Spatiotemporal Variability of Compound Heat Drought Events in Sahel Region
Fredy Edson Mhenzi *
State Key Laboratory of Climate System Prediction and Risk Management/Key Laboratory of Meteorological Disaster, Ministry of Education/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044, China and National Meteorological Training Centre, Kigoma, Tanzania.
Philemon Henry King’uza
School of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China and Tanzania Meteorological Authority, Dodoma, Tanzania.
Innocent John Junior
State Key Laboratory of Climate System Prediction and Risk Management/Key Laboratory of Meteorological Disaster, Ministry of Education/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044, China and School of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China.
*Author to whom correspondence should be addressed.
Abstract
Compound heat-drought events (CHDEs) represent an important climate-related hazard in semi-arid regions, where high-temperature extremes and precipitation deficits can occur simultaneously and intensify environmental and socioeconomic stress. This study investigated the spatiotemporal variability of CHDEs across the Sahel during the June-September season for the period 1990-2020. Daily mean air temperature and daily precipitation data from ERA5 reanalysis were used to identify high-temperature extremes (HTEs) and low-precipitation extremes (LPEs) based on percentile thresholds. HTEs were defined using the 90th percentile of daily temperature, whereas LPEs were defined using the 25th percentile of daily precipitation. CHDEs were identified when both extremes occurred concurrently at the same grid cell and time step. Trend magnitudes were estimated using Sen's slope estimator, statistical significance was assessed using the Mann-Kendall test, and dominant modes of variability were examined using empirical orthogonal function analysis. The results showed that HTEs were most frequent over the northern Sahel, while LPEs occurred mainly across the northern and central Sahel. The highest frequencies of CHDEs were found over the southern and central Sahel. HTEs increased across much of the northern and eastern Sahel, whereas LPE trends showed spatial heterogeneity. CHDE trends were spatially mixed, with localised increases in parts of the central and northeastern Sahel. The leading empirical orthogonal function mode explained 33.4% of the total variance and indicated broad regional variability, with a tendency towards increased events in recent years. These findings highlight the importance of monitoring compound climate extremes for climate risk assessment and adaptation planning in the Sahel.
Keywords: Compound climate extremes, compound heat drought events, extreme temperature, percentile-based threshold, Sahel region, ERA5 reanalysis, percentile thresholds, Mann-Kendall test