Flash droughts cause more rapid declines in gross primary productivity than slow droughts on the Qinghai-Tibetan...

Sub-seasonal droughts, including flash and slow droughts, are increasing in frequency and significantly affect terrestrial carbon cycling. However, systematic comparisons of their differential impacts on gross primary productivity (GPP) remain limited. Here, we identified flash and slow drought events on the Qinghai-Tibetan Plateau (QTP) from 2000 to 2023 based on root-zone soil moisture dynamics and quantitatively assessed vegetation productivity responses to both drought types. The results showed that flash droughts occurred significantly more frequently and faster than slow droughts on the QTP. The response characteristics of GPP to flash and slow droughts exhibited notable differences across most vegetated areas. Specifically, in 62.10% of vegetated areas, the GPP response rate was higher during flash drought than during slow drought, while the response lag time and duration were shorter in 59.15% and 73.49% of areas, respectively. In contrast, the overall difference in the magnitude of GPP response between the two drought types was small. Among the five major vegetation types, the difference in lag time and duration of GPP response to the two types of droughts was most significant in steppe ecosystems. Extreme Gradient Boosting (XGBoost) analysis further revealed that temperature, solar radiation, and soil moisture were the dominant drivers of GPP responses, outweighing the influence of drought-specific characteristics. These findings provide new insights into the distinct ecological effects of flash and slow droughts and offer a scientific basis for targeted ecological conservation and climate adaptation strategies on the QTP.