Sensitivity of modeled urban climate to urban canopy parameters over central Europe

Abstract

Urban areas are characterized by modifications of the local climate, leading to so-called urban meteorology islands (UMIs). A UMI is the result of the different physical properties of surfaces in cities compared to their rural surroundings. In this study, we performed a set of multi-year simulations with the Weather Research and Forecasting model and two urban schemes to investigate the sensitivity of urban climate modifications (i.e. UMIs) to changes in characteristics of the urban environment, described in models by so-called urban canopy parameters (UCPs). Our results reveal a high sensitivity of urban-induced changes in all mentioned meteorological variables to alterations in UCPs. Temperatures in urban areas are mainly influenced by changes in urban fraction (UF), roof albedo, green roofs with irrigation, and also by anthropogenic heat in winter, with a magnitude around 0.5 degrees C. On the contrary, urban wind speed is impacted by parameters that describe the urban morphology, about 0.1 m s-1. Our study also shows substantial differences between both urban models used, mainly in urban-induced temperatures in winter, with a difference of around 1.5 degrees C. The results of the study can also be used as a primary evaluation of different mitigation strategies represented by changes in UCP values. The decrease of UF and the increase in roof albedo seem to be the most suitable possibilities to reduce the intensity of urban heat islands in summer; vegetation-covered roofs have a noticeable impact only if they are also irrigated.