Dynamic compound droughts in the Contiguous United States

Abstract

Severe meteorological and hydrological drought synergy contributes to adverse and large-scale social, economic, and environmental impacts beyond the individual occurrences. The risk, memory, and causality of this combination can be expressed by a compound dynamic perspective under a changing climate. In this study, we show that the concurrent risk of hydrological and metrological droughts has increased by up to 10% to 20% for moderate and severe events, and up to 8% to 12% for extreme events in recent decades, across watersheds in the western and southeastern Contiguous United States (CONUS).A bivariate Generalized Autoregressive Conditional Heteroskedasticity (GARCH) model also indicates that the dynamic compound droughts have strong short-term memory based on co-volatility, especially in the western CONUS. The results also suggest a short-memory causative dynamic mechanism, through which meteorological droughts may exponentially increase the occurrence of long-lasting and severe compound droughts, especially in the western CONUS. Given the broad impacts of extreme compound droughts, our findings have critical relevance for the ongoing proactive and long-term adaptive plans to mitigate adverse consequences arising from droughts, especially in the western territories of the CONUS.