Assessing Water Balance Closure Using Multiple Data Assimilation- and Remote Sensing-Based Datasets for Canada

Obtaining reliable water balance estimates remains a major challenge in Canada for large regions with scarce in situ measurements. Various remote sensing products can be used to complement observation-based datasets and provide an estimate of the water balance at river basin or regional scales. This study provides an assessment of the water balance using combinations of various remote sensing- and data assimilation-based products and quantifies the nonclosure errors for river basins across Canada, ranging from 90 900 to 1 679 100 km(2), for the period from 2002 to 2015. A water balance equation combines the following to estimate the monthly water balance closure: multiple sources of data for each water budget component, including two precipitation products-the global product WATCH Forcing Data ERA-Interim (WFDEI), and the Canadian Precipitation Analysis (CaPA); two evapotranspiration products-MODIS, and Global Land surface Evaporation: The Amsterdam Methodology (GLEAM); one source of water storage data-GRACE from three different centers; and observed discharge data from hydrometric stations (HYDAT). The nonclosure error is attributed to the different data products using a constrained Kalman filter. Results show that the combination of CaPA, GLEAM, and the JPL mascon GRACE product tended to outperform other combinations across Canadian river basins. Overall, the error attributions of precipitation, evapotranspiration, water storage change, and runoff were 36.7%, 33.2%, 17.8%, and 12.2%, which corresponded to 8.1, 7.9, 4.2, and 1.4 mm month(-1), respectively. In particular, the nonclosure error from precipitation dominated in Western Canada, whereas that from evapotranspiration contributed most in the Mackenzie River basin.

Automated summary

In Canada, using combinations of remote sensing and data assimilation products can provide more accurate estimates of water balance, with the combination of CaPA, GLEAM, and JPL mascon GRACE products performing well. Precipitation and evapotranspiration are the main factors leading to nonclosure errors in different regions.