| Impacts of vegetation manipulation treatments on the hydrologic regime of ponderosa pine watersheds in Arizona were evaluated in this dissertation. First, the Seasonal-Kendall test was applied to detect trends in the precipitation and water yield of the control watershed. Then the long-term implications of two levels of forest cutting (clear cut and strip cut with thinning) on the water yield of the treated watersheds were assessed by means of the traditional paired watershed method and plots of cumulative recursive residuals (CUSUM). CUSUM plots were proposed as a complementary tool to evaluate the duration of water yield changes following treatment. Next, BROOK90, a conceptual hydrologic model, was used to assess water yield changes of ponderosa pine watersheds associated with vegetative practices. The model was optimized and verified in the control watershed to determine if the model was applicable to the environment where the experiment was conducted. Then the model was optimized for the pre-treatment period of the treated watersheds and the optimized parameters were used to simulate the water yield of the post-treatment period. Finally, results obtained with the traditional paired watershed approach were compared with those obtained with the modeling simulation. The two methods were in reasonable agreement. |
