Toward the use of coupled atmospheric and hydrologic models at regional scale

The purpose of this study is to present the possibilities offered by couple d atmospheric and hydrologic models as a new tool to validate and interpret results produced by atmospheric models. The advantages offered by streamfl ow observations are different from those offered by conventional precipitat ion observations. The dependence between basins and subbasins can be very u seful, and the integrating effect of the large basins facilitates the evalu ation of state-of-the-art atmospheric models by filtering out some of the s patial and temporal variability that complicate the point-by-point verifica tions 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 stre amflow predicted by the coupled atmospheric-hydrologic model versus the mea sured streamflow is sufficiently sensitive to clearly assess atmospheric mo del improvements resulting from increasing horizontal resolution and alteri ng the treatment of precipitation processes in the model. A case study using the WATFLOOD hydrologic model developed at the Universit y of Waterloo is presented for several southern Ontario river basins. WATFL OOD is one-way coupled to a nonhydrostatic mesoscale atmospheric model that is integrated at horizontal resolutions of 35, 10, and 3 km. This hydrolog ic model is also driven by radar-derived precipitation amounts from King Ci ty radar observations. Rain gauge observations and measured streamflows are also available fur this case, permitting multiple validation comparisons. These experiments show some uncertainties associated with each tool indepen dently, and also the interesting complementary nature of these tools when t hey are used together The predicted precipitation patterns are also compare d directly with rain gauge observations and with radar data, It is demonstr ated that the hydrologic model is sufficiently sensitive and accurate to di agnose model and radar errors. This tool brings an additional degree of ver ification that will be very important in the improvement of technologies as sociated with atmospheric models, radar observations. and water resource ma nagement.