Cláudia Reis (Portugal) 1; António Lopes (Portugal) 1
1 - Instituto de Geografia e Ordenamento do Território - Universidade de Lisboa
The main goal is to develop a methodology to evaluate the cooling capacity of green spaces based on a biomass model which can be useful for Urban Heat Island (UHI) mitigation and climate change adaptation.
The city of Lisbon presents some particularly unique climatic features, namely a hot and dry season with predominant N and NW winds. The climate predictions for the city indicate an increase in frequency and duration of heat waves and in the number of hot days and tropical nights, exacerbating the Urban Heat Island (UHI) effect, with an UHI intensity of about 3ºC (more intense in summer and at night) have been reported by several authors. These facts show the need to understand which urban features, namely the quantity, quality and location of vegetation, require modifications to improve the quality and comfort of urban population and mitigate the heat.
In this study, two gardens with different dimensions and compositions (Fundação Calouste Gulbenkianmainly with trees and Fernando Pessa with a central area with grass) and two streets, one with trees (Defensores de Chaves) and one without vegetation (Actor Isidoro). were chosen as sample areas. In the gardens and adjacent areas, 13 thermo-hygrometers were installed to evaluate the variation of climatic elements with increasing distance. In the two streets the thermal benefits of vegetation were evaluated based on mobile measurements. Respecting biomass, models were based based on remote sensing products applied in areas with climatic similarities in Lisbon using NDVI calculated from Landsat 8 summer and winter images. The final output was correlated with the climatic data collected to estimate the amount of vegetation needed to decrease 1ºC in the city and to mitigate the UHI. Results show that all green spaces analyzed, at some moment, reduced air temperatures in their surroundings. Gulbenkian garden was, in average, 2.2ºC cooler. In contrast, Jardim Fernando Pessa was, in average, 0.2ºC hotter than surroundings, although maximum Park Cool Island (PCI – difference between air temperature inside an urban green space and in the surrounding building area) was 3.5ºC. These differences may be explained by the dimension of green spaces and the type and area occupied by vegetation (trees are far more effective than grass). The linear regression model built with air temperature and kernel density of vegetation (predictive variable) showed that in order to reduce 1ºC in difference of air temperature vegetation must be increased in 50m2 (planar measure).