Water budget imbalance and error source for Canada’s major drainage basins

English Abstract:

Assessing water budget closure helps identify knowledge gaps, data quality issues and research needs for better understanding the water cycle and water resources. This study assessed the 30-year (1979-2008) water budget closure for 19 large drainage basins in Canada covering an area of 3.5 million km², or about 35% of the entire Canadian landmass. Datasets recently developed for precipitation (P), land surface evapotranspiration and water surface evaporation from the land surface model EALCO, in situ streamflow measurements, and total water storage (TWS) from the GRACE satellite observations were used for the assessment. The objectives are to quantify the magnitudes of the water budget imbalance (e) over Canada and to assess the sources of errors. 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. Water imbalance in the north and mountainous regions were large mainly due to inaccurate precipitation. There are 11 basins showing significant trends in TWS over 2003-2008, which accounted for 31% of their e on average. As such, long-term average ET calculated using surface water budget approach (i.e., ET=P-Q) might induce large errors. Improvements in the observation network, data quality assurance, and spatial models for P are critical for further improving the water budget closure.