Standardized compound drought and heatwave index: A new compound drought and heatwave events monitoring index considering evapotranspiration effects

Compound drought and heatwave events (CDHEs), as critical extreme climate phenomena, have attracted substantial scientific attention because of their profound impact on the sustainability of socioecological systems. Nevertheless, current identification methods rely only on the combined influence of precipitation and temperature changes and fail to consider the contribution of evapotranspiration in drought‒heatwave. This resulted in a low estimation of the spatial extent and severity of such compound events. Here, we developed a new standardized compound drought and heatwave index (SCDHI) using the Gaussian copula probability distribution modeling, combining the standardized precipitation evapotranspiration index (SPEI) with the standardized temperature index (STI). We found that compared with the existing indicator, the SCDHI improved significantly in monitoring accuracy and monitoring capability for CDHEs, particularly in assessing vegetation responses. By explicitly considering the impact of evapotranspiration on the intensification of droughts, the SCDHI effectively corrected the underestimated deviations that are commonly present in traditional methods in vegetation areas. The proposed index demonstrates strong potential for multiscale monitoring of CDHEs, enhancing assessments of their impact on the environment and society.