High temperatures increasingly influence urban residents through interactions of global and regional climate changes. As an adaptation to increasing heat risks, urban vegetation is increasing recognized for the capacity to reduce urban temperature distributions. However, the effectiveness of vegetation for cooling likely differs within and among cities. We evaluated vegetation cooling capacity across a continental scale network of thirteen cities in the United States. For each city we combined satellite derived vegetation greenness and land surface temperature (LST) data with census tract boundaries centered on 2010. We then used an atmospheric climate forecasting model to project future surface temperature distributions based on relationships observed circa 2010. To better understand how differences in plant species may affect cooling capacity and tree health we are beginning an evaluation of urban tree trait distributions across a dramatic temperature gradient and the initiation of a new common garden experiment to evaluate plant responses to drought.
Results/Conclusions
Our results found consistent support across all cities that vegetation cooling capacity is enhanced in hotter and drier compared to cooler and wetter conditions. This was consistent both within cities, shown by maximum vegetation derived cooling in dry summer conditions, and among cities, with the greatest cooling in cities located in an arid climate. Our results also showed consistent segregation in vegetation greenness associated with income, which further was associated with hotter temperatures in lower income neighborhoods. In future forecasts, we project hotter surface temperatures that are moderated by vegetation. These results imply greater future inequities in surface temperature distributions unless corresponding changes to vegetation distributions or social segregation are enacted. Nevertheless, these results obscure the effects of species differences, which vary substantially in key traits associated with tree health. Initial results suggest that urban tree traits can respond to climate variability. Integrating species differences with vegetation cooling remains a central challenge for predicting future urban climates and the equity of urban microclimates.