Urban heat island (UHI) has been evidenced as a phenomenon having a series of negative consequences in energy use, human thermal comfort, citizens' health, wellbeing and air quality. Thus, all ...professions, faculties and disciplines of society are actively seeking for effective UHI mitigation techniques and strategies. Previous studies have indicated that synoptic variables such as wind, precipitation, cloud coverage, fog and air quality have significant impacts on UHI phenomenon. In accordance with this basis, we devise to develop UHI mitigation techniques and strategies based on meteorological characteristics and synoptic conditions. This paper therefore has reviewed the influences of meteorological characteristics and synoptic conditions, such as precipitation, wind, cloud coverage, fog, air pollution and haze on UHI effects. Through this work, people can obtain better understandings of using them to mitigate UHI effects. Meanwhile, some suggestions on urban planning and development have been briefly presented for the alleviation of UHI effects.
•Precipitation, wind, cloud cover and fog can effectively mitigate UHI effects.•Rainwater and wind mitigation effects are undermined by unreasonable urban planning.•The formations of cloud and fog are reducing due to urban temperature increase.•Air pollution and haze aggravated UHI effects.•Sustainable urban construction enhance MSCC to mitigate UHI.
This study investigated monthly variations of surface urban heat island intensity (SUHII) and the applicability of the local climate zones (LCZ) scheme for land surface temperature (LST) ...differentiation within three spatial contexts, including urban, rural and their combination, in Shenyang, China, a city with a monsoon-influenced humid continental climate. The monthly SUHII and LST of Shenyang were obtained through 12 LST images, with one in each month (within the period between 2018 and 2020), retrieved from the Thermal InfraRed Sensor (TIRS) 10 in Landsat 8 based on a split window algorithm. Non-parametric analysis of Kruskal-Wallis H test and a multiple pairwise comparison were adopted to investigate the monthly LST differentiations with LCZs. Overall, the SUHII and the applicability of the LCZ scheme exhibited spatiotemporal variations. July and August were the two months when Shenyang underwent strong heat island effects. Shenyang underwent a longer period of cool than heat island effects, occurring from November to May. June and October were the transition months of cool–heat and heat–cool island phenomena, respectively. The SUHII analysis was dependent on the definition of urban and rural boundaries, where a smaller rural buffering zone resulted in a weaker SUHI or surface urban cool island (SUCI) phenomenon and a larger urban area corresponded to a weaker SUHI or SUCI phenomenon as well. The LST of LCZs did not follow a fixed order, where in July and August, the LCZ-10 (Heavy industry) had the highest mean LST, followed by LCZ-2 (Compact midrise) and then LCZ-7 (Lightweight low-rise). In comparison, LCZ-7, LCZ-8 (Large low-rise) and LCZ-9 (Sparsely built) had the highest LST from October to May. The LST of LCZs varied with urban and rural contexts, where LCZ-7, LCZ-8 and LCZ -10 were the three built LCZs that had the highest LST within urban context, while LCZ-2, LCZ-3 (Compact low-rise), LCZ-8, LCZ-9 and LCZ-10 were the five built LCZs that had the highest LST within rural context. The suitability of the LCZ scheme for temperature differentiation varied with the month, where from July to October, the LCZ scheme had the strongest capability and in May, it had the weakest capability. Urban context also made a difference to the suitability, where compared with the whole study area (the combination of urban and rural areas), the suitability of built LCZs in either urban or rural contexts weakened. Moreover, the built LCZs had a higher level of suitability in an urban context compared with a rural context, while the land-cover LCZs within rural had a higher level of suitability.
•This study frames heat injustice in aspects of cause-related, effect-related and process-related injustice.•Empirical survey was conducted in Yangtze River Delta and Chengdu-Chongqing urban ...agglomerations.•This study geographically revealed effect-related and process-related injustice in YRD and CCEC regions.•The cause-related, effect-related and process-related injustice depended on the socioeconomic factors.•Urban planning and design for heat-resilient cities and setting temporary shelters should be prioritised in heat actions.
Urban heat has affected numerous cities with increasingly severe environmental, social, economic, and health impacts. It is urgent to develop plans and take actions to beat the heat before cities are locked into unintended consequences. An understanding of heat injustice is important to support heat plans and actions for accurately alleviating heat-related risks and threats, scientifically avoiding unexpected conflicts and disputes, and actively driving citizens to participate in actual implementation. Existing studies have primarily focused on effect-related injustice (e.g., morbidity and mortality), while a systematic understanding of heat injustice is lacking. To overcome this research gap, this study framed heat injustice in terms of cause-related, effect-related, and process-related injustice, and empirically verified them based on a questionnaire survey in the Yangtze River Delta (YRD) and Chengdu-Chongqing Economic Circle (CCEC) regions. The survey results from 2704 respondents indicated that effect-related injustice and process-related injustice were geographically prominent in the YRD and CCEC regions. Socioeconomically, cause-related, effect-related, and process-related injustice occurred with the identification of groups who thought the heat was more severe were more susceptible to physiological and psychological impacts, and had lower levels of heat-related awareness and knowledge. The results also indicated that both YRD and CCEC regions should urgently develop heat action plans, which should be regionalized and group-specific. Urban planning and design for heat-resilient cities and setting temporary cooling shelters should be prioritized. Moreover, this study identified inconsistencies among higher levels of heat-related knowledge, lower levels of cooling strategy familiarity, and lower urgency of heat actions among the elderly, less educated, unhealthy, and wealthy groups. Overall, this study provides a reference for understanding heat injustice and formulating unbiased and implementable heat action plans.
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.
The environmental challenges in cities urge people to explore feasible strategies for resilient, sustainable, healthy and livable built environments, of which designing and building green roof (GR) ...is an important approach. Whilst extensive studies have been proving GR benefits in energy, environmental and ecological aspects, GR implementation (GRI) for achieving such multi-benefits has received limited attention. In order to facilitate GRI, therefore, this paper aims to delineate factors that can affect GRI. This study conducted a systematic review of 186 published papers from 2000 to 2019, for the identification of drivers, motivations and barriers to the GRI. The results indicate that the drivers to GRI include policy pressure, market pressure, and innovation and technology advancement. Besides, GRI can be potentially motivated by multiple factors including energy efficiency, urban heat island mitigation, roof longevity prolongation, air purification, runoff control, water purification, urban infrastructure improvement, sound insulation and noise reduction, biodiversity increase, recreation and aesthetics, property value enhancement and employment improvement. Nevertheless, GRI can be constrained by several barriers such as a lack of government policy, unsound technological level, unsound economic benefit assessment and individual unwillingness. According, this study proposed strategic recommendations in policy, technical, economic and social aspects, with the considerations of various GRI stakeholders (e.g. designer, engineer, constructor and builder, contractor, building operator, owner, end-user, government agent), to strengthen GRI drivers, foster GRI motivations and overcome GRI barriers. Overall, this study is of significance to inform the people with knowledge of factors affecting GRI, which can further promote researchers to explore interrelationships among multiple factors on the one hand and can further promote decision-makers to develop sound policies on the other for GR adoption.
This paper reviews urban heat (UrHT) challenges following the SBAR (situation, background, assessment and recommendation) framework. The results indicate that heatwaves become more frequent, lasting ...and intense, especially after 1990s. Above 1960s level, heatwaves across China doubled in both magnitude and frequency by 2018. Jianghuai and Southern China underwent the largest magnitude and most widespread increases. Under 1.5 °C warming limit, the average heatwave days and duration across China will increase by 10.8 days and 3.9 days. Drought–heatwave co–occurrence is increasingly frequent at 7–11%/decade (from 1961 to 2018) and the co–occurrence leads to more intense heatwaves. UHIs are a common issue for almost all Chinese cities and UHIs have been aggravating annually. Daytime UHIs peak in summer, indicating the synergies with heatwaves. The synergies are prominent in southeastern cities for strong summer daytime UHIs in eastern cities and intense heatwaves in southern regions. UrHTs have not been recognised and there are no dedicated/mandatory plans. Mega–challenges of climate change, rapid urbanisation, carbon– and labour–intensive economic growth and demographic changes can potentially lock China into UrHT challenges. Addressing UrHT challenges is urgent in China not only for environmental, ecosystem, social and health consequences, but also for economic impacts relevant to labour, capital, and goods or services. Efforts are suggested in technical improvement, policy formulation, social participation, economic investment and co-benefit approach recognition. Overall, this paper provides a comprehensive understanding of heat–related challenges in China and can guide the creation of cool cities and communities in practice.
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•Almost all cities in China are under the impacts of urban heat islands.•Heatwaves and urban heat islands can synergise, especially in Southeastern China.•China has not well recognised urban heat challenges and no dedicated plan.•UrHT affects economic productivity by affecting outputs, labour, capital and goods.•UrHT may drive population migrating out the extreme heat areas.
The energy consumption in buildings accounts for a significant proportion of total energy and carbon emissions over the world. To reduce the building energy consumption and achieve sustainable ...development of buildings, nearly zero energy buildings (NZEBs) have attracted widespread attention as a future building energy target. This paper reviews energy-efficient measures (EEMs) and renewable energy technologies (RETs) in NZEBs and discusses the application and suitability of the key technologies, i.e. minimizing the energy demand in NZEBs by EEMs and adopting RETs to meet the remaining energy needs. EEMs contain efficient thermal insulation system, high-performance window system, good airtightness and fresh air heat recovery system. RETs are composed of solar photovoltaic/thermal (PV/T) system, air source heat pump system (ASHP), ground source heat pump system (GSHP), and wind power. In addition, this paper emphasizes further research works, which involve life cycle energy analysis (LCEA), meteorological parameters change, intelligent building operation management (IBOM) system, energy storage system and social policy issues. This paper will provide some references for the further development of NZEBs in different climatic regions in China.
•This paper systematically reviews application of EEMs and RETs in NZEBs in China.•Feasibility and suitability of EEMs and RETs are evaluated from different aspects.•Further research work and development direction of NZEBs are pointed out.
•Local-scale urban ventilation and urban climate studies•Validation of precinct ventilation performance of precinct ventilation zone scheme.•Compact high-rise gridiron precinct has strong influences ...on precinct ventilation performance.•Precinct ventilation forced by sea breeze has significant cooling potentials.•Street orientation is not longer a critical factor influencing precinct ventilation performance, UHIs and outdoor thermal comfort at the precinct scale.
Many cities are facing the problem of urban heat island (UHI) and UHI mitigation is becoming crucial in urban planning and design. The reasonable wind-sensitive design may be a feasible approach to UHI mitigation and outdoor thermal comfort improvement, as cool wind (i.e. sea breeze) is a good cooling intervention. Consistent with the precinct ventilation zone scheme, this study experimentally investigated relationships among urban morphology, precinct ventilation performance, UHIs and outdoor thermal comfort in a compact high-rise gridiron precinct in the coastal Sydney, Australia.
Results indicate that precinct morphological characteristics had a strong modification effect on precinct ventilation. As a result, under different combination of external meteorological conditions and precinct morphological characteristics, there was no significant difference in precinct ventilation performance (i.e. relative wind velocity ratio). The precinct ventilation performance forced by sea breeze could significantly mitigate UHIs. Meanwhile, the precinct ventilation performance forced by the sea breeze could significantly improve relative humidity which could further significantly improve outdoor thermal comfort. The street orientation was no longer a critical factor affecting precinct ventilation performance, UHIs and outdoor thermal comfort at the precinct scale.
Overall, this study preliminarily revealed precinct ventilation performance and its influence on UHIs and outdoor thermal comfort. The cooling and humidifying effects of wind background cannot be ignored in microclimate studies and should be considered for microclimate regulation in urban planning and design.
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