Emergence of new heat stress hotspots over West Africa

Motivated by the recent record-breaking heatwaves over western Africa, the authors analyzed 50 years of hourly wet-bulb globe temperature (WBGT) data to identify emerging heatwave hotspots, characterize their timing and types, and evaluate whether simpler heatwave metrics, more commonly used by meteorological agencies, can be employed to estimate dangerous WBGT conditions. They find that exposure to WBGT ≥30 °C and <33 °C (conditions dangerous during light physical activity) has been increasing across almost all of western Africa, at rates of 30–100 h per decade. The researchers highlight two major heat stress hotspots: the border region of Senegal, Mauritania, and Mali, and southwestern Niger, where the WBGT threshold of 33 °C (dangerous even at rest) has recently been exceeded for up to 40 h per year, increasing by 1–4 h per decade.

These regions experience dangerous heat stress conditions as a consequence of high temperatures in the late spring, and moderately high temperatures and high humidities in early autumn. Current extreme heat monitoring operates from April to June, while our analysis suggests that it should be extended to also include September and October, when high humidity makes dangerous conditions possible at lower air temperatures. Moreover, because episodes of dangerous heat stress can occur over a wide range of temperatures, relying solely on high temperature percentiles would have missed over 60% of dangerous WBGT episodes across most of the region. Employing the extreme heat indicators that also account for humidity is thus essential.