Spatial-temporal monitoring of compound droughts over global land areas

Recent decades have witnessed frequent droughts across spatial-temporal scales (or compound droughts), which challenges current drought monitoring systems that are usually designed based on drought information at a specific period or location. To address the challenge, this study proposed monitoring approaches for compound droughts, including preconditioned droughts, multivariate droughts, temporally compounding droughts, and spatially compounding droughts. Based on the designed indicator for each type of droughts, the performance of the compound drought monitoring approach was evaluated based on case studies, including the preconditioned droughts and multivariate droughts during 2022, temporally compounding drought during 2012–2015 in California, and spatially compounding drought during 1983 across eastern United States, northeastern Brazil, and southern Africa. Overall, the proposed drought monitoring approach performs well in capturing compound droughts and provides a useful tool for drought planning and management across different regions.