An assessment of long-term water budget closures for large drainage basins in Canada

Abstract:

This study assessed the long-term (1979-2008) water budget closures for 19 large drainage basins in Canada using recently developed datasets for precipitation (P), land surface evapotranspiration and water surface evaporation, and observed streamflow. Total water storage (TWS) trends from the GRACE satellite observations were also used to assist the assessment. The objectives are to quantify the magnitudes and spatial patterns of the water budget imbalance (e) and its sources of errors over Canada. Results show that the water budget was closed within 10% of the P on average for all the basins. The e showed a general pattern of positive values in the south and negative values in the north and mountainous regions. The positive and negative values of e among the 19 basins were largely offset and the all-basin average e was close to zero. Uncertainties in the water budget variables, particularly P, were found to play a major role in the e. There are 11 basins showing significant trends in TWS over 2003-2008, which accounted for 31% of their e on average. Improvements in the observation network, data quality assurance, and spatial models for P are critical for further improving the water budget closure.