Long-term Trend of Urban Heat Island Intensity and Climatological Affecting Mechanism in Bejing City
Huang Qunfang1,2,, Lu Yuqi2
1. College of Urban, Resources and Environmental Science, Jiangsu Second Normal University, Nanjing 210013, Jiangsu, China2. College of Geographical Science, Nanjing Normal University, Nanjing 210023, Jiangsu, China
National Natural Science Foundation of China (41430635);
Urban heat island (UHI) has an important effect on urban eco-environment, living and production, and physical and mental health of the residents. In addition, urban warming especially summer heat wave caused by UHI significantly affects many aspects of the global economy, such as energy and water consumption, transportation, and social economy. Understanding of long-term trend of urban heat island intensity and its climatological driving mechanism will help the rational urban planning, urban livable construction, and urban sustainable development. Beijing is the center of the Beijing-Tianjin-Hebei metropolitan area, and has experienced a rapid urbanization process in the past few decades. This study aims to elucidate the long-term trends of UHI intensities of mean air temperature, minimum air temperature, and maximum air temperature and the climatological driving mechanism based on 50 years (1967-2016) meteorological observation data from urban station (Beijing station) and rural station (Miyun station). In the past five decades, the UHI intensities of mean air temperature, and minimum air temperature showed a significant increasing trend with the increasing rates of 0.29℃/decade (r2=0.59, P<0.001) and 0.45℃/decade (r2=0.62, P<0.001) respectively. In contrast, no marked variability trend was observed for the UHI intensities of maximum air temperature. Statistical analysis has shown that relative humidity, wind speed, and sunshine duration decreased significantly and air temperature increased significantly in Beijing over the past 50 years, which is conducive to the formation of UHI and the enhancement of UHI intensity. Multiple stepwise linear regressions showed that relative humidity, maximum wind speed, and atmospheric pressure were the key climatological factors controlling UHI intensities of mean air temperature and minimum air temperature, which could explain 92.4% and 87.6% of variabilities respectively. Atmospheric pressure, relative humidity, and sunshine duration were the key climatological factors controlling UHI intensities of maximum air temperature. Under the background of global warming and rapid urbanization, UHI effect in Beijing will further intensify, resulting in more frequent and prolonged summer urban heat waves, which will seriously endanger urban residents' production, life and health. Therefore, it is necessary to consider the effects of UHI on the future urban planning and construction. By optimizing urban layout, carrying out reasonable road system planning, energy planning and ecosystem planning and other measures, we can alleviate UHI effects and reduce high temperature and heat waves harm caused by UHI.
urban heat island intensity;long-term trend;relative humidity;wind speed;atmospheric pressure;Beijing City;
IPCC第五次评估报告表明,近60 a来地面气温每十年上升0.12℃,约为过去100 a气温增温率的2倍。相对于全球气候变暖,作为土地利用/土地覆盖变化最激烈形式的城市地区经历了更剧烈的增温[2,3,4],形成了城市气温显著高于周边乡村和郊区的城市热岛现象。城市热岛效应广泛存在于全球各类、各级别城市中,据研究,全球超过1 100个城市、中国98.9%的城市都观测到了城市热岛效应[5,6]。在当前城市快速发展的背景下,2050年全球城市化率将达到70%,未来的城市热岛效应强度和发生范围将进一步强化,可以预见,城市热岛将成为当今世界面临的巨大挑战。因此,在城市热岛效应被发现的100多年时间内,国内外不同领域包括气象、城市规划、环境保护、园林设计和医疗卫生等专家学者从各个角度对城市热岛的形成和生态环境效应开展了大量的研究。在Web of Science数据库以“Urban heat island”作为关键词进行检索,1997~2016年与城市热岛相关的研究论文呈现快速增长态势,由1997年的20篇左右增加到2016年的500余篇,翻了近30倍。
Determination coefficient and significance level of linear relationships between urban heat island intensity of daily mean temperature, daily maximal temperature, and daily minimal temperature and main meteorological factors of urban station (Beijing station)
Determination coefficient and significance level of linear relationships between urban heat island intensity of daily mean temperature, daily maximal temperature, and daily minimal temperature and main meteorological factors of urban station (Beijing station)
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Analyses taken over all observed weather conditions of daily 0600 EST climate data from a network of monitoring stations in and around the large city of Melbourne, Australia, revealed a 20-yr mean urban heat island (UHI) value of 1.13C. The UHI varied seasonally between summer (1.29C), spring (1.25C), autumn (1.02C), and winter (0.98C). Investigations undertaken with daily wind speed and cloud amount data enabled a detailed investigation of the relative importance of factors such as the turbulent and radiative exchanges on Melbourne's UHI. Analysis of variance and regression techniques were used to explore these processes and to predict the behavior of the UHI in numerical terms for mean seasonal and annual periods between 1972 and 1991. Over the 20-yr period, analyses of the association among Melbourne's UHI, wind, and cloud revealed that the UHI was inversely proportional to approximately the fourth root of both the wind speed and the cloud amount. This relationship explained more of the UHI variance during summer and the least variance during winter. Increases in the amount of cloud cover and in the frequency of wind speeds in excess of 2.0 m sresulted in a statistically significant (95% confidence level) reduction in UHI magnitude. The influence of wind in limiting Melbourne's UHI magnitude was greatest during clear to near-clear sky conditions. Similarly increases in cloud were most restrictive to UHI development during calm to low wind speeds. Unlike most previous studies, the linear regression analysis presented here revealed that cloud was more limiting than the wind speed to UHI development for all seasons except summer. Contour plots of the UHI are presented for the various associations between each category of cloud and wind. These plots enable a clear visual presentation of the most to least favorable conditions for UHI intensity and development. The analyses indicate that low wind speeds and little or no cloud were typically associated with the largest UHI development. Eight octas of cloud and wind speeds in excess of 5.0 m swere usually associated with modest (but still apparent) UHI development.
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Global dimming is currently an active area of research in climate change. Trends of temporal (on the order of decades, years, seasons or even months) and spatial patterns in sunshine hours and associated climatic factors (average air temperature, relative humidity, precipitation and wind speed) over North China are evaluated for the period 1965~1999 based on data from 81 standard meteorological stations. The results show that: (1) North China is experiencing decreasing sunshine hours (82.855h/decade); (2) seasonally, decline in sunshine hours is highest in summer and lowest in winter; (3) spatially, decrease in sunshine hours is highest in inland and plain regions and lowest in the northwest mountain and coastland regions; (4) sunshine hours have a high correlation with precipitation, relative humidity and wind speed, with wind speed having the strongest influence on sunshine hours implicit in the close correlation (temporally and spatially) between the two variables; (5) cloud cover could not be any significant driver of sunshine-hour decline because it is more or less stable; (6) spatially and seasonally, wind speed is an important driving factor of decreasing sunshine hours in North China. Furthermore, the interactions between wind speed and aerosol loading may be an enabling factor of wind speed in driving (strongly) the changes in sunshine hours.
VautardR, CattiauxJ, Yiou P et al. Northern hemisphere atmospheric stilling partly attributed to an increase in surface roughness[J]. , 2010, 3(11):756-761.
Surface winds have declined in China, the Netherlands, the Czech Republic, the United States and Australia over the past few decades. The precise cause of the stilling is uncertain. Here, we analyse the extent and potential cause of changes in surface wind speeds over the northern mid-latitudes between 1979 and 2008, using data from 822 surface weather stations. We show that surface wind speeds have declined by 5-15% over almost all continental areas in the northern mid-latitudes, and that strong winds have slowed faster than weak winds. In contrast, upper-air winds calculated from sea-level pressure gradients, and winds from weather reanalyses, exhibited no such trend. Changes in atmospheric circulation that are captured by reanalysis data explain 10-50% of the surface wind slowdown. In addition, mesoscale model simulations suggest that an increase in surface roughness-the magnitude of which is estimated from increases in biomass and land-use change in Eurasia-could explain between 25 and 60% of the stilling. Moreover, regions of pronounced stilling generally coincided with regions where biomass has increased over the past 30years, supporting the role of vegetation increases in wind slowdown.
XuM, Chang CP, FuCet al. Steady decline of east Asian monsoon winds, 1969-2000: Evidence from direct ground measurements of wind speed[J].
 It is commonly believed that greenhouse-gas-induced global warming can weaken the east Asian winter monsoon but strengthen the summer monsoon, because of stronger warming over high-latitude land as compared to low-latitude oceans. In this study, we show that the surface wind speed associated with the east Asian monsoon has significantly weakened in both winter and summer in the recent three decades. From 1969 to 2000, the annual mean wind speed over China has decreased steadily by 28%, and the prevalence of windy days (daily mean wind speed > 5 m/s) has decreased by 58%. The temperature trends during this period have not been uniform. Significant winter warming in northern China may explain the decline of the winter monsoon, while the summer cooling in central south China and warming over the South China Sea and the western North Pacific Ocean may be responsible for weakening the summer monsoon. In addition, we found that the monsoon wind speed is also highly correlated with incoming solar radiation at the surface. The present results, when interpreted together with those of recent climate model simulations, suggest two mechanisms that govern the decline of the east Asian winter and summer monsoons, both of which may be related to human activity. The winter decline is associated with global-scale warming that may be attributed to increased greenhouse gas emission, while the summer decline is associated with local cooling over south-central China that may result from air pollution.
It indicates that hot summers will become more frequent in eastern China in the future. The region will face a great risk in the absence of any adaptation measures taken towards reducing its vulnerability to effects of extreme heat. Beijing Tianjin Hebei Region is identified as the biggest metropolitan in northern China. Rapid urbanization and the recent frequent occurrence of hot summers in the region raises questions about influencing factors at the regional scale and the spatiotemporal variability of heat waves. Using the newly developed Heatwave Index (HI), a statistical analysis is conducted on the temporal and spatial distribution characteristics of heat waves in the Beijing Tianjin Hebei Region over a period from 1960 to 2013. More specifically, based on the history of relocations, the heat wave trends between Beijing and Fengning is compared to investigate the influence of urbanization, and also analyse the relationship between atmospheric circulation anomalies and observed heat wave trends. It shows that based on variations in heat wave trends, two distinct phases are identified in Beijing Tianjin Hebei Region. Owing to some abrupt changes in the mid 1970s, the frequency of heat waves decrease from 1960 to 1973, and then increase from 1974 to 2013. Heat waves show a decreasing trend in the southern part and an increasing trend in the northern part of Beijing Tianjin Hebei Region. A significant increasing trend is found in the northern and western biological conservation area, and decreasing trend in the south eastern plains. At the regional scale, urbanization and relocations affects the occurrence of slight to moderate rather than extreme heat waves. In the period of global warming and rapid urbanization, the frequency of heat waves in Beijing is higher than that of Fengning. In recent global warming hiatus, the frequency of heat waves in Beijing is lower than Fengning. Driving factors behind the temporal and spatial patterns are deemed complicated. The inter decadal variations are significantly and closely related to the offsetting of western Pacific subtropical high (WPSH) ridge and the anomalous anticyclone over the Tibetan Plateau (TPAI) in summer. In other words, there is a positive correlation between the number of heat wave days and WPSH and TPAI. Furthermore, the probability of a summer with a mega heat wave would increase with the 坅nomalies in WPSH and TPAI.