Assessing the effects of tree cover on urban heat mitigation and population health

The effects of climate change, such as intense and prolonged heat waves, are particularly evident in cities where high urbanization and soil sealing make these environments less livable for citizens. In fact, the air temperature recorded in urban centers is higher than the surrounding areas where a greater presence of vegetation and soil permeability enhance the water and energy balance. The effects of high temperatures on health are threatening, particularly for the elderly, causing respiratory and cardiovascular problems that may in some circumstances lead to death. An increase in mortality was observed in Italian cities during the summer heat waves of 2003 and 2012, with an increase in the first case of up to 46% for the over-65 age group, compared with an earlier reference period (1998-2002). Heat mitigation is therefore a priority considering that more than half of the world's population lives in cities and is expected to reach 75% in 2050. Increasing tree cover through reforestation programs has been suggested to improve the microclimate of urban areas thanks to the ability of trees to promote surface shading (reducing sensible heat) and the cooling effect by evapotranspiration (reducing latent heat). In order to quantify the contribution of tree cover on urban heat mitigation and the related effects on human health, we used the i-Tree Cool Air model for the first time on an Italian city (Naples). Input data on land use, tree cover density, impervious area and digital elevation model have been derived from Copernicus Land Monitoring Service. Population census data (Italian National Institute of Statistics - ISTAT) and temperature-mortality statistics (Italian National Institute of Health - ISS) were used to quantify health effects. Simulations were performed during May-September considering current tree cover and potential future scenarios. The modeling application proposed in this study is based on freely available data and code, and is applicable to all main Italian cities. The use of these decision support tools can contribute to the appropriate planning and management of urban green areas to maximize ecosystem services for the population and promote adaptation and resilience of cities to the effects of climate change.