A national‐scale assessment of long‐term water budget closures for Canada's watersheds

Abstract This study examined the long‐term water budget closures for 370 watersheds over Canada's landmass by using 30 years' (1981–2010) data products recently produced for precipitation (P) gridded using climate station measurements, land surface evapotranspiration (ET), and water surface evaporation (E0) obtained by the Ecological Assimilation of Land and Climate Observations (EALCO) model, and observed streamflow (Q). The results show that 29%, 58%, and 83% of the watersheds were closed within 5%, 10%, and 20% of P, respectively. The positive and negative imbalances among the 370 watersheds are largely offset and the national scale average is −24 mm yr −1 , or 4.2% of P. Water budget closures have large variation across the landmass. Regions with sparse or less accurate monitoring of P such as the mountainous region and the Arctic exhibit the largest water imbalances. Further efforts on enhancing the climate observation networks, improving spatial models for P and ET estimates, and streamflow measurements are all likely critical for a better understanding of Canada's water budgets. Key Points Water budget is closed within 5% and 20% of P for 29% and 83% of watersheds Mountain and the North have largest water imbalance likely due to inaccurate P Estimating ET using a surface water budget approach may induce large errors