Does hydrologically consistent data improve model performance? The importance of closing the water balance of input and evaluation data

Due to the lack of accurate representation of hydrological processes and parameter measurements, physically-based hydrological models consist of many parameters requiring calibration to historical observations so that reliable hydrological inference can be obtained. With the increasing data availability from various sources (e.g., satellite remote sensing, climate model reanalysis), additional information on different water balance components (e.g., soil moisture, groundwater storage, etc.) are used to constrain and validate hydrological models, resulting in better model performance and parameter identifiability. However, given the emergence of multiple datasets for various water budget components, and their differences in temporal and spatial resolutions, the uncertainties in these datasets, when used together in driving and evaluating hydrological models, could introduce potential inconsistencies in water balance estimation and lead to a non-closure problem, which could result in potentially biased parameter and water balance component estimates in hydrological modelling.

This study addresses this issue by examining the impact of inconsistent water balance component data on model performance and exploring the importance of hydrologically consistent data for robust hydrological inference. The assessment is done using a Canadian Hydrologic-Land Surface Models named MESH in the Saskatchewan River basin, Canada over the period of 2002 to 2016. Seven precipitation datasets, seven evapotranspiration products, one source of water storage data – GRACE from three different centers using spherical harmonic and mass concentration approaches – and observed discharge data from hydrometric stations are selected as the input and evaluation data. A reference water balance dataset is developed to optimally combine all available data sources for each water balance component and to obtain water balance closure though a constrained Kalman filter data assimilation technique. The MESH model is rerun with this reference dataset and results are assessed and compared to different combinations of input and evaluation data. Preliminary results reveal great variations of model performance in the water balance components when using different combinations of input and evaluation data and results of using the reference dataset is expected to have less biased water balance component estimates. This study aims to highlight the necessity of using a set of hydrologically consistent data before any model runs and model evaluation.