Urban vegetation mitigates elevated temperatures in cities. Drought presents an important challenge to urban heat mitigation as prolonged dry periods cause reduced evapotranspiration and losses of green vegetation cover. To measure drought impacts on the urban environment and climate, we used visible short-wave infrared satellite imagery acquired throughout the 2012–16 drought in California to quantify effects on fractional vegetation cover in the Los Angeles urbanized region. We then used satellite thermal imagery with repeat high-resolution airborne thermal imagery to measure how drought-induced reductions of green vegetation cover affected urban land surface temperature (LST) and the cooling effect of urban vegetation. Green vegetation cover declined from 29.3% in 2011 to 24.6% in 2016 in urban Los Angeles County. Over the drought, the annual mean daytime LST increased from 34.4 °C in 2010 to 37.1 °C in 2014. Despite the large-scale homogenization of LST, tree- and grass-dominated areas differed in how they were affected by the drought, with larger losses of vegetation fractional cover and stronger reductions in cooling effect for grass compared to tree-covered areas due to different plant physiological responses and irrigation changes. Results suggest that drought presents a challenge to urban resiliency, as vegetation is often a main component of heat mitigation plans.

城市植被减轻了城市的高温。干旱对缓解城市热量提出了重要的挑战，因为长时间的干旱会导致蒸散量减少，绿色植被覆盖度降低。为了衡量干旱对城市环境和气候的影响，我们使用了整个加利福尼亚州2012-16干旱期间获得的可见短波红外卫星图像，以量化对洛杉矶城市化地区植被覆盖率的影响。然后，我们使用卫星热成像和重复的高分辨率机载热成像来测量干旱引起的绿色植被减少如何影响城市土地表面温度（LST）和城市植被的降温效果。洛杉矶县市区的绿色植被覆盖率从2011年的29.3％下降至2016年的24.6％。在干旱中 年平均LST从2010年的34.4°C上升到2014年的37.1°C。尽管LST进行了大规模均质化，但以树木和草为主的地区受干旱影响的方式不同，植被损失更大由于植物生理反应和灌溉方式不同，与树木覆盖的地区相比，草覆盖面积小，降温效果更强。结果表明，干旱对城市的适应力构成了挑战，因为植被通常是减热计划的主要组成部分。与不同的植物生理反应和灌溉方式相比，与树木覆盖的地区相比，植被的植被覆盖度损失更大，草的降温效果更强。结果表明，干旱对城市的适应力构成了挑战，因为植被通常是减热计划的主要组成部分。与不同的植物生理反应和灌溉方式相比，与树木覆盖的地区相比，植被的分数覆盖层损失更大，草的降温效果更强。结果表明，干旱对城市的适应力构成了挑战，因为植被通常是减热计划的主要组成部分。