Impacts of compound hot-dry events on vegetation productivity in the Tibetan Plateau under climate change

Tibetan Plateau is one of the sentinels of climate warming, with complex vegetation types and noticeable regional differences. Tibetan Plateau also has the largest area of permafrost and seasonal frozen soil. With global warming and increasing compound hot-dry events, the ecohydrological processes have been changed substantially. On one hand, high temperatures can promote vegetation gross primary productivity (GPP) and respiration (Re), and also affect them by altering the permafrost freeze-thaw state. On the other hand, drought events can cause water stress and affect vegetation growth. However, the net primary productivity (NPP) of alpine ecosystem in response to compound hot-dry events is unclear. This study incorporates the carbon-nitrogen processes into a high-resolution land-hydrology coupled model, i.e., Conjunctive Surface-Subsurface Process model version 2 (CSSPv2), and conducts long-term simulations to investigate the ecohydrological effect of the changes in compound hot-dry events. Specifically, we find that GPP on the Tibetan Plateau is more sensitive to changes in soil moisture than vapor pressure deficit during flash droughts. However, the sensitivity of GPP to high vapor pressure deficit in the southeastern Tibetan Plateau increased during the hot periods of flash droughts, which have higher temperatures and more intensive radiation. Whether the soil water stress or atmospheric water stress dominates the changes in NPP is also being investigated, by using both high-resolution land-eco-hydrology model simulation and satellite remote sensing.