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.
With the doubling of urban population within the next two decades and the disproportionate growth of megacities, it is critical to explore the synergism between urban heat and pollution. In this ...paper, a systematic review is conducted on the existing knowledge, collected since 1990, on the link between urban heat island (UHI) and urban pollution island (UPI). Results from 16 countries and 11 Köppen-Geiger climatic zones are perused and compared to delineate methodological and experimental trends, geographical dependencies and research gaps. Detailed content analysis is conducted according to five prominent topics: i) the role of UHI on temperature-dependent chemistry, ii) the daytime/nighttime variability in the UHI-UPI interaction, iii) the role of urban geomorphic types, forms and growth schemes, iv) future trends and v) primary and secondary effects of UHI mitigation on urban air quality. Different approaches and observations are eventually harmonized to outline opportunities and challenges towards the disentanglement and/or the two-way mitigation of both phenomena. This will help governments and urban planners to deliver coping strategies and precautions towards a more salutogenic urban design.
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•30 years of knowledge on the link between urban heat and pollution islands are revised.•Results from 16 countries and 11 climatic zones are collected and analyzed.•Geographical dependencies, methodological and experimental trends are compared.•Five prominent aspects related to chemistry, meteorology and urbanism are covered.•Major findings, areas of debate and outstanding research questions are identified.
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Daytime radiative cooling is regarded as the gold promise of future sustainable building energy systems and a breakthrough in the fight against local climate change. Despite the ...fervid research interest, most literature reports exceptional theoretical performances under ideal, desert-like conditions, but overlooks the cooling impairment that occurs under low atmospheric transparency (cloudy, humid, polluted conditions) and reduced sky access (packed urban contexts). Power recovery and stabilization call for decoupling of incoming and outgoing radiation at equal wavelengths. Enhanced directionality and high-contrast, broadband asymmetric transmission have been recently proposed to expand the applicability of radiative coolers over a wider spectrum of climates, weathers and terrains. This review offers itself as a first, timely synthesis of the current technological arena. Physical principles, materials and designs, collected from a variety of applicative fields, are detailed and discussed in terms of performance and feasibility, to inspire the transition into sustainable building cooling, worldwide. Major grey areas and serious concerns on potential violations of the 2nd law of thermodynamics reinforce the need for experimental demonstrations in future research.
•Next-generation radiative coolers require dynamic emissivity modulation.•Several modulation strategies are revised in this paper from different research fields.•Designs, materials, fabrication ...techniques and modulation performances are compared.•Most effective strategies and underexplored, yet promising, pathways are delineated.
Passive daytime radiative cooling represents one of the boldest answers to tackle the future cooling needs of the built environment and to mitigate urban heat island effects. Recent developments in the field targeted sub-ambience with several successful examples. On the other side, heating demands may get exacerbated unless effective countermeasures against overcooling are identified, especially in wintertime or heating-dominated climates. This review aims at collecting state-of-the-art technologies and techniques to dynamically control the heat transfer to and from the radiative emitter and ultimately modulate its cooling capacity. Potential solutions are selected from different applicative fields, including spacecraft thermal control, thermal camouflage and electronics. Environmentally-responsive solutions are analyzed in depth given their perfect match with radiative cooling design requirements. Among them, VO2-tuned Fabry-Perot resonators are given particular emphasis, owing to their proven applicability. Active solutions are presented for completeness, but in less detail. Underlying principles, structural composition and experimental/simulated results are detailed and discussed to identify prominent pathways towards technically and economically effective integration in the built environment.
•Environmental parameters triggering users’ actions on windows were assessed.•An automatic system for windows opening was developed to achieve IEQ in a classroom.•The system was driven by an adjusted ...version of Humphreys’ adaptive algorithm.•The algorithm was adapted including CO2 concentration and reducing the dead band.•The system guarantees low CO2 levels, thermal comfort and users satisfaction.
Thermal comfort and indoor air quality in school classrooms are essential requirements to promote students’ productivity and reduce health symptoms. This paper presents the development of an automatic system for window openings, based on thermal comfort and indoor air quality correlations. The research was carried out in two adjacent classrooms. The initial phase aimed at assessing environmental conditions in classrooms, testing objective and subjective comfort models and establishing trigger parameters for window opening events; the second phase regarded the implementation of an adaptive control algorithm in an automatic system piloting windows with the aim of maintaining a satisfactory environment both in terms of IAQ and thermal comfort. The main results show that: (1) the IAQ is a relevant issue in school classrooms, because students usually suffer high CO2 levels; (2) the stronger driving force for undertaking adaptive actions is thermal comfort, while the need to improve the air quality is a secondary constraint; (3) the mechanized system ensures a good quality in terms of IAQ, thermal comfort and users’ satisfaction.
•A novel prototype of water nebulizers was optimized to mitigate the urban climate.•Climate adaptive features were imparted by implementing a fuzzy controller.•Fuzzy and on-off logics were monitored ...and compared in two different urban settings.•The energy saving touched 70% with ambient conditions very close to neutrality.•The cooling capacity reached −7.5 °C mostly dependent on wind.
Several mature urban climate mitigation technologies have been proposed to date. What mostly hinders their wide implementation is that their efficiency heavily depends on the local microclimatic specificities, since they cannot self-adjust to the environmental changes. This study aims at investigating benefits and impacts of smart logics applied to outdoor cooling, by field testing a web of nebulizers coupled to a bespoke fuzzy controller piloting the pump. The cooling action was tweaked as convenient to maintain comfortable conditions and to avoid energy wastage whenever unneeded. To the best of the authors’ knowledge, this is the first application of fuzzy logic to water spraying systems (or to any other controllable urban climate mitigation technology) targeting comfort and energy optimization. The prototype was field monitored in comparison with the conventional on-off control, in two Italian urban contexts (Cfa and Csa climatic zones) over 15 days in the hottest months of the year. The cooling and humidification action was thoroughly characterized by mapping both the horizontal and vertical profiles and by applying advanced Artificial Intelligence techniques to spot the main environmental drivers. The maximum cooling (measured between the sprayed area and an undisturbed reference) touched 7.5 °C and 6.14 °C in the two locations, respectively. The energy saving achieved under fuzzy control versus the temporized control, was spectacularly high in the wetter and windier location with an average of −51.2% and a maximum of −67.5%. The comfort benefit was also substantial: the temperature never deviated from neutrality by more than ±2 °C, whereas with the on–off, this threshold was surpassed between the 14% and the 20% of the time by even more than 5 °C. The results suggest that smartly controlled nebulization is an energy-efficient and comfort-effective strategy to counteract urban overheating. Furthermore, solar-powered solutions are well suited as proved by the preliminary design estimation we included.
•Existing knowledge on outdoor mist cooling was first-time systematically reviewed.•The potential for comfort enhancement and energy saving was comparatively assessed.•Climate sensitivity, ...technological options and driving forces were discussed.•Numerical and experimental methodologies were critically analyzed.•Design guidelines were inferred by merging dominant trends and results.
For the first time, a systematic review was conducted on mist spraying systems used for outdoor cooling by perusing twenty years of publications from 12 countries and 7 climatic zones. The twofold aim was to emphasize both the potential against local overheating in a variety of climatic contexts and the extreme heterogeneity in terms of investigation techniques and performance metrics that hinder the construction of a cohesive body of knowledge. In addition to statistics and patterns, data were screened to outline theoretical and methodological trends and gaps and to detect geographic biases and climate dependencies. Indeed, each study was thoroughly described and comparatively discussed according to (i) the investigational method (purely experimental studies, purely numerical studies and those combining field tests with simulations), (ii) the results in terms of cooling, humidification and comfort, also in relation to the adopted performance metrics (iii) the design novelty. Most relevant approaches and findings were discussed and compared to identify governing variables, optimized configurations, unchartered solutions and criticalities. Overall, the collected data qualify water spraying as a cost-effective, versatile and high-impact blue mitigator. Opportunities and challenges towards an informed use emerged and will help delineating appropriate guidelines for practitioners involved in town development, to deliver strategies and precautions.
Abstract
Overheated outdoor environments adversely impact urban sustainability and livability. Urban areas are particularly affected by heat waves and global climate change, which is a serious threat ...due to increasing heat stress and thermal risk for residents. The tropical city of Darwin, Australia, for example, is especially susceptible to urban overheating that can kill inhabitants. Here, using a modeling platform supported by detailed measurements of meteorological data, we report the first quantified analysis of the urban microclimate and evaluate the impacts of heat mitigation technologies to decrease the ambient temperature in the city of Darwin. We present a holistic study that quantifies the benefits of city-scale heat mitigation to human health, energy consumption, and peak electricity demand. The best-performing mitigation scenario, which combines cool materials, shading, and greenery, reduces the peak ambient temperature by 2.7 °C and consequently decreases the peak electricity demand and the total annual cooling load by 2% and 7.2%, respectively. Further, the proposed heat mitigation approach can save 9.66 excess deaths per year per 100,000 people within the Darwin urban health district. Our results confirm the technological possibilities for urban heat mitigation, which serves as a strategy for mitigating the severity of cumulative threats to urban sustainability.
Abstract
This paper sheds light on the importance of evaluating climate justice concerns when forging climate-neutral strategies at the city level. Climate justice can be a useful policy lever to ...develop measures that promote simultaneously greenhouse gas emissions reductions and their social justice dimension, thus reducing the risk of adverse impacts. As a result, evaluating policymakers’ awareness of (i) recognition (ii) distributive (iii) procedural, and (iv) intergenerational issues about the transition to climate neutrality might help identify where to intervene to ensure that decisions towards more sustainable urban futures are born justly and equitably. This study uses data from the European Mission on 100 Climate Neutral and Smart Cities by 2030 and a principal component analysis to build an index of climate justice awareness. It then identifies control factors behind different levels of climate justice awareness. The empirical analysis suggests that the more cities are engaged in climate efforts, the more they implement these efforts considering also the social justice dimension. It also reveals that the geographical location and the relationship with higher levels of governance contribute to shape the heterogeneity in a just-considerate climate action by virtue of different governance structures, historical legacies, and economic, cultural, and political characteristics. Overall, the analysis unveils that the availability of governmental support in capacity building and financial advisory services, and the breadth of the city’s legal powers across different fields of action are positively related to justice awareness. Conversely, the perception of favourable geo-climatic conditions is negatively correlated. These relationships can be read as assistance needs that cities perceive in their pathway to just climate neutrality and highlight where future efforts in research and policy-making should focus in the following years to pave the way to a just transition.
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