ESTIMATING TRANSIENT WATER STORAGE FROM PRECIPITATION-DISCHARGE HYSTERESIS

Understanding how water is routed through short- and long-term storage is fundamental to modeling water resources under future climate and land use changes. Furthermore, water storage controls the balance between chemical and physical weathering, thus setting the stage for geomorphic processes at and near Earth’s surface. Despite widespread recognition of the importance of temporary water storage, direct measurement is difficult at watershed scales; at regional scales the GRACE satellite provides assimilated estimates. Using gauging station data for rivers draining monsoon Asia we demonstrate a clear lag between precipitation and river discharge depicting a seasonal counterclockwise hysteresis loop. We propose that the area and shape of the precipitation-discharge hysteresis loop can be used as a proxy for seasonal water storage for a wide range of watershed sizes (10³ to 10⁶ km²), even when evapotranspiration is not known and only monthly mean precipitation and discharge data are available. Neither seasonal water storage nor specific storage, determined from hydrograph recession for stations with daily data, correlate with any independent topographic or land use parameters. Although snow and glacial melt are important contributions for High Asia, they are found to play a minimal role in the continental scale hydrology cycle for monsoon Asia. Furthermore, specific storage is significantly lower than, and does not correlate with, measures of seasonal water storage, suggesting that specific storage only captures some compartments of seasonal water storage. Our results depict how multiple methods, from classical hydrograph analysis to space borne observations, can be incorporated to investigate one compartment of the hydrological cycle that is otherwise very difficult to quantify.