Compound risk dynamics of drought by extreme precipitation and temperature events in a semi-arid watershed

With the acceleration of global warming, the correlations between climate factors and drought events remain an important topic, presenting special consequences in arid and semi-arid areas with significant warming. We analyzed the spatiotemporal variations for extreme climate events including indices based on the Expert Team on Climate Change Detection and Indices (ETCCDI), heatwave, and Standardized Precipitation Index (SPI) in a semi-arid watershed, and then quantified their relationship. Observations indicated a significant increasing trend of extreme warm events, and the spatial distribution of these trends varied with latitude, longitude, and altitude. Precipitation-related extreme indices (heavy precipitation days and extreme precipitation intensity) also displayed increments of 5.1 mm/10 yr and 0.1 days/10 yr. The average drought events calculated by the SPI were 3.8 times, and the events from 1994 to 2018 was more than those from 1969 to 1993, especially in moderate, severe, and extreme drought. We found that extreme warming events were significantly correlated with drought, so we considered heatwaves and drought events occurring simultaneously. The more frequent drought-heatwave compounds showed that strong warming amplified the drought conditions, and drought could also lead to a more rapid increase for the intensity and duration of heatwaves (0.7 °C/10 yr and 0.23 days/10 yr) compared with those in heatwaves alone (0.4 °C/10 yr and 0.15 days/10 yr). Our findings emphasize the connections between drought conditions and extreme warm events, which is conducive to improving the understanding of the mechanisms of extreme events and facilitating disaster prevention and control.