A proportionality-based multi-scale catchment water balance model and its global verification

Abstract

Unifying the description of catchment hydrological partitioning across spatial and temporal scales has long been an important research topic within the hydrological community. As an effort to that, here we develop a conceptual water balance model based on the proportionality hypothesis (denoted PWBM) and for the first time, test the proportionality hypothesis using hydrologic observations across global catchments at varying time scales. The PWBM has a transparent and parsimonious model structure with only two model parameters, and requires precipitation, potential evapotranspiration and leaf area index as model inputs. To test PWBM, we apply the model to simulate streamflow (Q), evapotranspiration (E) and storage change (ΔS) in 22 large basins and 255 small basins globally and find an overall good model performance in reproducing all three water balance components at the daily (only in small basins), monthly, seasonal, annual and mean-annual time scales. Compared with three other conceptual hydrological models developed for specific time scales, the PWBM substantially outperforms the SCS model at the daily scale and the ABCD model at the monthly scale and performs similarly as the long-standing Budyko model at the mean-annual scale. In summary, our study verifies the robustness of PWBM and offers convincing evidence regarding the applicability of the proportionality hypothesis for enhanced hydrological system understanding at multiple spatial and temporal scales.