The mitigation potential of greenery during heat waves

Heat waves become more and more frequent as global warming intensifies. Mitigation of heatwaves will benefit cities in terms of public health, energy consumption, and ecology. Among the mitigation techniques, vegetation-based strategies like installing green roofs/facades and planting more trees are commonly used in practice. On a city scale, strategies like building more parks and planting more trees in the city have been proposed or been applied to combat heat waves. However, the question that whether these strategies will be effective enough on a city scale is not well answered. Because people still lack quantitative knowledge of vegetation-based mitigation strategies on a city-scale in terms of the magnitude of mitigation effect. At the same time, recent studies reveal that the behaviors of vegetation in heat waves are not well understood. Therefore, this thesis tries to answer the following questions: 1) how effective it is for the vegetation-based mitigation strategy on a city scale? 2) What factors influence the effectiveness of vegetation-based mitigation strategies? 3) Does the vegetation behave very differently in heat waves? 4)And how does the behavior of vegetation in heat waves impact the mitigation and prediction of heat waves? To answer questions one and two, a series of studies were performed. These include 1) The mesoscale simulation targeted at vegetation-based mitigation strategy in Riyadh in Saudi Arabia. This simulation was the very first mesoscale simulation study of vegetation-based mitigation strategy both in high resolution (500m) and large spatial scale (over 110km*120km). By setting up simulations on such scale, the thesis was able to comprehensively analyze and discuss the cooling potential, climatic consequences, and the influencing factors of different vegetation-based strategies in the desert city Riyadh. 2) The mesoscale simulation targeted at irrigation cooling strategy in Sydney in Australia. This is also one of the very few simulations that paid attention to the irrigation ...