热浪背景下城市树木降温效应的变化研究

Changes in the Cooling Efficiency of Urban Trees Under Heat Waves

为探究热浪对城市树木降温能力的影响机制,基于遥感技术计算城市树木降温效率(CE),分析干热浪与湿热浪环境下CE的变化情况。结果表明:西安市和运城市频发干热浪,北京市和襄阳市频发湿热浪,且干热浪的发生频次高、持续时间长;发生干热浪时,西安市、运城市日间CE升高,而发生湿热浪时,北京市、襄阳市日间CE下降;热浪环境下,干热浪频发的城市日间CE较高,而非热浪环境下,湿热浪频发的城市日间CE略高,总体来看,西安市树木降温能力最强;不同城市日间CE对气候条件的响应存在差异,当相对湿度增加时,城市日间CE均减小,当最高气温升高时,西安市和运城市日间CE增加,而北京市和襄阳市日间CE减小;在任何环境下,城市夜间CE差异微弱,且远远小于日间CE。研究结果对于缓解热浪灾害、保护生态系统具有重要意义。

In order to expound the influence of heat wave on tree cooling capacity,the cooling efficiency(CE)was calculated based on remote sensing,and the change of CE under dry and wet heat waves was analyzed.The result showed that dry heat wave occurred frequently in Xi'an and Yuncheng,wet heat wave occurred frequently in Beijing and Xiangyang,and dry heat wave occurred more frequently and lasted longer.Daytime CE rises in Xi'an and Yuncheng cities during dry heat wave.Daytime CE drops in Beijing and Xiangyang during wet heat wave.In heat wave,the daytime CE was higher in dry heat wave-frequent cities,while in non-heat wave,the daytime CE was higher in wet heat wave-frequent cities,Xi'an had the strongest tree cooling capacity.The response of daytime CE to climatic conditions varied among cities.When relative humidity increases,daytime CE decreases in all cities.When the maximum temperature increased,the daytime CE increased in Xi'an and Yuncheng,but decreased in Beijing and Xiangyang.In any context,nighttime CE is stable and much smaller than daytime CE in all cities.The results have great significance for heat wave mitigation and ecosystem protection.