The urban heat budget derived from satellite data

Abstract. The study of the interactions between urban surfaces and the urban boundary layer plays an important role in urban climatology, especially seen against the background of increasing urbanisation in most parts of the world. Measurements of radiation and heat fluxes suffer from the extreme heterogeneity of the urban landscape. It is therefore difficult to get accurate and representative measurements. To bridge the gap between accurate point measurements and their spatial representation, satellite data from Landsat-TM are used. Methods and results of the investigation of radiation properties, net radiation and heat fluxes of urban areas in the Basel Region, NW-Switzerland are presented. In addition to field measurements, satellite data from Landsat-TM were linked to numerical models to compute net radiation and heat fluxes of the whole region. By integrating the normalized difference Vegetation index (NDVI) from multi-spectral satellite data, storage heat fluxes could be estimated with high accuracy. The next step was to compute latent and sensible heat fluxes by using a Bowen-ratio approach attributed to a land use Classification. Of interest is the Observation that the idea of an «Urban Heat Island» (UHI) has to be defined very carefully. Very often an «Urban Cooling Island» may be found during daytime and under clear sky conditions. This feature could be explained using the results of the satellite based radiation and heat budget analysis.