Enhanced thermal load in urban areas through climate change using the example of Aachen (Germany)

This study addresses the air temperature distribution within the city of Aachen to identify those areas where high levels of thermal load are likely to be observed. Therefore, a mobile measurement network is set up. The observations are used to model air temperature patterns for the whole city area by a statistical regression approach. Significant correlations are determined between air temperature and terrain height, building density, surface sealing, forest and green spaces. The analysis for the months May-September shows that the UHI is most pronounced in industrial areas with a high degree of surface sealing during daytime while the inner-city residential quarters with a dense building structure show the highest thermal load during the evening. The spatial structure of the modeled temperature distribution is in accordance with the spatial structure of the surface radiant temperatures from a thermal image over wide areas of Aachen supporting the idea that surface temperature airborne data also deliver useful information regarding patterns of air temperature. A multi-model ensemble of regional climate projections (A1B scenario; REMO, COSMO-CLM, WETTREG and STARII) is used to estimate the climate change signal in terms of temperature and precipitation for the summer months June, July and August until the end of the current century. Since the combination of heat and high moisture content in the ambient air is assumed to adversely affect human health, the equivalent temperature is employed as an indicator for heat stress. It is applied to identify heat waves. Based on the median realizations of the model runs, further warming of 3-4 K and an increase in variance may provoke heat waves that are likely to last longer and occur more often in future whereas their intensity has not been found to change significantly. An increasing number of heat waves is concurrent with a decreasing amount of rainfall in the summer months until 2100. Analog to heat wave events dry periods are expected to occur more often and to last longer compared to the period of 1971–2000 which may cause failure of crops and an increasing demand of irrigation water. Mixed and meridional circulation types can be ascertained to the heat waves identified for the period of 1971 to 2000. Weather types with a high pressure center over Central Europe and eastern weather types bringing warm and dry air to Europe are likely to increase at the expense of westerly weather types. The finding indicates an amplification of heat load in future due to the variability of weather types with global climate change