Assessment of Hydrological Climate Change Impacts on the Upper Green River Basin, WY

The Upper Green River Basin (UGRB) is a complex terrain and a snow-dominated area. The water resource in the UGRB is sensitive to changes of the hydrological variables by the global warming. Moreover, the UGRB is the important headwater area to secure the water resources in the UGRB. Thus, it is important to understand and assess the spatial and temporal climate changes of the hydrological variables and extreme weather events in the UGRB. Therefore, this study will investigate and discuss the regional climate change impacts on the hydrological variables and the extreme weather events over the UGRB.;For the assessment of regional climate change impacts over the UGRB, this study uses the monthly 1/8th degree Bias-Corrected Spatially Downscaled (BCSD) precipitation and temperature projections from World Climate Research Programme (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) datasets. However, the climate projections need to be temporally downscaled before being applied to the Variable Infiltration Capacity (VIC) model for streamflow simulations. For downscaling the climate projections, this study proposes the Bias Adjusted Gamma - Gamma Transformation (BAGGT) to preserve statistical properties such as mean, frequency, distribution, and the range, and to overcome the limitation of the coarse - resolution climate projection. For grid cells where historical monthly precipitation is zero, but the monthly climate projection expects precipitation, this study applies the Nearest Neighbor Resampling method to assign temporal precipitation patterns. The proposed downscaling method (BAGGT) preserves statistical properties better than other methods for precipitation data and it serves better for assessing the climate change impact on a regional scale.;After statistical downscaling, this study investigates the climate change impacts on the downscaled precipitation and temperature, and evapotranspiration and streamflow simulated by the VIC model. The projected temperature shows the increasing trend with respect to the three periods (2010 - 2039, 2040 - 2069, and 2070 - 2099) and the spatial change of temperature is sensitive to the latitude and elevation. The uncertainty of temperature increases in time; however, the spatial uncertainty of temperature doesn't much change. The projected precipitation temporally increases. Particularly, winter precipitation increases and summer precipitation decreases based on all climate scenarios. The uncertainty of precipitation is high, which means that the timing of precipitation couldn't capture. The increasing pattern of evapotranspiration is associated with temperature. Both the increasing temperature and precipitation have a strong influence on the increasing evapotranspiration. The spatial and temporal uncertainty in evapotranspiration increases as the period increases. The projected streamflow during the 21st century shows the increasing trend as a result of combination of precipitation and evapotranspiration. The timing of projected maximum streamflow shifts from June to May because of influence of snowmelting.;Furthermore, this study assesses the climate-change impacts on flood and drought in the UGRB. In contrast to the traditional flood frequency analysis (FFA) which we use historical streamflow under the stationarity assumption, this study uses the 50-years projected streamflow to estimate the non-stationary design flows for 2, 5, 10, 20, 25, 40, 50, 100, and 200 year return periods. Discharges for the return periods show the increasing trend in the future. Frequency of high flow significantly increases and frequency of low flow decreases in the 21st century. Moreover, to understand the temporal and spatial patterns of drought in the 21st century in the UGRB, this study proposes the modified Palmer Drought Severity Index (PDSI) from 1950 to 2099, which overcomes the several shortcomings of the traditional PDSI. Drought occurs more frequent, becomes severer, and intensifies across the basin in the 21st century.;This study has broadened our understanding on the regional climate change impacts over the Upper Green River Basin. Furthermore, it would serve as a foundation for the long-term water resources management and planning. (Abstract shortened by UMI.).