Response of gross primary productivity to flash droughts on the Qinghai-Tibetan Plateau

Flash droughts are expected to become the 'new normal' in the future, significantly affecting the carbon dynamics of terrestrial ecosystems. The rapid onset, swift intensification, and short duration of flash droughts make their impact on terrestrial carbon dynamics challenging to capture. To date, the response pattern of regional terrestrial carbon dynamics to flash droughts on the Qinghai-Tibetan plateau (QTP) remains unclear. Utilizing ERA5-Land soil moisture data, we identified numerous sub-seasonal flash drought events on the QTP by analyzing the decline rate of soil moisture and drought duration. Based on the dynamics of Moderate Resolution Imaging Spectroradiometer (MODIS) gross primary productivity (GPP) changes observed during flash droughts, we proposed the Response Intensity Index (RII) to quantify the intensity of GPP responses to these events. Additionally, through partial correlation analysis, we examined the effects of climatic factors on GPP during flash droughts. We found that areas with high frequencies of flash droughts are distributed in the northern, eastern, and southeastern margins of the QTP (more than 1.6 times/year), while areas with low frequencies are located in the western region (less than 0.4 times/year). GPP significantly responded to 50.36% of the flash drought events on the QTP. The intensity of GPP response varied significantly among vegetation types, with meadow GPP exhibiting the highest responsiveness (RII of 1.867) and forest GPP the lowest (RII of 1.585). Climatic factors exerted significant effects on GPP during flash droughts, with variations observed across different vegetation types. Differences in GPP response to flash droughts may be attributed to vegetation type, climatic conditions, and the frequency and duration of flash droughts. These findings provide valuable insights for managing carbon sequestration in ecosystems, offering essential guidance for future environmental management, climate change adaptation, and ecological conservation.