Drought sensitivity and vegetation vulnerability decouple under compound drought across dryland ecosystems

We developed a comprehensive drought index (C-SSTI) by integrating precipitation–evapotranspiration conditions, soil moisture, thermal stress, and solar-induced chlorophyll fluorescence using a Copula–Kendall framework, and combined it with event-based drought–vegetation loss matching and copula-based conditional probability analysis. Using monthly 1-km data from 2001 to 2020, we quantified the propagation rate, response time, and amplification of vegetation productivity loss across croplands, forests, and grasslands.

The C-SSTI showed consistent spatial and temporal variations with independent Palmer-type drought indices, with mean spatial correlations of 0.546 and 0.544 with sc-PDSI and PDSI, respectively.