A scenario analysis of thermal environmental changes induced by urban growth in Colorado River Basin, USA

Rapid urban population growth in the cities of South Western United States has led to significant modifications in its environment at local and regional scales. In this study, three densely populated cities in Colorado River Basin (CRB), viz. Phoenix, Las Vegas, and Denver are selected to capture the various dimensions of the impacts of land use changes on emergent hydroclimatic patterns in the entire CRB. We hypothesize that different modes of urban growth will lead to markedly different modification of the thermal environment as well as surface energy balance. To test the hypothesis, we adopted the mesoscale Weather Research and Forecasting model, incorporating the latest urban modeling system, for regional climate simulations. Projected future urban growth in the period 2010-2100 was obtained from Integrated Climate and Land Use Scenarios developed by the U.S. Environmental Protection Agency. The simulations of urban growth in CRB demonstrated significant nocturnal warming of about 0.36 °C, 1.07 °C, and 0.94 °C in near-surface temperatures in Phoenix, Denver, and Las Vegas respectively, with comparatively insignificant changes in daytime temperature. In addition, it was found that the thermal environment of Denver is the most susceptible to the projected future urban growth. Responses in urban surface energy budgets also differ in three cities due to the combined effect of local climatology and mode of urban growth.