Responses of annual runoff, evaporation, and storage change to climate variability at the watershed scale

In this study, the impact of interannual variability of soil water storage change on the annual water balance is assessed for 277 watersheds located in a spectrum of climate regions. The annual water storage change is quantified on the basis of water balance closure given the available data of precipitation, runoff, and evaporation estimated from remote sensing data and meteorology reanalysis. The responses of annual runoff, evaporation, and storage change to the interannual variability of precipitation and potential evaporation are then analyzed. Both runoff and evaporation sensitivities to potential evaporation are higher under energy-limited conditions, but storage change seems to be more sensitive to potential evaporation under the conditions in which water and energy are balanced. Runoff sensitivity to precipitation is higher under energy-limited conditions, but both evaporation and storage change sensitivities to precipitation are higher under water-limited conditions. Therefore, under energy-limited conditions, most of the precipitation variability is transferred to runoff variability, but under water-limited conditions, most of the precipitation variability is transferred to storage change, and some of the precipitation variability is transferred to evaporation variability. The main finding is that evaporation variability will be overestimated by assuming negligible storage change in annual water balance, particularly under water-limited conditions.