气候变化背景下人为热估算和效应研究

人为热是指由人类活动产生而释放到大气中的热量,这部分热量以感热和潜热的形式释放到城市冠层和城市边界层中,是城市生态系统的重要能量来源之一。在城市系统中,建筑物、交通运输和人类新陈代谢所释放的热量构成了总的人为热,具有明显的日变化和季节变化特征:清晨和傍晚出现一天中的两大峰值,而冬季和夏季分别是全年中最显著的两个季节。人为热的计算方法通常分为仪器观测法和能源消费清单法,其中能源消费清单法是目前普遍使用的方法。人为热主要通过改变大气的热力学能量方程和水汽方程中的热量和水汽量来影响区域和全球气候。在城市中,人为热是冬季和夜间城市热岛形成的主要原因,会影响大气边界层的稳定度和增加边界层高度。在全球范围内,人为热会对大气环流产生扰动,但对全球增温效应不显著。随着全球能源消费和人口的增加,人为热将成为气候变化的重要人为因子之一,因此如何观测和估算出一套高精度的人为热数据集极为重要。

Review of research on anthropogenic heat under climate change

Anthropogenic heat is wasted heat in the form of sensible and latent heat that is released to the urban canopy and planetary boundary layer of cities as a result of human activities, often involving combustion of fuels. It is estimated that nearly 70% of energy produced is consumed within cities that only occupy 2% of the global land area. Buildings, transportation, and human metabolism are the primary sources of heat discharge in cities. For example, in Manchester, the source fractions are 60%, 32% and 8%, respectively. However, the relative contributions of these sources vary greatly in different regions. The magnitude of the anthropogenic heat flux (AHF) in urban areas is very large and shows clear daily and seasonal changes. The peak of anthropogenic heat occurs in the dawn and dust during a day and summer and winter during a year. AHF can be calculated using observation or inventory approaches. Observation methods include surface energy balance and in situ eddy covariance observations. The surface energy balance method is usually based on meteorological and remote sensing data. IMAS (identification of micro-scale anthropogenic sources) filtering on data observed with eddy covariance systems was proposed to identify anthropogenic heat. Currently, inventory approaches (bottom-up and top-down) are widely used. In the top-down approach, energy consumption aggregated at coarse temporal and spatial resolutions is mapped to a finer spatial grid. Unlike the bottom-up method that demands detailed statistics of traffic and building height and floor space to determine the overall growth of the entire urban area from the subsystem scale upward, the top-down approach is suited for estimating anthropogenic heat at large scales. On the regional scale, impacts on regional climate, human health and urban ecology are posed by anthropogenic heat through adding heat and water vapor in thermodynamic energy and water vapor equations. It has been reported that the annual mean warming across western Europe is 0.1 K to 0.5 K due to AHF. On the global scale, the effect of anthropogenic heat release on global temperature is not significant at present. However, with the increasing of energy demand, there will be more anthropogenic heat discharged and accordingly more effect on global climate system. For example, the global average temperature is projected to increase by 0.4 K to 0.9 K from 2004 to 2100 if the elevated rate of energy consumption in 2004 is maintained. AHF may also affect regional precipitation and disrupt global atmospheric circulation patterns. With soaring increscent of global energy demand and population especially in developing countries, there will be a large quantity of anthropogenic heat released into the atmosphere, which will become one of the anthropogenic forcing for regional and global climate change. It is therefore important to estimate a high precise dataset of anthropogenic heat for simulating its climatic effects.