Influence of urban park on local climate based on a temperature decomposition of comparative eddy covariance measurements

Abstract:

The urban heat island has received much attention as an important environmental problem. Urban parks have abilities to mitigate the urban heat island, because surface and surrounding air temperature are often lower in urban parks than urban built-up. In this study, we have conducted a comparative measurements of the surface energy balance at an urban built-up and a large urban park. We clarify the important factors mitigating surface temperatures by creating the urban park based on a methodology called the temperature decomposition (Lee et al., 2011). Two observation sites have been set at the urban built-up and the large urban park, Oizumiryokuchi, in Sakai, Japan. Sensible and latent heat fluxes have been measured by the eddy covariance method. Ground heat flux was estimated using the Objective Hysteresis Model (Grimmond et al., 1991). Anthropogenic heat flux was estimated by the inventory data for the urban built-up area. To decompose the change in surface temperatures due to a land use change from the urban built-up to the urban park, the temperature decomposition method was applied for daytime and nighttime. We separated the contributions of the surface temperature changes by change in albedo, surface roughness, Bowen ratio, ground heat flux, and anthropogenic heat. The result indicates that increasing surface roughness in the urban park was the most effective factor in cooling daytime surface temperature. For nighttime, decreasing ground heat flux due to increasing vegetation cover was the most effective factor in cooling surface temperature. The comparative measurement in the urban area is a powerful tool for developing mitigation strategies for the urban heat island. References Grimmond et al., 1991: Atmos. Environ., 25, 311-326. Lee et al., 2011: Nature, 479, 384-387.