Highest Urban Heat Island Intensity Research Articles

Effects of the Western Pacific Subtropical High on the urban heat island characteristics in the middle and lower reaches of the Yangtze River, China

The middle and lower reaches of the Yangtze River are frequently affected by the Western Pacific Subtropical High (WPSH) in summer. This leads to phenomena including air subsidence, high temperatures, low rainfall, and weak winds, all of which affect the urban heat island (UHI) effect. Currently, there are few studies on the influence of WPSH on the UHI effect. In this study, we analysed the temporal and spatial distributions of the influence of WPSH on the UHI effect by establishing two scenarios: with and without WPSH. We calculated the UHI intensity and the urban heat island proportion index (UHPI) to analyse the temporal and spatial distributions of the UHI effect. The geographical detector method was then used to analyse the factors influencing UHI. The results indicate the strong heat island effect during the day in provincial capitals and some developed cities. The area of high UHI intensity was larger under the influence of WPSH than in the years without WPSH. WPSH affected UHPI at both day and night, although the effect was more pronounced at night. The factors affecting daytime UHI intensity are mainly POP and NTL, O3 plays a large role in the years with WPSH control. The main factors affecting the UHI intensity at night are AOD, POP and NTL were mainly factors in the years without WPSH control, POP and WPSH were mainly factors in the years with WPSH control. The interactions of the factors are mainly POP and multi-factors during the daytime, and DEM and multi-factors during the nighttime. It was found that the UHI intensity was enhanced under the control of the WPSH, and the influencing factors of the diurnal UHI differed with and without the WPSH control, which ultimately provides realistic suggestions for mitigating the intensity of the UHI in areas affected by the WPSH.

Simulating influences of land use/land cover composition and configuration on urban heat island using machine learning

Urban heat island (UHI) has become a worldwide concern under global warming and urbanization waves, which pose significant threats to human health and urban sustainability. Despite Land Use/Land Cover (LULC) being regarded as a crucial factor influencing UHI, few studies simulated the nonlinear influences from LULC compositions and configurations, especially considering the difference between monocentric and polycentric cities. Therefore, we measured the patterns of LULC and UHI from 2006 to 2022 using cases of a monocentric city (Chengdu) and a polycentric city (Chongqing). Further, we simulated future and land surface temperature (LST) using Machine Learning (ML) models, and further calculated the simulated UHI in 2030 by urban-rural LST differences. The results showed that Chengdu had prominent UHI intensity in cores and the surrounding satellite towns. Chongqing's main center and subcenters had high UHI intensity under clustered patterns. ML results indicated that built-up percentage was the most crucial factor driving LST. Configuration factors dominated in impacting Chengdu's LST, while composition factors were more critical in Chongqing. Moreover, future UHI is estimated to decrease in Chongqing's core, compared with the remaining high UHI in Chengdu's core. These results might provide insights for understanding and mitigating future UHI effects.

Improvement of spatial-temporal urban heat island study based on local climate zone framework: A case study of Hangzhou, China

Large-scale long-period urban heat island (UHI) intensity (UHII) prediction with high spatiotemporal resolutions, satisfactory accuracy, and calculation efficiency is crucial and challenging for UHI mitigation studies. This study proposes a framework combining an urban weather generator (UWG), local climate zone (LCZ), deep-learning method, and Python automatic cyclical calculation to obtain hourly UHII throughout one year and over a total of 1920 blocks in Hangzhou City. The spatial-averaged hourly UHII are between −2 °C and 6 °C in more than 96 % time, and those at 0 °C–1 °C contribute to 43.80 % of the total time. Spring gives the most intense nocturnal UHII, while winter has the weakest one. A significant diurnal UCI phenomenon could accompany the strong nocturnal UHI phenomenon. From the synthetic (based on seasonal data) 24-h curves, mean UHII and UCII (average of the positive and negative values, respectively) drop by approximately 25 % in winter compared to spring. Spatially, UHII is higher in the central regions with compact buildings but significantly lower in the high-vegetation-coverage regions. Based on LCZ framework, LCZ 1 (compact high-rise configurations) has the highest UHII, independent of examined periods. UHII relations to building coverage, vegetation ratio, and building height are individually quantified. The building coverage has the highest influence on annual UHII, with a correlation coefficient as high as 0.76. Results indicate that, for UHI mitigation purposes, the percentage of compact high-rise configurations (LCZ 1) in the urban area shall be limited, and the vegetation ratio is better to be greater than 20 %.

Heat vulnerability of Latino and Black residents in a low-income community and their recommended adaptation strategies: A qualitative study

Latino, Black, and economically disadvantaged individuals in the U.S. have been shown to disproportionately live in areas characterized by urban heat islands, yet little qualitative data exist to inform heat adaptation. In a low-income community of color, we explored residents' heat-related health and well-being outcomes, heat vulnerability, and recommended adaptation strategies. From July–September 2021, we conducted qualitative interviews with 18 economically disadvantaged adults (female = 17, Latino = 16, Black = 2) in an area with high urban heat island intensity in Austin, Texas. We identified six themes using NVivo. First, heat impacted residents' physical health (fatigue, headaches, nausea, dizziness, trouble breathing), mental health (uncomfortable, stress), physical activity, and social relationships. Second, heat exposure was only mentioned outdoors (active transportation, outdoor work, recreation). Third, residents perceived children and those with diabetes and hypertension as most sensitive. Fourth, adjusting to heat included staying home, drinking liquids, changing schedules, and using air conditioning. Fifth, barriers to adjusting to heat were lack of trees, shade, greenspace, and bluespace, along with electricity cost and power outages. Sixth, residents recommended adding trees, shade structures, parks, pools, splash pads, and drinking fountains. Findings complement quantitative data to support municipal efforts in designing equitable, heat-resilient cities.

Experimental Research with Computer Simulation (Case Study Of Urban Cool Island)

This research will describe experimental research methodology using computer simulation with the case study of urban cool island research. The urban cool island is one of the urban heat island mitigation technology strategies. This technology uses a geometric and material intervention process that forms an urban cool island in an area with high urban heat island intensity. The urban cool island will expand and reduce the temperature of the hot islands so that the urban heat island gets smaller. In the research process, a series of experimental methodologies were carried out. Experimental methodology is carried out on a regional scale will be difficult and expensive. So a computer simulation is needed to facilitate urban cool island experiments in the area. The stages of experimental research with computer simulations use two process stages (1) Quasi-measurement experiments and field observations in the UCI area, (2) Validation of field measurements versus simulation models, (3) Experiments with computer simulations by creating test models and comparison models. The scope of research on the scale of urban areas with experimental methodology becomes efficient with the help of computer simulations. In Urban Cool Island, several countries have also used this methodology. Computer simulation used: ENVI-MET, CFD-Ansys, and others. Before starting the research, a clear frame or research design is needed, determining variables, replicating the real conditions, mastering the use of simulations, and always paying attention to the results, which are continuously controlled and validated to produce simulations that are close to the real conditions.

Urban heat health risk assessment in Singapore to support resilient urban design — By integrating urban heat and the distribution of the elderly population

Elderly people are more vulnerable than other age groups to the increasing urban heat risk caused by both climate change and urbanization. This study developed a systematic method to assess the urban heat health risk to the aging population in high-density tropical cities. Based on the assessment, the study identifies high heat health risk districts, diagnoses specific reasons in individual districts, and suggests specific solutions. First, we applied an existing GIS model to quantitatively evaluate urban heat island (UHI) intensity, which is influenced by both longwave radiation and anthropogenic heat. Second, the urban heat health risk to the elderly in individual districts was weighted by UHI intensity, density and proportion of the elderly population in different districts. The integrated mapping results showed that the old HDB neighborhoods in the Central Region are at the highest risk, with a higher UHI intensity, density and proportion of the elderly population than other districts. Based on the analysis, we suggest both UHI mitigation strategies, social support, and facilities for the elderly population at Singapore HDB neighborhoods. Research outputs allow different stakeholders to understand various issues of individual neighborhoods regarding the urban heat health risk to the elderly and to develop corresponding solutions. • A new method is developed to assess heat health risks on aging population, by heat, exposure, and vulnerability. • GIS overlapping map is used to identify specific heat health risk reasons at districts. • Nighttime air temperature is used to assess urban heat health issue, rather than land surface temperature. • Older neighborhoods in the Central Region of Singapore are at the highest risk. • Both adaptation and mitigation recommendations are provided to develop systematic and specific strategies.

Spatial and temporal characteristics of nighttime UHII based on local climate zone scheme using mobile measurement-A case study of Changsha

The local climate varies with time and space because of diversified urban patterns across the complex urban region. Achieving accurate local climatic characteristics by efficient field survey method will contribute to the theoretical and technical reference for urban heat island intensity (UHII) alleviation and eco-friendly environment construction. This study takes the main urban area of Changsha as an example, and focuses on the local-scale UHII characteristics under the Local Climate Zone (LCZ) scheme. An efficient method integrating both the mobile measurement and the GIS-based method is proposed and applied. By applying temporal corrections to the obtained mobile data, the local UHII along the mobile route are expressed. Then based on the UHII values along the mobile route and the LCZ map, a stepwise multiple regression model was built to predict the spatial distributions of UHII within the whole main urban area of Changsha. Results indicated that the built-up LCZs accounted for 42.07% and the land cover LCZs took up 57.93%. The monthly average UHII of Changsha ranged from 1 °C to 4 °C and the core UHII overlayed the city center. The mean UHII of different LCZs ranged from 0.6 °C to 4.8 °C, and the high UHII was more likely to be observed in the compact LCZs. The proposed methodology could be useful for supporting local scale UHII adaptation and mitigation efforts, thus encouraging a more sustainable built environment.

Urban heat island effect-related mortality under extreme heat and non-extreme heat scenarios: A 2010–2019 case study in Hong Kong

The urban heat island (UHI) effect exacerbates the adverse impact of heat on human health. However, while the UHI effect is further intensified during extreme heat events, prior studies have rarely mapped the UHI effect during extreme heat events to assess its direct temperature impact on mortality. This study examined the UHI effect during extreme heat and non-extreme heat scenarios and compared their temperature-mortality associations in Hong Kong from 2010 to 2019. Four urban heat island degree hour (UHIdh) scenarios were mapped onto Hong Kong's tertiary planning units and classified into three levels (Low, Moderate, and High). We assessed the association between temperature and non-external mortality of populations living in each UHIdh level for the extreme heat/non-extreme heat scenarios during the 2010–2019 hot seasons. Our results showed substantial differences between the temperature-mortality associations in the three levels under the UHIdh extreme heat scenario (UHIdh_EH). While there was no evidence of increased mortality in Low UHIdh_EH areas, the mortality risk in Moderate and High UHIdh_EH areas were significantly increased during periods of hot temperature, with the High UHIdh_EH areas displaying almost double the risk (RR: 1.08, 95%CI: 1.03, 1.14 vs. RR: 1.05, 95 % CI: 1.01, 1.09). However, other non-extreme heat UHI scenarios did not demonstrate as prominent of a difference. When stratified by age, the heat effects were found in Moderate and High UHIdh_EH among the elderly aged 75 and above. Our study found a difference in the temperature-mortality associations based on UHI intensity and potential heat vulnerability of populations during extreme heat events. Preventive measures should be taken to mitigate heat especially in urban areas with high UHI intensity during extreme heat events, with particular attention and support for those prone to heat vulnerability, such as the elderly and poorer populations.

Urban Heat Island Mitigation Strategy based on Local Climate Zone Classification using Landsat 8 satellite imagery

Appropriate strategies on urban climate mitigation should be formulated by considering the physical morphology of the urban landscape. This study aimed to investigate, analyze, and promote possible strategies to mitigate Jakarta’s urban heat island (UHI) phenomena. Jakarta’s local climate zone (LCZ) was classified into 17 classes using Landsat 8 data and the random forest method. Land surface temperature (LST) characteristic in each LCZ class was analyzed from 2018, 2019 and 2020. The result revealed that most of the local climate zone in Jakarta is dominated by LCZ 6 (open low-rise) and LCZ 3 (compact low-rise), which is the typical residential area in Jakarta. However, the mean LST in 2018, 2019 and 2020 showed that LCZ 3 (compact low-rise) and LCZ 7 (lightweight low-rise) are the areas that were most likely causing high surface temperature with the highest UHI intensity. During the COVID-19 pandemic in 2020, LST in Jakarta decreased drastically in some parts of the area, especially in public facility such as airport. However, the LST value in low-rise areas (LCZ 3 and LCZ 7) remains higher than the other LCZ classes. Materials of the building and land cover play a significant role in raising the land surface temperature. Therefore, mitigation strategies for urban heat islands in Jakarta should be focused on such particular areas mentioned.

DEVELOPMENT OF ANNUAL URBAN HEAT ISLAND IN BAGHDAD UNDER CLIMATE CHANGE

This study investigated the confirmation of climate change by analyzing the long-term records of annual means of temperature taken from synoptic station located at International Baghdad Airport (rural site) available for the period from 1978 to 2019. Furthermore, based on annual temperature data recorded by automatic weather station installed at Mustansiriyah University (urban station), available for the period 2008–2019, the difference between urban and rural temperatures called as urban heat island (UHI) intensity was annually calculated. Statistic descriptive methods including temperature trend, percentile function and R-square were employed to recognize the contribution of UHI in enhancing the local warming climate. The results show that there was a warming trend of 0.052 °C/year for period of 42 years and 0.02 °C/year for recent 12 years at rural station which is lower than 0.13 °C/year observed at urban station. Also the results for annual UHI were found to be always positive intensity which ranges from 0.8 to 2.4 °C with a mean value of 1.78 °C. As a result of high annual UHI intensity, hot day events during 2008–2019 were extracted from daily temperatures exceeding of threshold value of 37.5 °C that dominate in summer months with totally 204 events and with an annual average of 17 days. Finally, under the continuing local warming climate, potential effects caused by UHI and its mitigation strategies are further presented.

Influences of landform and urban form factors on urban heat island: Comparative case study between Chengdu and Chongqing

Although the degraded urban thermal environment has been widely concerned, whether monocentric or polycentric urban development can alleviate urban heat island (UHI) is still debatable, particularly considering different types of cities in plain and mountainous settings. To fill the gap, this study chose the cases of Chengdu on alluvial flatlands and Chongqing on mountainous landforms in China for comparison. Adapting to natural landforms, Chengdu has a dominated monocentric urban form, whereas Chongqing has a naturally polycentric urban form. This study found that areas with high UHI intensity were located in the urban center and peripheral suburbs in Chengdu, while those were located in the peripheral industrial zones in Chongqing. The spatial error model and random forest regression results showed that natural elements such as vegetation and water had similar influences and contributions to UHI. However, distinct landforms and urban forms played critical roles in UHI differences among the two cities. Impervious surface and building density were the dominant variables to UHI of Chengdu, while sky view factor and industrial zones were the main contributors to UHI of Chongqing. The findings called for corresponding policy strategies to optimize urban form and improve the urban thermal environment.

Procedure for the selection and evaluation of prefabricated housing buildings for the implementation of green roofs in the context of Urban Heat Island mitigation. The example of Wrocław, Poland.

The assessment of the suitability of existing buildings for implementation of green roofs is an important research issue, especially in the context of Urban Heat Island (UHI), the negative impacts of which are locally exacerbated by the global warming. The studies carried out so far have covered a variety of buildings and have taken into account a range of different conditions. Relatively little attention has been paid to the possibilities of greening the roofs of prefabricated apartment blocks from the second half of the 20th century in the context of the potential climate effect. Yet, these buildings are found in many cities around the world, and seem in fact attractive for greening. In view of the above, we proposed a three-stage investigatory procedure to: (I) identify and classify buildings based on the number of floors and the rooftop available area; (II) select buildings by designating priority areas depending on the highest UHI intensity and roof density; (III) analyse the roof load capacity to develop retrofit scenarios. The procedure was applied to prefabricated housing estates built in the 1970s and 1980s in Wrocław, Poland. The research shows that there are 1962 buildings of different heights and roof area of 722405 m2, of which 480 buildings with a roof area of 122749.1 m2 were selected for greening within priority areas. The structure of the studied roofs was not designed to carry additional loads, which requires the application of complementary solutions. Scenario 1 assumes extensive greening provided that the existing ventilated roof is strengthened, scenario 2 –semi-intensive greening, which however requires the conversion of the ventilated roof to a non-ventilated one. The presented procedure can be applied in any other city with prefabricated apartment blocks and available UHI data, and serve to support the decision to implement green roofs to mitigate UHI.

A Method for Selecting the Typical Days with Full Urban Heat Island Development in Hot and Humid Area, Case Study in Guangzhou, China

The urban heat island (UHI) poses a significant threat to urban ecosystems, human health, and urban energy systems. Hence, days with a relatively higher UHI intensity should be selected for UHI observation and analysis. However, there is still a lack in the method and criteria for selecting the typical meteorological days for UHI survey and simulation. In this study, field measurements were conducted based on Local Climate Zone (LCZ) schemes over a one-year period to assess the UHI behavior in Guangzhou, China. The relationship between the diurnal temperature range (DTR) and UHI intensity was evaluated and analyzed quantitatively under different meteorological conditions classified by precipitation. The average daily maximum UHI intensity (UHIImax) during precipitation days was approximately 1.8 °C lower than that during non-precipitation days, confirming that precipitation has a negative effect on UHI development. The monthly DTR distribution was similar to the daily UHIImax distribution, which was higher in autumn and winter, but lower in spring and summer. DTR has a significant linear correlation with the daily UHIImax, with a Pearson’s correlation coefficient of >0.7 and statistical significance of <0.001. Based on a quantitative evaluation of our results, we determined that 10 °C could be regarded as the appropriate DTR threshold to identify the meteorological conditions conducive to UHI development; the meteorological conditions exhibited a high daily UHIImax in Guangzhou. This study provides a simple method to select typical meteorological days for UHI measurement and simulation, and a method to early-warning of intense UHI events based on weather forecasts.

Localized synergies between heat waves and urban heat islands: Implications on human thermal comfort and urban heat management

Heat waves (HWs) and urban heat islands (UHIs) can potentially interact. The mechanisms behind their synergy are not fully disclosed. Starting from the localized UHI phenomenon, this study aims i) to reveal their associated impacts on human thermal comfort through three different definitions of HW events, based on air temperature (airT), wet-bulb globe temperature (WBGT) and human-perceived temperature (AppT) respectively, and ii) to understand the role of air moisture and wind. The analysis was conducted in four districts (NH, JD, MH and XJH) with different urban development patterns and geographic conditions, in the megacity of Shanghai with a subtropical humid climate.Results evidenced the localized interplay between HWs and UHIs. The results indicate that less urbanized districts were generally more sensitive to the synergies. JD district recorded the highest urban heat island intensity (UHII) amplification, regardless of the specific HW definition. Notably, during AppT-HWs, the increment was observed in terms of maximum (1.3 °C), daily average (0.8 °C), diurnal (0.4 °C) and nocturnal UHII (1.0 °C). Nevertheless, localized synergies between HWs and UHIs at different stations also exhibited some commonalities. Under airT-HW, the UHII was amplified throughout the day at all stations. Under WBGT-HW, diurnal UHII (especially at 11:00–17:00 LST) was consistently amplified at all stations. Under AppT-HW conditions, the nocturnal UHII was slightly amplified at all stations. Air moisture and wind alleviated the synergistic heat exacerbation to the benefit of thermal comfort. The extent depended on geographic condition, diurnal and nocturnal scenarios, temperature type and HW/normal conditions. Stronger HW-UHI synergies indicate the necessity to develop specific urban heat emergency response plans, able to capture and intervene on the underlying mechanisms. This study paves to way to their identification.

Urban Heat Island intensity and buildings’ energy needs in Duran, Ecuador: Simulation studies and proposal of mitigation strategies

Urban Heat Island (UHI) is a phenomenon that is affecting cities across the world. In tropical climates, an increased UHI intensity can cause a significant rise in heat stress probability, both indoors and outdoors. A general increase in the air-conditioning energy consumption of buildings should also be expected as a consequence. This paper evaluates the case of Duran, Ecuador. It estimated, through a spatial distribution analysis, urban morphology parameters, properties of materials, and anthropogenic heat emissions in the streets. Twenty-eight urban, randomly selected samples were classified using the k-means clustering technique, which resulted in four preliminary clusters. Exploratory UHI simulations were carried out in the Urban Weather Generator tool (UWG) using the four clusters to investigate the relevance of the main UHI driving factors through a sensitivity analysis. Urban samples were weighted, considering the sensitivity analysis, for better classifying the driving factors. Results indicate that Duran city is strongly affected by UHI, especially in informal settlements with high anthropogenic heat release. The urban temperatures obtained by the model were compared to the experimental measurements in different locations in the city. Besides, the building cooling needs were simulated by using the TRNSYS v. 17 tool for residential and commercial buildings of the city, showing that UHI is increasing cooling-related energy consumption in a 30–70 % for residential buildings and a 10–20 % for commercial buildings. Finally, general mitigation strategies and policy implications to reduce the UHI intensity are proposed, and a set of scenarios is tested for the cluster with the highest UHI intensity.

Quantifying the cooling effect of urban vegetation by mobile traverse method: A local-scale urban heat island study in a subtropical megacity

Increasing vegetation is considered one of the most efficient ways to mitigate the urban heat island (UHI) effect due to the cooling effect of evapotranspiration. Considering the adverse consequences of the UHI effect on sustainable development and health problems among city dwellers, the effectiveness of urban vegetation on regulation of the UHI effect should be quantitatively evaluated and analyzed to satisfy the needs of urban planning and policy making. Therefore, in this study we analyzed an one-year field experiment data along an 8-km-long belt transect with various land use types and measured the air temperature at 2-h intervals in Shenzhen, a subtropical megacity in China. The results showed that (1) a higher UHI intensity (UHII) was found during the nighttime throughout the year, with a maximum UHII of 4.02 °C during a heat wave night. (2) Both UHI intensity and the Discomfort Index showed a significant negative linear relationship to vegetated area ratio, especially during nighttime with a strong UHI effect. (3) The UHII decreases by 0.16–0.55 °C during nighttime and 0.05–0.15 °C during daytime, when the vegetated area ratio increases by 10%. (4) Increasing vegetation coverage could significantly reduce air temperature fluctuations and areas with vegetation coverage greater than 55% could maintain a relative stable thermal environment for the dwellers. These results could be useful for urban thermal environmental management and urban planning.

EVALUATING THE SPATIAL-SEASONAL VARIATION, HETEROGENEITY AND DISTRIBUTION OF URBAN THERMAL ENVIRONMENT: CASE STUDY OF NANJING, CHINA

Abstract. Urban thermal environment (UTE), as a important parameter in urban ecosystem, strongly and directly linking to urban development and human health. In recently decades, rapid urbanization and population development resulted in serious urban thermal environment problem particularly the urban heat island (UHI) phenomenon. Today, it’s urgent to control and curb urban thermal environment based on the UTE’s spatial-temporal characteristics, in addition, the seasonality of UTE lacked in-depth understanding, which is also a significant question in UTE management, a better understanding the UTE will help human improve governing efficiency and effect. Thus, in our study, we investigated the spatial-seasonal variation and distribution of UTE by statistic analysis, spatial index analysis and landscape metric analysis. We found that: there has a significant spatial and temporal differences on UTE under different seasons, the UHI intensity and mean LST showing a significant difference and stability, additionally, “heat island” of urban showing a cluster trend in urban space particularly in high UHI intensity seasons. These results extend our understanding on the spatial-seasonal variation, heterogeneity and distribution of UTE and which can provide very significant reference and information for urban decision-makers to govern UTE.

Mutual Influences of Urban Microclimate and Urban Trees: An Investigation of Phenology and Cooling Capacity

This paper presents an empirical study on urban tree growth and regulating ecosystem services along an urban heat island (UHI) intensity gradient. The UHI effect on the length of the growing season and the association of cooling and shading with species, age, and size of trees was studied in Salzburg, Austria. Results show that areas with a low UHI intensity differed from areas with a medium or high UHI intensity significantly in three points: their bud break began later, the leaf discoloration took longer, and the growing season was shorter. After leaves have developed, trees cool the surface throughout the whole growing season by casting shadows. On average, the surfaces in the crown shade were 12.2 °C cooler than those in the sun. The tree characteristics had different effects on the cooling performance. In addition to tree height and trunk circumference, age was especially closely related to surface cooling. If a tree’s cooling capacity is to be estimated, tree age is the most suitable measure, also with respect to its assessment effort. Practitioners are advised to consider the different UHI intensities when maintaining or enhancing public greenery. The cooling capacity of tall, old trees is needed especially in areas with a high UHI intensity. In the future, species differences should be examined to determine the best adapted species for the different UHI intensities. The present results can be the basis for modeling future mutual influences of microclimate and urban trees.

Quantifying urban heat island intensity and its physical mechanism using WRF/UCM

Reliable quantification of urban heat island intensity (UHII) is crucial for the evaluation of extreme heat waves and the related heat stress. As a powerful approach for the study of urban climate, numerical models can simulate urban heat island (UHI) in both high spatial and temporal resolutions. However, accurate quantification of UHII using modelling grid data is still a challenge at present, due to the different criterions for the selection of urban/rural grids. This study simulates the high-resolution UHI in the city of Berlin using the Weather Research and Forecasting Model coupled with Urban Canopy Module. A new method to quantify UHII, which is based on the fitted linear functions of simulated 2-m air temperature (T2m) using the impervious surface area in WRF grids (ISAWRF), was adopted and evaluated. The simulated T2m matches the observations well, with a correlation coefficient of 0.95 (P < 0.01) and RMSE of 1.76 °C. The study area shows a strong UHI at nighttime. The simulated nighttime T2m increases with the increase in the ISAWRF. The linear functions of simulated nighttime T2m against ISAWRF are well fitted. The UHII is calculated as the products of the slopes of fitted functions and the largest ISAWRF. The derived UHII shows U-shaped diurnal variations, with high values at nighttime. The difference of simulated surface temperature and sensible heat flux between the impervious surface and the vegetation surface jointly determines the derived UHII. The large difference of surface temperature and the small difference of sensible heat flux between the impervious and the vegetation surface generate the high UHII at nighttime and vice versa during the daytime. The method of ISAWRF-based function of T2m overcomes the problems of traditional methods in arbitrary selecting urban/rural grids. It can be used easily to quantify UHII and to do the comparison study of UHII between different cities.

Spatiotemporal variability in building energy use in New York City

Abstract Data on building energy use for large and dense cities is not yet available at adequate spatial and temporal scales. The energy consumption from buildings significantly influences the local climate and this impact is not adequately integrated into regional or local scale weather models. The primary objective of his study is to understand and map building energy consumption and quantify its impact on the urban environment; here, New York City (NYC) is used as a test case. The project involved a detailed classification of buildings in NYC using a high-resolution landuse/landcover dataset. The customized classification was then coupled with a single building energy model (SBEM) to estimate the building energy use. The developed model matched the annual energy use of NYC within 5% of the observed value. Coupled energy simulations were then performed with the Weather Research and Forecasting (WRF) model. The results show that heat released from building's heating and air conditioning system during extreme heat events can be as high as 18% of the overall available energy. Finally, a comparison between the average annual energy use, the urban heat island intensity (UHI) and the landcover/landuse fraction for various parcels during extreme heat events indicated that neighborhoods surrounding the highly-commercialized zones were disproportionately impacted by high UHI values. The increase was related to advection of heat.