research on the planning methods of mitigating summer urban heat island effects among basin cities a case study at xi an china

Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 169 (2016) 248 – 255 4th International Conference on Countermeasures to Urban Heat Island (UHI) 2016 Research on the Planning Methods of Mitigating Summer Urban Heat Island Effects among Basin Cities——A Case Study at Xi'an, China Duo Xua*, Dian Zhoua a School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, 28 Xianning west road, Xi'an and 710049, China Abstract Along with the process of urbanization, urban heat island effects (UHI) has become an important issue which affecting the quality of human settlements especially for clam wind basin cities In this paper, take basin city-Xi’an as the research object, based on the actual investigation of summer environmental climate parameters in central areas of Xi'an, combined with the average air temperature distribution map of summer typical meteorological day of Xi'an Analyze the spatial distribution of the UHI and "cool source", the urban ventilation channel is planned initially and the mitigation suggestions of UHI is proposed 2016The TheAuthors Authors Published by Elsevier Ltd is an open access article under the CC BY-NC-ND license © 2016 Published by Elsevier Ltd This (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the organizing committee of the 4th IC2UHI2016 Peer-review under responsibility of the organizing committee of the 4th IC2UHI2016 Keywords: Heat Island Effects; Basin Cities; Urban Planning; Ventilation Channel Introduction With rapid propulsion of urbanization process in our country, urban population and land utilization scale have been expanded continuously, while the contradictions between the infinitely increasing urban population and the limited environment and resource capacity have also been generated Cities are already incapable of bearing the heavy burden, while a series of urban problems such as air pollution and urban thermal environment changes have also been brought As one of the problems, the “urban heat island effect” comes first * Corresponding author Tel.: +86-15029971898; fax: +86-029-83395100 E-mail address: 715004831@qq.com 1877-7058 © 2016 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the organizing committee of the 4th IC2UHI2016 doi:10.1016/j.proeng.2016.10.030 249 Duo Xu and Dian Zhou / Procedia Engineering 169 (2016) 248 – 255 The “urban heat island effect” will lead to problems such as decrease in urban thermal comfort, urban microclimate environmental degradation and even harms to public health and safety Till now, domestic and foreign scholars have made extensive researches on influential factors of urban heat island effect, temporal and spatial variation characteristics and countermeasures for relieving heat island effect through methods such as ground meteorological data observation, remote sensing monitoring and boundary layer numerical simulation [1] Despite of the obtained major progress, the scholars in our country have rarely researched the urban heat island effect from the perspective of urban planning improvement strategies due to the lack in communications among the meteorological departments and urban planning departments in our country as well as the planners’ and architects’ lack in relevant meteorological knowledge and simulation technologies [2] In recent years, German scholars of urban planning are thinking about leading the suburb fresh and cool air into cities to relieve urban heat island effect and air pollution [3] Specifically speaking, they’ve obtained major progress in the planning for urban ventilation channel, while the planning achievements of the ventilation channel have been gradually applied in land use planning and overall urban planning The paper takes Xi’an – a basin city with hot summer as the research object Based on the implemented actual measurement survey experiment of climate environment in typical areas of Xi’an, and drawing of the summer thermal environment climate map of the main urban area with application of digital technologies such as GIS, the paper takes theories of German ventilation channel planning as the basis, focuses on the urban summer thermal environment, and analyzes urban prevailing wind direction, urban space and functional layout, the urban distribution of “cold sources” and other aspects in order to make preliminary research and discussion of construction of ventilation channel in Xi’an The Overview of Research Area 2.1 Analysis of the meteorological condition of the basin city - Xi’an Xi’an is located at the central Guanzhong plain Basin in the middle area of Weihe River, with Loess Plateau to the north and with the Qinling Mountains to the south, covering a municipal administrative area of 10,108 kmϡ and an urban area around the downtown of 275 kmϡ, boasting a population of 8.62 million Subordinate to Xi’an City are districts and counties Belonging to semi-humid continental climate over the warm temperature zone, Xi’an has four distinctive seasons and clement climate [4] The summer is torrid and rainy, with the rainfall accounting for 37% of the annual rainfall According to the table of outdoor meteorological parameters GB50736-2012, the average outdoor wind speed in summer is 1.6 m/s, the prevailing wind direction is northeastward in summer, and the wind frequency is 18% 2.2 Summer Urban Heat Island effects in Xi’an By browsing relevant literatures [5], the average temperature changing data of Xi’an and the surrounding districts and counties during the recent 30 years can be found It is found in the table that in urban areas, suburb areas and villages of Xi’an showed an overall increase tendency, while the temperature increase rate sequence is: “urban area>suburb area>village” Such difference was more prominent in summer, as shown in Table It indicated that the obvious heat island effect existed between urban area and rural area in Xi’an Table Changes of annual temperature in urban areas, suburb areas and villages of Xi’an from year 1981-2010 in Summer Factors Seasons Factors Seasons Urban areas of Xi'an Lantian 1981-1990 1991-2000 2001-2010 Annual AVG TEMP summer districts and counties average 1981-1990 1991-2000 2001-2010 1981-1990 1991-2000 2001-2010 24.9 26.2 26.7 24.5 25.7 25.6 24.7 25.8 25.8 Highest TEMP summer 30.5 31.8 32.0 30.1 31.5 31.4 30.2 31.6 31.5 Lowest TEMP summer 20.2 21.4 22.2 19.3 20.2 20.2 19.8 20.6 20.9 250 Duo Xu and Dian Zhou / Procedia Engineering 169 (2016) 248 – 255 Basic Research Theory 3.1 Wind speed is a main factor influencing the Urban Heat Island effect In order to know how to relieve the heat island effect phenomenon, key factors influencing heat island effect shall be analyzed at first in order to solve the problem in a targeted manner Research results show that influencing degrees of each influential factor for heat island effect in Xi’an are as follows: rainfall>average wind speed>exhaust gas emission>construction land area>population>energy consumption of artificial coal gas>energy consumption of liquefied petroleum gas>freight volume>greening area>GDP>total industrial value [6] Apparently, the natural factor is still the major factor influencing the thermal environment in Xi’an The rainfall continuously decreased and the annual average wind speed also decreased year by year in Xi’an during the recent 10 years, as shown in the following table: Table Influential factors for heat island effect in Xi’an from year 1995 to 2013 Influential factor 1995 1999 2000 2004 2006 2010 2011 2013 Rainfall value 531.1 600.5 589.5 883.2 541.74 660.3 504.4 426.7 2.1 1.7 1.5 0.9 1.0 1.5 1.4 1.2 Wind speed (m/s) The rainfall value is a natural factor which cannot be changed, so that the wind speed becomes the major factor influencing urban heat island effect The higher wind speed leads to the smaller urban-rural temperature difference Based on the current scientific and technological level, the industrial structure cannot be immediately changed and pollutant discharge cannot be reduced quickly, it is necessary to explore how to lead the suburb fresh and cool air into the urban area, motivate internal local circulation of the city, promote urban ventilation, relieve urban heat island effect and improve the urban ecological environment in the city Xi’an with frequent occurrence of calm wind 3.2 Construction theories of urban ventilation channel During construction of the urban ventilation channel, the external wind is led into the city, the heat island effect in summer will be relieved by the temperature reduction and humidity increase caused by natural wind and water vapour The research results show that the adjustment effect is better when the urban ventilation channel conforms to the prevailing wind Researches of our country on urban ventilation corridor still stay at the initial stage [7], while a complete set of planning formulation system has not been formed yet At present, scholars in our country mainly adopt the German method of ventilation corridor construction The paper also makes use of this method Specific contents are as follows: The method divides the urban underlying surface into acting space, compensation space and air guidance channel Acting space refers to the built and to-be-built areas suffering thermal pollution or air pollution; the full name of compensation space is eco-climate compensation space which is affiliated to the adjacent acting space, wherein the thermal pollution and the air pollution in the acting space can be relieved through air exchange realized by virtue of the position relations of the two kinds of space Air guidance channel is mainly used to lead the fresh air in compensation space into the acting space, playing a role of connecting the acting space with the compensation space Even for the weather with calm wind, the compensation air mass will not be hindered from flowing from the suburb compensation space to the urban areas The ventilation corridor is built mainly in order to relieve heat island effect During urban planning, a ventilation opening on suburb edge zone should be opened, and the natural wind should be led into the city by the good urban-rural edge structure More importantly, a generation area used for producing cold air is built, and the urban ventilation channel is applied to open up the internal urban microcirculation, improve local small environment of the city and promote local air circulation so as to relieve the heat island effect under the calm wind condition Duo Xu and Dian Zhou / Procedia Engineering 169 (2016) 248 – 255 251 3.3 Identification method of urban potential ventilation channel According to above construction theories of urban ventilation channel, effect areas and compensation areas can be identified in specific researches according to high-temperature areas and low-temperature areas in a city [8] The high-temperature area refers to an old urban area with dense population and concentrated building groups The lowtemperature area refers to an urban area with “cold sources”, such as urban green land, natural vegetation area and natural water body around the suburb Hence, high-temperature areas and low-temperature areas in the city can be analysed according to the thermal urban climate map in summer With Xi’an as the object, the research was carried out based on the actual measurement survey experiment of climate environment in typical areas of Xi’an Research Methods 4.1 Basic survey methods (the actual investigation of summer environmental climate in typical areas of Xi'an) Measurement of urban-scale thermal environmental basic data of Xi’an should be completed on underlying surfaces of different land use types within the scope of Ring Expressway (namely the main urban area) In this research, measurement sites were selected according to Xi’an Land Use Planning Map (2008-2020) During measurement of thermal environmental basic data, 24 different sites namely 24 measurement sites of land use types including lands for education and scientific research lands, residential lands, public green lands, medical health lands, commercial financial lands, road and square lands, sport lands and cultural relic & historic site lands were mainly selected During the period from June 11, 2014 to August 27, 2014, the research team measured air temperature, relative humidity, wind speed, wind direction, and total plane solar radiation intensity at each measurement site for continuous days, and also completed issuance and statistics of the thermal comfort questionnaires during on-site measurement As for the experimental measurement instruments, Jinzhou Sunshine PC-5 ultrasonic aero vane was applied to measure wind speed and wind direction; TR-72wf temperature and humidity recorder was used to measure temperature and humidity; and TES1333R was used to measure solar radiation intensity 4.2 Data processing results The paper only researched urban heat island effect, so the urban-scale thermal environmental basic data was processed mainly through the measured air temperature data The thermal-environmental actually-measured air temperatures in the urban scale of Xi’an were recorded every At first, the research team needed to work out every day per-hour average value of the air temperature which measured at different measurement points on the corresponding measurement day Measurement of thermal environment basic data in Xi’an was not completed simultaneously at different measurement points on the same day, but the thermal urban climate map drawn in Arc GIS must reflect the data at different measurement points on the same day as well as the temperature distribution characteristics in the same period Hence, before drawing of the thermal urban climate map, the air temperature data at different measurement points and different measurement time should be amended to the same moment corresponding to the same day This is the normalization processing method By this method, the temperature data was normalized to the summer typical weather day, namely July 19 4.3 The process of drawing of the map about temperature distribution on the typical summer weather day in central zone of Xi’an The member Liu Fengrong in our research team has completed the thermal urban-scale climate maps of Xi’an Focusing on the urban heat island effect, the paper only introduces the mapping process of the drawn maps about temperature distribution on the typical summer weather day in central zone of Xi’an [9] 252 Duo Xu and Dian Zhou / Procedia Engineering 169 (2016) 248 – 255 Fig The distribution situations of measurement points of Xi’an; Fig The distribution map of average air temperatures on July 19th At first, with the Xi’an land use planning map as the base map, the Xi’an road network map was drawn in AutoCAD 2008 CAD documents were loaded into Arc GIS for data conversion and spatial correction The paper mainly focused on the central zone in Xi’an, namely the area within Xi’an Ring Expressway, so vector data of the Xi’an road network map was clipped to obtain the road network map of Xi’an central zone Secondly, distribution of the actual measurement points in Xi’an should be determined Longitude and latitude information of 24 different measurement points mentioned above as well as the longitude and latitude information of weather stations arranged by Shaanxi Meteorological Bureau in the central zone of Xi’an were input into Arc GIS to obtain the distribution situations of measurement points in the central zone of Xi’an, as shown in the Fig At last, according to the air temperature data at different measurement points on July 19, 2014, the temperature distribution map of central zone in Xi’an could be drawn in the Arc GIS by the Kriging interpolation method [9] Namely, the distribution map of average air temperatures on the 2014 typical summer weather day (July 19) in the central zone of Xi’an is shown Analysis of Research Area Results According to theories of German ventilation channel construction, effect area, compensation area and urban ventilation path in the research area shall be analyzed at first 5.1 Effect area Effect area refers to the core area in Xi’an heat island, which is also the area with highest urban surface temperature and most serious thermal pollution According to the distribution map of average air temperatures on typical summer weather day in Xi’an, the heat island core areas in central urban zone of Xi’an include those from H1 to H10, wherein H1 is the economic development zone in Xi’an northern suburb, H2 is a spacious urban relic park of Daming Palace, H3 is an old industrial resident concentration area in the textile city of Xi’an eastern suburb, H4 is a commercial pedestrian zone at the urban centre, H5 is a concentrated residence area in eastern suburb, H6 and H9 are residence areas in Qujiang New District of Xi’an, H7 and H10 are high-tech development areas, and H8 is a Xiaozhai business area Apparently, core areas of summer heat island effect in Xi’an are mainly located in dense residence areas, development areas and business concentration areas 5.2 Compensation area Compensation area is also the low-temperature area of a city and also the location of “cold sources” According to distribution map of average air temperatures on typical summer weather day in Xi’an, urban low-temperature areas are mainly located at large-scale rivers including Chan River and Ba River on the northeastern side of Xi’an, Duo Xu and Dian Zhou / Procedia Engineering 169 (2016) 248 – 255 Wei River on the northern side and surrounding farmland and cultivated lands Xi’an Fengqing Park, large-scale urban lands in Qujiang New District as well as other urban parks and urban green lands are also taken as “small green lungs” inside the urban areas to send out fresh air for the city Green lands inside the city, as important compensation areas, can relieve stuffiness and high-temperature effect in surrounding areas During construction and planning of an urban ventilation channel, it is necessary to take full account of functions of urban green land parks, wherein intra-city green lands shall be connected in series and integrated into a whole through planning as much as possible so as to form the large ventilation coverage Fig The distribution analysis map of effect areas and compensation areas of Xi’an; Fig Ventilation channel planning for Xi’an city 5.3 Assumption of ventilation channel planning for Xi’an city based on addressing the heat island effect issue The construction of the ventilation channel for Xi’an City should be based on the planning that the predominant wind blows northeastward in the summer of Xi’an, under the principle of theories on urban ventilation channel construction, and also in full combination with and making full use of the planning for urban green space At present, the layout of “The Planning for a System of Green Space over the Administrative Region of Xi’an” is generalized as one centre, one axis, one circle, two networks, four rings, four belts, six zones, eight corridors and multiple blocks Among them, the one centre refers to the system of green space over the main urban districts being the green core; the one axis refers to the green landscape axis along the Weihe River; the one circle refers to the ecological vegetation protection circle around the metropolitan area; the two networks refers to the water system network and the road network; the four rings refers to the afforesting ring around the city wall, the afforesting ring around the city’s Second Ring Road, the afforesting ring around the city ring road, and the afforesting ring around the Xi’an-Xianyang road; the four belts refers to the cultural and scenic belt along the emperor’s mausoleum, the cultural belt of four great sites, the historical and cultural belt of the ancient capital, and eco-tourism belt along the Qinling Mountains; the six zones refers to the Weihe River CBD sight-seeing zone, the recreation zone of commerce and trade of the ancient city, the cultural leisure zone of Qujiang River, the national tourist resort zone in Lintong, the cultural sight-seeing zone in Qin palaces, and the urban recreation zone of Xianyang; the eight corridors refers to the eight ecological belts - the ecological protection forest landscape corridors along the rivers - Wei, Jing, Feng, Lao, Ju, Hao, Chan and Ba Rivers; each of the multiple blocks refers to the system of parks unfolded by hierarchy within the municipal administrative region Based on the foregoing analysis on effect area and compensation area, and with simultaneous consideration to the predominant wind direction of Xi’an City and the planning for green space over the municipal administrative region, four urban ventilation channels are to be constructed: x Baqiao Ecological Wetland Park - Ba and Chan Rivers in the northeastern area - Xi’an Expo Park - Qujiang River ecological green space in the southeastern area As the natural water areas beside the outskirts of Xi’an, the Ba and Chan Rivers are areas where cold air is created, which can relieve the heat island effect on the industrial zone in the eastern suburbs and the manufacturing living quarter of Xi’an under the effect of the predominant 253 254 Duo Xu and Dian Zhou / Procedia Engineering 169 (2016) 248 – 255 northeastward wind Cold air and fresh air are continuously supplied for ventilation and temperature drop by virtue of the rivers and wetland x Chan and Ba Rivers in the northeastern area - Chan River Wetland Park - Peach Blossom Pond Park - Guangyun Pond Park As a larger point source for transportation of cold air and fresh air in the eastern suburb of Xi’an, the Chan River is connected to the Wetland Park, forming a ventilation channel for cold air supply in the eastern suburb of Xi’an, which will carry away vast heat from the east zone of the city Cold air will also be transported to the central downtown along with the trend of northeastward wind in the summer of Xi’an x Grassland Town - Weihe River Wetland Park - Weiyang Avenue - Whole section of Chang’an Road - Greenbelt along Chang’an Avenue As the sole south-north ventilation channel, it forms a south-north ventilation channel traversing the main urban districts of Xi’an by connecting Grassland Town in the north, Weihe River Wetland Park as well as the urban main roads and peripheral greenbelt This will drive to relieve the heat island effect on both sides of main roads in the urban area x Weihe River Wetland Park - Hancheng Lake - site of Chang’an of the Han Dynasty - Greenbelt along Tangyan Road in Xi’an High-tech Industries Development Zone - Greenbelt along the Third Ring of Xi’an - Landscape greenbelt along the bank of Feng River.As the most important belt for cold air supply in north Xi’an, Weihe River Wetland Park can provide strong cold air for the northwestern side of the city Hancheng Lake, site of the Chang’an of the Han Dynasty, Greenbelt along Tangyan Road in Xi’an High-tech Industries Development Zone, and Greenbelt along the Third Ring of Xi’an act the role as replenishing point sources of cold air in the ventilation channel This ventilation channel connects these cryogenic zones in series, ultimately merging into the Feng River Landscape Belt on the southwestern side of the city 5.4 Suggestions for planning For the construction of potential ventilation channels through Xi’an City, the current overall urban planning and layout can hardly support effective implementation of the urban ventilation channels, hence suggestions are raised for the planning: x The two ventilation channels - one from Baqiao Ecological Wetland Park to Qujiang River Ecological Greenland in the southeast, and the other from the Chan and Ba Rivers in the northeast to Guangyun Pond Park - are focused on the city’s northeastern side as well as the peripheral areas of tableland It is suggested that “wedge-like” ecological lands be planned to supply fresh air for the city’s northeastern side along with the ecological wetland and rivers Enterprises settled in the chemical parks where the predominant northeastward wind blows across the city need to enhance the capacity of cleaner production, adjust industrial structure and configuration, take good control of the total amount of pollution, as well as to pay attention to forestation construction of the parks and improve their greening rate x The ventilation channel from Grassland Town to Greenbelt along Chang’an Avenue is focused on controlling the height of buildings on both sides of the road For the central urban area of Xi’an, the development projects and density of buildings in the neighborhood of the main roads need to be limited particularly Meanwhile, green looking ratio and green coverage ratio should be increased by means of roof greening, vertical greening and broken wall to expose green, so that the climatic environment of this area can be improved x The ventilation channel from Weihe River Wetland Park to Landscape greenbelt along the bank of Feng River is focused on limiting the density and height of buildings on both sides of the northern air inlet And “wedge-like” ecological vegetation should be planned southwestward in Xi’an to get through the ventilation channel from north to southwest Plus, by connecting in series the urban vegetation to the peripheral vegetation midway, the effective radius can be increased for ventilation and temperature drop Conclusion Urban heat island effect is an inevitable product generated during urban formation and development, which makes urban residents’ production and life inconvenient in many aspects, seriously influences human body’s thermal comfort and performs prominent especially in basin cities and high-temperature summers The planning Duo Xu and Dian Zhou / Procedia Engineering 169 (2016) 248 – 255 method for ventilation channel construction put forward by this paper is an important manner to relieve these urban problems Nevertheless, contents involved and concerned in this paper only focus on planning strategies of ventilation channel In the future, the research will further discuss about how to apply numerical simulation technology to realize simulation and quantitative inspection of ventilation effect and heat island relief effect after the channel construction Acknowledgements This research was funded by Ministry of Education, China under the issue: Comprehensive survey of the quality of the living environment in typical cities and the establishment of the atlas of urban environment climate map References [1] Xue J, Research on spatial forming mechanism of urban heat island and its mitigation countermeasures -a point of view of urban planning doctoral dissertation, Zhejiang University, Zhejiang, China,2008 [2] Bai Y., Wang, X Y., 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