Effect of asymmetrical street canyons on pedestrian thermal comfort in warm-humid climate of Cuba

Walkability and livability in cities can be enhanced by creating comfortable environments in the streets. The profile of an urban street canyon has a substantial impact on outdoor thermal conditions at pedestrian level. This paper deals with the effect of asymmetrical street canyon profiles, common in the historical centre of Camagüey, Cuba, on outdoor thermal comfort. Temporal-spatial analyses are conducted using the Heliodon2 and the RayMan model, which enable the generation of accurate predictions about solar radiation and thermal conditions of urban spaces, respectively. On these models, urban settings are represented by asymmetrical street canyons with five different height-to-width ratios and four street axis orientations (N-S, NE-SW, E-W, SE-NW). Results are evaluated for daytime hours across the street canyon, by means of the physiologically equivalent temperature (PET index) which allows the evaluation of the bioclimatic conditions of outdoor environments. Our findings revealed that high profiles (façades) located on the east-facing side of N-S streets, on the southeast-facing side of NE-SW streets, on the south-facing side of E-W street, and on the southwest-facing side of SE-NW streets, are recommended to reduce the total number of hours under thermal stress. E-W street canyons are the most thermally stressed ones, with extreme PET values around 36 °C. Deviating from this orientation ameliorates the heat stress with reductions of up to 4 h in summer. For all analysed E-W orientations, only about one fifth of the street can be comfortable, especially for high aspect ratios (H/W > 3). Optimal subzones in the street are next to the north side of the E-W street, northwest side of the NE-SW street, and southwest side of the SE-NW street. Besides, when the highest profile is located on the east side of N-S streets, then the subzone next to the east-facing façade is recommendable for pedestrians. The proposed urban guidelines enable urban planners to create and renovate urban spaces which are more efficient in diminishing pedestrian thermal stress.     

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.     

Effect of the position of the visible sky in determining the sky view factor on micrometeorological and human thermal comfort conditions in urban street canyons

Poor daytime and night-time micrometeorological conditions are issues that influence the quality of environmental conditions and can undermine a comfortable human lifestyle. The sky view factor (SVF) is one of the essential physical parameters used to assess the micrometeorological conditions and thermal comfort levels within city streets. The position of the visible sky relative to the path of the sun, in the cardinal and ordinal directions, has not been widely discerned as a parameter that could have an impact on the micrometeorological conditions of urban streets. To investigate this parameter, different urban streets that have a similar SVF value but diverse positions of visible sky were proposed in different street directions intersecting with the path of the sun, namely N–S, NE–SW and NW–SE. The effects of daytime and night-time micrometeorological variables and human thermal comfort variables on the street were investigated by applying ENVI-met V3.1 Beta software. The results show that the position of the visible sky has a greater influence on the street’s meteorological and human thermal comfort conditions than the SVF value. It has the ability to maximise or minimise the mean radiation temperature (Tmrt, °C) and the physiological equivalent temperature (PET, °C) at street level. However, the visible sky positioned to the zenith in a NE–SW or N–S street direction and to the SW of a NW–SE street direction achieves the best daytime micrometeorological and thermal comfort conditions. Alternatively, the visible sky positioned to the NE for a NW–SE street direction, to the NW and the zenith for a NE–SW street direction and to the zenith for a N–S street direction reduces the night-time air temperature (Ta, °C). Therefore, SVF and the position of the visible sky relative to the sun’s trajectory, in the cardinal and ordinal directions, must be considered during urban street planning to better understand the resultant micrometeorological and human thermal comfort conditions.     

Thermal bioclimate in idealized urban street canyons in Campinas, Brazil

Among several urban design parameters, the height-to-width ratio (H/W) and orientation are important parameters strongly affecting thermal conditions in cities. This paper quantifies changes in thermal comfort due to typical urban canyon configurations in Campinas, Brazil, and presents urban guidelines concerning H/W ratios and green spaces to adapt urban climate change. The study focuses on thermal comfort issues of humans in urban areas and performs evaluation in terms of physiologically equivalent temperature (PET), based on long-term data. Meteorological data of air temperature, relative humidity, wind speed and solar radiation over a 7-year period (2003–2010) were used. A 3D street canyon model was designed with RayMan Pro software to simulate the influence of urban configuration on urban thermal climate. The following configurations and setups were used. The model canyon was 500 m in length, with widths 9, 21, and 44 m. Its height varied in steps of 2.5 m, from 5 to 40 m. The canyon could be rotated in steps of 15°. The results show that urban design parameters such as width, height, and orientation modify thermal conditions within street canyons. A northeast–southwest orientation can reduce PET during daytime more than other scenarios. Forestry management and green areas are recommended to promote shade on pedestrian areas and on façades, and to improve bioclimate thermal stress, in particular for H/W ratio less than 0.5. The method and results can be applied by architects and urban planners interested in developing responsive guidelines for urban climate issues.     

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.     

热气候指数在人体舒适度预报中的适用性

为进一步提高夏季舒适度预报质量,该文根据国际生物气象研究学会制定的体感指标计算软件和国内现行指标的计算方法,引进并修正了热气候指数(UTCI),根据对2009年8月21—25日在南京信息工程大学205名军训大学生开展的问卷调查资料,对比验证了国内外多种指标,结果表明:国内指标基本能够表征人体热感觉,但仍需进一步完善;热气候指数较其他体感指标能更好地表达人体实际热舒适度,结合天气数值预报结果和SolAlt模型预报的太阳辐射,非常适宜作为南京市人体舒适度的预报指标。热气候指数的建立,提高了南京市的公共气象服务质量。     

Microclimatic variation of thermal comfort in a district of Lisbon (Telheiras) at night

Summary The microclimatic spatial variation of air temperature, wind speed, radiative fluxes and Physiological Equivalent Temperature (PET) was studied in Telheiras, a northern district of the city of Lisbon. The main goal was to assess how to improve outdoor thermal conditions based on research results. An empirical model was developed to estimate PET in Telheiras under different weather types; the model allows the continuous spatial representation of PET, using a Geographical Information System (GIS) and can be used in other areas of Lisbon. Although there is a small microclimatic variation in air temperature, the PET presents a much stronger variation, due to the influence of wind and radiative fluxes. Urban geometry, expressed by the Sky View Factor (SVF), is the main factor controlling the microclimatic diversity of the neighbourhood. The coolest conditions occur in open areas (centre of large courtyards and marginal areas) and the warmest in streets with low SVF that are sheltered from the wind. Authors’ address: H. Andrade and M.-J. Alcoforado, Centro de Estudos Geográficos, Universidade de Lisboa, Alameda da Universidade, 1600-214 Lisboa, Portugal     

Urban-rural fog differences in Belgrade area,Serbia

Urban/rural fog appearance during the last 27 years in the Belgrade region is analysed using hourly meteorological records from two meteorological stations: an urban station at Belgrade-Vra?ar (BV) and a rural station at Belgrade-Airport (BA). The effects of urban development on fog formation are discussed through analysis of fog frequency trends and comparison with a number of meteorological parameters. The mean annual and the mean annual minimum temperatures were greater at the urban BV station than at the rural BA station. The mean monthly relative humidity and the mean monthly water vapour pressure were greater at the rural than urban station. During the period of research (1988–2014), BA experiences 425 more days with fog than BV, which means that BV experiences fog for 62.68% of foggy days at BA. Trends in the number of days with fog were statistically non-significant. We analysed the fog occurrence during different types of weather. Fog in urban BV occurred more frequently during cyclonal circulation (in 52.75% of cases). In rural BA, the trend was the opposite and fog appeared more frequently during anticyclonic circulation (in 53.58% of cases). Fog at BV occurred most frequently in stable anticyclonic weather with light wind, when a temperature inversion existed (21.86% of cases). Most frequently, fog at BA occurred in the morning and only lasted a short time, followed by clearer skies during the anticyclonic warm and dry weather (22.55% of cases).     

Human thermal perception related to Föhn winds due to Saharan dust outbreaks in Crete Island,Greece

Crete Island is located in the southmost border of East Mediterranean basin, facing exacerbating atmospheric conditions (mainly concentrations of particulates) due to Saharan dust outbreaks. It is worth to note that these episodes are more frequent during spring and autumn, when mild biometeorological conditions become intolerable due to the synergy of the so called Föhn winds. Cretan mountains, especially Psiloritis Mt. (summit at 2456 m), are orientated perpendicularly to the southwest air mass flow, generating the Föhn winds. Propagating from the leeward of the mountains, these dry, hot winds have an effect on prevailing biometeorological conditions. While descending to the lowlands on the leeward side of the range, the wind becomes strong, gusty, and desiccating. This wind often lasts less than an hour to several days, with gradual weakening after the first or the second day. Sometimes, it stops very abruptly. In this work, the authors examined and analyzed the abrupt changes of human thermal perception within specific case studies during which Föhn winds appeared in Heraklion city at the leeward of Psiloritis Mt, associated with extreme Saharan dust episodes, observed within the period 2006–2010. In order to verify the development of Föhn winds, Meteorological Terminal Aviation Routine Weather Reports (METARs, meteorological observations every half hour), were acquired from the Heraklion meteorological station installed by the Hellenic National Meteorological Service (HNMS). The biometeorological conditions analyzed are based on human thermal bioclimatic indices such as the Physiologically equivalent temperature (PET) and the Universal Thermal Climate Index (UTCI). METAR recordings of meteorological variables, such as air temperature, vapor pressure, wind speed, and cloudiness, were used as input variables in modeling the aforementioned thermal indices, so that to interpret the grade of the thermo-physiological stress. The PET and UTCI analysis was performed by the use of the radiation and bioclimate model, “RayMan,” which is well-suited to calculate radiation fluxes and human biometeorological indices. The results of the performed analysis showed even an increase of air temperature from 20 to 30 °C within 5 h, associated with a decrease in the vapor pressure from 11.5 to 9.3 hPa. In addition, the wind speed at 10 m increased from 5.1 to 20.1 m/s, 3.7 to 14.3 m/s with respect to 1.1 m height, during the events of Föhn winds. The biometeorological analysis has given evidence that slight/moderate heat stress classes of the examined thermal indices appear during Saharan dust episodes. Such conditions are uncommon at the beginning of spring season, indicating that Saharan dust episodes are not only responsible for acute health impacts but also for adverse biometeorological conditions, due to the very likely development of Föhn winds towards the wider area of Heraklion, a coastal city in the eastern Mediterranean.     

Temperature projection in a tropical city using remote sensing and dynamic modeling

Recent temperature projections for urban areas have only been able to reflect the expected change due to greenhouse-induced warming, with little attempt to predict urbanisation effects. This research examines temperature changes due to both global warming and urbanisation independently and applies them differentially to urban and rural areas over a sub-tropical city, Hong Kong. The effect of global warming on temperature is estimated by regressing IPCC data from eight Global Climate Models against the background temperature recorded at a rural climate station. Results suggest a mean background temperature increase of 0.67 °C by 2039. To model temperature changes for different degrees of urbanization, long-term temperature records along with a measureable urbanisation parameter, plot ratio surrounding different automatic weather stations (AWS) were used. Models representing daytime and nighttime respectively were developed, and a logarithmic relationship between the rate of temperature change and plot ratio (degree of urbanisation) is observed. Baseline air temperature patterns over Hong Kong for 2009 were derived from two ASTER thermal satellite images, for summer daytime and nighttime respectively. Dynamic raster modeling was employed to project temperatures to 2039 in 10-year intervals on a per-pixel basis according to the degree of urbanization predicted. Daytime and nighttime temperatures in the highly urbanized areas are expected to rise by ca. 2 °C by 2039. Validation by projecting observed temperature trends at AWS, gave low average RMS errors of 0.19 °C for daytime and 0.14 °C for nighttime, and suggests the reliability of the method.     

The effect of air temperature and human thermal indices on mortality in Athens, Greece

This paper investigates whether there is any association between the daily mortality for the wider region of Athens, Greece and the thermal conditions, for the 10-year period 1992–2001. The daily mortality datasets were acquired from the Hellenic Statistical Service and the daily meteorological datasets, concerning daily maximum and minimum air temperature, from the Hellinikon/Athens meteorological station, established at the headquarters of the Greek Meteorological Service. Besides, the daily values of the thermal indices Physiologically Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI) were evaluated in order to interpret the grade of physiological stress. The first step was the application of Pearson’s χ ² test to the compiled contingency tables, resulting in that the probability of independence is zero (p?=?0.000); namely, mortality is in close relation to the air temperature and PET/UTCI. Furthermore, the findings extracted by the generalized linear models showed that, statistically significant relationships (p?<?0.01) between air temperature, PET, UTCI and mortality exist on the same day. More concretely, on one hand during the cold period (October–March), a 10°C decrease in daily maximum air temperature, minimum air temperature, temperature range, PET and UTCI is related with an increase 13%, 15%, 2%, 7% and 6% of the probability having a death, respectively. On the other hand, during the warm period (April–September), a 10°C increase in daily maximum air temperature, minimum air temperature, temperature range, PET and UTCI is related with an increase 3%, 1%, 10%, 3% and 5% of the probability having a death, respectively. Taking into consideration the time lag effect of the examined parameters on mortality, it was found that significant effects of 3-day lag during the cold period appears against 1-day lag during the warm period. In spite of the general aspect that cold conditions seem to be favourable factors for daily mortality, the air temperature and PET/UTCI exceedances over specific thresholds depending on the distribution reveal that, very hot conditions are risk factors for the daily mortality.     

A comprehensive analysis of physiologically equivalent temperature changes of Iranian selected stations for the last half century

As a preliminary and major step for land use planning of the coming years, the study of variability of the past decades’ climatic conditions with comprehensive indicators is of high importance. Given the fact that one of the affected areas by climatic change includes variability of thermal comfort, this study uses the physiologically equivalent temperature (PET) to identify and evaluate bioclimatic conditions of 40 meteorological stations in Iran. In this study, PET changes for the period of 1960 to 2010 are analyzed, with the use of Mann-Kendall non-parametric test and Pearson parametric method. The study focuses particularly on the diversity in spatio-temporal distribution of Iran’s bioclimatic conditions. The findings show that the mean frequency percentage of days with comfort is 12.9 % according to the total number of selected stations. The maximum and minimum frequency percentage with values of 17.4 and 10.3 belong to Kerman and Chabahar stations, respectively. The findings of long-term trend analysis for the period of 1960–2010 show that 55 % of the stations have significant increasing trend in terms of thermal comfort class based on the Pearson method, while it is 40 % based on Mann-Kendall test. The results indicate that the highest frequency of days with thermal comfort in the southern coasts of Iran relates to the end of autumn and winter, nevertheless, such ideal conditions for the coastal cities of Caspian Sea and even central stations of Iran relate to mid-spring and mid-autumn. Late summer and early autumn along with late spring can be identified as the most ideal times in the west and northwest part of Iran. In addition, the most important inhibiting factors of thermal comfort prove to be different across the regions of Iran. For instance, in the southern coasts, warm to very hot bioclimatic events and in the west and northwest regions, cold to very cold conditions turn out to be the most important inhibiting factors. When considering the variations across the studied period, an increase in the frequency of thermal comfort condition is observed in almost half of the stations. Moreover, based on Pearson and Mann-Kendall methods, the trend of changes in monthly averages of PET has decreased in most stations and months, which can lead to different consequences in each month and station. Thus, it is expected that due to PET changes in recent decades and to the intensified global warming conditions, Iran’s bioclimatic conditions change in a way that transfers the days with comfort to early spring and late autumn.     

Modeling of changes in thermal bioclimate: examples based on urban spaces in Freiburg, Germany

The Place of the Old Synagogue is a popular place in the city center of Freiburg, a medium-sized city in southwest Germany. It is going to be redesigned soon. In this paper the impact of urban street design and surface material on human thermal comfort is analyzed using the example of the Place of the Old Synagogue. The models SkyHelios, RayMan, and ENVI-met were applied to quantify and qualify the changes. All three models are freely available. Their combination allows analysis of development in long-term conditions, as well as changes in spatial distribution of thermal comfort, as well as of heat stress in summer. Results show that the models can provide valuable information. About the Place of the Old Synagogue, quantitative results show that the period with heat stress will become longer, while the intensity of heat stress increases. The spatial results show that the most significant changes are due to changes in shading. Nevertheless, an increase in thermal stress up to 10 °C is calculated for areas, where ground coverage changes from grass to pavement.     

The extent and intensity of the urban heat island in Iași city,Romania

The study underlines the characteristics of the urban heat island of Ia?i (Ia?i’s UHI) on the basis of 3 years of air temperature measurements obtained by fixed-point observations. We focus on the identification of UHI development and intensity as it is expressed by the temperature differences between the city centre and the rural surroundings. Annual, seasonal and daily characteristics of Ia?i’s UHI are investigated at the level of the classical weather observation. In brief, an intensity of 0.8 °C of UHI and a spatial extension which corresponds to the densely built area of the city were delineated. The Ia?i UHI is stronger during summer calm nights—when the inner city is warmer with 2.5–3 °C than the surroundings—and is weaker during windy spring days. The specific features of Ia?i’s UHI bear a profound connection to the specificity of the urban structure, the high atmospheric stability in the region and the local topography. Also, the effects of Ia?i’s UHI upon some environmental aspects are presented as study cases. For instance, under the direct influence of UHI, we have observed that in the city centre, the apricot tree blossoms earlier (with up to 4 days) and the depth of the snow cover is significantly lower (with up to 10 cm for a rural snow depth of 30 cm) than in the surrounding areas.     

城市气象研究进展

中国数十年来在城市气象研究这一新兴学科领域开展了大量研究并获得了多方面的丰硕成果。文中从城市气象观测网与观测试验、城市气象多尺度模式、城市气象与大气环境相互影响、城市化对天气气候的影响等4个方面论述了城市气象的主要研究进展:中国各大城市已建立或正在完善具有多平台、多变量、多尺度、多重链接、多功能等特点的城市气象综合观测网;北京、南京、上海等地开展了大型城市气象观测科学试验,被世界气象组织列入研究示范项目;成功开展了风洞实验、缩尺度外场实验研究;建立了多尺度城市气象和空气质量预报数值模式,并应用于业务;在城市热岛效应、城市对降水影响、城市气象与城市规划、城市化对区域气候及空气质量的影响、城市气象与大气环境相互作用等研究领域取得长足进展。最后指出,未来需要重点从新观测技术及观测资料同化应用、城市系统模式研究、城市化对天气气候的影响机理、城市化对大气环境和人体健康的影响、城市水文气象气候与环境综合服务等方面开展科学研究与应用,为中国城市化、生态文明建设、防灾减灾和应对气候变化等国家需求提供科技支撑。      

Basic analysis of climate and urban bioclimate of Dar es Salaam, Tanzania

Better understanding of urban microclimate and bioclimate of any city is imperative today when the world is constrained by both urbanisation and global climate change. Urbanisation generally triggers changes in land cover and hence influencing the urban local climate. Dar es Salaam city in Tanzania is one of the fast growing cities. Assessment of its urban climate and the human biometeorological conditions was done using the easily available synoptic meteorological data covering the period 2001–2011. In particular, the physiologically equivalent temperature (PET) was calculated using the RayMan software and results reveal that the afternoon period from December to February (DJF season) is relatively the most thermal stressful period to human beings in Dar es Salaam where PET values of above 35 °C were found. Additionally, the diurnal cycle of the individual meteorological elements that influence the PET index were analysed and found that air temperature of 30–35 °C dominate the afternoon period from 12:00 to 15:00 hours local standard time at about 60 % of occurrence. The current results, though considered as preliminary to the ongoing urban climate study in the city, provide an insight on how urban climate research is of significant importance in providing useful climatic information for ensuring quality of life and wellbeing of city dwellers.     

北京地区城郊极端温度事件的变化趋势及差异分析

利用北京地区城郊16个气象观测站1979～2008年逐日平均、最高和最低温度的均一化资料,分析了近30年北京地区城、郊区极端温度事件发生频次(强度)的变化趋势,并对比了城郊差异以及城市热岛强度对城郊差异的影响.研究结果显示:从发生频次来看,近30年城区极端低温事件的减小幅度[5.94 d (10 a)-1]高于郊区的减小幅度[-5.28 d (10 a)-1],而极端高温事件的增加幅度在城区[4.33 d (10 a)-1]和郊区[4.42 d (10 a)-1]之间差别不大,定量化的诊断结果进一步证明了城区和郊区在极端温度事件发生频次上的差别很小.从发生强度来看,近30年城区极端温度事件的年平均发生强度明显高于郊区,但在变化趋势上,城区极端低温事件的减弱幅度略高于极端高温事件的增强幅度,相差0.042℃(10 a)-1,而在郊区极端低温事件的减弱幅度却略低于极端高温事件的增强幅度,相差0.052℃(10 a)-1.城郊差异的定量化分析结果表明,极端温度事件在城区强度一般大于郊区强度,城区与郊区强度差值均为正值(除1982年和1985年极端高温事件强度差值为负).热岛强度与极端温度事件城郊差异的相关性统计发现,极端温度事件发生频次和发生强度在城郊之间的差别与热岛强度均没有明显的相关特征,该结果说明城市热岛效应对北京超大城市市区和郊区影响基本一致,其差异性是有限的.     

Observed Trends in Severe Weather Conditions Based on Humidex,Wind Chill,and Heavy Rainfall Events in Canada for 1953–2012

Observed trends in severe weather conditions based on public alert statements issued by Environment Canada are examined for Canada. Changes in extreme heat and extreme cold events represented by various humidex and wind chill indices are analyzed for 1953–2012 at 126 climatological stations. Changes in heavy rainfall events based on rainfall amounts provided by tipping bucket rainfall gauges are analyzed for 1960–2012 at 285 stations. The results show that extreme heat events, defined as days with at least one hourly humidex value above 30, have increased significantly at more than 36% of the stations, most of which are located south of 55°N; days with nighttime hourly humidex values remaining above 20 have increased significantly at more than 52% of the stations, most of which are located south of 50°N. Extreme cold events represented by days with at least one hourly wind chill value below ?30 have decreased significantly at more than 76% of the stations across the country. No consistent changes were found in heavy rainfall events. Because city residents are very vulnerable to severe weather events, detailed results on changes in extreme heat, extreme cold, and heavy rainfall events are also provided for ten urban centres.     

近30年成都西部人体舒适度变化特征分析

利用1961-2017年成都市西部邛崃国家气象观测站日平均气温、日最高气温、日平均风速、日平均相对湿度和日最小相对湿度计算逐日人体舒适度指数及白天和夜间舒适度指数,并通过线性倾向估计方法分析近30年邛崃市人体舒适度变化特征。结果表明：近30年邛崃市没有暑热和寒冷天气,人体舒适度日数舒适级别日数最多,其次是冷不舒适级别日数,热不舒适级别日数最少;年平均人体舒适度指数呈现较小的上升趋势;舒适日数集中在春季、夏季、秋季三个季节;热不舒适日数和舒适日数21世纪初期相比20世纪90年代有所增加,冷不舒适日数有所减少;近30年白天人体舒适度指数有着较明显的升高趋势,夜间人体舒适度指数变化不大。     

Urban–rural contrasts of meteorological parameters in Łódź

Summary Data from two automatic stations in Łódź (one urban and one rural) for the period 1997–2002 are analyzed to reveal urban–rural contrasts of such parameters as air temperature, relative humidity, water vapour pressure and wind speed. Under favourable weather conditions the highest temperature differences between the urban and rural station exceeds 8 °C. Relative humidity is lower in the town, sometimes by more than 40%. Water vapour pressure differences can be either positive (up to 5 hPa) or negative (up to −4 hPa). Wind speed at the urban station is on average lower by about 34% in night and 39% during daytime. Regression analysis shows that for rural winds lower than 1.13 m s⁻¹ urban winds can be stronger than rural speeds. Attention has also been paid to singularities in the course of the analyzed parameters over 24 hour periods. It is shown that the typical course of the urban heat island intensity under favourable conditions is similar in all season. Four stages of this course have been distinguished. Wind speed differences also seem to change in a typical way. Case studies show that humidity contrasts, unlike temperature, can evolve in different ways under fine weather conditions. Types of relative humidity evolution are proposed.