Drought-Heatwaves’ Dynamics with Land Use Land Cover Types under the West African Monsoon System

Abstract

Heatwaves are prolonged periods of abnormal heat that can adversely impact human and animal well-being, public infrastructure, agriculture, wildfire occurrence and severity, and workplace efficiency. With increasing global warming, heatwaves and droughts are predicted to worsen. However, there are only a few documented cases of heatwaves in Africa, and less research in West Africa has explored the thermodynamics of heatwaves in the region. This study seeks to comprehensively investigate the dynamics of heatwaves, particularly their interaction with landatmosphere processes and droughts as compound events in three climate zones in West Africa. The research compares heatwave and heat-stress occurrences and their coincidental intensity with drought, using satellite, reanalysis, and in-situ datasets from 1981 to 2020. The study uses Cumulative Heat (CumHeat or Heatcum) and Universal Thermal Climate Index (UTCI) to measure heatwaves, Standardized Precipitation (Evapotranspiration) Index (SPI or SPEI) for drought, and Normalized CumHeat for temperature (Tmax and Tmin), UTCI, and Wet-Bulb Globe Temperature (WBGT) to examine heatwave dynamics. The study employs the ECMWF Year of Polar Prediction (YOPP) dataset to determine the main temperature advection and tendency terms that contribute to heatwaves in selected cases (2018, 2019, and 2020) covering different climate zones, from 1000 hPa, 925 hPa, to 850 hPa, and 700 hPa. The study also uses validated coupled RegCM-CLM simulation outputs initialized with soil moisture to compute SPEI and the normalized heatwave indices. The Drought-heatwave (D-HW) events from observational data showed lower frequency and intensity than the gridded dataset. The West African monsoon system is experiencing an increase in the intensity and duration of UTCI and Tmax heatwaves, mainly before or after the monsoon phase, with some occurrences during the monsoon phase. An increasing trend in the intensity and duration of heatwaves, up to 40 days, has been observed in the gridded dataset, and there is a higher likelihood of WBGT occurrence during the night. The study found that the differences in heatwave indices are primarily due to the sensitivity to moisture and wind. The intensity of heatwaves exhibits asymmetric statistical responses to moisture content deficits, particularly in the Guinea zone and some parts of Sudan (Coast of Senegal). In the Eastern part of West Africa, the opposite reaction to mid-latitudes is observed, where there is an increase in moisture before and during a high heatwave. The impact of soil moisture on heatwaves extends to the 6th level (8th level) about 0.492912 m (1.38283 m) into the soil. These findings could help improve weather forecasting, predict the impacts of heatwaves, and design adaptation strategies to reduce the vulnerability of populations to heatwaves. Additionally, the results contribute to developing more accurate and robust climate models that can better simulate the behaviour of heatwaves and their interactions with other climate variables.