Entropy frameworks for urban heat storage can support targeted adaptation strategies

Abstract

The attribution of urban temperatures to biophysical processes (Zhao et al., 2014; Ridgen and Li, 2017; Li et al., 2019) improves the understanding of the urban heat island (UHI) phenomenon. Traditionally, UHI studies are based on satellite observations, which are limited in their spatial resolution. Little is known about how the biophysical contributions are composed at micro-scale (some meters) and how they interact. Here we suggest an entropy concept for the heat storage cycle, reducing the complexity of the system and improving the understanding of resulting hysteresis. The entropy framework was applied to different surface types based on micrometeorological simulations (3 m × 3 m horizontal resolution) that are validated by an airborne thermal scan. In addition to the effects of reduced convection and evapotranspiration we found that heat storage can make a very dominant UHI contribution locally proceeding in entropy loops, where steep slopes and maximally symmetrically closed loop areas are optimal for achieving a balance between heat storage and release. The characteristics of the entropy cycles help suggest new and optimised strategies to attenuate urban heat episodes and we present a stepwise procedure (workflow) for the application of this method.