Urban greenness and its cooling effects are influenced by changes in drought, physiography, and socio-demographics in Los Angeles, CA

Abstract

The multidecadal change in urban microclimate and greenness, particularly in response to drought and a warming climate, has implications for urban residents' well-being. Urban greenness, temperature, and vegetative cooling vary spatially. However, the dynamics of the relationships among these variables and their influencing factors are poorly characterized. Using the Los Angeles Urban Region, USA as a case study we evaluate the dynamics among urban vegetation and climate through an evaluation of satellite-based observations between 1985 and 2021. We hypothesize that microclimate changes are driven by water demand and aridity, with increasing aridity enhancing transpiration and vegetation-cooling, but that irrigation variation, assessed through proxy demographic variables of income modify water availability. Our results show that the L.A. region warmed by 0.13 °C/year, NDVI increased annually by 4.81 × 10−4, and vegetative cooling increased by 0.08 °C/NDVI/year. A consequence of these dynamics was that the luxury effect of income as a mediator of NDVI and LST declined 41% and 28%, respectively, between 1990 and 2020. The changes in urban microclimates over time and from drought are affected by social and physiographic variables associated with water availability and water demand and are increasingly leading to less racially equitable neighborhood distributions of heat.