Influence of urban green on human thermal bioclimate – application of thermal indices and micro-scale models

For the quantification of the atmospheric conditions and their impact on humans methods from human biometeorology can be applied. For the thermal component air temperature, humidity, wind and radiation fluxes are the factors which are required. Most significant for urban areas and urban green is the quantification of heat stress which can be estimated by thermal indices (e.g., the physiologically equivalent temperature (PET), the perceived temperature (PT), or the universal thermal climate index (UTCI)). For an overall assessment, different approaches can be applied based on measurements and models (e.g., RayMan, ENVI-met, SkyHelios) for single points (hotspots) within urban areas or neighbourhoods and city quarters. The most relevant reduction of heat stress can be obtained by increasing shade with specific trees and by improving wind conditions. These two factors (radiation and wind modification) can be extremely helpful in the creation of optimised thermal comfortable urban places and green areas. The application of models, which focus on long-term quantifications, can deliver valuable results and information for whole year assessment of the effect of urban green on human thermal bioclimate. In addition, models deliver additional basic parameters (sun paths, sunshine duration, roughness), which are important in the estimation of the effects of urban green on human thermal bioclimate.