Elucidating the Mechanisms of GPP Decline Triggered by Compound Drought-Heatwave extremes

The summer of 2022 was marked by unprecedented heatwaves and droughts across Europe and the Yangtze River Basin (YRB) in China, triggering record-breaking negative anomalies in gross primary productivity (GPP) since 2000. To elucidate the drivers of these shifts, we employed a machine-learning-based factorial experimental design using FluxSat GPP data to quantify the contributions of concurrent climatic drivers and short-term legacy effects—specifically biotic vegetation growth carryover (VGC) and abiotic lagged climatic effects (LCE). Our results demonstrate that legacy effects are the primary drivers of GPP fluctuations, with the preceding month exerting the strongest influence. Attribution analysis further reveals that during the peak of these compound hot-dry events, vapor pressure deficit (VPD) was the dominant driver of GPP anomalies. However, VGC from the previous month subsequently emerged as the leading factor, with its relative contribution intensifying as the events progressed.