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

TLDR

The study assesses how interannual soil‑water storage variability influences the annual water balance across 277 watersheds worldwide. The authors quantify annual storage change via water‑balance closure using remote‑sensing precipitation, runoff, and evaporation data, then analyze how runoff, evaporation, and storage respond to precipitation and potential evaporation variability. Runoff and evaporation are more sensitive to potential evaporation under energy‑limited conditions, while storage change is more sensitive to potential evaporation when water and energy are balanced; runoff sensitivity to precipitation is higher under energy‑limited conditions, whereas evaporation and storage change sensitivities to precipitation are higher under water‑limited conditions, so most precipitation variability is transferred to runoff in energy‑limited regimes and to storage change in water‑limited regimes, and evaporation variability is overestimated when storage change is assumed negligible, especially in water‑limited conditions.

Abstract

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.