【作者】 吴耀兴；

【导师】 康文星；

【作者基本信息】 中南林业科技大学 ， 生态学， 2010， 博士

【摘要】 随着城市化进程的加快,人口高度密集,城区面积越来越大,导致了下垫面性质改变,高强度的经济活动中消耗大量能源,释放出有害气体和粉尘对人类生产和生活产生影响。如此种种变化改变了原有区域的气候状况,在城市区域形成了特有的小气候特征——城市热岛效应。本文利用长沙市有关气象资料等数据,对长沙市热岛效应形成的原因、分布规律、热岛效应的危害以及城市绿地在缓解城市热岛效应中的作用进行了研究。其目的在于为城市的规划与建设,城市经济社会的可持续发展提供有科学价值的参考依据。本文研究的结果归纳如下。1.长沙城区内部结构特征是城市热岛形成的主要原因。老城区街道走向、几何形状及建筑物的密度大,新建城区的设计也不尽合理,建筑物过高也过密,使城区风速小,热量不易扩散,导致局部气温过高。下垫面多为水泥、混凝土等硬质铺砌,反射率低,热容量大,白天在相同的太阳辐射条件下,城市下垫面比郊区能吸收更多的热量,另外,参差不齐的建筑物使城市建筑墙壁与墙壁、墙壁与地面之间长波辐射进行多次反射与吸收,这些为长沙热岛形成奠定了能量基础。日落后,城市与郊区气温下降的速率不同,是夜晚城市热岛形成的直接原因。2.城区人为热的释放对热岛的形成起着非常重要的作用。城区工厂、企业、机动车辆、空调运转和居民烹饪要消耗大量的能源,由此释放的人为热量是郊区的3-6倍。人为热的排放对城市热岛的影响具有双重作用,一方面直接增加了城市的热量,为热岛形成奠定了基础；另一方面,人为热排放的同时,也排放大量的粉尘和各种污染气体,形成了覆盖在城市上空的“尘罩”与“气罩”,加重了城市热岛的强度。3.一定的气候条件也是长沙城区形成热岛的外部因素。本研究表明,发生城市热岛的天气条件具有相似性,即大多数热岛出现在晴朗、云量少、无风(或微风)、大气温度层结稳定的天气条件下。4.长沙城区热岛水平分布基本上与城市建城区轮廓一致,并且随着城市的发展已有向外扩展的趋势。白天,城区热岛分布构成以中心城区为主,面积大,分布集中,但又出现城区有多个中心热岛分布的特征,夜间城市热岛范围较小,强度较强,以工业区和人口密度的居民区以及水体效应(大的湖泊)为主构成热岛零星分布。长沙城区热岛的垂直分布,城区对最高气温的影响高度约在50m以下,对最低气温的影响其高度超过70m。5.近20年来,长沙市热岛强度逐年增大,2008年热岛年平均强度为1.46℃。热岛强度的季节性变化表现为秋季>冬季>春季>夏季。长沙市热岛日变化有2种类型,一种类型是其变化特征表现出日变化明显,白天强度较弱,夜间热岛强度在深夜或日出前达到了最大值,这种变化过程多出现在秋冬季天气晴稳的条件下；另一类型是日变化特征可以明显地看出热岛强度日变化周期,有时也有明显的峰期出现,但总体变化平稳,变化幅度小,且最大热岛强度出现时间变化较大。这类热岛大都出现在多云、有风以及降水多的湿润天气。6.由于热岛效应的存在,长沙城区年平均气温从本世纪初的17.2℃,猛增到2008年的18.1℃。最近几年来,夏季极端高温达到39.8℃～40.6℃,一年内,日平均气温在30℃以上的天数由85天,气温出现高于35℃的炎热日数有56天,热岛效应造成持续的高温和频繁的热浪冲击,已严重地影响城市居民正常生活和健康。城区热岛效应有利形成城区和郊区的辐合环流,促成了郊区的大气中污染物流向城区,另外,若出现静风或者逆温层存在,污染物不易扩散,被抑制在低空逆温层内,增大了近地面层污染物的浓度,使城区经常遭受各种高浓度污染源的封闭性污染。热岛效应改变了一些植物的习性。长沙城区的一些植物发芽、开花、长叶出现的时间比郊区同种植物药提前3-5天,落叶时间要延迟5-7天。7.夏天热岛效应带来了酷热,增大了制冷能源的消耗,消耗能源的同时,也增大了温室气体的排放量,温室气体的排放又直接加速全球气候变暖,气温进一步上升,反过来加重热岛效应,形成一种恶性循环。8.在炎热的季节,城区内的城市森林较无林的城区地带,舒适天数增加了31.18%,较舒适天数增加38.57%,而稍不舒适天数减少了7.38%,稍闷热天数减少18.24%,闷热天气减少53.71%。城市森林缓解城市热岛效应的作用是巨大的。9.不同类型的绿地降低城市热岛效应的效果不一样,降温效果和增湿效应表现出乔木林>乔灌林>灌丛>草地。乔木林、乔灌林、灌丛和草地的温度变化指数分别为7.32、6.59、5.33和4.10,湿度变化指数依次是16.87、13.23、9.42、7.61。绿地面积、形状不同,林分的郁闭度和树种不同,它们削减热岛效应的效果不一样。10.随着天气的不同,城市绿地系统降温的效果不一样,降温的效果晴天>阴天>雨天。绿地系统降温的日变化(白天)规律是,降温作用最大的时段是日出以后不久,上午降温作用逐渐下降,到午后14:00时左右,降温作用最小,下午到日落前,降温作用又逐渐回升。更多还原

【Abstract】 With the accelerated urbanization process, population density become more dense, and urban area is enlarged continuously, which lead to the quality of underlying surface changed. The harmful gases and dust that are released from a large amount of energy consumed in high-intensity economic activity have great influence on human being’s production and living. Regional climatic condition are different from the original by variety changes, a unique microclimate characteristic is forming in urban areas-- urban heat island effect. This paper conducts a special research on the reasons, distribution law and hazards of Changsha’s urban heat island effect, and studies the function of urban green space in relieving urban heat island effect, using the meteorological data of Changsha City. The purpose is to provide references with scientific value for the urban planning and construction and sustainable economic and social development of the city. Research resluts are summarized as following.1. Internal structure of Changsha city is the main reason for the formation of urban heat island. These complexions such as street direction, geometric shapes and high-density buildings in old city area, not quite reasonable design and too high too close buildings in new city area all make the wind speed low in the city zone and make it difficult to diffuse heat, which result in the local temperature too high. In most cases, underlying surface are paved with cement, concrete and other hard materials with low reflectance, high heat capacity characteristics. On the same day the solar radiation condition, the city underlaying surface can absorb more calories than the suburbs’. In addition, jagged building walls make longwave radiation between wall and wall, wall and ground reflected by many times with absorption, which provide energy base for the formation of Changsha heat island. Sunset, different rate of temperature drop between urban and rural areas is the direct cause of forming urban heat island at night.2. Released urban artificial heat plays an important role in forming urban heat island. Urban factories and enterprises, vehicles, air conditionings and residents cooking consume large amounts of energy, artificial heat released from that is of 3 to 6 times to suburb. Artificial heat emission has dual role to urban heat island effect. On the one hand to increase the city’s heat directly lays the foundation for the formation of heat island; On the other hand, large quantities of dust and a variety of polluting gases are emitted when emitting heat, which form a covering over the city’s "dust cover" and "hood" and increase the intensity of urban heat island.3. Certain climatic conditions are also external factors in forming the heat island in Changsha City. This research shows that the occurrence of urban heat island has similar weather conditions, i.e. most of the heat island in sunny, less clouds, no wind (or breeze) and the atmospheric temperature structure of a stable layer of weather conditions. 4. The level distribution of Changsha urban heat island is basically consistent with the outline of the city urban construction, and with the development of the city has the tendency to expand outward. During the day, urban heat island is mainly in downtown and of large area, centralized distribution, but also there are distribution characteristics of multi-centre heat island. At night urban heat island has characteristics of smaller range and strong intensity. Industrial areas, densely populated residential areas, and water effects (large lakes) constitute the main heat island scattered. The vertical distribution of Changsha urban heat island is the effect height of the highest temperature of the city about in 50m, the effect height of the lowest temperature of the city over 70m.5. Changsha’s heat island intensity has been enhancing year by year in the nearly 20 years, its average degree was 1.46 degrees celsius in 2008. The seasonal variation of heat island intensity manifested as that autumn is stronger than winter than spring than summer. There are two types of Changsha’s heat island diurnal variation:one type is that the variation characteristics show obvious changes during the day and its strength is weak, heat-island intensity late at night or before sunrise reaches a maximum, this change process often appears in autumn-winter days with sunny weather conditions; Another type is that diurnal variation period can be clearly seen by diurnal variation characteristics, sometimes also has the obvious peak amplitude,steady overall change and small change range, and the appearing time of largest heat island intensity changes greatly. This kind of heat island mostly appears in the cloudy, windy and more rainfall wet weather.6. Because of the existence of heat island effect, the mean annual temperature soared from 17.2 degree celsius at the beginning of this century to 18.1 degree celsius in 2008. In recent years, the summer temperature extremely reached 39.8 degree celsius to 40.6 degree celsius, there are 85 days’diurnal average temperature above 30 degrees celsius in one year and 56 days above 35 degrees celsius, the continuous high temperature and frequency heat shock caused by heat-island have seriously effected urban residents’normal life and health. Urban heat island effect is helpful to the convergence circulation between urban area and suburban area, forcing the atmospheric pollutants in suburban area gush to urban area. In addition, if the static wind or temperature inversion layer existing, pollutants, suppressed in low-altitude temperature inversion layer, are difficulty to spread, increasing the concentration of near-surface pollutant, making urban often suffered from closed pollution by various high concentration pollution sources. Heat island effect change the habit of some plants.The time of sprouting, blossing and frondescing of some plants in urban area of Changsha are 3-5 days ahead of the same plants in suburban, and the defoliation time postpones 5-7 days.7. Summer heat island effect brought blazing hot, increased the consumption of cooling energy, which increased the emissions of greenhouse gas at the same time. The emissions of greenhouse gas directly accelerated the global warmmer. In turn, temperatures rise aggravated heat island effect, leading to a vicious circle.8. In the hot season, the number of more comfortable days in urban forest area increased 31.18% more than this in urban non-forest area, the number of comfortable days increased 38.57%, slightly uncomfortable days reduced 7.38%, slightly hot days reduced 18.24%, hot days decreased 53.71%. Urban forest hugely alleviated the urban heat island effect.9.Different types of green space have different effects to reduce the urban heat island, Cooling effect and humidifying effect are showed that the arbor forests’is higher than shrubberys’ than thicket’s than grasslands’. Temperature Changing indices of arbor forest, shrubbery, thicket, and grassland were 7.32,6.59,5.33 and 4.10, humidity index were 16.87,13.23,9.42,7.61 in order. Different greenbelt area and shape, different forest types and its crown density have different effects of reducing the heat island.10. The cooling effect of urban green space system is different along with the different weather, the cooling effect of sunny day is higher than cloudy day, and this of cloudy day higher than rainy day. The diurnal variation regularity of urban green space system is that, the supreme cooling effect period is shortly after the sunrise, the cooling effect gradually declines in the morning, and it reaches to the minimum in the afternoon around 14:00, it picks up gradually again before sunset.更多还原