Hydrological implications of pervasive permafrost thaw across the Tibetan Plateau

Rivers originating from the Tibetan Plateau (TP) provide water to more than one billion people living downstream. Almost 40% of the TP is currently underlain by permafrost, which serves as both an ice reserve and a flow barrier and is expected to degrade drastically in a warming climate. The hydrological impacts of permafrost thaw across the TP, however, remain poorly understood. Here we quantify the permafrost change on the TP over 1980-2100 and evaluate its hydrological impacts using a physically-based cryospheric-hydrological model. Our results indicate widespread permafrost thaw and prominent ground ice losses under warming. The declining ground ice reserve provides locally important but unsustainable meltwater runoff. In addition, the lowering of the permafrost table and removal of permafrost as a flow barrier would enhance infiltration and raise subsurface storage capacity. The diminished water supply from ground ice melt and enhanced subsurface storage capacity could jointly reduce annual runoff and exacerbate the risk of regional water shortage when facing future droughts. Our findings highlight the important role of permafrost thaw in future water resources management and drought risk assessment across the TP.