Stronger vegetation productivity responses to simultaneous atmospheric and soil compound drought–heat events

Under climate warming, compound drought–heat events have become increasingly frequent and intense, posing growing threats to terrestrial ecosystem productivity. However, the spatiotemporal patterns of atmospheric and soil drought–heat stresses under different compound occurrence modes, and their impacts on vegetation productivity, remain poorly understood. In particular, atmospheric drought–heat events (ACDHE), soil drought–heat events (SCDHE), and simultaneous atmospheric and soil drought–heat events are often not explicitly distinguished, limiting clear assessments of ecosystem responses to compound climate extremes. Here, we identify ACDHE and SCDHE during 1982–2020 using ERA5 reanalysis data and the daily Standardized Precipitation Evapotranspiration Index (SPEI). ACDHE was detected based on maximum air temperature (Tmax) and SPEI, while SCDHE was identified using soil temperature and soil moisture. Based on their temporal concurrence, compound events are classified into three occurrence modes, including independently occurring ACDHE events (Indep_ACDHE), independently occurring SCDHE (Indep_SCDHE), and simultaneous atmospheric–soil compound events (Simultaneous). We quantified long-term changes in event frequency, duration, and intensity across the three modes, and further assess vegetation productivity losses using FluxSat gross primary productivity (GPP) data. Results show that during 1982–2020, all three compound drought–heat modes exhibit significant increasing trends in event frequency, duration, and intensity (p < 0.001). Indep_SCDHE shows the fastest increase in occurrence frequency (+0.14 events decade⁻¹), whereas simultaneous events display the strongest increase in duration (+0.51 days decade⁻¹). Indep_ACDHE exhibits comparatively smaller increases across all event characteristics. Analyses of vegetation responses indicate that simultaneous events are associated with more prolonged and severe vegetation impacts than independent events. Specifically, simultaneous events are associated with longer decline and recovery times than independent events, with decline and recovery times extended by about 1–2 days. In addition, simultaneous events exhibit greater productivity losses, with maximum GPP loss (Z-score) and cumulative GPP loss exceeding those of Indep_ACDHE by 0.09 and 4.60, and those of Indep_SCDHE by 0.01 and 0.99, respectively. This study explicitly distinguishes Indep_ACDHE, Indep_SCDHE, and simultaneous events, enabling a clearer quantification of vegetation productivity responses across compound drought–heat occurrence modes and highlighting the disproportionate impacts of simultaneous atmospheric–soil drought–heat events on ecosystem productivity under climate extremes. Building on these results, we are further investigating the relative roles of atmospheric, soil, and ecosystem-related drivers in shaping vegetation productivity responses across different compound drought–heat occurrence modes.