The effects of urban stream improving the thermal environment in urban area

Abstract

Urban areas create distinctive urban climates by Urban Heat Island (UHI) that is the temperature increase in urban areas compared to that in surrounding rural areas and is caused by number of factors, such as land use / land cover (LULC) change, concentration of population and increase anthropogenic heat. In general, the study of thermal environment in urban area focused on UHI intensity and phenomenon. Recently, climate improvement has been studied using water and green belt of urban, as interest in UHI phenomenon mitigation or enhancement has been increased. Therefore in this study, effects of urban stream on urban thermal environment were analyzed using remotely sensed data. The Landsat 7 ETM+ data acquired on 6 September 2009 were utilized to derive the surface Temperature (T s ) and surface energy balance using Surface Energy Balance Algorithms for Land (SEBAL) (Bastiaanssen et al., 1998). The surface energy budget consists of net radiation at the surface (Rn), sensible heat flux to the air (H), latent heat flux (LE) and soil heat flux (G). The net radiation flux is computed by subtracting all outgoing radiant fluxes (K↑: shortwave outgoing, L↑ longwave outgoing) from all incoming radiant fluxes (K↓ shortwave incoming, L↓: longwave incoming). This is given in the surface energy budget equation: Rn = H + LE + G = K↓ - K↑ + L↓ - L↑. The result indicates that the Ts of urban stream are1 °C lower than circumjacent urban area, LE flux of urban stream is higher than surrounding urban area. However, land covers of streamside and around stream with concrete, asphalt and barren belt are comprised of hot spot zone that deteriorates urban thermal environment. And urban stream does perform a role of cool spot zone that improves urban thermal environment.