Ilot de chaleur a Quebec: Cas d'ete

This paper studies the urban heat island in Quebec City and its suburbs on one summer night. The region under study covers an area of 20 km by 20 km which streches from lake Saint-Charles on the north to Levis on the south and from the western suburb of Cap-Rouge to Beauport on the east. The total population of the region is about 400 000.On August 22, 1979 from 22:00 to 23:30 EDT, 109 measurements of wet- and dry-bulb temperatures were taken at preselected points. On that day, a large high pressure system gave clear skies to central Quebec while Quebec City Airport recorded a maximum temperature of 23 °C. The average wind measured at Duberger meteorological tower between 6 and 121 m above ground was 1.8 m s^-1 at 22:00 EDT and 0.9 m s^-1 at 23:30 EDT. Additional data were obtained from three thermographs installed at strategic points and five regular climatological stations, which were used to estimate cooling rates.During the period of measurement, the cooling rate averaged over the eight reference points was about 0.7 °C h^-1. However, the maximum cooling rate, which occured earlier, ranged from 2.2 °C h^-1 at Duberger to 4.4 °C h^-1 at Courville-de-Poissy. No relation seems to exist, in our case, between the maximum cooling rate and the heat island spatial structure. Comparison of these results with the ones given by Oke et al. (1972) shows that the eight stations behaved more like rural stations than urban ones.The temperature gradient measured between the center of old Quebec City and the suburbs averaged 6 °C while it was 9 °C for the coldest spot. Clo units were used to characterize the microclimates prevailing on the region for that night; 1 clo would be sufficient for comfort downtown while 1.5 clo is needed in the coldest spot for a slowly walking person. Large open areas like parks or the Laval University campus had a definite effect on temperature.The humidity was calculated for each point using standard psychrometric tables; no significant difference could be found over the area expect at points near or above the St. Laurent river where the average dew point was 1.5 °C higher.Each point was classified into 6 categories according to its predominant land-use as reported by the observers. A multiple regression between temperature on the one hand and altitude and land-use on the other hand was tried; it showed that temperature was significantly correlated with both. Such an equation could be used by town-planners to locate temperature gradients in future urban development over the area; land uses could be planned to enhance or reduce these gradients.This study confirms the idea that urban climate is a mosaic of interacting micro-climates. More measurements, including possibly airborne infra-red thermal imagery, will be taken during winter in order to assess the winter urban climate of Quebec City.     

Effects of the large-scale atmospheric circulation on the onset and strength of urban heat islands: a case study

Air temperature was monitored at 13 sites across the urban perimeter of a Brazilian midsize city in winter 2011. In this study, we show that the urban heat island (UHI) develops only at night and under certain weather conditions, and its intensity depends not only on the site's land cover but also on the meteorological setting. The urban heat island intensity was largest (6.6 °C) under lingering high-pressure conditions, milder (3.0 °C) under cold anticyclones and almost vanished (1.0 °C) during the passage of cold fronts. The cooling rates were calculated to monitor the growth and decay of the UHI over each specific synoptic setting. Over four contiguous days under the effect of a lingering high-pressure event, we observed that the onset of cooling was always at about 2 h before sunset. The reference site attained mean cooling rate of ?2.6 °C h^?1 at sunset, whilst the maximum urban rate was ?1.2 °C h^?1. Under a 3-day cold anticyclone episode, cooling also started about 2 h before sunset, and the difference between maximum rural (?2.0 °C h^?1) and urban (?1.0 °C h^?1) cooling rates diminished. Under cold-front conditions, the cooling rate was homogeneous for all sites and swang about zero throughout the day. The air temperature has a memory effect under lingering high-pressure conditions which intensified the UHI, in addition to the larger heat storage in the urban area. Cold anticyclone conditions promoted the development of the UHI; however, the cold air pool and relatively light winds smoothed out its intensity. Under the influence of cold fronts, the urban fabric had little effect on the city's air temperature field, and the UHI was imperceptible.     

Modeling the impact of urbanization on the local and regional climate in Yangtze River Delta, China

The Yangtze River Delta Economic Belt is one of the most active and developed areas in China and has experienced quick urbanization with fast economic development. The weather research and forecasting model (WRF), with a single-layer urban canopy parameterization scheme, is used to simulate the influence of urbanization on climate at local and regional scales in this area. The months January and July, over a 5-year period (2003–2007), were selected to represent the winter and summer climate. Two simulation scenarios were designed to investigate the impacts of urbanization: (1) no urban areas and (2) urban land cover determined by MODIS satellite observations in 2005. Simulated near-surface temperature, wind speed and specific humidity agree well with the corresponding measurements. By comparing the simulations of the two scenarios, differences in near-surface temperature, wind speed and precipitation were quantified. The conversion of rural land (mostly irrigation cropland) to urban land cover results in significant changes to near-surface temperature, humidity, wind speed and precipitation. The mean near-surface temperature in urbanized areas increases on average by 0.45?±?0.43°C in winter and 1.9?±?0.55°C in summer; the diurnal temperature range in urbanized areas decreases on average by 0.13?±?0.73°C in winter and 0.55?±?0.84°C in summer. Precipitation increases about 15% over urban or leeward areas in summer and changes slightly in winter. The urbanization impact in summer is stronger and covers a larger area than that in winter due to the regional east-Asian monsoon climate characterized by warm, wet summers and cool, dry winters.     

Maximum urban heat island intensity in a medium-sized coastal Mediterranean city

This paper studies the maximum intensity of the urban heat island (UHI) that develops in Volos urban area, a medium-sized coastal city in central Greece. The maximum temperature difference between the city center and a suburb is 3.4°C and 3.1°C during winter and summer, respectively, while during both seasons the average maximum UHI intensity is 2.0°C. The UHI usually starts developing after sunset during both seasons. It could be attributed to the different nocturnal radiative cooling rate and to the different anthropogenic heat emission rate that are observed at the city center and at the suburb, as well as to meteorological conditions. The analysis reveals that during both seasons the daily maximum hourly (DMH) UHI intensity is positively correlated with solar radiation and with previous day’s maximum hourly UHI intensity and negatively correlated with wind speed. It is also negatively correlated with relative humidity during winter but positively correlated with it during summer. This difference could be attributed to the different mechanisms that mainly drive humidity levels (i.e., evaporation in winter and sea breeze (SB) in summer). Moreover, it is found that SB development triggers a delay in UHI formation in summer. The impact of atmospheric pollution on maximum UHI intensity is also examined. An increase in PM10 concentration is associated with an increase in maximum UHI intensity during winter and with a decrease during summer. The impact of PM10 on UHI is caused by the attenuation of the incoming and the outgoing radiation. Additionally, this study shows that the weekly cycle of the city activities induces a weekly variation in maximum UHI intensity levels. The weekly range of DMH UHI intensity is not very large, being more pronounced during winter (0.4°C). Moreover, a first attempt is made to predict the DMH UHI intensity by applying regression models, whose success is rather promising.     

2014-2017年西安市城市热岛、冷岛精细化时空特征分析

选取1971—2017年7个国家级气象站的气温资料,分析年代际气温变化特征及城郊温差、城县温差;选取2014—2017年103个国家考核区域气象站及7个国家级气象站逐时气温资料,利用标准化相对气温法,研究西安市城市热岛、冷岛的年、季平均空间分布特征,以及逐日热岛、冷岛变化规律。结果显示:1971—2017年城区、郊区和郊县气温均呈上升趋势,城区增温速率最大,郊县增温速率最小,进入21世纪后,城市热岛效应较为显著。西安市城市热岛、冷岛现象明显,且均呈"多中心"特征,热岛中心多为老城区及旅游中心,建筑物面积和人口密度占绝对优势;冷岛中心多为地势较高、水域绿被覆盖较大、非人口密集区的秦岭坡脚线附近。城区代表站的年、春季、夏季、秋季基本处于平稳状态,年、春季、夏季06—07时热岛强度最大,秋季、冬季23时热岛强度最大;郊区代表站和郊县代表站的年及四季热岛、冷岛强度均有明显的日变化特征,且变化趋势相反;郊区代表站10时热岛转为冷岛,春、夏季16—17时转为热岛,年及秋、冬两季19—20时转为热岛;郊县代表站年、春季、夏季06—07时冷岛强度最大,秋季、冬季2时冷岛强度最大,08时后冷岛开始减弱,12—13时为最弱后开始增强。     

Impact of Anthropogenic Heat Release on Regional Climate in Three Vast Urban Agglomerations in China简

We simulated the impact of anthropogenic heat release （AHR） on the regional climate in three vast city agglomerations in China using the Weather Research and Forecasting model with nested high-resolution modeling.Based on energy consumption and high-quality land use data,we designed two scenarios to represent no-AHR and current-AHR conditions.By comparing the results of the two numerical experiments,changes of surface air temperature and precipitation due to AHR were quantified and analyzed.We concluded that AHR increases the temperature in these urbanized areas by about 0.5℃-1℃,and this increase is more pronounced in winter than in other seasons.The inclusion of AHR enhances the convergence of water vapor over urbanized areas.Together with the warming of the lower troposphere and the enhancement of ascending motions caused by AHR,the average convective available potential energy in urbanized areas is increased.Rainfall amounts in summer over urbanized areas are likely to increase and regional precipitation patterns to be altered to some extent.     

Fine-scale spatial temperature patterns across a UK conurbation

The public health implications of a warming urban environment mean that appropriate action by planners, designers and health workers will be necessary to minimise risk under future climate scenarios. Data at an appropriate spatial scale are required by user groups in order to identify key areas of vulnerability. Thermal mapping of a UK urban conurbation was carried out during the summers of 2007 and 2008 with the aim of providing high spatial resolution temperature data. The air temperature results showed an average daytime (night time) urban?Crural thermal contrast of 3°C (5°C) on summer days (nights) with ideal urban heat island (UHI) conditions. The intensity of the daytime surface temperature heat island was found to exceed 10°C. The measured data were used to derive an empirical model of spatial temperature patterns based upon characteristics of land use, distance from urban centre and building geometry. This model can be used to provide sub-kilometre resolution temperature data which are required by decision makers and can provide a mechanism for downscaling climate model output.     

基于NOAA/AVHRR资料的城市热岛效应研究方法

本文以2006年1、2、7、8月、2007年1月和2008年7月天空状况晴朗的NOAA16和NOAA18的AVHRR白天和夜晚的遥感资料为基础,利用地理信息系统,分析成都市中心城区与近郊不同季节昼间、夜晚遥感监测的量温大小;研究昼、夜亮温的空间分布;使用统计方法,分析亮温与下垫面性质的关系。结果表明:成都市夏季城市白天平均热岛强度最大,为3.7℃,冬季白天城市平均热岛强度最小,只有0.5℃,夏季夜晚平均热岛强度为1.5℃,冬季夜晚为0.6℃;尽管成都中心城区平均亮温高于近郊,但亮温的分布并不一定逐渐降低的,且冬季夜间亮温的高值区大部分不在中心城区;夏、冬季的白天和夜晚亮温的分布也不尽一致。统计分析表明城市热岛的强度与地表植被指数呈负相关,夏季的相关性很好,显著性水平达到0.01,而冬季的相关性较差,显著性水平也比较低。      

Urban boundary layer analysis in the complex coastal terrain of Bilbao using Enviro-HIRLAM

This study analyses the atmospheric boundary layer over the Bilbao metropolitan area during summer (13–18 Jul 2009) and winter (20–29 Jan 2010) episodes using the Environment–High Resolution Limited Area Model (Enviro-HIRLAM) coupled with the building effect parameterisation (BEP). The main objectives of this study are: to evaluate the performance of the model to simulate the land–sea breezes over this complex terrain; to assess the simulations with the integration of an urban parameterisation in Enviro-HIRLAM and finally; and to analyse the urban–atmosphere interactions. Even if the hydrostraticity of the model is a limitation to simulate atmospheric flows over complex terrain, sensibility tests demonstrate that 2.4 km is the optimal horizontal resolution over Bilbao that allows at the same time: to obtain satisfactory reproducibility of the large-scale processes and to explore the urban effects at local scale. During the summer episode, a typical regime of diurnal sea breeze from the NW-N-NE direction and nocturnal valley breezes from the SE direction are observed over Bilbao. The urban heat island (UHI) phenomenon is developed in the city centre expanding to the suburbs from 22 to 10 local time (LT), covering an area of 130 km². The maximum UHI intensity, 1 °C, is reached at the end of the night (5 LT), and it is advected 12 km towards the sea by the land breezes. The urban boundary layer (UBL) height amplitude varies from 100 (night time) to 1,360 m (at 14 LT). During the winter episode, the land breeze dominates the atmospheric diffusion during the day and night time. The maximum UHI intensity, 1.7 °C, is observed at 01 LT. It is spread and remained over the city covering an area of 160 km², with a vertical extension of 33 m. The UBL reaches 780 m height at 16 LT the following day.     

The contribution of urbanization to recent extreme heat events and a potential mitigation strategy in the Beijing–Tianjin–Hebei metropolitan area

This paper addresses the contribution of urban land use change to near-surface air temperature during the summer extreme heat events of the early twenty-first century in the Beijing–Tianjin–Hebei metropolitan area. This study uses the Weather Research Forecasting model with a single urban canopy model and the newest actual urban cover datasets. The results show that urban land use characteristics that have evolved over the past ~20 years in the Beijing–Tianjin–Hebei metropolitan area have had a significant impact on the extreme temperatures occurring during extreme heat events. Simulations show that new urban development has caused an intensification and expansion of the areas experiencing extreme heat waves with an average increase in temperature of approximately 0.60 °C. This change is most obvious at night with an increase up to 0.95 °C, for which the total contribution of anthropogenic heat is 34 %. We also simulate the effects of geo-engineering strategies increasing the albedo of urban roofs, an effective way of reducing urban heat island, which can reduce the urban mean temperature by approximately 0.51 °C and counter approximately 80 % of the heat wave results from urban sprawl during the last 20 years.     

Effects of Urbanization on Extreme Warmest Night Temperatures During Summer near Bohai

Many previous studies have focused on the impacts of urbanization on regional mean temperatures. Relatively few have analyzed changes in extreme temperatures. Here, we examine the impact of urbanization on extreme warmest night temperatures from 33 stations in the Bohai area between 1958 and 2009. We compute the Generalized Extreme Value（GEV） distribution of extreme warmest night temperatures and analyze long-term variations in its characteristic parameters. A new classification method based on the factor analysis of changes in extreme night temperatures is developed to detect the efects of urbanization in diferent cities. Of the three parameters that characterize the GEV distribution, the position parameter is the most representative of long-term changes in extreme warmest night temperatures. During the period of rapid urbanization（i.e., after 1978）, all three parameters of the GEV distribution are larger for the urban station group than for the reference station group, so are the magnitudes of their variations, and the urban areas have been experiencing higher extreme warmest night temperatures with larger variability. Diferent types of cities in the Bohai area have all experienced an urban heat island efect, with an average urbanization efect of approximately 0.3 per decade.     

青藏高原东坡一座世界上最滋润的城市——雅安市生态旅游气候资源研究

本文基于较详尽的资料,研究了雅安市的气候概况,日照,相对湿度,降水,温度,风等。结果表明:①雅安市具有优良的人居环境和生态旅游气候资源。②雅安市北部是全球层状云分布最高的地区,“阳伞效应”显著。③雅安市中部的温度和湿度非常宜人,是世界上最“滋润”的一座城市。④雅安市是世界著名的“雨城”,中部年平均雨日高达188.4~231.8d,全市年平均夜雨率高达71%~78%。⑤雅安市境内立体气候特征十分显著,在青藏高原东坡以东沿30°N附近的中国大陆地区比较,雅安市冬季是最暖地区之一,夏季是最凉地区之一,年和四季平均气温日较差都是最小值区之一,夏季平均气温为23℃左右,是不可多得的疗养胜地。⑥雅安市中部年、冬、春、夏和秋的平均风速为0.5~1.8 m.s-1,和煦宜人。      

济宁市城市化对气温的影响

利用1981—2010年济宁及周边郊区3县台站的气温资料,研究分析了济宁城区、郊区的气温变化趋势和特点,并探讨了城市化发展对济宁城郊温度的影响。研究发现：（1）近30a来,尽管济宁城区、郊区最高气温、年平均气温、最低气温均呈显著增加趋势,且增温幅度依次增大,但城、郊气温增幅有所差异。其中,年平均气温、最低气温增温幅度郊区高于城区,而最高气温增幅二者相差不大,这表明城市化发展对最低气温的影响最大。此外,一年之中城、郊增暖均表现为：冬季、春季增幅最大,秋季次之,夏季最弱,且城、郊温差逐渐缩小;（2）济宁城市热岛强度总体呈上升趋势,但不同年代、不同季节变化趋势不尽相同。其中,1980年代热岛上升微弱,总体低于平均水平,而1990年代维持在一个较高的水平,2000年以后又明显下降;除秋季外,热岛强度均呈现缓慢上升趋势,其中冬季最强,夏季最弱。城市热岛效应具有明显的季节和日变化特征,表现为：冬半年明显高于夏半年,白天明显低于夜间;（3）济宁市区人口和建成区面积与城市热岛具有很大的相关性,两者的相关系数分别为0．81和0．75。     

Quantitative relationships between precipitation and temperature over Northeast China, 1961–2010

This paper investigates monthly and seasonal precipitation–temperature relationships (PTRs) over Northeast China using a method proposed in this study. The PTRs are influenced by clouds, latent and sensible heat conversion, precipitation type, etc. In summer, the influences of these factors on temperature decrease are different for various altitudes, latitudes, longitudes, and climate types. Stronger negative PTRs ranging from ?0.049 to ?0.075 °C/mm mostly occur in the semi-arid region, where the cold frontal-type precipitation dominates. In contrast, weaker negative PTRs ranging from ?0.004 to ?0.014 °C/mm mainly distribute in Liaoning Province, where rain is mainly orographic rain controlled by the warm and humid air of East Asian summer monsoon. In winter, surface temperature increases owing to the release of latent heat and sensible heat when precipitation occurs. The stronger positive PTRs ranging from 0.963 to 3.786 °C/mm mostly occur at high altitudes and latitudes due to more release of sensible heat. The enhanced atmospheric counter radiation by clouds is the major factor affecting increases of surface temperature in winter and decreases of surface temperature in summer when precipitation occurs.     

A diagnosis of twentieth century temperature records at West Lafayette,Indiana

A diagnostic study of 80 yrs(1901–80) of surface temperatures collected at West Lafayette, Indiana, has been found to be in tune with the global trend and that for the eastern two-thirds of the United States, namely, cold at the turn of the century, warming up to about 1940, and then cooling to present. The study was divided into two cold periods (1901–18, 1947–80) and a warm period (1919–46), based on the distribution of annual mean temperature. Decadal mean annual temperatures ranged from 10 °C in period I to 12.2 °C in period II, to 9.4 °C during the present cold period. Themean annual temperature for the 80 yr ranged from the coldest of 8.7 °C in 1979 to the warmest of 13.6 °C in 1939. Thedaily mean temperature for the entire 80-yr ranged from -4.7 °C on 31 January to 25.1 °C on 27 July. Thecoldest daily mean was -26.7 °C on 17 January, 1977, and thewarmest daily mean was 35 °C on 14 July, 1936. The range of values for thedaily mean maximum temperatures was -.2 °C on 31 January to 31.4 °C on 27 July. Corresponding values for thedaily mean minimum are -9.2 °C on 31 January and 18.7 °C on 27 July. The all-time extreme temperatures are -30.6 °C on 26 February, 1963 and 43.9 °C on 14 July, 1936. Climatic variability has been considered by computing the standard deviations of a) the daily mean maximum and minimum temperature per year, and b) the daily mean maximum and minimum temperatures for each day of the year for the 80-yr period. These results have shown that there is more variability in the daily mean maximum per year than in the daily mean minimum, for each year of the 80-yr period. Also the variability for both extremes has been greater in each of the two cold periods than in the warm period. Particularly noticeable has been theincrease in the variability of the daily mean minima per year during the current cooling trend. Further, it has been determined that the variability in the daily mean maxima and minima for each day of the year (based on the entire 80 yrs is a) two times greater in the winter than in the summer for both extremes, and b) about the same for each in the summer, greater for daily maximum in the spring and fall, but greater for the daily minimum during the winter. The latter result is undoubtedly related to the effect of snow cover on daily minimum temperatures. An examination of daily record maximum and minimum temperatures has been made to help establish climatic trends this century. For the warm period, 175 record maxima and 68 record minima were set, compared to 213 record minima and 105 record maxima during the recent cold period. For West Lafayette, the present climatic trend is definitely one of extreme record-breaking cold. Evidence has also been presented to show the substantial increases in snowfall amounts in the lee regions of the Great Lakes during the present cold period, due to the lake-induced snow squalls associated with cold air mass intrusions. The possible impact of the cooling trend on agricultural activities has also been noted, due to a reduced growing season.     

湿地小气候效应特征研究

湿地对局地小气候具有调节作用,研究湿地小气候效应特征能更具体地了解湿地对局地小气候的影响。本文以河北省衡水市的衡水湖为例,利用衡水市11个常规气象观测站数据,通过对湖区及湖区外各季节不同气象要素的对比,对衡水湖各个季节的小气候效应进行了分析。结果表明:（1）衡水湖具有冷岛效应、湿岛效应和风岛效应,能够调节周围的气候特征;（2）衡水湖的小气候效应具有季节特征,衡水湖各季节平均的冷岛效应由强到弱依次为春季、冬季、秋季、夏季,湿岛效应由强到弱分别为夏季、春季、秋季、冬季,风岛效应由强到弱依次为春季、夏季、冬季、秋季,春季小气候效应最强;（3）衡水湖的小气候效应具有昼夜特征,夜晚的冷岛效应强于白天,湿岛和风岛效应正相反,白天的强度大于夜晚。     

绵阳城市热岛效应分析

本文首先采用模糊c-均值聚类法和剔除法,筛选出用于计算绵阳城市热岛强度的10个城市站和15个郊区站,然后利用这25个自动气象站的逐时气温资料,分析2018年绵阳城市热岛效应不同时间尺度的变化特征。结果表明:2018年绵阳存在城市热岛效应,平均热岛强度为0.64℃,表现为弱热岛等级;四季热岛效应冬季最强,其次是春季,夏季和秋季相当;逐月热岛强度3月最大、7月最小;绵阳城市热岛效应存在明显的日变化,热岛强度夜间大于白天,日最大热岛强度几乎均出现在晚上。      

福建省晋江市城市热岛强度时空变化特征分析

利用传统的气象站法, 结合空间统计学方法(普通克里金插值法), 对福建省晋江市2010—2014年40个自动气象站逐小时温度资料加以计算处理, 分析了晋江市年、季、昼夜热岛强度时空变化规律。(1)晋江市年、季、昼夜热岛强度都呈带状分布, 等值线呈西南-东北走向, 年、季、昼夜变化趋势显著, 北部热岛强度高于南部。五年间热岛强度持续增强, 但增幅不大, 增速放缓。(2)城市化水平的提高, 会导致热岛强度高值出现季节提前, 故旅游区秋冬季热岛强度高于春夏季, 中心城区和产业经济区夏秋季热岛强度高于冬春季。(3)晋江市热岛效应昼夜空间分布格局差异性大, 夜间热岛强度显著高于白天, 最低值出现在14—16时, 中心城区和产业经济区最低值出现时间较旅游区略推迟, 三个功能区的最高值均出现在凌晨。      

Asymmetric changes in maximum and minimum temperature in Beijing

Summary Based on observational data at Beijing since 1940, trends in daily maximum, mimimum and mean temperatures are studied. It is shown that the linear rate of increase in minimum temperature is 4.08 °C/100 yr; whereas the maximum temperature decreases with a linear rate of — 0.245 °C/100 yr. Consequently, the diurnal temperature range (DTR) becomes smaller.Warming in Beijing occurred mainly in the daytime in the 1940s; but in the night in the 1980s. Although the latter has been found in other studies, the former is a new discovery. The difference of temperature and the diurnal temperature range between urban and surburban areas in Beijing are also analysed. The results show that the urban heat island effect (UHIE) has been becoming larger, and during 1960–1989 the change in UHIE in summer is larger than that in winter. Since the warning trend does not match the change of UHIE in last two decades, it is thought that UHIE is not the main factor contributing to climatic warming.With 2 Figures     

Modeling the relative roles of the foehn wind and urban expansion in the 2002 Beijing heat wave and possible mitigation by high reflective roofs

Rapid urbanization has intensified summer heat waves in recent decades in Beijing, China. In this study, effectiveness of applying high-reflectance roofs on mitigating the warming effects caused by urban expansion and foehn wind was simulated for a record-breaking heat wave occurred in Beijing during July 13–15, 2002. Simulation experiments were performed using the Weather Research and Forecast (WRF version 3.0) model coupled with an urban canopy model. The modeled diurnal air temperatures were compared well with station observations in the city and the wind convergence caused by urban heat island (UHI) effect could be simulated clearly. By increasing urban roof albedo, the simulated UHI effect was reduced due to decreased net radiation, and the simulated wind convergence in the urban area was weakened. Using WRF3.0 model, the warming effects caused by urban expansion and foehn wind were quantified separately, and were compared with the cooling effect due to the increased roof albedo. Results illustrated that the foehn warming effect under the northwesterly wind contributed greatly to this heat wave event in Beijing, while contribution from urban expansion accompanied by anthropogenic heating was secondary, and was mostly evident at night. Increasing roof albedo could reduce air temperature both in the day and at night, and could more than offset the urban expansion effect. The combined warming caused by the urban expansion and the foehn wind could be potentially offset with high-reflectance roofs by 58.8 % or cooled by 1.4 °C in the early afternoon on July 14, 2002, the hottest day during the heat wave.