Seasonal variations of recharge-storage-runoff process over the Tibetan Plateau

Abstract

The Tibetan Plateau (TP) is a vital and vulnerable water tower that supports the livelihoods of billions of people. The use of a data-driven recharge-storage-runoff perspective enables a more comprehensive estimation of multiple aspects of the water cycle. Through an analysis of the diagnostic net water flux from ERA5, water storage changes (dS/dt) from GRACE, runoff estimations (R) from the land-atmosphere water balance, and river discharge measurements (Rd), the annual cycle of recharge-storage-runoff has been studied over the TP and its basins. The net water flux determines a recharge of 326 mm/yr over the TP. Recharge in coupled storages, leading to an increase in water mass (dS/dt >0) and runoff (R >0) during the wet season, is considered the fast response and measured using the ratio of runoff to net water flux (r1). Conversely, the slow response determined by the water storage release (dS/dt <0) during the dry season, is quantified by the ratio of storage release to runoff (r2). The ratios of r1 and r2 are influenced by climatic and terrain drivers, indicating specific characteristics of recharge-storage-runoff at the basin scale. Small r1 values and large r2 values suggest high buffer capacity, while the basin of Amu Darya (Salween) is characterized by the highest (lowest) buffer capacity over the TP. However, measurements of river discharge at Amu Darya suggest an uncoupled recharge-storage-runoff. The imbalance between river discharge and runoff estimation was most severe in the first decade of the 21st century but has been mitigated since 2012. River discharge at Amu Darya is likely constrained by energy during summer.