Likelihood of compound dry and hot extremes increased with stronger dependence during warm seasons

Compound extreme climates may pose disproportionate and serious impacts on humanity and natural ecosystems, and thus it is valuable to explore the patterns and mechanisms of changes in compound climate extremes. However, quantitative analysis of extreme climate tends to be univariate statistics with a lack of focusing on the interactions between multiple climatic variables. In this study, the spatiotemporal changes in the likelihood of compound dry and hot extremes were investigated, using the copula method and the Standardized Precipitation Index (SPI). Our study demonstrated that the probability of compound dry and hot extremes increased with a stronger dependence between the SPI and temperature. The SPI and temperature showed negative correlations with large spatial difference on the global land, and variations in the negative correlation induce changes in the high-risk areas of occurring dry and hot extremes. The Mediterranean region, western United States, Southeast Asia, the Amazon, and southern Africa were typically affected. Moreover, most of the global land experienced an increase in the joint probability of concurrent dry and hot extremes as well as the conditional probability of hot under dry conditions, whereas small proportion of the global land exhibited an increase in the conditional probability of dry under hot conditions. The changes in high-risk hotspots indicate that regions with a strong negative correlation between the SPI and temperature are vulnerable to a warming climate. Our findings have implications in aiding mitigation the impacts of compound dry and hot extremes under global warming.