How will the urban heat island in growing cities behave under climate change?

热岛热主要是由于建筑物吸收热量，将热量困于封闭空间，以及与自然植被相比，建筑区域的蒸发量减少所致。其他热源包括柏油路面的热量和建筑物冬季的热量排放。一些欧洲城市(Jones和Lister，2009年)、美国和中国的城市使用了覆盖几十年到百年的长时间序列配对数据(城市/农村)，或使用基于卫星观测的当地温度空间变化(周等人，2013年)。由于具体的数据要求和区域利益，城市热带雨林的特点通常是地方到区域一级的。已发表的研究表明，它最初是随着城市的发展而增长的，但当城市化达到一定的成熟水平时，它往往会饱和。然而，这些研究涵盖的城市和地理/气候环境有限。因此，我们不能完全了解是什么因素决定了城市热岛指数的增长率和饱和程度，以及这些因素在沿海或干旱地区可能产生多大程度的不同影响。将首先根据所有可用的长时间序列配对站点数据(即包括城市内外的数据)，对城市热岛变暖进行系统评估。然而，高质量的农村-城市站对的可获得性在各个城市和地理上都是有限的。因此，还建议使用陆地表面温度(LST)数据，例如来自MODIS光谱仪的数据。LST在绝对值上不能直接与2m气温测量进行比较，但可以用来探索空间模式，并帮助解释有限数量的较长站记录。通过将这些城市热岛数据与城市的环境和社会经济特征(如大小、土地利用、气候制度、地理环境、绿色/蓝色空间、反照率)的数据结合起来，将确定城市热岛特征和潜在驱动因素之间的机械关系。还将使用高分辨率全球(CMIP5和CMIP6)和区域(CORDEX)气候模型的输出。除了一些有限的敏感性研究(McCarthy等人，2012年)外，这些模型不会隐含地模拟城市热岛指数，因此，如果时间允许，将探索使用相对简单的比例方法的可能性，即使用模型的温度变化统计数据来修改当今的城市气候统计数据。该项目还将探索本世纪预计的城市热岛效应对与热相关的健康负担的影响(使用与热应激相关的指数，如湿球温度)，并可能提出将其降至最低的解决方案。虽然该项目将侧重于热，但也将对湿度给予一定的关注，因为它对健康和人类舒适度具有重要影响(蒸发冷却的程度有助于确定城市热岛的大小)。

The UHI is caused primarily by the absorption of heat by buildings, the trapping of that heat in enclosed spaces, and the reduced evaporation from built areas compared to natural vegetation. Further heat sources include heat from tarmac and heat emissions by buildings in winter. The UHI has been documented for a number of European (Jones and Lister, 2009), American, and Chinese cities using long time series of paired data (urban/rural) covering multiple-decades to century, or using local spatial variations in temperature based on satellite observations (Zhou et al., 2013). The UHI is generally characterised at the local-to-regional level because of the specific data requirements and regional interests. Published studies indicate that it grows initially as the city develops, but it tends to saturate when urbanization reaches a certain level of maturity. However, these studies cover a limited number of cities and geographical/climate settings. Thus we do not fully understand what factors determine the rate of growth and the saturation level of the UHI and the extent to which these factors may have a different influence in say coastal or arid settings. A systematic assessment of UHI warming will be undertaken, initially based on all available long time-series paired station data (i.e. including data within and outside cities). The availability of high-quality rural-city station pairs is however limited both for individual cities and geographically. Thus it is also proposed to use Land Surface Temperature (LST) data, for example from the MODIS spectroradiometer. LST is not directly comparable in absolute terms to 2m air temperature measurements but can be used to explore spatial patterns and to help in the interpretation of the limited number of longer station records. By combining this UHI data with data on the environmental and socio-economic characteristics of cities (such as size, land use, climate regime, geographic setting, green/blue space, albedo) mechanistic relationships will be identified between the characteristics of the UHI and the underlying drivers. Outputs from high-resolution global (CMIP5 and CMIP6) and regional (CORDEX) climate models will also be used. Apart from some limited sensitivity studies (McCarthy et al., 2012) such models do not implicitly model the UHI, so, if time permits, the possibility of using a relatively simple scaling approach in which temperature change statistics from the models are used to modify the present-day urban climate statistics will be explored. This would allow the development of climate projections which do account for the UHI and thus are more appropriate for impact studies.The project will also explore the implications of projected UHI effects this century for heat-related health burden (using heat stress related indices such as Wet Bulb Globe Temperature), and possibly propose solutions to minimise it. Although the project will focus on heat, some attention will also be given to humidity as it has important implications for health and human comfort (and the extent of evaporative cooling helps to determine the magnitude of the UHI).