While an effect of urban vegetation configuration on land surface temperature (LST) has been identified worldwide, the mechanism underlying configuration-LST relationships remains unclear as most urban LST data only resolve to neighborhood scales. Here we ask: does urban vegetation provide more cooling arranged in fewer and larger patches or more numerous but smaller patches in the Phoenix metropolitan area, Arizona, USA? We hypothesized the combination of energy exchanges between adjacent patches and microclimate cooling induced by vegetation are key processes determining how configuration affects LST. Using high resolution thermal data (7 m), we evaluated predictions from this hypothesis through a multiple scale analysis spanning from within individual patches to among neighborhoods. We found tree cover is the dominant factor influencing urban cooling and that tree and grass configurations also substantially affect cooling, with effects generally exceeding 40% that of tree cover. The effects of tree and grass cover and configuration on LST were scale-dependent and reflect differences from within individual patches to among neighborhoods. In general, greater edge density and shape complexities of vegetation patches cool the landscape but may warm individual vegetation patches. Conversely, increasing individual vegetation patch size and reducing shape complexity may lead to cooler vegetation patches but a hotter landscape. Our findings suggest more edge area strengthens energy exchanges between vegetation and surroundings and more vegetation core area lead to greater cooling within individual patches. Through applications of high resolution thermal remote sensing, we are able to more directly connect effects of land cover composition and configuration to LST distributions that can help cities plan and evaluate local climate adaptation strategies.
Yan, JL; Zhou, WQ; Jenerette, GD
Testing an energy exchange and microclimate cooling hypothesis for the effect of vegetation configuration on urban heat
Agricultural And Forest Meteorology