UC Davis

Exposure to heat exacerbated by an increase in urbanization as well as increasing global temperatures has become a growing concern for cities and their residents. Excess heat can cause increased heat-related morbidity, mortality, and energy costs. A large goal of climate adaptation is to reduce this urban heat island effect. However, cooling strategies for dryland cities will likely be different from those for wetter, temperate cities. In addition, different socioeconomic and racial groups often face unequal exposure to heat as well as increased heat-related sickness, mortality, and energy costs. Many experts have found that historically red lined neighborhoods often experience the greatest amount of excess urban heat with the least amount of resources to mitigate it.This dissertation consists of three standalone articles that make independent scientific contributions to the same problem of measuring and mitigating urban heat in dryland cities. The articles use thermal infrared remote sensing to measure the thermal footprint of cities, and a variety of sociodemographic and biophysical ancillary data. In the first article we measure how urban heat behaves in 10 large global cities in relation to different types of land cover and built form. The cities included desert cities of Cairo, Egypt and Dubai, UAE, as well as monsoon dryland cities like Delhi, India which goes 9 months of the year with almost no rainfall. The results showed that urban forest and green spaces can be up to 12° C cooler than city wide averages for both day and night. We also found spillover cooling of up to 5 km for the urban green spaces. In the second article we mapped the thermal footprint of 20 southwestern US cities for average summer, and extreme heat event temperatures. We then compared the wealthiest and poorest block groups as well as LatinX and white neighborhoods. We found that low income block groups were subject to temperatures 2-5° C warmer than wealthier block groups as were LatinX neighborhoods. In the final chapter we developed a vulnerability index for the cities of Bakersfield and Fresno California as well as utilizing the InVEST Urban Cooling model from the Stanford Natural Capital Project to model cooling scenarios from planning interventions such as increasing surface albedo of built form and increasing tree canopy. By modeling 10 and 25% increases of tree canopy and albedo we found increasing tree canopy on developed land uses by as little as 10% could lead to a decrease in temperatures of 1.2° C (2° F) or more throughout the cities, and made a greater difference for low income block groups compared to higher income block groups. The cooling impact of urban trees based on the InVEST model extended up to 2 kilometers. Increasing albedo of paved surfaces by 10% resulted in a non substantial decrease in temperatures throughout the cities. Our research using this model showed that increasing tree canopy is more effective at mitigating high temperatures for vulnerable neighborhoods than decreasing albedo, and high vulnerability neighborhoods. This research demonstrates that unequal heat burden exists amongst dryland cities, but there are effective ways to mitigate the excess heat.