Recent progress on urban heat mitigation technologies

Regional climate change in cities is the most documented phenomenon of climate change. Higher urban temperatures are documented experimentally for more than 450 major cities in the world. Numerous investigations demonstrate that the mean magnitude of the temperature increase may exceed 4–6 C, while at the peak it may exceed 10 C. The serious increase of the frequency and the strength of heat waves creates strong synergies between the global and regional climate change and intensify the magnitude of the overheating. Urban overheating causes a serious impact both on the energy demand and generation sectors. It increases the cooling energy consumption of buildings, rises the peak electricity demand, and obliges utilities to build additional power plants, it affects seriously health issues and in particular heat related mortality and morbidity, impacts the concentration of pollutants, and damages the urban environmental quality, and finally deteriorates the levels of local vulnerability and thermal comfort. To counterbalance the problem of urban overheating, numerous heat mitigation systems and technologies are proposed, and implemented in more than 250 large scale urban projects. Mitigation policies and technologies aim to strengthen the cooling potential of heat sinks and weaken the intensity of the heat sources. Among the developed mitigation technologies, the use of advanced, materials like the recently developed photonic components and the reflective, cool materials, the implementation of additional greenery in buildings and open spaces, the use of passive evaporative systems involving additional irrigation of urban zones and finally the dissipation of the excess heat into the ground seems to provide higher mitigation potential. The present lecture reviews and reports the recent progress and knowledge on the specific impact of current and projected urban overheating in energy, peak electricity demand, air quality, mortality and morbidity and urban vulnerability. In parallel, it discusses new findings related to the characteristics and the magnitude of urban overheating, and reports and analyses recent knowledge on the synergies between urban heat island and heat waves. Finally, it presents recent developments in the field of mitigation and adaptation technologies for buildings and cities and provides inside information on current and future potential.