Cities overheating. Causes and measures for mitigation of the heat island in Lisbon

Abstract

Urban heat islands (UHI) are the most obvious example of climatic modifications induced by man, having been observed in most cities of the world. This thermal pattern suggests the existence of a hot city surrounded by cooler rural areas. The UHI can be seen as an energy resource (in cold climates avoiding the excessive consumption of energy in the winter), but also as a limitation (in hot climates), because it can lead to an additional consumption of energy to cool indoor spaces. From an economic point of view few studies about mediterranean cities show that the saving of energy for heating the spaces in the winter is lower than the costs of cooling spaces during the summer. In this work several types of UHI are described. The modifications of radiation and heat balances are summarized to explain the existence, regime and intensity of this thermal pattern. Several studies conducted by researchers of the Geo-ecology group from the Centre for Geographical Studies of the University of Lisbon and measures for the mitigation of the UHI are presented, as a contribution to the increase of the energy efficiency in the city, with the purpose to attain a sustainable urban development.