification of Sahel rainfall as a possible dynamic response to future warming." Earth System Dynamics 8, no. 3 (July 5, 2017): 495–505. http://dx.doi.org/10.5194/esd-8-495-2017.
Анотація:
Abstract. Projections of the response of Sahel rainfall to future global warming diverge significantly. Meanwhile, paleoclimatic records suggest that Sahel rainfall is capable of abrupt transitions in response to gradual forcing. Here we present climate modeling evidence for the possibility of an abrupt intensification of Sahel rainfall under future climate change. Analyzing 30 coupled global climate model simulations, we identify seven models where central Sahel rainfall increases by 40 to 300 % over the 21st century, owing to a northward expansion of the West African monsoon domain. Rainfall in these models is non-linearly related to sea surface temperature (SST) in the tropical Atlantic and Mediterranean moisture source regions, intensifying abruptly beyond a certain SST warming level. We argue that this behavior is consistent with a self-amplifying dynamic–thermodynamical feedback, implying that the gradual increase in oceanic moisture availability under warming could trigger a sudden intensification of monsoon rainfall far inland of today's core monsoon region.
5
Rangel de Moraes, Fernanda. "Mudanças climáticas, conflitualidades e sistemas de crises no Sahel (África ocidental)." Boletim GeoÁfrica 1, no. 1 (April 18, 2022): 76–90. http://dx.doi.org/10.59508/geoafrica.v1i1.51609.
Анотація:
A região da África ocidental conhecida como Sahel é palco de diversas tensões e conflitos que a definem como um espaço geopoliticamente instável. A conflitualidade regional do Sahel é alimentada por um conjunto de problemas estruturais e conjunturais de naturezas diferentes que se articulam de forma complexa e multiescalar. O objetivo central deste trabalho é analisar os efeitos das mudanças climáticas nas crises e conflitos e existentes no Sahel. A metodologia objetiva elaborar um marco conceitual valorizando uma perspectiva de análise sistêmica, com o conceito de sistema regional de crise estruturando nossa abordagem. Sendo assim, concluiu-se que as mudanças climáticas estão realmente gerando uma grande ameaça à segurança regional, não apenas pela escassez hídrica, insegurança alimentar, prevalência de doenças, alteração nas linhas de costa e a redistribuição da população, mas também por inflamar antigos conflitos e gerar novas tensões em um ambiente tão complexo como Sahel, tomando o papel de multiplicador de ameaças e catalisador da disseminação e longevidade dos conflitos.
6
Marteau, Romain, Vincent Moron, and Nathalie Philippon. "Spatial Coherence of Monsoon Onset over Western and Central Sahel (1950–2000)." Journal of Climate 22, no. 5 (March 1, 2009): 1313–24. http://dx.doi.org/10.1175/2008jcli2383.1.
Анотація:
Abstract The spatial coherence of boreal monsoon onset over the western and central Sahel (Senegal, Mali, Burkina Faso) is studied through the analysis of daily rainfall data for 103 stations from 1950 to 2000. Onset date is defined using a local agronomic definition, that is, the first wet day (>1 mm) of 1 or 2 consecutive days receiving at least 20 mm without a 7-day dry spell receiving less than 5 mm in the following 20 days. Changing either the length or the amplitude of the initial wet spell, or both, or the length of the following dry spell modifies the long-term mean of local-scale onset date but has only a weak impact either on its interannual variability or its spatial coherence. Onset date exhibits a seasonal progression from southern Burkina Faso (mid-May) to northwestern Senegal and Saharian edges (early August). Interannual variability of the local-scale onset date does not seem to be strongly spatially coherent. The amount of common or covariant signal across the stations is far weaker than the interstation noise at the interannual time scale. In particular, a systematic spatially consistent advance or delay of the onset is hardly observed across the whole western and central Sahel. In consequence, the seasonal predictability of local-scale onset over the western and central Sahel associated, for example, with large-scale sea surface temperatures, is, at best, weak.
7
Koné, Brahima, Arona Diedhiou, Adama Diawara, Sandrine Anquetin, N'datchoh Evelyne Touré, Adama Bamba, and Arsene Toka Kobea. "Influence of initial soil moisture in a regional climate model study over West Africa – Part 1: Impact on the climate mean." Hydrology and Earth System Sciences 26, no. 3 (February 11, 2022): 711–30. http://dx.doi.org/10.5194/hess-26-711-2022.
Анотація:
Abstract. The impact of soil moisture initial conditions on the mean climate over West Africa was examined using the latest version of the regional climate model of the International Centre for Theoretical Physics (RegCM4) at a 25 km horizontal resolution. The soil moisture reanalysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis of the 20th century (ERA-20C) was used to initialize the control experiment, while its minimum and maximum values over the entire domain were used to establish the respective initial dry and wet soil moisture conditions (hereafter referred to as dry and wet experiments, respectively). For the respective control, wet and dry experiments, an ensemble of five runs from June to September was performed. In each experiment, we analyzed the two idealized simulations most sensitive to the dry and wet soil moisture initial conditions. The impact of soil moisture initial conditions on precipitation in West Africa is linear over the Central and West Sahel regions, where dry (wet) experiments lead to a rainfall decrease (increase). The strongest precipitation increase is found over the West Sahel for wet experiments, with a maximum change value of approximately 40 %, whereas the strongest precipitation decrease is found for dry experiments over the Central Sahel, with a peak change of approximately −4 %. The sensitivity of soil moisture initial conditions can persist for 3–4 months (90–120 d) depending on the region. However, the influence on precipitation is no longer than 1 month (between 15 and 30 d). The strongest temperature decrease is located over the Central and West Sahel, with a maximum change of approximately −1.5 ∘C in wet experiments, whereas the strongest temperature increase is found over the Guinea coast and Central Sahel for the dry experiments, with a maximum change of around 0.6 ∘C. A significant impact of soil moisture initial conditions on the surface energy fluxes is noted: in the wet (dry) experiments, a cooling (warming) of the surface temperature is associated with a decrease (increase) in sensible heat flux, an increase (decrease) in latent heat flux and a decrease (increase) in the boundary layer depth. Part 2 of this study (Koné et al., 2022) investigates the influence of soil moisture initial conditions on climate extremes.
8
D'Andrea, A. C., S. Kahlheber, A. L. Logan, and D. J. Watson. "Early domesticated cowpea (Vigna unguiculata) from Central Ghana." Antiquity 81, no. 313 (September 1, 2007): 686–98. http://dx.doi.org/10.1017/s0003598x00095661.
Анотація:
From examining the remains of charred cowpeas from rock shelters in Central Ghana, the authors throw light on the subsistence strategies of the Kintampo people of the second millennium BCE. Perhaps driven southwards from the Sahel by aridification, the Kintampo operated as both foragers and farmers, cultivating selected plants of the West African tropics, notably cowpea, pearl millet and oil palm.
9
Li, Laifang, Raymond W. Schmitt, Caroline C. Ummenhofer, and Kristopher B. Karnauskas. "North Atlantic salinity as a predictor of Sahel rainfall." Science Advances 2, no. 5 (May 2016): e1501588. http://dx.doi.org/10.1126/sciadv.1501588.
Анотація:
Water evaporating from the ocean sustains precipitation on land. This ocean-to-land moisture transport leaves an imprint on sea surface salinity (SSS). Thus, the question arises of whether variations in SSS can provide insight into terrestrial precipitation. This study provides evidence that springtime SSS in the subtropical North Atlantic ocean can be used as a predictor of terrestrial precipitation during the subsequent summer monsoon in Africa. Specifically, increased springtime SSS in the central to eastern subtropical North Atlantic tends to be followed by above-normal monsoon-season precipitation in the African Sahel. In the spring, high SSS is associated with enhanced moisture flux divergence from the subtropical oceans, which converges over the African Sahel and helps to elevate local soil moisture content. From spring to the summer monsoon season, the initial water cycling signal is preserved, amplified, and manifested in excessive precipitation. According to our analysis of currently available soil moisture data sets, this 3-month delay is attributable to a positive coupling between soil moisture, moisture flux convergence, and precipitation in the Sahel. Because of the physical connection between salinity, ocean-to-land moisture transport, and local soil moisture feedback, seasonal forecasts of Sahel precipitation can be improved by incorporating SSS into prediction models. Thus, expanded monitoring of ocean salinity should contribute to more skillful predictions of precipitation in vulnerable subtropical regions, such as the Sahel.
10
Diba, Ibrahima, Moctar Camara, and Arona Diedhiou. "Investigating West African Monsoon Features in Warm Years Using the Regional Climate Model RegCM4." Atmosphere 10, no. 1 (January 10, 2019): 23. http://dx.doi.org/10.3390/atmos10010023.
Анотація:
This study investigates the changes in West African monsoon features during warm years using the Regional Climate Model version 4.5 (RegCM4.5). The analysis uses 30 years of datasets of rainfall, surface temperature and wind parameters (from 1980 to 2009). We performed a simulation at a spatial resolution of 50 km with the RegCM4.5 model driven by ERA-Interim reanalysis. The rainfall amount is weaker over the Sahel (western and central) and the Guinea region for the warmest years compared to the coldest ones. The analysis of heat fluxes show that the sensible (latent) heat flux is stronger (weaker) during the warmest (coldest) years. When considering the rainfall events, there is a decrease of the number of rainy days over the Guinea Coast (in the South of Cote d’Ivoire, of Ghana and of Benin) and the western and eastern Sahel during warm years. The maximum length of consecutive wet days decreases over the western and eastern Sahel, while the consecutive dry days increase mainly over the Sahel band during the warm years. The percentage of very warm days and warm nights increase mainly over the Sahel domain and the Guinea region. The model also simulates an increase of the warm spell duration index in the whole Sahel domain and over the Guinea Coast in warm years. The analysis of the wind dynamic exhibits during warm years a weakening of the monsoon flow in the lower levels, a strengthening in the magnitude of the African Easterly Jet (AEJ) in the mid-troposphere and a slight increase of the Tropical Easterly Jet (TEJ) in the upper levels of the atmosphere during warm years.
11
Neupane, Naresh, and Kerry H. Cook. "A Nonlinear Response of Sahel Rainfall to Atlantic Warming." Journal of Climate 26, no. 18 (September 9, 2013): 7080–96. http://dx.doi.org/10.1175/jcli-d-12-00475.1.
Анотація:
Abstract The response over West Africa to uniform warming of the Atlantic Ocean is analyzed using idealized simulations with a regional climate model. With warming of 1 and 1.5 K, rainfall rates increase by 30%–50% over most of West Africa. With Atlantic warming of 2 K and higher, coastal precipitation increases but Sahel rainfall decreases substantially. This nonlinear response in Sahel rainfall is the focus of this analysis. Atlantic warming is accompanied by decreases in low-level geopotential heights in the Gulf of Guinea and in the large-scale meridional geopotential height gradient. This leads to easterly wind anomalies in the central Sahel. With Atlantic warming below 2 K, these easterly anomalies support moisture transport from the Gulf of Guinea and precipitation increases. With Atlantic warming over 2 K, the easterly anomalies reverse the westerly flow over the Sahel. The resulting dry air advection into the Sahel reduces precipitation. Increased low-level moisture provides moist static energy to initiate convection with Atlantic warming at 1.5 K and below, while decreased moisture and stable thermal profiles suppress convection with additional warming. In all simulations, the southerly monsoon flow onto the Guinean coast is maintained and precipitation in that region increases. The relevance of these results to the global warming problem is limited by the focus on Atlantic warming alone. However, confident prediction of climate change requires an understanding of the physical processes of change, and this paper contributes to that goal.
12
Breil, Marcus, Hans-Jürgen Panitz, and Gerd Schädler. "Impact of soil-vegetation-atmosphere interactions on the spatial rainfall distribution in the Central Sahel." Meteorologische Zeitschrift 26, no. 4 (October 26, 2017): 379–89. http://dx.doi.org/10.1127/metz/2017/0819.
13
Laing, Arlene G., Stanley B. Trier, and Christopher A. Davis. "Numerical Simulation of Episodes of Organized Convection in Tropical Northern Africa." Monthly Weather Review 140, no. 9 (September 1, 2012): 2874–86. http://dx.doi.org/10.1175/mwr-d-11-00330.1.
Анотація:
Abstract A large-domain convection-permitting numerical model is used to simulate episodes of deep convection, which are generated during the day over the Ethiopian Highlands and then propagate westward over the eastern and central Sahel region (5°–20°N) of northern Africa. The simulation comprises 12.5 days within the African Monsoon Multidisciplinary Analysis (AMMA) field campaign in 2006. During this period, long-lived precipitation episodes that survived beyond a single diurnal cycle occurred in the lee of the Ethiopian Highlands only every 2–3 days in both the simulation and observations. This contrasts with some other latitudinal corridors in the lee of major topography, such as the central United States, where long-lived heavy precipitation episodes frequently occur on successive nights. The intermittency of long-lived events for the current case occurs despite regular daily triggering of convection along the upstream orography, and is linked to strong lower-tropospheric stabilization and reduction of daytime surface sensible heat flux due to residual cloudiness in the wake of long-lived precipitation events during the previous diurnal cycle. The vertical shear that helps organize deep convection is also weakened in the wake of the long-lived events by temporary disruptions of the midtropospheric African easterly jet. The environments of mesoscale convection are presented for the eastern Sahel, a region where most Sahelian convection originates, but about which little is known at the mesoscale. The study describes the potential for early identification of long-lived convection episodes that are likely to have high impact on the central Sahel and West Africa.
14
Jackson, Lawrence S., John H. Marsham, Douglas J. Parker, Declan L. Finney, Rory G. J. Fitzpatrick, David P. Rowell, Rachel A. Stratton, and Simon Tucker. "The Effect of Explicit Convection on Climate Change in the West African Monsoon and Central West African Sahel Rainfall." Journal of Climate 35, no. 5 (March 1, 2022): 1537–57. http://dx.doi.org/10.1175/jcli-d-21-0258.1.
Анотація:
Abstract The West African monsoon (WAM) is the dominant feature of West African climate providing the majority of annual rainfall. Projections of future rainfall over the West African Sahel are deeply uncertain, with a key reason likely to be moist convection, which is typically parameterized in global climate models. Here, we use a pan-African convection-permitting simulation (CP4), alongside a parameterized convection simulation (P25), to determine the key processes that underpin the effect of explicit convection on the climate change of the central West African Sahel (12°–17°N, 8°W–2°E). In current climate, CP4 affects WAM processes on multiple scales compared to P25. There are differences in the diurnal cycles of rainfall, moisture convergence, and atmospheric humidity. There are upscale impacts: the WAM penetrates farther north, there is greater humidity over the northern Sahel and the Saharan heat low regions, the subtropical subsidence rate over the Sahara is weaker, and ascent within the tropical rain belt is deeper. Under climate change, the WAM shifts northward and Hadley circulation weakens in P25 and CP4. The differences between P25 and CP4 persist, however, underpinned by process differences at the diurnal scale and large scale. Mean rainfall increases 17.1% in CP4 compared to 6.7% in P25 and there is greater weakening in tropical ascent and subtropical subsidence in CP4. These findings show the limitations of parameterized convection and demonstrate the value that explicit convection simulations can provide to climate modelers and climate policy decision makers.
15
Leauthaud, C., J. Demarty, B. Cappelaere, M. Grippa, L. Kergoat, C. Velluet, F. Guichard, E. Mougin, S. Chelbi, and B. Sultan. "Revisiting historical climatic signals to better explore the future: prospects of water cycle changes in Central Sahel." Proceedings of the International Association of Hydrological Sciences 371 (June 12, 2015): 195–201. http://dx.doi.org/10.5194/piahs-371-195-2015.
Анотація:
Abstract. Rainfall and climatic conditions are the main drivers of natural and cultivated vegetation productivity in the semiarid region of Central Sahel. In a context of decreasing cultivable area per capita, understanding and predicting changes in the water cycle are crucial. Yet, it remains challenging to project future climatic conditions in West Africa since there is no consensus on the sign of future precipitation changes in simulations coming from climate models. The Sahel region has experienced severe climatic changes in the past 60 years that can provide a first basis to understand the response of the water cycle to non-stationary conditions in this part of the world. The objective of this study was to better understand the response of the water cycle to highly variable climatic regimes in Central Sahel using historical climate records and the coupling of a land surface energy and water model with a vegetation model that, when combined, simulated the Sahelian water, energy and vegetation cycles. To do so, we relied on a reconstructed long-term climate series in Niamey, Republic of Niger, in which three precipitation regimes can be distinguished with a relative deficit exceeding 25% for the driest period compared to the wettest period. Two temperature scenarios (+2 and +4 °C) consistent with future warming scenarios were superimposed to this climatic signal to generate six virtual future 20-year climate time series. Simulations by the two coupled models forced by these virtual scenarios showed a strong response of the water budget and its components to temperature and precipitation changes, including decreases in transpiration, runoff and drainage for all scenarios but those with highest precipitation. Such climatic changes also strongly impacted soil temperature and moisture. This study illustrates the potential of using the strong climatic variations recorded in the past decades to better understand potential future climate variations.
16
Stith, Mimi, Alessandra Giannini, John del Corral, Susana Adamo, and Alex de Sherbinin. "A Quantitative Evaluation of the Multiple Narratives of the Recent Sahelian Regreening*." Weather, Climate, and Society 8, no. 1 (January 1, 2016): 67–83. http://dx.doi.org/10.1175/wcas-d-15-0012.1.
Анотація:
Abstract A spatial analysis is presented that aims to synthesize the evidence for climate and social dimensions of the “regreening” of the Sahel. Using an independently constructed archival database of donor-funded interventions in Burkina Faso, Mali, Niger, and Senegal in response to the persistence of drought in the 1970s and 1980s, the spatial distribution of these interventions is examined in relation to population density and to trends in precipitation and in greenness. Three categories of environmental change are classified: 1) regions at the northern grassland/shrubland edge of the Sahel where NDVI varies interannually with precipitation, 2) densely populated cropland regions of the Sahel where significant trends in precipitation and NDVI decouple at interannual time scales, and 3) regions at the southern savanna edge of the Sahel where NDVI variation is independent of precipitation. Examination of the spatial distribution of environmental change, number of development projects, and population density brings to the fore the second category, covering the cropland areas where population density and regreening are higher than average. While few, regions in this category coincide with emerging hotspots of regreening in northern Burkina Faso and southern central Niger known from case study literature. In examining the impact of efforts to rejuvenate the Sahelian environment and livelihoods in the aftermath of the droughts of the 1970s and 1980s against the backdrop of a varying and uncertain climate, the transition from desertification to regreening discourses is framed in the context of adaptation to climate change.
17
Janicot, Serge, Flore Mounier, Sébastien Gervois, Benjamin Sultan, and George N. Kiladis. "The Dynamics of the West African Monsoon. Part V: The Detection and Role of the Dominant Modes of Convectively Coupled Equatorial Rossby Waves." Journal of Climate 23, no. 14 (July 15, 2010): 4005–24. http://dx.doi.org/10.1175/2010jcli3221.1.
Анотація:
Abstract This study is the last in a series of papers addressing the dynamics of the West African summer monsoon at intraseasonal time scales between 10 and 90 days. The signals of convectively coupled equatorial Rossby (ER) waves within the summer African monsoon have been investigated after filtering NOAA outgoing longwave radiation (OLR) data within a box delineated by the dispersion curves of the theoretical ER waves. Two families of waves have been detected in the 10–100-day periodicity band by performing a singular spectrum analysis on a regional index of ER-filtered OLR. For each family the first EOF mode has been retained to focus on the main convective variability signal. Within the periodicity band of 30–100 days, an ER wave pattern with an approximate wavelength of 13 500 km has been depicted. This ER wave links the MJO mode in the Indian monsoon sector with the main mode of convective variability over West and central Africa. This confirms the investigations carried out in previous studies. Within the 10–30-day periodicity band, a separate ER wave pattern has been highlighted in the African monsoon system with an approximate wavelength of 7500 km, a phase speed of 6 m s−1, and a period of 15 days. The combined OLR and atmospheric circulation pattern looks like a combination of ER wave solutions with meridional wavenumbers of 1 and 2. Its vertical baroclinic profile suggests that this wave is forced by the deep convective heating. Its initiation in terms of OLR modulation is detected north of Lake Victoria, extending northward and then propagating westward along the Sahel latitudes. The Sahel mode identified in previous studies corresponds to the second main mode of convective variability within the 10–30-day periodicity band, and this has also been examined. Its pattern and evolution look like the first-mode ER wave pattern and they are temporally correlated with a coefficient of +0.6. About one-third of the Sahel mode events are concomitant with an ER wave occurrence. The main difference between these two signals consists of a stronger OLR and circulation modulation of the Sahel mode over East and central Africa. Thus, the Sahel mode occurrence and its westward propagation could be explained in part by atmospheric dynamics associated with the ER waves and in part by land surface interactions, as shown in other studies.
18
Goutorbe, J. P., J. Noilhan, P. Lacarrere, and I. Braud. "Modelling of the atmospheric column over the Central sites during HAPEX-Sahel." Journal of Hydrology 188-189 (February 1997): 1017–39. http://dx.doi.org/10.1016/s0022-1694(96)03181-2.
19
Lebel, Thierry, and Abdou Ali. "Recent trends in the Central and Western Sahel rainfall regime (1990–2007)." Journal of Hydrology 375, no. 1-2 (August 2009): 52–64. http://dx.doi.org/10.1016/j.jhydrol.2008.11.030.
20
Panthou, G., T. Vischel, and T. Lebel. "Recent trends in the regime of extreme rainfall in the Central Sahel." International Journal of Climatology 34, no. 15 (March 25, 2014): 3998–4006. http://dx.doi.org/10.1002/joc.3984.
21
Vizy, Edward K., and Kerry H. Cook. "Mid-Twenty-First-Century Changes in Extreme Events over Northern and Tropical Africa." Journal of Climate 25, no. 17 (March 9, 2012): 5748–67. http://dx.doi.org/10.1175/jcli-d-11-00693.1.
Анотація:
Abstract Changes in rainfall and temperature extremes are predicted by many global climate models as a response to greenhouse gas increases, and such changes will have significant environmental and social impacts. A regional climate model is used to predict changes in extremes across tropical and northern Africa for 2041–60 under a midline emissions forcing scenario. Six indicators are examined, including annual extreme and daily diurnal temperature ranges, heat wave days, number of dry days, number of extreme wet days, and extreme wet day rainfall intensity. Confidence in the projections is evaluated by examining the ensemble spread and the validation of extreme events in the twentieth-century simulation. Despite an increase in both daily minimum and maximum temperatures, diurnal temperature ranges decrease from West Africa to Ethiopia during spring and fall, over the Sahel during summer, and over the Congo basin during winter and spring. Diurnal temperature ranges increase over the Horn of Africa during boreal winter and over Kenya and Tanzania during boreal summer. The number of heat wave days increases north of 8°N with the largest increase (60–120 days) over the western Sahel. The number of dry days decreases over the Congo and the central Sahel but increases over East Africa, the latter associated with a reduction in the springtime long rains. The number of extreme wet rainfall days is projected to increase over West Africa, the Sahel, and the Ethiopian Highlands but decrease over the Congo. The predicted changes in extreme wet rainfall intensity are highly regional.
22
Bathiany, Sebastian, Martin Claussen, and Victor Brovkin. "CO2-Induced Sahel Greening in Three CMIP5 Earth System Models." Journal of Climate 27, no. 18 (September 10, 2014): 7163–84. http://dx.doi.org/10.1175/jcli-d-13-00528.1.
Анотація:
Abstract The existence and productivity of vegetation is the basis for food and energy supply in the Sahel. Past changes in climate and vegetation abundance have raised the question whether the region could become greener in the future as a result of higher CO2 levels. By analyzing three Earth system models (ESMs) from phase 5 of the Coupled Model Intercomparison Project (CMIP5) with dynamic vegetation, the authors demonstrate why an answer to this question remains elusive in contrast to more robust projections of vegetation cover in the extratropics. First, it depends on the location and the time scale whether vegetation expands or retreats. Until the end of the twenty-first century, the three models agree on a substantial greening in the central and eastern Sahel due to increased CO2 levels. This trend is reversed thereafter, and vegetation retreats in particular in the western Sahel because the beneficial effect of CO2 fertilization is short lived compared to climate change. Second, the vegetation cover changes are driven by different processes in different models (most importantly, precipitation change and CO2 fertilization). As these processes tend to oppose each other, the greening and browning trends are not a reliable result despite the apparent model agreement. The authors also find that the effect of vegetation dynamics on the surface energy balance crucially depends on the location. In contrast to the results of many previous studies, the Sahel appears as a hotspot where the physiological effects of CO2 can exert a cooling because vegetation structure and distribution overcompensate for the decreased stomatal conductance.
23
Rodríguez-Fonseca, Belen, Elsa Mohino, Carlos R. Mechoso, Cyril Caminade, Michela Biasutti, Marco Gaetani, J. Garcia-Serrano, et al. "Variability and Predictability of West African Droughts: A Review on the Role of Sea Surface Temperature Anomalies." Journal of Climate 28, no. 10 (May 12, 2015): 4034–60. http://dx.doi.org/10.1175/jcli-d-14-00130.1.
Анотація:
Abstract The Sahel experienced a severe drought during the 1970s and 1980s after wet periods in the 1950s and 1960s. Although rainfall partially recovered since the 1990s, the drought had devastating impacts on society. Most studies agree that this dry period resulted primarily from remote effects of sea surface temperature (SST) anomalies amplified by local land surface–atmosphere interactions. This paper reviews advances made during the last decade to better understand the impact of global SST variability on West African rainfall at interannual to decadal time scales. At interannual time scales, a warming of the equatorial Atlantic and Pacific/Indian Oceans results in rainfall reduction over the Sahel, and positive SST anomalies over the Mediterranean Sea tend to be associated with increased rainfall. At decadal time scales, warming over the tropics leads to drought over the Sahel, whereas warming over the North Atlantic promotes increased rainfall. Prediction systems have evolved from seasonal to decadal forecasting. The agreement among future projections has improved from CMIP3 to CMIP5, with a general tendency for slightly wetter conditions over the central part of the Sahel, drier conditions over the western part, and a delay in the monsoon onset. The role of the Indian Ocean, the stationarity of teleconnections, the determination of the leader ocean basin in driving decadal variability, the anthropogenic role, the reduction of the model rainfall spread, and the improvement of some model components are among the most important remaining questions that continue to be the focus of current international projects.
24
Tindan, Jacob Z., Qinjian Jin, and Bing Pu. "Understanding day–night differences in dust aerosols over the dust belt of North Africa, the Middle East, and Asia." Atmospheric Chemistry and Physics 23, no. 9 (May 16, 2023): 5435–66. http://dx.doi.org/10.5194/acp-23-5435-2023.
Анотація:
Abstract. Utilizing the well-calibrated, high-spectral-resolution equal-quality performance of daytime and nighttime (09:30 and 21:30 local solar Equator-crossing time (local solar ECT)) products of the Infrared Atmospheric Sounder Interferometer (IASI) from the Laboratoire de Météorologie Dynamique (LMD), this study investigates the day–night differences in dust aerosols over the global dust belt of North Africa, the Middle East, and Asia. Both daytime dust optical depth (DOD) and nighttime DOD at 10 µm show high consistency with solar and lunar observations of coarse-mode aerosol optical depth (CAOD) from AErosol RObotic NETwork (AERONET) sites across the dust belt, with correlation coefficients of 0.8–0.9 for most sites. Both IASI DOD and dust layer height show a significant (95 % confidence level) day–night difference over the major dust sources within the dust belt. Daytime DOD over the central to northern Sahara, the central to eastern Arabian Peninsula, and the Taklamakan Desert is significantly higher than that of nighttime but lower than nighttime over the southern Sahel to the Guinea Coast and the western to central Indian subcontinent in the annual mean. The magnitude of the day–night differences in DOD is larger and more evident in boreal winter and spring than in other seasons. The positive day–night differences in DOD (i.e., higher daytime values than nighttime) over the central Sahara, the Middle East, and Asia are likely associated with greater dust emissions driven by higher dust uplift potential (DUP) and stronger wind speeds during daytime. Dust layer heights demonstrate negative day–night differences over dust source regions in the central Sahara, central Arabian Peninsula, and Taklamakan Desert and positive height differences in the southern Sahel to the Guinea Coast, southern parts of the Arabian Peninsula, and large parts of the Indian subcontinent. The higher dust layer height over the Guinea Coast and the Indian subcontinent during the daytime is associated with a deeper planetary boundary layer height and greater convective instability during daytime than nighttime, which promotes vertical transport and mixing of dust aerosols. The corresponding lower daytime DOD over the Sahel and the Indian subcontinent indicates a possible dilution of dust aerosols when they are transported to higher altitudes by convection where they are more susceptible to horizontal transport. Ground-based observations of dust show surface PM10 concentration and CAOD exhibit a spatially varying diurnal cycle across the dust belt. CAOD and PM10 concentrations generally peak in late morning and from late afternoon to midnight in the Sahel and in early afternoon and around early morning in the Middle East, the timings of which are largely consistent with the day–night differences in IASI DOD. It is also found that DOD from reanalysis products (e.g., Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) and ECMWF Atmospheric Composition Reanalysis 4 (EAC4)) failed to capture the day–night differences in IASI DOD in large parts of the dust belt except in small dust source hotspots over North Africa.
25
Habib, Adnane, Kamal Labbassi, Nadia Akdim, and Amina Tadji. "Contribution des données Alos et Landsat dans la cartographie et l'analyse des linéaments dans le Sahel Central (Maroc occidental)." Revue Française de Photogrammétrie et de Télédétection, no. 203 (April 8, 2014): 33–42. http://dx.doi.org/10.52638/rfpt.2013.28.
Анотація:
Dans la région du Sahel, l'avance du biseau salé lié à la surexploitation de nappes et la dégradation de la côte constituent un problème majeur dans cette région où les nappes phréatiques constituent la seule ressource d'alimentation en eau. En conséquence, plusieurs recherches hydrogéologiques ont été entamées dans le secteur afin d'assurer une bonne alimentation en eau pour les populations locales, l'agriculture et l'industrie. Dans cette étude, plusieurs techniques d'extraction des linéaments ont été appliquées sur des données ALOS et LANDSAT dans la région du Sahel central (entre Sidi-Moussa et Oualidia), incluant différents types de rehaussement, ainsi que l'application de différents filtres directionnels sur des produits ACP dérivés des images d'origine. Les linéaments extraits ont été évalués à la base des cartes géologiques et cartes hydrogéologiques de la zone d'étude. Des analyses statistiques ont été aussi réalisées pour déterminer les longueurs et les densités des linéaments. Ces nouveaux documents générés permettront une meilleure compréhension de la relation fracturation - circulation des eaux, à l'identification des zones de recharge et de minéralisation, et permettront aussi par la suite l'orientation de la prospection hydrogéologique dans ce secteur qui fera l'objet d'une prochaine publication.
26
Haour, Anne. "Power and permanence in precolonial Africa: a case study from the central Sahel." World Archaeology 37, no. 4 (December 2005): 552–65. http://dx.doi.org/10.1080/00438240500412816.
27
Schwarz, Maximilian, Tobias Landmann, Damien Jusselme, Eduardo Zambrano, Jens Danzeglocke, Florian Siegert, and Jonas Franke. "Assessing the Environmental Suitability for Transhumance in Support of Conflict Prevention in the Sahel." Remote Sensing 14, no. 5 (February 24, 2022): 1109. http://dx.doi.org/10.3390/rs14051109.
Анотація:
Increasing conflicts between farmers and pastoralists continue to be a major challenge in the Sahel. Political and social factors are in tandem important underlying determinants for conflicts in the region, which are amplified by the variability and scarcity of natural resources, often as a result of climate variability and climate change. This study aimed at holistically assessing the main environmental parameters that influence the patterns of seasonal migratory movements (transhumance) in a transboundary area in the southern Republic of Chad and northern Central African Republic through a broad set of Earth observation (EO) data and data from the Transhumance Tracking Tool. A spatial model was applied to the datasets to determine the spatiotemporal dynamics of environmental suitability that reflects suitable areas and corridors for pastoralists. A clear difference in environmental suitability between the origin and destination areas of herders was found in the dry season, proving the main reason for pastoralists’ movements, i.e., the search for grazing areas and water. Potential conflict risk areas could be identified, especially along an agricultural belt, which was proven by conflict location data. The results demonstrate the potential and innovation of EO-derived environmental information to support the planning of transhumance corridors and conflict prevention in the Sahel. In the future, a combination of real-time tracking of herders and EO-derived information can eventually lead to the development of an early warning system for conflicts along transhumance corridors in the Sahel.
28
Hanan, N. P., and S. D. Prince. "Stomatal conductance of West-Central supersite vegetation in HAPEX-Sahel: measurements and empirical models." Journal of Hydrology 188-189 (February 1997): 536–62. http://dx.doi.org/10.1016/s0022-1694(96)03192-7.
29
Pierre, C., J. L. Rajot, I. Faye, G. S. Dorego, C. Bouet, B. Marticorena, G. Bergametti, et al. "A contrasting seasonality of wind erosivity and wind erosion between Central and Western Sahel." Aeolian Research 62 (June 2023): 100879. http://dx.doi.org/10.1016/j.aeolia.2023.100879.
30
Sacré Regis M., Didi, Ly Mouhamed, Kouadio Kouakou, Bichet Adeline, Diedhiou Arona, Coulibaly Houebagnon Saint. J., Kouadio Koffi Claude A., Coulibaly Talnan Jean H., Obahoundje Salomon, and Savané Issiaka. "Using the CHIRPS Dataset to Investigate Historical Changes in Precipitation Extremes in West Africa." Climate 8, no. 7 (June 30, 2020): 84. http://dx.doi.org/10.3390/cli8070084.
Анотація:
This study aims to provide improved knowledge and evidence on current (1986–2015) climate variation based on six rainfall indices over five West African countries (Senegal, Niger, Burkina Faso, Ivory Coast, and Benin) using the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) dataset. On average, precipitation has increased over the central Sahel and the western Sahel. This increase is associated with increase in the number of rainy days, longer wet spells and shorter dry spells. Over the Guinea Coast, the slight increase in precipitation is associated with an increase in the intensity of rainfall with a shorter duration of wet spells. However, these mean changes in precipitation are not all statistically significant and uniform within a country. While previous studies are focused on regional and sub-regional scales, this study contributes to deliver a climate information at a country level that is more relevant for decision making and for policy makers, and to document climate-related risks within a country to feed impact studies in key sectors of the development, such as agriculture and water resources.
31
Filippov, Vasily R. "African Policy of France in 2017–2023." Asia and Africa Today, no. 5 (2023): 65. http://dx.doi.org/10.31857/s032150750025686-6.
Анотація:
The geopolitical transformations of modern times marked the beginning of the end of French dominance in Western and Central Tropical Africa. The article names the main determinants of the process of degradation of the French model of neo-colonialism. Among these, the author refers to the destruction of Libyan statehood, the ensuing invasion of militants of Islamist associations into the territory of the Sahel and the consolidation of Islamists into the Al-Qaeda in the Islamic Maghreb (AQIM) unit, the uprising of the Tuareg in northern Mali and the proclamation of the unrecognized state of Azawad in the Sahel, the operation of the French troops “Barkhane” in the territory of the countries of the military-political bloc G5S.According to the author, the failure of operation “Barkhane”, the inability of the French troops to effectively resist Islamic terrorists provoked discontent among the citizens of the CAR, Mali and Burkina Faso. In these African states, coups d’état took place, as a result of which puppet pro-French political elites were removed from power and regimes oriented towards Moscow were established.
32
Deroubaix, Adrien, Cyrille Flamant, Laurent Menut, Guillaume Siour, Sylvain Mailler, Solène Turquety, Régis Briant, Dmitry Khvorostyanov, and Suzanne Crumeyrolle. "Interactions of atmospheric gases and aerosols with the monsoon dynamics over the Sudano-Guinean region during AMMA." Atmospheric Chemistry and Physics 18, no. 1 (January 16, 2018): 445–65. http://dx.doi.org/10.5194/acp-18-445-2018.
Анотація:
Abstract. Carbon monoxide, CO, and fine atmospheric particulate matter, PM2.5, are analyzed over the Guinean Gulf coastal region using the WRF-CHIMERE modeling system and observations during the beginning of the monsoon 2006 (from May to July), corresponding to the Africa Multidisciplinary Monsoon Analysis (AMMA) campaign period. Along the Guinean Gulf coast, the contribution of long-range pollution transport to CO or PM2.5 concentrations is important. The contribution of desert dust PM2.5 concentration decreases from ∼ 38 % in May to ∼ 5 % in July. The contribution of biomass burning PM2.5 concentration from Central Africa increases from ∼ 10 % in May to ∼ 52 % in July. The anthropogenic contribution is ∼ 30 % for CO and ∼ 10 % for PM2.5 during the whole period. When focusing only on anthropogenic pollution, frequent northward transport events from the coast to the Sahel are associated with periods of low wind and no precipitation. In June, anthropogenic PM2.5 and CO concentrations are higher than in May or July over the Guinean coastal region. Air mass dynamics concentrate pollutants emitted in the Sahel due to a meridional atmospheric cell. Moreover, a part of the pollution emitted remotely at the coast is transported and accumulated over the Sahel. Focusing the analysis on the period 8–15 June, anthropogenic pollutants emitted along the coastline are exported toward the north especially at the beginning of the night (18:00 to 00:00 UTC) with the establishment of the nocturnal low level jet. Plumes originating from different cities are mixed for some hours at the coast, leading to high pollution concentration, because of specific disturbed meteorological conditions.
33
Gronenborn, Detlef. "Anne Haour: Rulers, warriors, traders, clerics: the central Sahel and the North Sea 800–1500." Azania: Archaeological Research in Africa 44, no. 1 (April 2009): 153–54. http://dx.doi.org/10.1080/00671990902796192.
34
Nan, Sulan, Ping Zhao, and Junming Chen. "Variability of summertime Tibetan tropospheric temperature and associated precipitation anomalies over the central-eastern Sahel." Climate Dynamics 52, no. 3-4 (May 23, 2018): 1819–35. http://dx.doi.org/10.1007/s00382-018-4246-8.
35
Cavalieri, O., F. Cairo, F. Fierli, G. Di Donfrancesco, M. Snels, M. Viterbini, F. Cardillo, et al. "Variability of aerosol vertical distribution in the Sahel." Atmospheric Chemistry and Physics Discussions 10, no. 7 (July 21, 2010): 17609–55. http://dx.doi.org/10.5194/acpd-10-17609-2010.
Анотація:
Abstract. We present and discuss ground-based and satellite observations of aerosol optical properties over Sahelian Africa for the years 2006, 2007 and 2008. This study combines data acquired by three ground-based micro lidar systems located in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analysis (AMMA), by the AEROsol RObotic NETwork (AERONET) sun-photometers and by the space-based Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). The 2006 seasonal pattern of the aerosols vertical distribution is presented. It shows the presence of aerosol mainly confined in the lower levels of the atmosphere during the dry season, with the aerosol layer increasing in vertical extension and absolute values in spring, reaching the largest values in summer in correspondence with a progressive clearing up of the atmosphere at the lowermost levels. Aerosol produced by biomass burning are observed mainly during the dry season, when north-easterly air masses pass over large biomass burning areas before recirculating over the measurement sites. This kind of aerosol is present mainly in layers between 2 and 6 km of altitude, although episodically it may show also below 2 km, as observed in Banizoumbou (Niger) in 2006. Biomass burning aerosol is also observed during spring when air masses originating from North and East Africa pass over sparse biomass burning sources, and during summer when biomass burning aerosol is transported from the southern part of the continent by the monsoon flow. The summer season on the whole is characterized by a large presence of desert dust along the entire Sahelian region, widespread in altitude with Aerosol Optical Depths above 0.2. The interannual variability in the three year monitoring period is not very significant. An analysis of the aerosol transport pathways, aiming at detecting the main source regions, revealed that air originated from the Saharan desert is present all year long and it is observed in the lower levels of the atmosphere at the beginning and at the end of the year. In the central part of the year it extends upward and the lower levels are less affected by air masses from Saharan desert when the monsoon flow carries inland air from the Guinea Gulf and Southern Hemisphere. Biomass burning is mainly confined in the higher layers and observable in winter and in autumn.
36
Aiyyer, Anantha, and Chris Thorncroft. "Interannual-to-Multidecadal Variability of Vertical Shear and Tropical Cyclone Activity." Journal of Climate 24, no. 12 (June 15, 2011): 2949–62. http://dx.doi.org/10.1175/2010jcli3698.1.
Анотація:
Abstract Spatiotemporal patterns of tropics-wide vertical shear variability are extracted after separating a 58-yr data record into high-frequency (HF, periods of 1.5–8 yr) and low-frequency (LF, periods greater than 8 yr) components. The HF vertical shear variability is dominated by circulation anomalies associated with the El Niño–Southern Oscillation (ENSO). The LF variability is primarily contained in two multidecadal patterns and a near-decadal pattern. The multidecadal modes are strongest within the tropical Atlantic and are correlated with Sahel precipitation and interhemispheric sea surface temperature (SST) anomalies. The results suggest that the multidecadal variability of vertical shear over the Atlantic is linked to atmospheric circulation anomalies forced by the variability in Sahel precipitation. The decadal mode is strongest within the central Pacific and is correlated with Pacific decadal oscillation (PDO)-like SST anomalies. The circulation associated with this anomalous shear pattern appears to be consistent with the atmospheric response to the PDO-related diabatic heating anomaly over the central Pacific. The relationship between vertical shear and seasonal tropical cyclone activity, as defined by the accumulated cyclone energy (ACE), is examined for the Atlantic, eastern Pacific, and western Pacific Oceans. The results show that global modes of vertical shear and seasonal average ACE are not consistently related in all three regions. It is only in the Atlantic Ocean that seasonal ACE is most consistently limited by vertical shear. This calls into question the utility of vertical shear as an independent predictor of seasonal tropical cyclone activity, particularly over the western Pacific Ocean.
37
Sidorov, Alexander. "THE MILITARY-POLITICAL BALANCE OF FRANCE’S CAPABILITIES IN THE SAHEL: STAGES AND MECHANISMS OF EXIT FROM THE THEATER OF OPERATIONS." Urgent Problems of Europe, no. 4 (2022): 79–108. http://dx.doi.org/10.31249/ape/2022.04.04.
Анотація:
The article discusses the unfavorable development of situation in the Sahel for France, which is associated, among other things, with a new geopolitical challenge - the penetration of new international actors into the France’s traditional interests zone in Africa. Despite the transformation of France’s defense priorities in favor of a European continent geolocation, the Sahel remains an important area for French military efforts in fighting terrorism. A bulk of scientific literature and expert opinions is analyzed to highlight and evaluate how France adapts to the changing character of the conflict and the new strategies of armed terrorist groups. The author pays special attention to the destructive role of endogenous, internal factors in the confrontation between jihadist groups and the central governments of the Sahel countries, especially Mali. The role and use by France of a number of mechanisms for an orderly exit from the theatre of operations are shown, and their effectiveness is assessed. It is concluded that it is impossible to stabilize the security situation in weak states through enhanced training of local armed forces. Among the exogenous factors that, from the point of view of France, continue to have a negative impact on the development of the situation in Mali and neighboring countries, the Libyan factor and the strengthening of the Russian military presence in the region are singled out. It is noted that even in the circumstances of the forced redeployment of the Barkhane and Takuba missions, France and its European allies will continue to fight terrorism in the areas bordering Mali. The author comes to the conclusion that the current events will lead to a rethinking of the goals of the French military presence in Africa and will create prerequisites for building a new security architecture in the region.
38
Adler, J. "Experience of a Medical Team at the Harbo Refugee Camp in Ethiopia." Prehospital and Disaster Medicine 2, no. 1-4 (1986): 224–27. http://dx.doi.org/10.1017/s1049023x00030892.
Анотація:
The famine presently ravaging the population of the Sahel belt in Central Africa is not a new occurrence. In the last 15 years, hundreds of thousands of people have died because of malnutrition and disease, caused by the successive failure of crops. In addition to the lack of adequate rainfalls, many other factors have contributed to the present situation:• Overgrazing of available land by increasing numbers of livestock.• Failure of the governments involved to modernize their agriculture by irrigation programs, fertilization, etc.• Consummation of grains for seeding and livestock by the famine stricken population—preventing rehabilitation.
39
Organ, Jake, David Dixon, and Kira Villa. "Climate Change, Fertility and Sahelian Demographics." Journal of Sustainable Development 16, no. 1 (November 19, 2022): 1. http://dx.doi.org/10.5539/jsd.v16n1p1.
Анотація:
Climate change, especially in Africa’s central Sahel region, is occurring in the context of exponential population rise with countries like Chad and Niger still in the “early expanding phase” of demographic growth. While many experts predict a mid-century climate and demographic ‘mega crisis’ for the region; our paper looks at the effect of the rising temperature, through the medium of increased temperature and precipitation variability upon fertility and hence demographic trends as we advance into the 21st century. The paper uses climate data and DHS (Demographic and Health Survey) data from Chad, which has demonstrated significant warming since the late 1960’s. We create a weather shock variable that is defined as a t>2 departure from the post-1960 mean of temperature and precipitation by month, year, and GIS location. We regress the following years’ human fertility outcomes by month and GIS location upon these shocks when occurring in the growing months of June, July, and August. We find that the effect is highly negatively significant with a one-year lag. Then we go on to look for the mechanism behind this significance; the literature suggesting that climate effects fertility through biological or food security related channels. We then regress the male/female sex ratio on the same weather shocks to see if there is a rise in miscarriages among male fetuses due to either the direct effect of heat or as an effect of increased female malnutrition. By running both these models with weather shocks from Chad’s dry season months of December, January, and February, we discern whether the significance is driven by pure temperature or by some sort of food security/household income channel. Though we see some dry season effect, most of the significance is driven by the shocks in the growing season and with the significant effect of these shocks on the sex ratio, we can assume that increased female malnutrition is a key driver of both the rise in miscarriages and the drop-in fertility. We then run these models within each of the three Chadian climate zones: the Sahara, the Sahel, and the Sudan. Seeing that the Sahel zone is the major driver for the significance of our models, we discuss if this can have implications for the wider African Sahel.
40
Ringrose, Susan, Cheryl Huckerby, and Wilma Matheson. "The use of low cost scanning data for land cover mapping in the west central Sahel." Geocarto International 11, no. 4 (December 1996): 91–96. http://dx.doi.org/10.1080/10106049609354565.
41
Ashley, Ceri. "Haour, A. 2007. Rulers, Warriors, Traders, Clerics: The Central Sahel and the North Sea, 800–1500." African Archaeological Review 25, no. 3-4 (September 23, 2008): 175–78. http://dx.doi.org/10.1007/s10437-008-9029-x.
42
Lare, Andrew R., and Sharon E. Nicholson. "A Climatonomic Description of the Surface Energy Balance in the Central Sahel. Part I: Shortwave Radiation." Journal of Applied Meteorology 29, no. 2 (February 1990): 123–37. http://dx.doi.org/10.1175/1520-0450(1990)029<0123:acdots>2.0.co;2.
43
ASHLEY, SCOTT. "Rulers, Warriors, Traders, Clerics: The Central Sahel and the North Sea, 800-1500 - By Anne Haour." Early Medieval Europe 17, no. 2 (April 16, 2009): 222–23. http://dx.doi.org/10.1111/j.1468-0254.2009.00267.x.
44
Rabé, Mahamane Moctar, Ibrahim B. Baoua, and Dieudonne Baributsa. "Enhancing Cowpea Productivity in the Sahel: Exploring Seed Access among Smallholder Farmers in South-Central Niger." Horticulturae 9, no. 12 (November 30, 2023): 1287. http://dx.doi.org/10.3390/horticulturae9121287.
Анотація:
Cowpea productivity in West Africa is low due to several challenges, including limited access to high-quality seeds. Despite the development of improved varieties, smallholder farmers face difficulties in accessing certified seeds. This study interviewed 634 households in south-central Niger to assess how farmers access cowpea seeds. Most farmers (94.6%) relied on informal seed systems, with local markets being the primary source (72.8%). The formal seed sector, including the private sector, had a limited role. Farmers typically stored seeds for seven months utilizing pesticides (54.9%) and hermetic methods (42.6%). Interestingly, the price of seeds of improved cowpea varieties in local markets was 1.19 times higher than that of local varieties, but only 25% of the cost of certified seeds. Interventions to strengthen informal seed systems and improve access to credit could enhance the adoption of high-quality cowpea seeds and increase productivity.
45
Marteau, Romain, Nathalie Philippon, Bernard Fontaine, and Vincent Moron. "Approche multi-scalaire du démarrage de la saison des pluies au Sahel central et occidental : cohérence spatiale et prévisibilité (Multiscalar approach of the onset of rainy season in central and western Sahel : spatial coherence and predictability)." Bulletin de l'Association de géographes français 87, no. 2 (2010): 207–20. http://dx.doi.org/10.3406/bagf.2010.8153.
46
Saidou, Salifou, and Jean-Marie Karimou Ambouta. "Part contributive de la densité démographique au reverdissement de certaines zones fortement anthropisées du Sahel : cas des Communes d’Aguié et d’Ibohamane au Niger." International Journal of Biological and Chemical Sciences 14, no. 3 (June 19, 2020): 816–34. http://dx.doi.org/10.4314/ijbcs.v14i3.14.
Анотація:
Cette étude porte sur l’analyse de la dimension humaine dans l’explication du reverdissement observé dans le paysage de certaines zones fortement anthropisées du Sahel. A cet effet, la commune d’Aguié et celle d’Ibohamane ont été choisies en prenant en compte leur forte densité démographique. La méthodologie utilisée repose sur l’application d’une analyse corrélative couplée à des tests statistiques sur les valeurs de pluies annuelles, les densités démographiques et les valeurs de l’indice normalisé de végétation sur la série chronologique 1980-2018. Les résultats obtenus mettent en évidence deux séquences pluviométriques sèche et humide statistiquement significatives. Pour autant, la période humide récente bien installée à partir de la décennie 90 n’explique pas en totalité l’expression du reverdissement de ces zones. Des taux de 60% et 45% de ce changement sont associés à la densité démographique respectivement au niveau de la commune d’Aguié et celle d’Ibohamane. Ces résultats permettent de replacer le rôle central de la dimension humaine dans la mutation paysagère récente de certaines zones sahéliennes. A ce titre ils peuvent canaliser les réflexions sur la recherche des facteurs et conditions favorables à la mise à l’échelle du reverdissement.Mots clés : NDVI, Pluviométrie, Anthropisation, Reverdissement, RUE.
English Title: Contributing part of population density to the regreening of certain highly anthropized area of the Sahel: the case of Agué and Ibohamane municipalities in NigerThis study focuses on human dimension in the explanation of the the regreening process observed in certain areas of the Sahel region. For this purpose, the municipalities of Aguié and Ibohamane were chosen according to their high population density. The methodology used is based on the application of the correlative analysis coupled with statistical test on the annual rainfall values, population density values and the normalized vegetation index values, over 1980-2018 time series. The results obtained highlight two significant dry and wet sequences. However, the recent wet period, well established from the 1990s does not fully explain the regreening of these areas. Rates of 60% and 45% of this change are due to population density respectively in Aguié and Ibohamane case. These results replace the central role of human dimension in the dynamic change of sahelian landscapes and provide the keys that can guide the reflection on the search of factors and conditions favorable of scaling up of regreening.Keywords: NDVI, Rainfall, Anthropization, Regreening, RUE.
47
Cavalieri, O., F. Cairo, F. Fierli, G. Di Donfrancesco, M. Snels, M. Viterbini, F. Cardillo, et al. "Variability of aerosol vertical distribution in the Sahel." Atmospheric Chemistry and Physics 10, no. 24 (December 16, 2010): 12005–23. http://dx.doi.org/10.5194/acp-10-12005-2010.
Анотація:
Abstract. In this work, we have studied the seasonal and inter-annual variability of the aerosol vertical distribution over Sahelian Africa for the years 2006, 2007 and 2008, characterizing the different kind of aerosols present in the atmosphere in terms of their optical properties observed by ground-based and satellite instruments, and their sources searched for by using trajectory analysis. This study combines data acquired by three ground-based micro lidar systems located in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analysis (AMMA), by the AEROsol RObotic NETwork (AERONET) sun-photometers and by the space-based Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the CALIPSO satellite (Cloud-Aerosol Lidar and Infrared Pathfinder Observations). During winter, the lower levels air masses arriving in the Sahelian region come mainly from North, North-West and from the Atlantic area, while in the upper troposphere air flow generally originates from West Africa, crossing a region characterized by the presence of large biomass burning sources. The sites of Cinzana, Banizoumbou and M'Bour, along a transect of aerosol transport from East to West, are in fact under the influence of tropical biomass burning aerosol emission during the dry season, as revealed by the seasonal pattern of the aerosol optical properties, and by back-trajectory studies. Aerosol produced by biomass burning are observed mainly during the dry season and are confined in the upper layers of the atmosphere. This is particularly evident for 2006, which was characterized by a large presence of biomass burning aerosols in all the three sites. Biomass burning aerosol is also observed during spring when air masses originating from North and East Africa pass over sparse biomass burning sources, and during summer when biomass burning aerosol is transported from the southern part of the continent by the monsoon flow. During summer months, the entire Sahelian region is under the influence of Saharan dust aerosols: the air masses in low levels arrive from West Africa crossing the Sahara desert or from the Southern Hemisphere crossing the Guinea Gulf while in the upper layers air masses still originate from North, North-East. The maximum of the desert dust activity is observed in this period which is characterized by large AOD (above 0.2) and backscattering values. It also corresponds to a maximum in the extension of the aerosol vertical distribution (up to 6 km of altitude). In correspondence, a progressive cleaning up of the lowermost layers of the atmosphere is occurring, especially evident in the Banizoumbou and Cinzana sites. Summer is in fact characterized by extensive and fast convective phenomena. Lidar profiles show at times large dust events loading the atmosphere with aerosol from the ground up to 6 km of altitude. These events are characterized by large total attenuated backscattering values, and alternate with very clear profiles, sometimes separated by only a few hours, indicative of fast removal processes occurring, likely due to intense convective and rain activity. The inter-annual variability in the three year monitoring period is not very significant. An analysis of the aerosol transport pathways, aiming at detecting the main source regions, revealed that air originated from the Saharan desert is present all year long and it is observed in the lower levels of the atmosphere at the beginning and at the end of the year. In the central part of the year it extends upward and the lower levels are less affected by air masses from Saharan desert when the monsoon flow carries air from the Guinea Gulf and the Southern Hemisphere inland.
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Diouf, Ibrahima, Souleymane Sy, Habib Senghor, Papa Fall, Diarra Diouf, Moussa Diakhaté, Wassila M. Thiaw, and Amadou T. Gaye. "Potential Contribution of Climate Conditions on COVID-19 Pandemic Transmission over West and North African Countries." Atmosphere 13, no. 1 (December 27, 2021): 34. http://dx.doi.org/10.3390/atmos13010034.
Анотація:
COVID-19, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), is a very contagious disease that has killed many people worldwide. According to data from the World Health Organization (WHO), the spread of the disease appears to be slower in Africa. Although several studies have been published on the relationship between meteorological parameters and COVID-19 transmission, the effects of climate conditions on COVID-19 remain largely unexplored and without consensus. However, the transmission of COVID-19 and sensitivity to climate conditions are also not fully understood in Africa. Here, using available epidemiological data over 275 days (i.e., from 1 March to 30 November 2020) taken from the European Center for Disease Prevention and Control of the European Union database and daily data of surface air temperature specific humidity and water vapor from the National Center for Environmental Prediction (NCEP), this paper investigates the potential contribution of climate conditions on COVID-19 transmission over 16 selected countries throughout three climatic regions of Africa (i.e., Sahel, Maghreb, and Gulf of Guinea). The results highlight statistically significant inverse correlations between COVID-19 cases and temperature over the Maghreb and the Gulf of Guinea regions. In contrast, positive correlations are found over the Sahel area, especially in the central part, including Niger and Mali. Correlations with specific humidity and water vapor parameters display significant and positive values over the Sahelian and the Gulf of Guinea countries and negative values over the Maghreb countries. Then, the COVID-19 pandemic transmission is influenced differently across the three climatic regions: (i) cold and dry environmental conditions over the Maghreb; (ii) warm and humid conditions over the Sahel; and (iii) cold and humid conditions over the Gulf of Guinea. In addition, for all three climatic regions, even though the climate impact has been found to be significant, its effect appears to display a secondary role based on the explanatory power variance compared to non-climatic factors assumed to be dominated by socio-economic factors and early strong public health measures.
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Koné, Brahima, Arona Diedhiou, Adama Diawara, Sandrine Anquetin, N'datchoh Evelyne Touré, Adama Bamba, and Arsene Toka Kobea. "Influence of initial soil moisture in a regional climate model study over West Africa – Part 2: Impact on the climate extremes." Hydrology and Earth System Sciences 26, no. 3 (February 11, 2022): 731–54. http://dx.doi.org/10.5194/hess-26-731-2022.
Анотація:
Abstract. The influence of soil moisture initial conditions on the climate extreme indices over West Africa was investigated using the fourth generation of the International Centre for Theoretical Physics regional climate model (non-hydrostatic) coupled with version 4.5 of the Community Land Model (RegCM4–CLM4.5) at a 25 km spatial resolution. We initialized the control experiments with the reanalysis soil moisture data from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis of the 20th century (ERA-20C), while we initialized the dry and wet experiments with the maximum and minimum soil moisture values over the West Africa domain, respectively. For each experiment, an ensemble of five runs was performed for 5 years (2001–2005) with soil moisture initial conditions for the runs prescribed on 1 June and the simulations being performed over 4 months (122 d) from June to September. The performance of RegCM4–CLM4.5 with respect to simulating the 10 extreme rainfall and temperature indices used in this study is presented. The results are then discussed for the two idealized simulations that are most sensitive to the dry and wet soil moisture initial conditions in order to highlight the impacts beyond the limits of soil moisture internal forcing in the model. Over the Central Sahel, dry (wet) experiments lead to a decrease (increase) in precipitation extreme indices related to the number of events, but this was not seen for indices related to the intensity of the events. Soil moisture initial conditions unequally affect the daily minimum and maximum temperatures. The strongest impact is found on the maximum temperature: wet (dry) experiments decrease (increase) the maximum temperature over the whole region. Over the Central Sahel, wet (dry) experiments lead to a decrease (increase) in the maximum values of the minimum temperature.
50
Lefebvre, Camille. "Ganin ya fi ji / Voir est mieux qu’entendre : lire l’identité sur la peau (Sahel central, XIXe siècle)." Critique internationale N° 68, no. 3 (2015): 39. http://dx.doi.org/10.3917/crii.068.0039.