The effect of climate on current and future urban vegetation outdoor surface cooling during periods of extreme heat

Abstract Vegetation is increasingly viewed as an important component of enhancing the heat resilience of cities. However, the amount of cooling vegetation can provide varies both geographically and temporally in ways that may depend on weather conditions. Within a city the distribution of vegetation can often exhibit patterns of inequality with high income and primarily white neighborhoods having the most vegetation and cooler temperatures, a clear indicator of inequitable human heat vulnerabilities. Here we test a landscape and ecophysiological framework for characterizing both the variation in vegetated cooling and the inequality in vegetation and outdoor surface temperature across 16 cities throughout the United States. Across all cities we identified a consistent negative relationship between satellite observations of vegetation greenness and surface temperature and this slope correlated with atmospheric aridity. Further, inequality in availability of vegetation and heat was non-linearly related to aridity, with a minimum of inequality over cities exhibiting intermediate aridity. We extended these results to evaluate potential future urban heat risk distributions by coupling our empirical ecophysiological model with a regional climate model projection. We showed that future conditions are anticipated to have higher rates of vegetative cooling, however, these changes cannot overcome overall climate warming effects. Consequently, social inequality decreases but only because vegetation has a reduced role in determining of neighborhood outdoor surface temperature.