Influence of Soil Moisture and Tree Evapotranspiration on an Urban Microclimate
Authors
Jeffrey Warren*, Melanie A. Mayes (mayesma@ornl.gov), Jiafu Mao, Chris DeRolph, Yaoping Wang
Institutions
Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN
URLs
Abstract
Urban microclimate varies spatially with degree of urbanization and vegetation composition. Residents in wealthier neighborhoods often have more green space and tree canopy cover than low-income communities (e.g., <$50,000 annual household income), leading to less extreme summer temperatures. The urban heat island effect thus impacts low socioeconomic households with increased heat stress and air conditioning costs. Consequently, heterogeneities in tree canopy cover and urban heat island effects can result in environmental injustice due to unequal distribution according to income and race. The goal of this project is to understand how temperature and relative humidity in an urban area are affected by plant evapotranspiration and soil moisture dynamics. The project hypothesizes that soil moisture, the extent of impervious surfaces, and tree canopy will influence local microclimate; specifically, low soil moisture, high percentages of impervious surfaces, and low extent of tree canopy will cause more intense heating in the summer and cooling in the winter. The team selected Knoxville, TN, for a coupled model-experiment pilot investigation based on a representativeness analysis of cities in the eastern United States. Researchers used geospatial information coupled with socioeconomic data such as population density, race, and income to select six urban parks that vary in temperature, tree canopy cover, imperviousness, and topography. Each site was instrumented to measure soil water, soil and air temperature, relative humidity, and solar radiation. Sap flow sensors were installed into representative trees at each site. The data will be used to determine relationships between urban microclimate and natural and built urban components as a function of diurnal and seasonal conditions. The team also uses pertinent observations to assess the capability of the E3SM Land Model to delineate the interplay between urban microclimates and natural ecosystems, such as soils and plants, across varying levels of urbanization.