| A new model, DRAIN-WARMF, has been developed by integrating WARMF and DRAINMOD models, to simulate surface and subsurface flows and nitrogen transport in a tile-drained watershed in eastern Canada. The new model takes advantage of the strong surface flow modeling capabilities of WARMF and the higher accuracy of subsurface flow modeling of DRAINMOD, and is thus superior performance-wise to both of these models individually. The new model allows for simulations to be carried out for scenarios and management practices which were not possible using these models individually. The DRAIN-WARMF model was applied to St. Esprit watershed, located in southwestern Quebec. Simulations were carried out from 1994 to 1996. The new model was able to adequately simulate hydrologic response and nitrate losses from the watershed. Comparing the observed daily/monthly flows with the model's outputs returned Nash-Sutcliffe coefficient of efficiency (E) values of 0.75/0.97 over the validation period (1996). The model improved predictions of monthly NO3--N loads, with an E value of 0.83. Overall, it was found that DRAIN-WARMF results, on a seasonal and monthly scale, were generally more reliable whereas daily simulations could be improved further by using a longer calibration period.;The potential impacts of climate change on flow and nitrogen pollution were also evaluated with DRAIN-WARMF. Simulations were performed based on the projected climate change conditions developed by the CRCM4.2.0 model for 1961 to 2100. The projected annual temperature and precipitation changes indicate that the climate in the study area would generally become warmer and wetter. The min/max temperatures would increase in winter, causing more rainfall-dominated regimes and less snow accumulations. The DRAIN-WARMF simulation results show an increase in the average annual surface and drainage outflows. The total flow will increase significantly during the months of March and April. It appears that climate change will be altering both the magnitude and the seasonality of flows. The impact of changed hydrologic conditions on nitrate-nitrogen losses was also assessed. The annual loss of NO3- -N will increase from the watershed. In general, results suggest that flow and nitrogen loads in the study area would experience significant changes in future years. |
