Contrasting Vegetation Productivity Responses to Four Compound Temperature and Soil Moisture Extremes Across China

Compound temperature and soil moisture extremes threaten terrestrial carbon uptake, but their contrasting ecological impacts remain poorly understood. We assessed dry–hot (DH), wet–hot (WH), dry–cold (DC), and wet–cold (WC) events across China from 2001 to 2025. The analyses combined daily air temperature, root-zone soil moisture, and MODIS-derived gross primary productivity (GPP). We quantified event occurrence, negative-response probability, cumulative GPP loss, and recovery time, and examined environmental predictors using explainable machine learning. WC events were most frequent, whereas DH events lasted longest. WH frequency increased over the study period, while DC frequency declined. DH and DC produced negative GPP responses in 63.5% and 67.1% of classifiable events, respectively. Among negative-response events, DH had the largest national mean cumulative event-period GPP loss below the −0.5 SD threshold (2.85 g C m−2) and the longest conditional recovery time (3.17 days). WC losses exceeded DC losses despite a lower negative-response probability. Losses varied with elevation, season, and event severity. Vapor pressure deficit dominated predictions of DH negative responses and losses, whereas other event types showed greater contributions from radiation, precipitation, and soil texture. These findings highlight the need to distinguish event occurrence, response probability, productivity loss, and recovery when assessing ecological risks from compound extremes.