Recent Climate Shocks in the Sahel: A Systematic Review

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.


Introduction
Global environmental changes cannot be excluded from the debates on development and environmental protection in Africa. The latter is true because ecosystems respond to climate change and climate change also determines the pace of global development in general and African development in particular [1,2]. The influence of climate change in sub-Saharan Africa is even more evident as in the last three and a half decades the region has witnessed temperatures increasing in the range of 0.2-2.0° C amidst declining precipitation [3]. The projections of future temperatures right up to 2100 shows that it will cumulatively exceed the range of 0.2-2.0° C that was observed in the last three and a half decades. The fifth assessment report (AR5) of the IPCC further supports this assertion by observing that mean temperatures will potentially increase on a decade basis by 1.8° C in 2020, by 1.9° C in 2030, by 1.8° C in 2040, by 1.7° C by 2050 and by 1.2° C by 2100 [4]. The impacts of the above observations are enhanced vulnerability of cropping systems and amplified poverty, low adaptive capacity, and more frequent climate shocks [5,6]. Despite the importance of climate factor in the region, non-climatic drivers such as agricultural expansion, deforestation, occasioned by rapid population growth have tilted the debate on which of climatic and non-climatic factors drives the shocks more [7].
Three main climate shocks (droughts, floods, and sandstorms (winds)) are dominant across Africa and the Sahel [8][9][10][11][12][13][14][15]. The Sahel is well known for its droughts and as a result, the region is one of the most susceptible to droughts globally [16][17][18]. The causes of these droughts are either human related (human induced climate change) or climatically driven (sea surface temperature, effects of vegetation, CO 2 emissions and land degradation, and dust feed backs) [11]. It has been reported that hydrological droughts are becoming frequent in the Sahel due to observations of enhanced discharge in rivers. Since the 1970s, river Niger for example has witnessed increase discharge of its tributaries. It is indeed surprising that while temperatures are observed to be rising in the Sahel and projections of the same are pessimistic, some rivers in the region are witnessing increase discharge in what has been termed the "Sahel paradox" [19][20][21][22][23]. Furthermore, the Sahel is increasingly impacted by airborne dust or sandstorms which are also impacting the climate of the region [3]. Satellite sensors have shown that Sahelian dust are not only regionally restricted but also globally distributed [14,24]. In fact, reports hold that most of the dust outbreaks around the world are linked to the Sahel [25][26][27].
Climate change stakeholders in the Sahel have been active seeking ways and means of addressing these climate shocks. In this context, adaptations actions, policies and programs have been designed to help address the surge [28][29][30]. For example, the United Nations Reductions of Emissions from Deforestation and Forest Degradation (REDD+); has been designed to support reforestation project across the world [12,[31][32][33][34][35][36][37]. We also have the United Nations Framework Convention on Climate Change (UNFCCC) [38] which enhances research and adaptive capacity in developing countries. The African Development Bank (AfDB) has created the African Climate Fund which focuses on enhancing increase to climate finance in Africa [39]. Additionally, the Pan African Agency for the "Great Green Wall (GGW)" has been involved in planting trees across the Sahel [40].
Even though there is an increase in the proliferation of studies on climate shocks in the Sahel, there is still a shortage of studies that provide updated and holistic information on the dominant shocks, their distribution, across the Sahel and their drivers. In fact, it is still unclear which climate shocks are most reported in the scientific literature over time. This enhances the ability to monitor existing gaps in the scientific scholarship and to pave the way for the future. In addition, it provides a holistic picture of the regional and country level variations in the dominant shocks impacting the Sahel and further provides and opportunity to leverage our understanding in shaping adaptation actions.

Country and regional distribution of climate change shocks and affiliation of authors
A total of 388 climate shocks (droughts, floods, and winds) were documented in 164 peer reviewed papers. The results show further that in terms of countries, Southern Niger recorded the highest frequency and percentage of reports of climate change shocks (n = 62, 15.97%) between 1975 and 2020. Ethiopia which is second recorded 46 or 11.85% of the shocks, Senegal next with 41 or 10.56% of the shocks and Kenya with 33 or 8.5% of the climate shocks (Figure 1). Regionally, West African Sahel recorded the highest number of shocks (n = 193, 49.97%), then second was East African Sahel (n = 116, 29.89%) and Central African Sahel with (n = 47, 12.11%) (Figure 2).
A total of 164 peer review papers were recorded for this chapter. Of this number, 55 authors are affiliated in the USA, 19 in France, 17 in the United Kingdom and 10 in Germany. These countries are countries that have colonial ties in Africa and   Table 1). The other shocks in order of importance are floods (n = 123) (Figure 2) and winds/sandstorms (n = 46) (Figures 3 and 4). It can be inferred that the Sahel is a zone of climatic extremes with droughts topping the chart during the dry periods and with floods taking over during periods of prolonged precipitation which confirms the fact that one of the consequences of climate change is the amplification of extreme events.
In terms of the distribution of these shocks in various countries, the following countries recorded the highest number of shocks in order of importance: in term of droughts, Kenya recorded 28, Ethiopia recorded 26 and Niger recorded 24. In the domain of floods, Cameroon was the highest with 27 shocks, Niger with 24 shocks, and Ethiopia with 20 shocks. In the case of winds/sandstorms Niger observed the most shocks with the highest of 14 shocks, Senegal recorded 10 shocks and Mali recorded 5 shocks (Figure 3).   which are more the 388 which are the total number of shocks reported as some studies reported both climatic and non-climatic drivers (Figure 6). Climatic drivers account for about 200 droughts, 111 floods and 30 winds/sandstorms. Non-climatic drivers accounted for 176 droughts, 102 floods and 36 winds/sandstorms. Climatic drivers account for most of the climate shocks but non-climatic drivers are increasingly becoming important. Some shocks such as droughts, floods, and winds (sandstorms) can result from a combination of climatic and non-climatic factors.

Discussion and implications
In this chapter, we examine the occurrence of climate shocks across the Sahel based on reports in the primary peer review literature. The work also examines the  role of climatic and non-climatic drivers of the climate shocks and their evolution over time. These results provide a basis for assessing where shocks are occurring and to design adaptation actions based on the latter.
An analysis of where climate change shocks are occurring, what climate change shocks researchers are focusing on and their evolution over time goes a long way in providing insights that can enhance the ability to cope with the shocks. Already, this work has shown that in the Sahel, current adaptation strategies must be tailored to cope against droughts which are the most frequently reported climate shock in the Sahel. Invariably, droughts should be followed by floods and winds in any policy strategies aimed at cubbing shock and enhancing climate resilience in the Sahel. Even though floods have gained importance in the scientific scholarship over time, droughts remain the dominant climate forcing in the Sahel around which most adaptation actions should be drawn. Basing adaptations on site specific drivers is consistent with the systematic approach described by [53] and [11] describing the drivers of forest degradation in Bolivia and Cameroon respectively and using these drivers to propose policy options. This approach provides room for sustainability and accuracy and is a departure from the approach that is based on generalizations the copy pasting of what has worked elsewhere. This chapter provides a snapshot of the frequency in which climate change shocks are reported in the scientific literature, the affiliations of the authors, when and where the shocks occurred and the relative contributions of climatic and non-climatic drivers of these shocks.
Furthermore, this chapter has found out that Southern Niger and West African Sahel recorded the highest number climate change shocks in the Sahel. Kenya however recorded the highest number of reported droughts, while Cameroon recorded the highest number of floods. On the other hand, Niger recorded the highest number of winds. Researchers, and other decision-making stakeholders must prioritize these dominant shocks. Most of the peer review studies reported here argue both climatic and non-climatic drivers are driving these climate shocks in the Sahel. For a long time, the scientific literature has noted that many of the environmental problems faced across Africa were caused by climate change. However, this current chapter notes that non-climatic drivers are gaining importance. There is scientific evidence across Africa and the Sahel that illustrates that most of the environmental issues facing the region are driven by non-climatic drivers such as deforestation, population growth, wars and unsustainable approaches of land tenure and use like shifting and slash and burn cultivation inter alia while climate change only playing a reinforcing role [1,7,44,[54][55][56][57][58].
The decade 1975-1985 recorded the highest number of shocks in the Sahel. This surge has been attributed to the ravaging droughts that impacted most sub-Saharan African countries in the 1970s and early 1980s [50,[59][60][61][62][63][64]. At the dawn of the mid 1980s, the droughts that ravaged the continent had reduced in intensity giving rise to a surge in other climate shocks such as floods. Recent normalized difference vegetation index (NDVI) studies across the Sahel show that from the mid-1980s onwards, the Sahel has witnessed increasing precipitation and greening of the landscape [7,54,60,61,[65][66][67][68][69][70][71]. This work is unique in that it is the first to use the systematic approach to verify the temporal and spatial distribution of climate shocks in the Sahel as well as their drivers. This approach has previously been used in tracking adaptations around the world as reported in the following studies, [1,41,43,63,64,[67][68][69][70][71][72]. It is important to caution that, this work provides a proxybased approach offering a baseline from which climate change can be evaluated and monitored in the Sahel.
As this work is a first attempt to track climate change adaptations in the Sahel, going forward, the following recommendations are made: 1. similar systematic reviews across larger scales across Africa such as African continent. *Address all correspondence to: epule.terence@um6p.ma both peer review and gray literature to better capture the shocks that might have been reported in non-standardized studies 3. Providing further insights into the leverage of research in the context of who is researching what and where are they affiliated. This option will help is encouraging a higher leverage of research funding for the region. Though this work is based on proxies, it has also been verified that through ground truthing that these results are generally valid as ground truthing has not resulted in any new information that can contradict these findings. equatorial north Atlantic: possible relationship to the Sahelian drought. Science, 1976Science, , 196, 1196Science, -1198