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Climate change is expected to increase the frequency and magnitude of hydro-climatic extremes events, such as floods and droughts, impacting economies, livelihoods, and the environment, particularly in vulnerable areas, such as in some African countries, where the occurrence of multi-hazard events is likely to amplify disaster impacts (IPCC, 2022) (1). The EM-DAT international disaster database indicates that over the last twenty years (2002-2021) floods (n=793) and droughts (n=137) represented 55% of natural hazards in Africa (n= 1,693), with 14,053 and 20,821 deaths, respectively.
Floods and drought are two extremes of the hydrological cycle. Despite their different physical processes, with different spatial and temporal scales, their interplay can enhance the resulting detrimental cascading effects. For instance, drought hazards lead to soil degradation, reduced sub-surface water storage, and a lower capacity for soil infiltration, which increases run off and proneness to flood risk. In comparison to the previous twenty years (1982-2001), EM-DAT indicates an increasing temporal trend in occurrences of floods and droughts in Africa, with a more important increase for floods (+180 %) than for drought (+30 %).
Figure 1 shows a fluctuating trend of annual drought-flood recurrences, indicating that the interplay of droughts with floods – as also observed by Di Baldassare et al. (2017) (2) – may merit further study. In numerical terms, floods occur more frequently than droughts, with annually an average of 40 flood events and seven drought events. Most floods in Africa occurred in 2007 (n=64) and 2020 (n= 66), while the highest number of drought events hit Africa in 2005 (n= 13), 2010 (n=10), and 2011 (n=11).
Floods are usually sudden, fast-moving phenomena, which are commonly limited to one or two catchments, even though this can vary, depending on the specific circumstances, while droughts are slow-onset extensive processes, characterized by a prolonged period of below-average precipitation, evolving over relatively long time scales. This can make documenting drought durations and losses more challenging than is the case for floods. Even though comparing numbers of people affected by floods and droughts must be done with care – as this can vary considerably, depending on a number of factors – the EM- DAT database indicates that droughts appear to affect more people than floods. In the past three to five years, flood events in Africa had considerable impacts, with a peak of seven million people being affected in 2020. In contrast, droughts affected about 33 million people in 2021, 30 million in 2015, and 24 million in 2011 (Fig. 1). The total number of people affected by droughts (about 295 million people) was about five times higher than the number of people affected by floods (about 58 mil- lion people) between 2002 and 2021.
The spatial distribution of impacts caused by droughts and floods in Africa indicates that some countries have been more affected than others during the last twenty years. Since 2002, the geographical distribution of drought mortality in Africa, has been concentrated exclusively on a few East African countries and South Africa (Fig. 2). The 2010 drought in Somalia alone caused 20,000 deaths, followed by severe droughts such as the one in Malawi with 500 deaths in 2002, and the one in Burundi in 2005, leading to 120 fatalities (Fig.2a). Floods affected the African continent more frequently and on a wider spatial scale than droughts. However, flood mortality has mainly affected Kenya (1,699 fatalities), Nigeria (1,551 fatalities), Ethiopia (1,540 fatalities), and Sudan (995 fatalities) during the last twenty years (Fig.2 b).