scholarly journals Observed and Simulated Changes in Precipitation over Sahel Region of West Africa

2016 ◽  
Vol 04 (01) ◽  
Author(s):  
Agumagu O
Keyword(s):  
West Africa ◽  
Sahel Region

scholarly journals Understanding the variability of the rainfall dipole in West Africa using the EC-Earth last millennium simulation

2021 ◽  
Author(s):  
Qiong Zhang ◽  
Ellen Berntell ◽  
Qiang Li ◽  
Fredrik Charpentier Ljungqvist
Keyword(s):  
West Africa ◽  
Model Simulation ◽  
Rainfall Variability ◽  
Low Pressure ◽  
Last Millennium ◽  
Tropical Atlantic ◽  
Gulf Of Guinea ◽  
Dipole Pattern ◽  
Sahel Region ◽  
Heat Low

AbstractThere is a well-known mode of rainfall variability associating opposite hydrological conditions over the Sahel region and the Gulf of Guinea, forming a dipole pattern. Previous meteorological observations show that the dipole pattern varies at interannual timescales. Using an EC-Earth climate model simulation for last millennium (850–1850 CE), we investigate the rainfall variability in West Africa over longer timescales. The 1000-year-long simulation data show that this rainfall dipole presents at decadal to multidecadal and centennial variability and long-term trend. Using the singular value decomposition (SVD) analysis, we identified that the rainfall dipole present in the first SVD mode with 60% explained variance and associated with the variabilities in tropical Atlantic sea surface temperature (SST). The second SVD mode shows a monopole rainfall variability pattern centred over the Sahel, associated with the extra-tropical Atlantic SST variability. We conclude that the rainfall dipole-like pattern is a natural variability mode originated from the local ocean–atmosphere-land coupling in the tropical Atlantic basin. The warm SST anomalies in the equatorial Atlantic Ocean favour an anomalous low pressure at the tropics. This low pressure weakens the meridional pressure gradient between the Saharan Heat Low and the tropical Atlantic. It leads to anomalous northeasterly, reduces the southwesterly moisture flux into the Sahel and confines the Gulf of Guinea's moisture convergence. The influence from extra-tropical climate variability, such as Atlantic multidecadal oscillation, tends to modify the rainfall dipole pattern to a monopole pattern from the Gulf of Guinea to Sahara through influencing the Sahara heat low. External forcing—such as orbital forcing, solar radiation, volcanic and land-use—can amplify/dampen the dipole mode through thermal forcing and atmosphere dynamical feedback.

Mode of Production and Population Patterns: Policy Implications for West African Development

1981 ◽  
Vol 11 (3) ◽  
pp. 361-387 ◽  
Author(s):  
Richard W. Franke
Keyword(s):  
West Africa ◽  
Population Growth ◽  
Production Systems ◽  
West African ◽  
Policy Implications ◽  
Population Policies ◽  
New Synthesis ◽  
Recent Developments ◽  
And Migration ◽  
Sahel Region

Recent developments in population theory have made possible a re-examination of demographic evidence from West Africa which suggests that population growth and migration are primarily responses to changes in the nature of the production system. Precolonial, colonial, and independence period data provide a series of correlations consistent with the approach and suggest a possible new synthesis of the West African data. The poorest countries of West Africa are those bordering on the Sahara Desert, known as the “Sahel” region. In response to the drought and famine in that region from 1968–1974, numerous proposals have been made for increased attention to reducing population growth. The analysis presented in this paper leads to the conclusion that population policies other than those attempting to lower the birth rate are called for. These would include relocation of populations previously displaced by colonial labor migrations and the re-integration of herding and farming production systems, both of which policies should be considered as population policies. Data are presented from specific projects underway in Senegal, Mauritania, and Mali, to illustrate the argument.

scholarly journals The TAMORA algorithm: satellite rainfall estimates over West Africa using multi-spectral SEVIRI data

2010 ◽  
Vol 25 ◽  
pp. 3-9 ◽  
Author(s):  
R. S. Chadwick ◽  
D. I. F. Grimes ◽  
R. W. Saunders ◽  
P. N. Francis ◽  
T. A. Blackmore
Keyword(s):  
West Africa ◽  
Estimation Algorithm ◽  
Radar Data ◽  
Local Calibration ◽  
Accumulated Rainfall ◽  
Satellite Rainfall ◽  
Sahel Region ◽  
Rain Rates ◽  
Improved Accuracy ◽  
Rainfall Estimates

Abstract. A multi-spectral rainfall estimation algorithm has been developed for the Sahel region of West Africa with the purpose of producing accumulated rainfall estimates for drought monitoring and food security. Radar data were used to calibrate multi-channel SEVIRI data from MSG, and a probability of rainfall at several different rain-rates was established for each combination of SEVIRI radiances. Radar calibrations from both Europe (the SatPrecip algorithm) and Niger (TAMORA algorithm) were used. 10 day estimates were accumulated from SatPrecip and TAMORA and compared with kriged gauge data and TAMSAT satellite rainfall estimates over West Africa. SatPrecip was found to produce large overestimates for the region, probably because of its non-local calibration. TAMORA was negatively biased for areas of West Africa with relatively high rainfall, but its skill was comparable to TAMSAT for the low-rainfall region climatologically similar to its calibration area around Niamey. These results confirm the high importance of local calibration for satellite-derived rainfall estimates. As TAMORA shows no improvement in skill over TAMSAT for dekadal estimates, the extra cloud-microphysical information provided by multi-spectral data may not be useful in determining rainfall accumulations at a ten day timescale. Work is ongoing to determine whether it shows improved accuracy at shorter timescales.

scholarly journals Rootstock Propagation Methods Affect the Growth and Productivity of Three Improved Cultivars of Ber in Mali, West Africa

2014 ◽  
Vol 24 (4) ◽  
pp. 418-423 ◽  
Author(s):  
Haby Sanou ◽  
Daouda Sidibé ◽  
Adama Korbo ◽  
Zewge Teklehaimanot
Keyword(s):  
West Africa ◽  
Fruit Production ◽  
Agroforestry Systems ◽  
Ziziphus Mauritiana ◽  
The South ◽  
Great Opportunity ◽  
Improved Cultivars ◽  
Propagation Methods ◽  
Sahel Region ◽  
Sudanian Zone

The adaptation of three improved cultivars of ber (Ziziphus mauritiana) from India to farming conditions in the Sudanian zone of the Sahel region was tested in Mali. The three cultivars used as scions were Seb, Umran, and Sotubata. The use of coppices of local ber resulted in a significantly better growth and higher fruit production on all the grafts of the three cultivars when compared with nursery seedling rootstocks. The cultivars also performed significantly better in the South Sudanian zone than in the more-arid North Sudanian zone. The highest fruit yield of 38 kg per tree was achieved on coppices in the South Sudanian zone. It was concluded that the high success of this experiment offers a great opportunity for adoption of the three improved cultivars of ber using coppice shoots as rootstock to optimize their use in parkland agroforestry systems in the South Sudanian zone of the Sahel region of West Africa.

scholarly journals ERS scatterometer surface soil moisture analysis of two sites in the south and north of the Sahel region of West Africa

2009 ◽  
Vol 375 (1-2) ◽  
pp. 253-261 ◽  
Author(s):  
M. Zribi ◽  
M. Pardé ◽  
P. De Rosnay ◽  
F. Baup ◽  
N. Boulain ◽  
...  
Keyword(s):  
Soil Moisture ◽  
West Africa ◽  
Surface Soil ◽  
Surface Soil Moisture ◽  
The South ◽  
Moisture Analysis ◽  
Sahel Region

scholarly journals Defining Crop–climate Departure in West Africa: Improved Understanding of the Timing of Future Changes in Crop Suitability

Climate ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 101 ◽  
Author(s):  
Egbebiyi ◽  
Crespo ◽  
Lennard
Keyword(s):  
Food Security ◽  
West Africa ◽  
Climate Models ◽  
Growth Conditions ◽  
Crop Growth ◽  
Global Climate Models ◽  
Future Climate ◽  
Climate Data ◽  
Crop Suitability ◽  
Sahel Region

The future climate is projected to change rapidly with potentially severe consequences for global food security. This study aims to improve the understanding of future changes in the suitability of crop growth conditions. It proposes a definition of crop realization, of the climate departure from recent historical variability, or crop–climate departure. Four statistically downscaled and bias-corrected Global Climate Models (GCMs): CCCMA, CNRM5, NOAA-GFDL, and MIROC5 performed simulations for the period 1960–2100 under the Representative Concentration Pathway RCP8.5 scenario to compute 20 year moving averages at 5-year increments. These were used to drive a crop suitability model, Ecocrop, for eight different crops across the three Food and Agriculture Organizations (FAO) AgroEcological Zones (AEZs) of West Africa (Guinea, Sahel, and Savanna). Simulations using historical climate data found that all crops except maize had a suitability index value (SIV) ≥0.50 outside the Sahel region, equivalent to conditions being suitable or strongly suitable. Simulations of future climate reveal that warming is projected to constrain crop growth suitability for cassava and pineapple in the Guinea zone. A potential for the northward expansion of maize is projected by the end of the century, suggesting a future opportunity for its growth in the southern Sahel zone. Crop growth conditions for mango and pearl millet remain suitable across all three AEZs. In general, crops in the Savanna AEZ are the most sensitive to the projected changes in climate. The changes in the crop–climate relationship suggests a future constraint in crop suitability, which could be detrimental to future food security in West Africa. Further studies to explore associated short- and long-term adaptation options are recommended.

scholarly journals Evolution Des Indices Pluviométriques Extrêmes Par L'analyse De Modèles Climatiques Régionaux Du Programme CORDEX: Les Projections Climatiques Sur Le Sénégal

2017 ◽  
Vol 13 (17) ◽  
pp. 206 ◽  
Author(s):  
Alioune Badara Sarr ◽  
Moctar Camara
Keyword(s):  
West Africa ◽  
Greenhouse Gas Emission ◽  
Precipitation Amount ◽  
Extreme Rainfall ◽  
Climate Indices ◽  
Rainfall Events ◽  
Western Sahel ◽  
Dry Spell ◽  
Sahel Region ◽  
Spell Length

This study aims at characterizing the extreme rainfall events over West Africa particularly in the Sahel region and Senegal by 2100 (far future) under the greenhouse gas emission scenario RCP8.5 by analyzing the simulations of four (4) regional climate models (RCMs) of CORDEX (Regional COordinated climate Downscaling Experiment) program. The study of these extreme climate indices is crucial for the understanding of the impacts of climate change on some vital socio-economic sectors such as the agriculture in Sahel and Senegal. The results show that almost all the RCMs predict a decrease of the rainfall over most parts of the Sahel region particularly over the Western Sahel. The analysis of the climate indices such as the highest one day precipitation amount, the 99th percentile and the maximum dry spell length (CDD) shows that the RCMs (except CanRCM4) project an increase of these exceptional rainfall events over the Sahel (especially over the Western Sahel) by 2100. In Senegal, the RCMs (except RCA4) agree on a decrease of the precipitation and the number of wet days by 2100. When considering the evolution of rainfall events intensity, the highest one day precipitation amount and the 99th percentile, the RCMs (except CanRCM4) predict an increase of the extreme events which may translate into strong floods in Senegal. As for the dry and wet sequences, the RCMs projections (except those of RCA4) show an increase (respectively a decrease) of the maximum dry spell length (respectively of the maximum wet spell length) in Senegal. This increase in extreme rainfall indices may translate into a strengthening of natural disasters such as floods and drought. This work can be considered as a support for the policymakers in West Africa and particularly in Senegal for the better long-term planning of water resources and disaster management as wells as the build of a resilient agricultural system.

scholarly journals Emission sources contributing to tropospheric ozone over equatorial Africa during the summer monsoon

2011 ◽  
Vol 11 (5) ◽  
pp. 13769-13827
Author(s):  
I. Bouarar ◽  
K. S. Law ◽  
M. Pham ◽  
C. Liousse ◽  
H. Schlager ◽  
...  
Keyword(s):  
West Africa ◽  
Atlantic Ocean ◽  
Summer Monsoon ◽  
Biomass Burning ◽  
Tropospheric Ozone ◽  
Anthropogenic Emissions ◽  
Model Calculations ◽  
Upper Troposphere ◽  
Sahel Region ◽  
Lightning Nox

Abstract. A global chemistry-climate model LMDz_INCA is used to investigate the contribution of African and Asian emissions to tropospheric ozone over central and West Africa during the summer monsoon. The model results show that ozone in this region is most sensitive to lightning NOx and to central African biomass burning emissions. However, other emission categories also contribute significantly to regional ozone. The maximum ozone changes due to lightning NOx occur in the upper troposphere between 400 hPa and 200 hPa over West Africa and downwind over the Atlantic Ocean. Biomass burning emissions mainly influence ozone in the lower and middle troposphere over central Africa, and downwind due to westward transport. Biogenic emissions of volatile organic compounds, which can be uplifted from the lower troposphere into higher altitudes by the deep convection that occurs over West Africa during the monsoon season, dominate the ozone changes in the upper troposphere and lower stratosphere region. Convective uplift of soil NOx emissions over the Sahel region also makes a significant contribution to ozone in the upper troposphere. Concerning African anthropogenic emissions, they make a lower contribution to ozone compared to the other emission categories. The model results indicate that most ozone changes due to African emissions occur downwind, especially over the Atlantic Ocean, far from the emission regions. The influence of Asian emissions should also be taken into account in studies of the ozone budget over Africa since they make a considerable contribution to ozone concentrations above 150 hPa. Using IPCC AR5 (Intergovernmental Panel on Climate Change; Fifth Assessment Report) estimates of anthropogenic emissions for 2030 over Africa and Asia, the model calculations suggest largest changes in ozone due to the growth of emissions over Asia than over Africa over the next 20 years.

African Dominion

2019 ◽  
Author(s):  
Michael A. Gomez
Keyword(s):  
West Africa ◽  
Social History ◽  
World History ◽  
Global History ◽  
New Vision ◽  
Sahel Region

Pick up almost any book on early and medieval world history and empire, and where do you find West Africa? On the periphery. This pioneering book tells a different story. Interweaving political and social history and drawing on a rich array of sources, the book unveils a new vision of how categories of ethnicity, race, gender, and caste emerged in Africa and in global history. Focusing on the Savannah and Sahel region, the book traces how Islam's growth in West Africa, along with intensifying commerce that included slaves, resulted in a series of political experiments unique to the region, culminating in the rise of empire. A radically new account of the importance of early Africa in global history, the book puts early and medieval West Africa on the map of global history.

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