Doctor of Philosophy (PhD)
Civil and Environmental Engineering and Construction
First Committee Member
Second Committee Member
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In the past century, the population explosion and economic development have resulted in global warming, which has raised a series of concerns, such as sea-level rise, food security, and water resources management. The water flow patterns and features experience both short-term and long-term changes in responses to the changes in the hydrologic processes and meteorologic conditions. On a watershed scale, it is crucial to understand, quantify, and attribute the influences of climate change on the local water resources system. Such understanding can be of great help to undertake local water management tasks, such as flood control, reservoir operation, ecosystem services, and water quality analysis.
The typical General Circulation Model (GCM) simulation products are too coarse for a local meteorologic study and local hydrologic responses to climate change, such as in the Lehman Creek watershed. Additionally, the Lehman Creek recharge the groundwater system that is a potential source of future water supply to Las Vegas Valley. An evaluation of the influences of groundwater pumping on the local water system is necessary for the purpose of environmental conservation.
To bridge these study gaps, three tasks were proposed. First, the Quantile-Quantile Mapping method was employed to further bias correct the downscaled GCM data from a 12-km resolution to a local resolution, and long-term changes were evaluated. Next, a physically-based parameter-distributed hydrologic model was developed and calibrated using the Precipitation-Runoff Modeling System (PRMS). By driving the developed PRMS with the bias-corrected GCM data, and the streamflow changes over the 21st century were analyzed in terms of rates and timings. Finally, a groundwater flow system model was developed using the three-dimensional finite-difference groundwater-flow system (MODFLOW). By coupling the developed PRMS model with MODFLOW model, the streamflow variation under climate change and groundwater-withdrawal influences were evaluated from the integrated physical perspective.
The results indicated that, in the study area, there was an increase of 2.3 °C, 2.2 °C, and 35.1 mm in maximum temperature, minimum temperature, and precipitation, respectively, which were mean annual differences from period of 2011-2099 when compared to the mean annual average of 1980-2010 in the study area (Great Basin NP station), by considering all potential climate scenarios. These meteorologic alternations would result in uncertain annual streamflow changes but featured monthly variations regarding timing and rates in both PRMS and GSFLOW model simulations. The integrated GSFLOW model showed a similar but mitigated features in streamflow simulation results, compared to the PRMS model simulation results. There were earlier time-shift in streamflow up to 30 days and 26.3 days by the end of this century, resulting from the PRMS and GSFLOW simulations, respectively. These findings were also supported by the monthly streamflow change pattern found in both models’ simulation results, as the streamflow tend to increase during the period of later-spring to early-summer (December to May) and tend to decrease during the summer-to-winter period (June to November). Additionally, the groundwater-pumping influence study showed 11.7 meters drawdown at a rate of 510 m3/d after 50-year water withdrawals, based on the hydraulic conductivity estimations in this study.
The long-term estimates of climate change and the variations observed in the hydrologic responses found in this research can help local water managers to better understand changes in the water resources in responses to future climate variability and groundwater pumping within the Lehman Creek watershed.
Climate Variability and Change; Groundwater Modeling; Integrated Hydrologic Modeling; Lehman Creek; Precipitation-Runoff Modeling System; Quantile-Quantile Mapping
Chen, Chao, "Understanding the Long-Term Changes in Hydrologic Processes on a Watershed Scale Due to Climate Variability and Change" (2017). UNLV Theses, Dissertations, Professional Papers, and Capstones. 3118.