Diminishing Light Precipitation Leads to the Concurrence of Droughts and Heatwaves in Southwest China

In recent decades, global precipitation patterns have undergone significant changes, mainly characterized by increases in heavy precipitation and decreases in light precipitation. The diminishing light precipitation may lead to compound events of droughts and heatwaves, which can have severe detrimental impacts on the human health and social-economic environment. This study investigates the varying characteristics of precipitation intensity, drought days (defined as Standardized Precipitation Evapotranspiration Index SPEI ≤ –1.0), and heat wave days in Southwest China from 1961 to 2018. The major findings are: Remarkable compounding changes in meteorological extremes occurred under global warming conditions in 1961–2018, including the top 10% heavy precipitation, bottom 10% light precipitation, dry days, droughts, and heat waves. In addition, the reduction in light precipitation primarily manifests as a decrease in light precipitation days, resulting in an equal increase in non-precipitation days. Total increases in compounding dry days (daily precipitation < 0.1 mm day–1), dry spell days (periods of at least five consecutive dry days), drought days (SPEI ≤ –1.0) and heat wave days during 1961–2018 were 9%, 16%, 13% and 24%, respectively. These increases are expected to continue with increasing global temperature. The 24% increase in heat wave days is particularly alarming due to its detrimental health impacts on human beings.