Population growth increases urbanization, impacting surface albedos and altering surface energy balances, including the reduction of urban evaporative cooling, thus forming surface urban heat islands (SUHIs). Neighborhoods with higher vegetative densities, therefore, tend to have lower temperatures than those with sparse vegetation. In the United States, racially and ethnically segregated neighborhoods have limited green infrastructure, exposing populations to higher ambient temperatures. The increase in the number and quality of urban forests has become popular to reduce intra-urban tree-canopy inequality and mitigate urban heat. The effectiveness of trees in heat mitigation is highly site-dependent. Different mitigation interventions thus must be evaluated with the use of numerical microscale models, which could facilitate decision-making. This study determined seasonal daytime and nighttime land surface temperature (LST) trends and distributions in Santa Clara County (SCC), California. It then related these results to vegetation (NDVI) and evapotranspiration (ET) values, as well as to census tract-level median household income, percentage of Hispanic/Latino populations, and the built environment per the Local Climate Zone (LCZ) classification framework. The level of segregation and socioeconomic status (SES) between Hispanics and non-Hispanic Whites and among Hispanic/Latinos was further explored and related to temperature exposures and health outcomes. In response to the findings, the ENVI-Met software was used to evaluate urban heat mitigation measures. The combination of these assessments comprised a comprehensive human-environment approach for health exposure evaluation emphasizing differences among Hispanics by the origin of birth by which to define environmental injustice. Results show upward trends in daytime summer (0.10°C per year) and winter (0.11°C per year) mean LST and weak nighttime trends (0.03 and 0.04°C per year, respectively). Winter NDVI and LST values exhibit positive correlations, but negative correlations are found for summer NDVI and LST values, which are stronger during daytime hours, indicating that the cooling effects of vegetation occur primarily during the daytime. Maximum LSTs occur in low-income neighborhoods characterized by scarce vegetation with a high percentage of Hispanic/Latino populations, particularly of Mexican origin. Mexicans live in highly segregated neighborhoods with low and very low SES and report low health insurance coverage rates. Evaluation of mitigation strategies suggests a non-linear relationship between tree coverage percentage and air temperature changes, with a threshold cooling effect associated with increasing tree coverage.
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