Impacts of climate change and weather modification on hydrologic characteristics of watersheds in the western United States

This research quantifies the impacts of climate change and weather modification (WM) on hydrologic characteristics of watersheds in the arid regions of the western United States. This research performs a long-term simulation of streamflow for present and future climate conditions in the North Platte (NP) Watershed, Wyoming; a shorter duration simulation is then performed to observe the likely impacts of event based changes in an urban watershed in Las Vegas, Nevada. First, a study is carried out in Chapter 3 that evaluates the impacts of WM on water supply by developing a hydrologic model for the NP Watershed. The variable infiltration capacity (VIC) model is calibrated using daily meteorological forcings and monthly streamflow data. An average increase of 0.3% to 1.5% in annual streamflow is simulated from the Wyoming area of the watershed for a 1% to 5% increase in precipitation. The centralwest and southwest regions of the watershed, which consist of higher percent coverage of evergreen needleleaf and woodland forest, are found to be more effective for cloud seeding operations. For proposed WM programs or programs that are claimed effective based on precipitation augmentation, the hydrological impacts can be evaluated based on this analysis. Second, Chapter 4 develops streamflow projections to assess water availability in the NP watershed under anthropogenic climate change conditions. The multi-model multi-scenario climate data available from the World Climate Research Programme\u27s (WCRP\u27s) are utilized. The simulated streamflows are compared using an inter-model inter-scenario approach. Average streamflow shows an increasing pattern over this century with maximum streamflow during 2085-2090. The simulated streamflows for future periods (2011-2040, 2041-2070, and 2071-2100) vary from -20% to 62% with respect to the baseline period (1971-2000). The wet months are getting wetter, while the dry months are found to become dryer under changing climatic conditions. The streamflow projections and the range of streamflow can be utilized by decision makers in future water supply and demand management study. Finally, the research is extended in the urban Las Vegas area (Flamingo- Tropicana watershed) that utilizes the Master Plan Update (MPU) model and the WCRP\u27s multi-model data to observe the impacts of climate change on extreme storm events. The summer storms, which are considered as extreme storms, are expected to be more intense in future. A larger change in peak streamflow and total runoff volume is simulated for the extreme storm under different climate scenarios and time periods; the simulated increase in peak streamflow varies from 40% to more than 150%. These results can be utilized for various design purposes in the watershed to mitigate runoff impacts of intense storms under changing climatic conditions. This research assesses water availability for the NP watershed and evaluates the vulnerability of existing flood control system for the FT watershed. These results can be utilized by water managers in regional water resources development and management