african sahel
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Author(s):  
Guillaume Chagnaud ◽  
Geremy Panthou ◽  
Theo Vischel ◽  
Thierry Lebel

Abstract The West African Sahel has been facing for more than 30 years an increase in extreme rainfalls with strong socio-economic impacts. This situation challenges decision-makers to define adaptation strategies in a rapidly changing climate. The present study proposes (i) a quantitative characterization of the trends in extreme rainfalls at the regional scale, (ii) the translation of the trends into metrics that can be used by hydrological risk managers, (iii) elements for understanding the link between the climatology of extreme and mean rainfall. Based on a regional non-stationary statistical model applied to in-situ daily rainfall data over the period 1983-2015, we show that the region-wide increasing trend in extreme rainfalls is highly significant. The change in extreme value distribution reflects an increase in both the mean and variability, producing a 5%/decade increase in extreme rainfall intensity whatever the return period. The statistical framework provides operational elements for revising the design methods of hydraulic structures which most often assume a stationary climate. Finally, the study shows that the increase in extreme rainfall is more attributable to an increase in the intensity of storms (80%) than to their occurrence (20%), reflecting a major disruption from the decadal variability of the rainfall regime documented in the region since 1950.


2021 ◽  
pp. 1-42

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-Africa 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 (8°W-2°E, 12-17°N). 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 north Sahel and the Saharan heat low regions, the sub-tropical subsidence rate over the Sahara is weaker, and ascent within the tropical rain belt is deeper. Under climate change, the WAM shifts northwards and Hadley circulation weakens in P25 and CP4. The differences between P25 and CP4 persist, however, underpinned by process differences at the diurnal and large-scales. Mean rainfall increases 17.1% in CP4 compared to 6.7% in P25 and there is greater weakening in tropical ascent and sub-tropical subsidence in CP4. These findings show the limitations of parameterized convection and demonstrate the value that explicit convection simulations can provide to climate modellers and climate policy decision makers.


2021 ◽  
Author(s):  
Terence Epule Epule ◽  
Driss Dhiba ◽  
Abdelghani Chehbouni

In Africa, the Sahel is increasingly susceptible to climate shocks such as droughts, sandstorms (winds), and floods. Through a systematic review this work tracks the frequency with which these shocks are reported in the literature during the period 1975–2020. This work examines trends to identify which shocks are most reported, documenting their spatial distribution and evaluating the impacts of climatic and non-climatic drivers. In general, 388 shocks were reported in 164 relevant peer review papers. Southern Niger recorded 15.97% of all the shocks while Ethiopia and Senegal recorded 11.85% and 10.85% respectively. Also, West African Sahel saw about 49.97% of all shocks followed by East African Sahel with 29.89% and Central African Sahel with 12.11%. Generally, droughts (n = 219), appear to be the most frequently reported shocks followed by floods (n = 123) and winds (n = 46). The 1975–1985 decade recorded the most shocks (n = 207), followed by the 1997–2007 decade which saw (n = 80) shocks while between 1986 and 1996 a total of 52 shocks were recorded. 52% of the shocks are driven by climatic factors while 47% are driven by non-climatic drivers.


2021 ◽  
Author(s):  
Tunde Amole ◽  
Ayantunde Augustine ◽  
Mulubrhan Balehegn ◽  
Adegbola T. Adesogoan

2021 ◽  
Vol 97 (6) ◽  
pp. 1805-1823
Author(s):  
Bruno Charbonneau

Abstract Since 2013, the multiplication of regional and international strategies and actions directed at stabilizing Mali and the Sahel, and at countering and preventing violent extremism, has not improved the situation there and, arguably, some of it has made it worse. This article analyses the type of political order and regional governance that has been and is being built after almost a decade of international interventions in the West African Sahel. It is an effort at theorizing and making sense of what is considered here to be a permanent state of intervention in the Sahel that has evolved into a form of counterinsurgency governance—a concept being proposed to point to the influence and the infusion of counterinsurgency principles into philosophies of governance. This article argues that counterinsurgency governance insists on a set of power relations and configurations that seeks to impose limits, parameters and boundaries to the purpose of and the form that Sahelian states, governments and governance ought to take. As such, counterinsurgency governance is simultaneously a mode of governance and a web of political practices and contestation whose mechanisms have failed at fully implementing its principles in the Sahel. Its fallback is the emergence of a regional strategy to manage and establish limits to Sahelian political possibilities.


2021 ◽  
Author(s):  
Edward K. Vizy ◽  
Kerry H. Cook

Abstract West African Sahel extreme rainfall events are impactful when strong mesoscale convective systems (MCSs) produce large amounts of rainfall in short periods. NASA IMERG rainfall estimates and the ERA5 reanalysis are examined to understand where the top 100 highest 12Z – 12Z 24-h rainfall totals and MCS storm genesis occur, and to assess the relative importance of environmental conditions in their generation including the influence of atmospheric moisture and vertical wind shear. Most of the top 100 events are located south of 14°N. Events cluster over three regions, namely, Mali, Burkina Faso, and northern Nigeria. The associated MCSs are typically not locally generated, forming instead at distances greater than 100 km upstream. Composites reveal that a significant increase in atmospheric moisture content occurs prior to development, but there is no evidence of significant changes in the 600 – 925 hPa vertical wind shear. This indicates that vertical wind shear is less influential in extreme storm development than atmospheric moisture preconditioning. The top 10 events are further evaluated. A change in these storms’ direction and speed near the maximum rainfall location is common, suggesting the MCSs are reorganizing around peak rainfall intensity time. Three atmospheric conditions are associated with these events. They are (1) moisture preconditioning of the atmosphere, (2) interaction of the storm in the wake of a region of anticyclonic flow, and (3) interaction of the storm in the wake of a region of anticyclonic flow and the Sahel/tropical dryline boundary.


Bringing together a wide diversity of authors based on three continents and from different disciplinary backgrounds, this book offers analyses of a wide range of factors that characterize and that are shaping the future of the African Sahel. In forty chapters, organized in nine sections, the book examines this complex and rapidly changing region on multiple dimensions. Collectively, the book attempts to offer an understanding of the specificity of the Sahel, and to examine its core characteristics as shaped by the geographic, cultural, and political parameters that define it. Following a series of chapters focused on the shaping of the Sahelian space as a region, six chapters explore the distinct national trajectories of the countries of the political Sahel: Senegal, Mali, Niger, Burkina Faso, Mauritania, and Chad. The extraordinary combination of environmental, economic, and political challenges, and the ways in which Sahelian states and societies have responded, are the primary focus of the three subsequent sections, while the various parameters of the lived realities of these societies in motion are explored in the four final sections of the book. Transversally throughout, the chapters aim to offer an interdisciplinary and holistic view of the challenges and the dynamics that are shaping a region at a historical crossroads, and an understanding of the many factors that feed and perpetuate its vulnerabilities and fragilities, as well as its sources of resilience.


2021 ◽  
pp. xviii-12
Author(s):  
Leonardo A. Villalón

Bringing together a wide diversity of authors based on three continents and from different disciplinary backgrounds, this book offers analyses of a wide range of factors that characterize and that are shaping the future of the African Sahel. In forty chapters, organized in nine sections, the book examines this complex and rapidly changing region on multiple dimensions. Collectively, the book attempts to offer an understanding of the specificity of the Sahel, and to examine its core characteristics as shaped by the geographic, cultural, and political parameters that define it. Following a series of chapters focused on the shaping of the Sahelian space as a region, six chapters explore the distinct national trajectories of the countries of the political Sahel: Senegal, Mali, Niger, Burkina Faso, Mauritania, and Chad. The extraordinary combination of environmental, economic, and political challenges, and the ways in which Sahelian states and societies have responded, are the primary focus of the three subsequent sections, while the various parameters of the lived realities of these societies in motion are explored in the four final sections of the book. Transversally throughout, the chapters aim to offer an interdisciplinary and holistic view of the challenges and the dynamics that are shaping a region at a historical crossroads, and an understanding of the many factors that feed and perpetuate its vulnerabilities and fragilities, as well as its sources of resilience.


2021 ◽  
Vol 39 ◽  
pp. 103110
Author(s):  
L. Champion ◽  
N. Gestrich ◽  
K. MacDonald ◽  
L. Nieblas-Ramirez ◽  
D.Q. Fuller

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