南京市夏季热岛特征及其与土地利用覆盖关系研究

利用南京市7月的Landsat TM热红外波段数据,根据单窗算法反演得到南京市地表温度,讨论了南京市热岛特征,并分析了产生这种现象的原因。通过遥感和地理信息系统相结合,运用Landsat TM数据,提取出南京市下垫面类型,分析了不同地表覆盖类型的热辐射特征并定量地分析了土地利用及植被对地表温度的影响。结果显示,南京市夏季主要存在3个热岛中心,分别是建成区、大厂区和八卦洲。南京城区地表温度明显比郊区地表温度高,通过地表温度对比分析发现,城区平均地表温度比城市边缘和远郊区地表温度分别高出3.5℃和5.7℃,城市热岛效应明显。不同地表覆盖类型的地表温度也有显著差异,从高到低依次为：城镇建设用地、耕地、草地、林地、水体。城镇建设用地与水体的表面温度最大相差14℃。城市地表温度与植被覆盖度具有明显的负相关关系,城市地表植被覆盖度低是城市热岛出现的主要原因,今后应当更加注重城市绿地建设,提高植被覆盖率。     

Formulation of a tropical town energy budget (t-TEB) scheme

This work describes the tropical town energy budget (t-TEB) scheme addressed to simulate the diurnal occurrence of the urban heat island (UHI) as observed in the Metropolitan Area of Rio de Janeiro (MARJ; ?22° S; ?44° W) in Brazil. Reasoning about the tropical urban climate have guided the scheme implementation, starting from the original equations from Masson (Bound-Lay Meteorol 94:357–397, 2000). The modifications include (a) local scaling approaches for obtaining flux–gradient relationships in the roughness sub-layer, (b) the Monin-Obukhov similarity framework in the inertial sub-layer, (c) increasing aerodynamic conductance toward more unstable conditions, and (d) a modified urban subsurface drainage system to transfer the intercepted rainwater by roofs to the roads. Simulations along 2007 for the MARJ are obtained and compared with the climatology. The t-TEB simulation is consistent with the observations, suggesting that the timing and dynamics of the UHI in tropical cities could vary significantly from the familiar patterns observed in mid-latitude cities—with the peak heat island intensity occurring in the morning than at night. The simulations are suggesting that the thermal phase shift of this tropical diurnal UHI is a response of the surface energy budget to the large amount of solar radiation, intense evapotranspiration, and thermal response of the vegetated surfaces over a very humid soil layer.     

成都精细下垫面信息对城市气象影响的模拟试验

为了提高成都市精细化天气预报水平,使用成都地区精细下垫面土地利用资料,在WRF中耦合了单层城市冠层模式,对2008年7月6 日晴空背景下的成都城市气象特征进行了模拟,并和使用旧土地利用资料、slab模式的模拟结果进行了对比分析.模拟结果表明城区因为不透水下垫面的增加,使得地表蒸发和地表水汽通量显著减小,潜热通量减小,感...     

上海城市集群化发展显著增强局地高温热浪事件

上海作为中国城市集群化发展的典型代表,经过30余年圈层式、集群化扩张,城市建设用地面积比例高达47.9%,接近50%的生态阈值。城市群快速扩张诱发了一个以徐家汇为中心覆盖周边40 km的区域性热岛,影响高温热浪的时空分布。基于DMSP/OLS遥感夜间灯光数据构建的城市发展指数,客观地反映出1992—2013年上海西郊嘉定、青浦和东郊的浦东集群化发展特征最凸出。利用Chow检验最优分段建模法,研究发现高温热浪期间城市群热岛突变转折与区县城市发展指数超过60%的年份相对应。城市发展指数超过60%后,近郊城市继续扩张将缩小城、郊气象站的温差,诱发更大范围热岛,增强高温热浪。1977—2000年近郊区县城市发展指数低于60%,高温热浪各要素项城郊差值显著上升,而2000年西郊城市发展指数超过60%后,和市中心差值减小,快速城市化明显增强西郊高温热浪强度和持续时间。1978年以来上海西郊与远郊高温日数差值增加了1.6倍,平均气温差值增加了34.4%,平均最高气温差值增加了41.7%。高温热浪期间遥感数据显示,向西郊伸展的城市群地表温度高值区规模扩大了32.8%,是西郊高温热浪增强的驱动因子。     

Further Development of the Vegetated Urban Canopy Model Including a Grass-Covered Surface Parametrization and Photosynthesis Effects

The vegetated urban canopy model (VUCM), which includes parametrizations of urban physical processes for artificial surfaces and vegetated areas in an integrated system, has been further developed by including physical processes associated with grass-covered surfaces in urban pervious surfaces and the photosynthesis effects of urban vegetation. Using measurements made from three urban/suburban sites during the BUBBLE field campaign in 2002, the model’s performance in modelling surface fluxes (momentum flux, net radiation, sensible and latent heat fluxes and storage heat flux) and canopy air conditions (canopy air temperature and specific humidity) was critically evaluated for the non-precipitation and the precipitation days. The observed surface fluxes at the urban/suburban sites were significantly altered by precipitation as well as urban vegetation. Especially, the storage heat at urban surfaces and underlying substrates varied drastically depending on weather conditions while having an important role in the formation of a nocturnal urban surface layer. Unlike the nighttime canopy air temperature that was largely affected by the storage-heat release, the daytime canopy air conditions were highly influenced by the vertical turbulent exchange with the overlying atmosphere. The VUCM well reproduced these observed features in surface fluxes and canopy air conditions at all sites while performing well for both the non-precipitation and the precipitation days. The newly implemented parametrizations clearly improved the model’s performance in the simulation of sensible and latent heat fluxes at the sites, more noticeably at the suburban site where the vegetated area fraction is the largest among the sites. Sensitivity analyses for model input parameters in VUCM elucidated the relative importance of the morphological, aerodynamic, hydrological and radiative/thermal properties in modelling urban surface fluxes and canopy air conditions for daytime and nighttime periods. These results suggest that the VUCM has great potential for urban atmospheric numerical modelling for a range of cities and weather conditions in addition to having a better physical basis in the representation of urban vegetated areas and associated physical processes.     

A Numerical Study of the Urban Intensity Effect on Fog Evolution in the Beijing-Tianjin-Hebei Region

The influence of urban intensity on fog evolution in the Beijing-Tianjin-Hebei (BTH) region (China) is investigated numerically with the the Weather Research and Forecasting (WRF) model coupled with the urban canopy parameterization-building energy model (UCP- BEM) urban physics scheme. The experiments were designed with a focus on the influence of different urban intensities, which are represented by a different fractional coverage of natural land, buildings, and energy consumption inside buildings in an urban environment. The results of this study indicate that urban areas notably influence fog evolution when natural land is reduced to a small fraction (e.g., less than 10%). Developed land changes fog evolution through urban effects. Higher urban intensity (HUI) generally results in warmer temperatures and lower wind speeds throughout the day, while inhibiting morning specific humidity loss and afternoon specific humidity gain because of the HUI effect on surface heat flux, surface roughness, and surface moisture flux. HUI leads to later and weaker liquid water content formation, with a higher liquid water content base, primarily due to its effect on near surface temperatures. This finding implies that HUI may inhibit the conditions for fog formation. In addition, urban areas with equal natural and developed land coverage seem to greatly enhance the upward surface moisture flux, which is attributed to the combination of a relatively large potential evaporation on developed land and an ample moisture supply from natural land. As a result, the specific humidity increases in the afternoon.     

Responses of urban heat island in Atlanta to different land-use scenarios

The urban heat island (UHI) effect changes heat and water cycles in urban areas, and has been accused of elevating energy consumption, deteriorating living environment, and increasing mortality rates. Understanding various UHI effects necessitates a systematic modeling approach. A major problem in UHI simulations is that urban areas were either considered to have only one category of land use/cover or outdated in land use/cover patterns due to the lack of high resolution data. Therefore, this study aims at integrating up-to-date remotely sensed land use/cover data with the Weather Research and Forecasting (WRF/UCM)/Urban Canopy Model modeling systems to simulate surface temperature patterns in Atlanta, Georgia. In addition, three land-use scenarios, i.e., spontaneous scenario (SS), concentrated scenario (CS), and local policy scenario (LPS), were designed and incorporated into the modeling. Five numerical experiments were conducted by using the Weather Research and Forecasting (WRF) model to explore the impact of urbanization-induced land-cover changes on temperature patterns. Land use and land-cover patterns under all three scenarios suggested that urban growth would continue through in-filling development and outward expansion. Compared to temperature simulations in 2011, temperature maps corresponding to the three urban growth scenarios showed warmer and cooler temperature patterns outside and inside the urban core, respectively. Analysis of the mean diurnal temperature cycle suggested that the highest temperature difference of 3.9 K was observed between 2011 and the LPS, and occurred around 22:00 local time. Overall, the simulations showed different UHI effects respond to the land-use scenarios in the summer. It is recommended for urban managers and policy makers to reflect on the potential impacts of alternative urban growth policies on thermal environment.     

Thermal bioclimate in Strasbourg - the 2003 heat wave

This case study highlights the implications of the 2003 heat wave for the city of Strasbourg, France. The urban centers of France and other European countries were particularly affected by the heat wave. In some urban areas, the mortality rate was 60% above the expected value (Institute de Veille Sanitaire, 2003). The 2003 heat wave demonstrated once again that populations in urban centers are much more affected by extreme meteorological events than people living in rural areas. The aim of this analysis is to explore differences in thermal comfort conditions of (a) the city center of Strasbourg, and (b) its hinterland. The differences in thermal conditions existing between rural and urban areas are quantified by using a bio-climatological index termed physiologically equivalent temperature (PET). This index is based on the human energy balance and builds a relevant index for the quantification of the thermal environment of humans. We calculate the PET for the years 2003 and 2004 to highlight the temporal changes in the severity of climate extremes. The spatial scope of this study is improved compared to previous works in the field through the inclusion of PET calculations for five different sites on a central place in Strasbourg (Place Kléber). The calculations are characterized by different sky view factors and are compared to the reference site, which is located in a rural area. In the rural hinterland (Entzheim), the analysis of PET indicates a strong cold thermal stress during the winter months but no significant stress in summer. In 2003, summer temperatures were sensed as warmer compared to other years, but did not reach the extreme temperatures that may cause severe heat stress. For both the rural and the urban study sites PET was higher in the summer of 2003 than in 2004, which reflects the inferior thermal conditions in the urban area during the heat wave in 2003. For the entire study period, urban and rural day-time PET reached similar maximal values. Strong differences in PET, however, were observed between the rural and urban areas at night-time. The study of PET for several study sites on a central place in the city (Place Kléber) of Strasbourg for the years 2003 and 2004 showed that the sites with a higher sky view factor present higher values than sites with a lower sky view factor. The comparison of these PET values (Place Kléber) to the results for the rural area showed that during the day and the night the rural city of Entzheim has the lowest PET. During the day, the site at Place Kléber, which is located under a tree, has the lowest PET. The comparison of PET for the years 2003 and 2004 shows that PET in 2003 was about 5 to 7 K higher.     

地表利用城市化在一次极端高温过程数值模拟中的影响

地表种类的城市化对城市区域的热力结构和局地环流都会产生巨大的影响。利用地面、高空观测资料和MODIS地表覆盖资料,使用耦合城市冠层模式(UCM)的区域中尺度数值模式(WRF),对2013年8月8日福州地区的一次极端高温天气过程进行数值模拟,研究地表利用变化对福州城市热岛效应及其对福州城市区域局地环流的影响。结果表明:地表利用的城市化使得午后城市热岛现象更加明显而夜间热岛效应呈现出减小的趋势;地表利用城市化后,中心城区的近地面风速减小,但城区与山区以及城区与海洋之间的局地热力环流明显加强,促进了山谷风和海陆风环流的发展;同时地表加热效应增强,促进了垂直运动的发展。      

2018年北京城区和远郊区低层大气风场特征分析

利用2018年1月1日至12月31日在北京国家综合气象观测实验基地获得的风廓线雷达资料和同时期在河北香河的华北香河全大气层野外科学观测研究站获得的多普勒声雷达资料,比较分析北京城区和远郊区的低层（0～600 m）大气风场特征。结果表明:水平风速随高度增加而增大,同一高度层,远郊区的平均水平风速大于城区,且受湍流活动影响,城区和远郊区水平风速日变化趋势均为白天小于夜间。春、夏季城区风向受局地山谷风影响显著,以偏西南偏南气流为主,城区和远郊区秋冬季受冷空气活动影响,以西北风为主,且水平风向日变化特征具有季节性差异。远郊区低层大气垂直速度分布特征四季相同,正、负速度出现频率相当,日变化趋势为单峰型;城区冬春季有差异,在390 m高度以下正速度出现频率明显大于负速度,且日变化趋势在四季差异较大。北京城区和郊区风场特征差异与其他特大城市相比无特殊性,主要受大气环流、局地地形、下垫面环境等因素影响。     

西安地区气温的年代际变化及其受城市化进程的影响

利用西安及周边14个观测站1966～2005年冬季(12～2月)、夏季(6～8月)平均气温及城市化信息的相关统计资料,以各站与14站区域平均气温的差值(空间距平值)反映城市热岛空间分布,以城区站与区域平均气温的差值代表城市影响程度,探讨了城市影响及城市化指数在气温突变和热岛效应中的作用。分析结果表明:1)冬夏季,近城区、平原区、浅塬山区与整个区域平均气温变化一致,表现为大尺度的气候变化特征,而城区和全区变化同步性差,呈现小尺度气候变化特征。2)冬季全区在1977年发生增温突变,这次突变以自然增温为主,与全国(1980年)突变时间基本同步,但略显偏早,比西北区(1984年)偏早7年。夏季全区在1988年发生第一次气温突变增温,比西北区(1993年)偏早5年,偏早原因可能是地形和城市化共同作用。3)冬、夏季平均热岛强度分别为0.65℃、0.46℃,具有典型性。4)城区冬季突变点(1989年)后西安城区的平均气温增加1.3℃,城市影响在气温突变中贡献了0.35℃。夏季突变点(1987年)后平均气温增加了0.4℃,城市影响贡献增温0.39℃,夏季气温突变可能主要是由城市影响造成的。5)城市房屋竣工面积、市区总人口、公...     

Estimating daily net radiation in the FAO Penman–Monteith method

Heatwave intensity and frequency are predicted to increase in the coming years, and this will bear adverse consequences to the environmental well-being and the socio-economic fabric in urbanized areas. The hazardous combination of increased heat storage and reduced water retention capacities of the land surface make the urban areas warmer than the surrounding rural areas in what is commonly known as the urban heat island (UHI) effect. The primary motives of this study are to quantify the interaction of this city-scale UHI with synoptic-scale heatwave episodes and to analyze the factors that mediate this interaction. A modified version of the Weather Research and Forecasting model (WRF) is utilized to simulate two heatwave episodes in New York City. The land surface scheme in the default WRF model is modified to better represent the surface to atmosphere exchanges over urban areas. Our results indicate that during the heatwave episodes, the daily-averaged UHI in NYC increased by 1.5 K. Furthermore, most of this amplification occurs in the mid-afternoon period when the temperatures peak. Wind direction and urban-rural contrasts in available energy and moisture availability are found to have significant and systematic effects on the UHI, but wind speed plays a secondary role.     

城市化对珠江三角洲强雷暴天气的可能影响

通过对2004年8月11日午后发生在珠江三角洲地区的一次强雷暴天气的高分辨数值模拟，研究了城市化发展可能对雷暴活动的影响问题，主要考察了与城市土地利用类型改变相关的“城市热岛”的形成和演变特征，城区粗糙度增大可能引起的低层辐合的增强过程，及其与雷暴发展强度变化的关系。结果表明:模拟的雷暴发展和演变过程与这一地区城市化的发展有密切的联系。引进了更加真实的关于珠江三角洲地区的土地利用类型资料之后，耦合了陆面模式Noah LSM的MM5模式可以更加成功地模拟出强雷暴天气的发展和演变过程。雷暴系统移经主要城市区后在珠江口西岸的增强过程与这一地区“城市热岛”的效应有关。中午时热岛开始形成于广州城区的上空，之后向南移动，范围扩大。另外，城区粗糙度增大引起的低层辐合增强可能在雷暴发展和演变过程中也起到了作用。模拟的与城市影响有关的低层辐合主要位于500 m以下的近地面层，开始时形成于城市的上风方向，并在下风方向增强， 由此引起的强烈上升运动有利于新的对流的启动和发展，促使雷暴强度增强。     

基于卫星遥感的长江三角洲地表热环境人口暴露空间特征

研究城市地表热环境变化的时空演变规律对防灾减灾具有重要意义。本研究以卫星遥感的夜间灯光,植被指数,高程和坡度为自变量构建了适用于人口空间分布估算的随机森林模型,结合卫星遥感反演的地表温度数据,以2016年夏季为例,研究了1km分辨率的长江三角洲地区夏季地表热环境人口暴露分布特征。研究表明:(1)利用随机模型对长江三角洲2016年人口进行1000m格网空间化分布模拟,变量解释度达到80%,人口空间化结果接近实际。(2)人口密度高值区和夏季大部分月份内的地表热环境高温区和人口暴露高和极高风险区总体有较好的对应。6月皖北地区高温区面积增大导致地表热环境的人口暴露风险较高等级的面积比例高于其他月份。(3)在月和季节平均尺度上,地表高温热环境暴露极高和高风险区域面积极少,处于沿海地区、长江下游沿线以及各县区的中心城市;中等暴露风险区域主要分布在东部及中心城市周边地区;低暴露风险区分布在东北部内陆地区和东北部人口数量相对较少地区。     

A Physically-Based Scheme For The Urban Energy Budget In Atmospheric Models

An urban surface scheme for atmospheric mesoscale models ispresented. A generalization of local canyon geometry isdefined instead of the usual bare soil formulation currently usedto represent cities in atmospheric models. This allows refinement ofthe radiative budgets as well as momentum, turbulent heat and ground fluxes.The scheme is aimed to be as general as possible, in order to representany city in the world, for any time or weather condition(heat island cooling by night, urban wake, water evaporation after rainfalland snow effects).Two main parts of the scheme are validated against published data.Firstly, it is shown that the evolution of the model-predictedfluxes during a night with calm winds is satisfactory, considering both the longwave budget and the surface temperatures. Secondly, the original shortwave scheme is tested off-line and compared to the effective albedoof a canyon scale model. These two validations show that the radiative energy input to the urban surface model is realistic.Sensitivity tests of the model are performed for one-yearsimulation periods, for both oceanic and continental climates. The scheme has the ability to retrieve, without ad hoc assumptions, the diurnal hysteresis between the turbulent heat flux and ground heat flux. It reproduces the damping of the daytime turbulent heat flux by the heat storage flux observed in city centres. The latent heat flux is negligible on average,but can be large when short time scales are considered (especially afterrainfall). It also suggests that in densely built areas, domesticheating can overwhelm the net radiation, and supply a continuous turbulentheat flux towards the atmosphere. This becomes very important inwinter for continental climates. Finally, a comparison with a vegetation scheme shows that the suburban environment can be represented with a bare soil formulation for large temporal or spatial averages (typical of globalclimatic studies), but that a surface scheme dedicated to the urban surface is necessary when smaller scales are considered: town meteorological forecasts, mesoscale or local studies.     

北非地区海-陆热力差异与夏季江淮流域旱涝的关系

基于NCEP/NCAR月均再分析资料和中国743站降水资料,根据夏季江淮流域51 a(1954-2004年)区域旱涝指数的年代际变化特征,确定北非地区作为研究的关键区.分析发现,关键区的地表温度异常在冬季具有较好的持续性,冬季北大西洋涛动是导致这种异常持续性的重要原因之一.通过对前冬北非地区地表温度和夏季江淮流域降水的SVD分析发现:当北非大陆地区偏冷,其西北侧的海区偏暖时,江淮流域夏季的降水将整体偏多;反之,江淮流域夏季的降水整体偏少.进一步研究发现,北非地区海陆地表温度异常的对比,要比其中单一海洋或陆地区域的异常对夏季江淮流域的旱涝有更好的指示能力.文中定义了一个海陆热力差异指数来表征这种地表温度异常的对比程度,该指数和夏季江淮流域旱涝指数呈较好的正相关关系,并且对夏季江淮流域极端旱涝年份也有较好的指示,认为该指数可以作为一个指示江淮流域整体旱涝事件的预报因子.     

Customization of regional climate model (RegCM4) over Indian region

The regional climate model (RegCM4) is customized for 10-year climate simulation over Indian region through sensitivity studies on cumulus convection and land surface parameterization schemes. The model is configured over 30° E–120° E and 15° S–45° N at 30-km horizontal resolution with 23 vertical levels. Six 10-year (1991–2000) simulations are conducted with the combinations of two land surface schemes (BATS, CLM3.5) and three cumulus convection schemes (Kuo, Grell, MIT). The simulated annual and seasonal climatology of surface temperature and precipitation are compared with CRU observations. The interannual variability of these two parameters is also analyzed. The results indicate that the model simulated climatology is sensitive to the convection as well as land surface parameterization. The analysis of surface temperature (precipitation) climatology indicates that the model with CLM produces warmer (dryer) climatology, particularly over India. The warmer (dryer) climatology is due to the higher sensible heat flux (lower evapotranspiration) in CLM. The model with MIT convection scheme simulated wetter and warmer climatology (higher precipitation and temperature) with smaller Bowen ratio over southern India compared to that with the Grell and Kuo schemes. This indicates that a land surface scheme produces warmer but drier climatology with sensible heating contributing to warming where as a convection scheme warmer but wetter climatology with latent heat contributing to warming. The climatology of surface temperature over India is better simulated by the model with BATS land surface model in combination with MIT convection scheme while the precipitation climatology is better simulated with BATS land surface model in combination with Grell convection scheme. Overall, the modeling system with the combination of Grell convection and BATS land surface scheme provides better climate simulation over the Indian region.     

Urban heat island and its effect on the cooling and heating demands in urban and suburban areas of Hong Kong

This study investigates the urban heat island characteristics of four major areas of Hong Kong. The areas of study include a densely populated and well-developed commercial area (i.e., Tsim Sha Tsui) and three suburban areas (i.e., Cheung Chau, Lau Fau Shan and Sha Tin) with differing degrees of development. The weather station data of respective areas were acquired from the Hong Kong Observatory. The urban heat island intensity, determined as the air-temperature difference between the selected urban/suburban area and the reference rural area (i.e., Ta Kuw Ling) with thin population and lush vegetation, was used for the analysis. Results showed stronger heat island effect during winter and nighttime than during summer and daytime. An investigation of the cooling and heating degree days indicate that all areas have observed higher number of cooling degree days. However, the cooling degree days were the maximum while heating degree days were the minimum in the urban area (i.e., Tsim Sha Tsui). Clearly, the minimum heating degree days and the maximum cooling degree days in the urban area were a direct consequence of urban heat island. The 10-year (i.e., from 1995 to 2005) average shows that Cheung Chau experienced the least number of cooling degree days while Lau Fau Shan experienced the highest number of heating degree days. Seemingly, the area of Cheung Chau offers better thermal comfort conditions with the minimum number of cooling and heating degree days.     

Modeling of urban heat island and its impacts on thermal circulations in the Beijing–Tianjin–Hebei region,China

Through regulating the land–atmosphere energy balance, urbanization plays an important role in modifying local circulations and cross-border transport of air pollutants. The Beijing–Tianjin–Hebei (BTH) metropolitan area in northern China is frequently influenced by complex atmospheric thermal circulations due to its special topography and geographic position. In this study, the Weather Research and Forecasting (WRF) model combined with remote sensing is used to explore the urbanization impacts on local circulations in the BTH region. The urban heat island (UHI) effect generated around Beijing and Tianjin shows complex interactions with local thermal circulations. Due to the combined effects of UHI and topography, the UHI circulation around Beijing and valley breeze at the southern slopes of Yan Mountain are coupled together to reinforce each other. At the coastal cities, the increased land/sea temperature gradient considerably accelerates the sea breeze along Bohai Bay and moves the sea breeze front further inland to reach as far as Beijing. This study may lay a foundation for the better understanding of air pollutant dispersion on complex terrain.