A calibration procedure using TOPMODEL to determine suitability for evaluating potential climate change effects on water yield

An evaluation was conducted on three forested upland watersheds in the nort heastern U.S. to test the suitability of TOPMODEL for predicting water yiel d over a wide range of climatic scenarios. The analysis provides insight of the usefulness of TOPMODEL as a predictive tool for future assessments of potential long-term changes in water yield as a result of changes in global climate. The evaluation was conducted by developing a calibration procedur e to simulate a range of climatic extremes using historical temperature, pr ecipitation, and streamflow records for years having wet, average, and dry precipitation amounts from the Leading Ridge (Pennsylvania), Fernow (West V irginia), and Hubbard Brook (New Hampshire) Experimental Watersheds. This s trategy was chosen to determine whether the model could be successfully cal ibrated over a broad range of soil moisture conditions with the assumption that this would be representative of the sensitivity necessary to predict c hanges in streamflow under a variety of climate change scenarios. The model calibration was limited to a daily time step, yet performed reasonably wel l for each watershed. Model efficiency, a least squares measure of how well a model performs, averaged between 0.64 and 0.78. A simple test of the mod el whereby daily temperatures were increased by 1.7 degrees C, resulted in annual water yield decreases of 4 to 15 percent on the three watersheds. Al though these results makes the assumption that the model components adequat ely describe the system, this version of TOPMODEL is capable to predict wat er yield impacts given subtle changes in the temperature regime. This sugge sts that adequate representations of the effects of climate change on water yield for regional assessment purposes can be expected using the TOPMODEL concept.