Responses of terrestrial water storage to climate variation in the Tibetan Plateau

Water storage in the Tibetan Plateau (TP) is extremely sensitive to climate change. Observations in TP have revealed warming and moistening trends before 2004 and weakening of those trends after 2004. These changes in the course of climate warming altered hydrological components in TP from the early years of 1992-2003 to the recent decade of 2004-2015, resulting in strong changes of the terrestrial water storage (TWS) in TP. In this study, hydrological and climatic data that determine the budget of TWS in TP were compiled from multiple data sources for 1992-2015. An empirical formula was developed by correlation analysis of TWS from these data with TWS derived from GRACE data for 2003-2015 in TP. The estimated TWS by the formula highly agrees with GRACE data in describing TWS variations across TP, even though it underestimates the absolute value of annual TWS in north TP. The formula was used to estimate TWS variations in 1992-2003, which were compared to those in 2004-2015. Major results show that (1) in the warm and wet region of south TP, the recently reduced rate of climate warming and moistening reversed the trend of annual TWS from increase in 1992-2003 to significant decrease in 2004-2015. This change is largely caused by decreases of soil water and groundwater storage and increased runoff. (2) In the cold and dry region of north TP, the increase of TWS in 1992-2003 accelerated in 2004-2015 because of increases of soil moisture and lake storage. (3) The difference of TWS change in the north and south TP altered the multi-year balance of water storage over the entire TP. Decreasing TWS from 2004 to 2015 lowered multi-year mean TWS in south TP, while increasing TWS in north TP raised its multi-year mean TWS. The reduction of TWS in south TP, with decrease of streamflow and groundwater storage, could threaten the sustainability of surface and subsurface water resources for this critical source region of Asia's large rivers. The accumulation of TWS following the rise of surface water in north TP could increase spilling of lakes and thus risks of floods and debris flows.