Toward the Use of Coupled Atmospheric and Hydrologic Models at Regional Scale

Abstract

The purpose of this study is to present the possibilities offered by coupled atmospheric and hydrologic models as a new tool to validate and interpret results produced by atmospheric models. The advantages offered by streamflow observations are different from those offered by conventional precipitation observations. The dependence between basins and subbasins can be very useful, and the integrating effect of the large basins facilitates the evaluation of state-of-the-art atmospheric models by filtering out some of the spatial and temporal variability that complicate the point-by-point verifications that are more commonly used. Streamflow permits a better estimate of the amount of water that has fallen over a region. A comparison of the streamflow predicted by the coupled atmospheric–hydrologic model versus the measured streamflow is sufficiently sensitive to clearly assess atmospheric model improvements resulting from increasing horizontal resolution and altering the treatment of precipitation processes in the model. A case study using the WATFLOOD hydrologic model developed at the University of Waterloo is presented for several southern Ontario river basins. WATFLOOD is one-way coupled to a nonhydrostatic mesoscale atmospheric model that is integrated at horizontal resolutions of 35, 10, and 3 km. This hydrologic model is also driven by radar-derived precipitation amounts from King City radar observations. Rain gauge observations and measured streamflows are also available for this case, permitting multiple validation comparisons. These experiments show some uncertainties associated with each tool independently, and also the interesting complementary nature of these tools when they are used together. The predicted precipitation patterns are also compared directly with rain gauge observations and with radar data. It is demonstrated that the hydrologic model is sufficiently sensitive and accurate to diagnose model and radar errors. This tool brings an additional degree of verification that will be very important in the improvement of technologies associated with atmospheric models, radar observations, and water resource management.