The impact of cool and green roofs on summertime temperatures in the cities of Jerusalem and Tel Aviv

Experiments were conducted to assess the potential impact of cool and/or green roofs to mitigate summertime conditions in two cities of Israel, Jerusalem and Tel Aviv, which differ in elevation, humidity, and housing density. Tel Aviv is located along the coastal plain and characterized by low- and medium-density housing in a humid climate. Jerusalem is in the central mountains (elevation >750 m), and characterized by medium- and high-density housing in a dry climate. The fraction of potential roofs available for reflective cooling and the fraction of green versus impervious surface areas were estimated from "Google Earth." Both were utilized as input into the Urban Canopy Model (UCM) within the Weather Research and Forecasting model, along with the residential building density. Increasing the albedo (cool roofs) had a larger impact on roof surface radiometric temperatures than covering the roof with irrigated soil and vegetation. Cool roof surface temperature differences were about 20 °C, compared to between 10 and 15 °C for wet soils with vegetation. The impact of varying albedo on 2-m. surface temperatures was about 0.4 °C, and the impact of varying soil moisture 0.1 °C. Increasing the leaf area index from 1.5 to 4.5 had a comparatively small impact on 2 m temperatures. Imposed anthropomorphic heating added about 0.2 °C to 2-m surface temperatures, which was less than values found in other studies conducted with more sophisticated building energy models. The surface temperature and heat index within Tel Aviv were more sensitive to mitigation efforts than those in Jerusalem, but both cities could benefit from mitigation efforts.