Microclimate Variation among Urban Land Covers: The Importance of Vertical and Horizontal Structure in Air and Land Surface Temperature Relationships

Air and land surface warming effects from urbanization are of increasing concern because of expanding heat-related impacts on human health. Many studies have investigated land-cover effects on air temperature Ta or land surface temperature (LST) individually, but relatively few studies have examined the relationships between these two heat indicators and other meteorological variables. The authors investigate how land cover influences local distributions of LST, Ta, and relative humidity (RH) and their interactions. During July 2016, 30 Ta and RH sensors were deployed at two heights above the ground (0.1 and 1.5 m) along with a thermal camera and an anemometer to quantify the influence of surface dynamics on atmospheric micrometeorological conditions. Sensors were distributed in Riverside, California, over five common urban land covers: asphalt, bare surface, turf grass, short trees, and tall trees. Stronger Ta–LST relationships were observed at 0.1 m for asphalt, bare surface, and grass and at 1.5 m for short and tall trees. Excluding grass, greater Ta–LST differences were found for daytime than for nighttime. To add to the complexity of Ta–LST relationships, increasing spatial variation in LST during the day for short- and tall-tree land covers were found. Furthermore, both wind velocity and LST were correlated with Ta vertical distributions. Higher RH and lower LST, Ta, and vapor pressure deficit were found in vegetated covers. Through the use of thermal imagery and meteorological measures, it was found that distinct land-cover influences on microclimate exist and that estimates of urban Ta using LST may improve with the use of land-cover-specific relationships.