Global climate change is driving more frequent, complex and severe droughts. However, precisely measuring the overall intensity of compound droughts—a spatiotemporal coupling of multiple drought types—has long been a challenge.

To address this, a research team led by Prof. YU Yang from the Xinjiang Institute of Ecology and Geography (XIEG) of the Chinese Academy of Sciences developed a multi-dimensional Copula-based framework to capture the nonlinear dependence among drought variables. Based on this framework, the researchers constructed a Standardized Compound Drought Severity (SCDS) index for the probabilistic quantification of compound drought intensity.

By integrating both bivariate and trivariate Copula structures, the framework characterizes the coupled behavior of meteorological drought, hydrological drought and ecological drought. The findings show that the SCDS index’s three-dimensional spatial distribution closely mirrors the patterns observed in individual drought indices. Crucially, its temporal variation demonstrates a high consistency rate of 83.5%, underscoring the index's robustness in tracking the dynamics of compound drought.

In addition, the researchers found compound droughts showed an overall intensifying trend in Xinjiang, China. They also revealed distinct seasonal shifts in the relative contributions of different drought types. Meteorological drought was found to dominate during spring, ecological drought took precedence in summer and autumn, and hydrological drought's influence grew more pronounced in winter.

“Our framework advances the quantitative understanding of the interactions among multiple drought types and provides an integrated tool vital for drought monitoring, risk assessment, and climate adaptation strategies,” said Prof. YU Yang, corresponding author of the study.