The responses of ecological indicators to compound extreme climate indices in Southwestern China

Global warming has been leading to frequent climate extremes, and a single variable of climate extremes is no longer sufficient to fully assess the impact of climate extremes on ecosystems, requiring a synergistic multivariate inquiry. We obtain the compound warm-dry index (CWD) and the compound cold-dry index (CCD), based on a Copula theory with a binary distribution of a standardized precipitation index (SPI) and a standardized temperature index (STI). Changes in the spatial and temporal patterns of the compound extreme climate indices (CECIs) and the direct and lag responses of ecological indicators (EIs) to the CECIs in Southwestern China (SWC) are analyzed using these two indices. We find that CECIs rise continually during 1980–2019 (p < 0.05), with spring CCD being particularly pronounced (74.8 %, p < 0.01). Moreover, there are regional asymmetries and seasonal asymmetries in the direct and lag responses of ecosystems to compound extreme climate events (CECEs). CWD promotes productivity in spring and the response diminishes in summer, with the response area shifting towards higher altitudes. Spring CWD has a strong lag effect that will suppress summer productivity at higher elevation (>3000 m). Spring CCD promotes the growth of vegetation at low elevation (<1000 m), while summer CCD inhibits it at high elevation. Meanwhile, spring CCD has a strong lag positive effect on summer vegetation growth at low elevation specifically in Sichuan Basin, especially for crops (46.8 %). Our findings highlight the impact of compound climatic conditions on vegetation at specific geographical terrain, and vegetation in different regions can have complex and different responses to compound climate extremes.