Multiapproach Analysis of Urban Heat Island Effect in a Central-Eastern European Agglomeration

The urban heat island (UHI) effect is probably the most often analyzed environmental phenomenon of large cities. We aim to use different approaches to evaluate the UHI effect of the agglomeration around the Hungarian Capital, Budapest. Specifically, measurements (both in-situ and satellite) as well, as mesoscale modeling serve as analyzing tools in this study. We completed several measuring campaigns with 24-hour continuous in-situ measurements of temperature and humidity in different districts of Budapest during different weather conditions and different seasons. Although these measurements can be used to evaluate the temporal evolution of the UHI effect, they do not cover fully the agglomeration area. In order to provide full spatial coverage of the agglomeration, satellite measurements serve as the basis of UHI analysis. For this purpose, surface temperature is used, which is derived from the radiation data of 7 infrared channels measured by the sensor MODIS (Moderate Resolution Imaging Spectroradiometer) onboard satellites Terra and Aqua. The UHI results certainly differ when air temperature or surface temperature is taken into account, however, the relationship between them is also analyzed. In addition to the measurements, mesoscale model simulations also have a great potential in analyzing the urban environment, especially, in terms of specific events. We used the Weather Research and Forecasting (WRF) mesoscale model coupled to multilayer urban canopy parameterization in this study to investigate the climatic conditions in their compexity for Budapest and its surroundings. For the winter and summer simulations the initial meteorological fields are derived from the publicly available GFS (Global Forecast System) outputs for the past, and a regional climate model (RegCM) for the future. To validate the simulation results, the calculated skin temperature over Budapest is compared to the surface temperature fields of the remotely sensed measurements of sensor MODIS. Moreover, the simulated air temperature fields are also evaluated, and special locations are selected to analyze the temporal evolution of UHI effect in details. RegCM-driven WRF simulations are analyzed to provide information for different users (including decision makers) on the future UHI effects of the Budapest agglomeration under different RCP scenarios.