The Expansion of the San Antonio Urban Heat Island

Interest in Urban Heat Island (UHI) studies is increasing as cities and populations continue to expand and grow. An Urban Heat Island’s annual mean air temperature of a large city can range from 1.8 - 5.4°F warmer than nearby rural areas. Urban Heat Islands affect communities by increasing summertime peak energy demand, air pollution, greenhouse gas emissions, heat-related illness and mortality, and water quality. Since the last UHI study in 2010, San Antonio has seen an average growth rate of 1.78%, making it the second-most populous city in Texas. The city is continuing to expand outside of Texas State Highway Loop 1604, with the possibility of adding a third loop highway that is approximately 26 miles from the heart of the city. The city rests widely spread out over 460.97 mi², with a population of just over 1.5 million. That’s approximately 3,000 people per square mile, which does not include the surrounding suburbs. As the city continues to grow, more houses and office buildings are being built which increases the heat island effects. Population projections for the greater San Antonio area estimate an increase in the population of just under 108% between the years 2010 and 2050.

This study used surface measurements to characterize the urban heat island. Data was collected using an instrument attached to a boom. The boom is attached to a car and will extended out approximately one foot in front of the vehicle. The instrument package collected time stamps, location, altitude, pressure, temperature, and relative humidity. The route was along Loop 410, Interstate Highway-35 and Interstate Highway-10, which goes around and through the city of San Antonio. The data was collected in the early morning hours, on calm, clear nights, to show the greatest difference in temperature. Prior forecasting over the city was performed to ensure that the conditions meet the threshold values. Post forecast validation and real-time data from the past 24 hours was collected from multiple ASOS sites in the city was also collected to supplement the mobile data set. A camera was attached to the car for reviewing purposes for any anomalies found in the data. Four stationary sites 50 miles outside the city were selected to represent the rural environment. Temperature, humidity, and pressure anomaly maps will be presented along with comparisons with the 2010 study results to correlate the urban environment modifications as a function of population and population density changes. Projections of future UHI impacts will be presented for the anticipated growth.