Projected Declining Cryospheric Meltwater and Its Impact on River Runoff Under Climate Change on the Interior Tibetan Plateau

Abstract The Source Region of the Yangtze River (SRYR), located on the hinterland of the Tibetan Plateau (TP), is significantly affected by cryospheric components such as snow, permafrost and glaciers. Nevertheless, there remains a lack of consensus regarding the contribution of cryospheric meltwater to river runoff and its potential changes in a changing climate. This study quantifies the contributions of different types of cryospheric meltwater in the SRYR during 1961–2100 using a physically based cryospheric‐hydrological model. Results show that snowmelt, ground ice melt from thawing permafrost and glacier melt contributed 23%, 3%, and 6% to river runoff in the historical period, respectively. Due to cryospheric degradation as indicated by diminishing snow cover, thickening permafrost active layer and declining ice storage, the runoff contributions of all three types of cryospheric meltwater are projected to decline in a warming climate, with the tipping point of snowmelt runoff already reached in the historical period. The tipping point of glacier runoff is expected to be reached soon, near the 2030s, followed by the contributions of thawing permafrost later in this century. The total contribution of cryospheric meltwater to river runoff is expected to decline in the future, with meltwater from thawing permafrost replacing snowmelt as the dominant cryospheric meltwater component. Consequently, the drought mitigation capacity of cryospheric meltwater will diminish in the future, despite an expected increase in total river runoff. This study highlights the widespread risks of declining cryospheric meltwater supply both in the TP and in other cold region catchments in a warming climate.