Pronounced trends in vegetation phenology responses to flash droughts across China (2003−2023)

Flash droughts develop rapidly and reach severe levels within a short time, which can significantly impact vegetation phenology. Quantifying vegetation responses to pre-season flash droughts is crucial for evaluating their ecological impacts, yet the mechanisms and temporal dynamics remain unclear. To address this gap, we introduced two metrics ( A SOS and A EOS ) representing anomalies in the start (SOS) and end (EOS) of the growing season to quantify phenological responses to pre-season flash droughts. Based on multi-source soil moisture and MODIS NDVI data, we systematically analyzed the response of vegetation phenology to flash drought and its temporal changes in China from 2003 to 2023. Partial correlation analysis was applied to assess the contributions of flash drought characteristics, climatic factors, and hydrological conditions to the interannual variability of vegetation phenological responses to flash droughts. Results show that 49.1% of pre-SOS flash droughts caused SOS advancement, with the advancement decreasing by 0.075 days/year ( p < 0.01). In contrast, 61.5% of pre-EOS flash droughts caused EOS advancement, and 38.5% caused delay, with both effects increasing by 0.063 and 0.062 days/year, respectively (both p < 0.01). These trends vary across hydroclimatic regions. The declining SOS response is likely driven by slower flash drought onset speeds, while enhanced EOS responses are mainly attributed to higher drought-period temperatures. This study elucidates the temporal evolution and dominant drivers of phenological responses to pre-season flash droughts, providing insights into ecosystem adaptation strategies under future climate change. • Vegetation phenology responds significantly to pre-SOS and pre-EOS droughts • Smaller SOS advancement occurred with pre-SOS flash droughts from 2003 to 2023 • Larger EOS advances and delays occurred with pre-EOS flash droughts from 2003 to 2023 • Rising temperatures largely drive the enhanced EOS response to pre-EOS flash drought