PNNL

Abstract

While global hydrological models (GHMs) are very useful in exploring water resources and interactions between the Earth and human systems, their use often requires numerous model inputs, complex model calibration, and high computation costs. To overcome these challenges, we construct an efficient open-source and ready-to-use hydrologic emulator (HE) that can emulate complex GHMs and can be applied at a range of spatial scales (e.g., basin, region, globe). To this end, based on the monthly “abcd” model, we first adopt values for two snow-related parameters out of three and only keep one of them tunable for parsimony. We also improve the partition of runoff between direct runoff and baseflow by introducing baseflow index (BFI) into the calibration process. Then, we evaluate the predictability and computational efficiency of the model for simulating global runoff from 1971-2010 with both the lumped and distributed schemes. The results are compared against the runoff product from the widely-used Variable Infiltration Capacity (VIC) model. Our evaluation indicates that the lumped and distributed schemes present comparable results regarding annual total quantity, spatial pattern and temporal variation of the major water fluxes (e.g., total runoff, evapotranspiration) across the global 235 basins (e.g., correlation coefficient r between the total runoff from either of these two schemes and the VIC is >0.96), except for several cold or dry regions (e.g., Arctic, Interior Tibet and North Africa ) or mountainous regions (e.g., Argentina). Compared against the total runoff product from the VIC, the global mean Kling-Gupta efficiencies are 0.75 and 0.79 for the lumped and distributed schemes, respectively, with the distributed one better capturing spatial heterogeneity. Notably, the computation efficiency of the lumped scheme is two orders of magnitude higher than the distributed one, and the latter is five orders of magnitude more efficient than the VIC model. Our results suggest that the revised lumped “abcd” model holds the promise to serve as an efficient and acceptable HE of complex GHMs and is suitable for broad practical use, and the distributed scheme is also an efficient alternative if spatial heterogeneity is of more interest.