Quantifying the Evolution of Extreme Drought Under Climate Change and Its Impacts on Vegetation Productivity Over the Hai River Basin of China

ABSTRACT There has been increasing attention paid to the effects of drought, especially extreme drought, on vegetation productivity under climate change. However, there are still challenges in quantifying the variations and the adverse effect of extreme drought on vegetation productivity at a regional scale within the context of historical climate change. This study quantified changes in the characteristics of extreme droughts and their effects on vegetation productivity in the Hai River Basin (HRB) of China, using factual climate (with climate trends) and counterfactual climate (detrended) data from the ISIMIP3a project. Standardised Precipitation Evapotranspiration Index (SPEI) and Run theory were utilised to determine characteristic factors (drought frequency, duration, severity, intensity and peak) under climate change. By comparing factual and counterfactual forcing simulations, the detected changes in characteristic factors were attributed to climatic trends. The negative effects of extreme droughts on gross primary productivity (GPP) were quantified. Results showed that there were more serious extreme drought events that occurred in HRB from 1901 to 2019 under factual climate than those under counterfactual climate. The difference was exacerbated in the late stages (1980–2019) over most of the basin. A deceleration was found in the rising pattern of GPP over the last four decades, exacerbating the adverse effects of extreme droughts on GPP under climate change. Compared to those during 1982–2000, GPP experienced further losses related to extreme droughts during 2000–2018 at a rate of 2°gC°m −2 °day −1 . Furthermore, extreme drought‐related GPP losses were most pronounced in summer, indicating that vegetation was more sensitive to extreme droughts during this season. These findings enhance our understanding of historically observed trends of extreme drought and suggest that more strategies should be implemented to protect vegetation from the increasing trends of extreme drought.