Heat Mitigation Research Articles

Potential drivers of urban green space availability in Latin American cities

AbstractUrban green spaces play a critical role in regulating air temperature, reducing air pollution and enhancing people’s well being. Yet, existing data and research on potential drivers of urban green space availability in Latin America are limited. Here, focusing on 371 large cities in 11 countries in Latin America, we described the total and per capita variability of urban green space, its spatial configuration and green urban parks across the categories of cities’ natural, built and socioeconomic environments. We tested the relative importance of geographic (climate) versus city-level built environment (population, population density, street intersection density) and socioeconomic (city gross domestic product per capita, unemployment, education) drivers in explaining urban green space availability. We found a high level of heterogeneity in green space quantity across cities and across categories of cities’ environments. Relative to other city factors, climate zone had the largest influence in explaining the quantity of green space, whereas education, street intersection density and population density were the most important drivers of urban park availability. The significance of climate for green space availability, combined with the inequitable quantity of green space, indicates that cities have differing capacities to implement nature-based solutions for heat mitigation and health promotion.

A scaling law for predicting urban trees canopy cooling efficiency

Urban heat mitigation is a pressing concern for cities. Intense urban heat poses a threat to human health and urban sustainability. Tree planting is one of the most widely employed nature-based heat mitigation methods worldwide. Therefore, city policy makers require knowledge of how much temperature will be reduced by increasing urban tree canopy (UTC). Cooling efficiency (CE), which was been proposed to quantify the magnitude of temperature reduction associated with a 1% increase in UTC, has been primarily investigated at smaller scales previously. However, such small-scale results cannot be used to develop policy at the whole-city scale. This study developed a method that reveals the scaling relations of CE so as to predict its effects at the city scale. CE was found to follow the form of a power law as spatial scale increased from the small analytical units through intermediate size units up to the extent of a whole city. The power law form appeared consistently across cities with different climate backgrounds during summer daylight hours. Furthermore, the power law form was robust within cities under different summer weather conditions. The power-law scaling approach can thus be used to predict CE at the whole-city scale, providing a useful tool for managers to set UTC goals to mitigate extreme urban heat.

Modeling Heat Mitigation in Hollow-Core Gas Fiber Lasers With Gas Flow

Modeling Heat Mitigation in Hollow-Core Gas Fiber Lasers With Gas Flow

Heat mitigation in basal compacted clay liners in municipal solid waste landfills.

In municipal solid waste (MSW) landfills, biodegradation of the organic MSW fraction results in elevated waste and basal liner temperatures which have the potential to cause the clay component of the basal liner to experience severe moisture loss over time and eventually undergo desiccation cracking. Cracking of the basal liner's clay component would result in an uncontrolled release of contaminants into the surrounding environment and ultimately give rise to a variety of major environmental concerns. Accordingly, this study examined the variation of temperature-moisture profiles along the depth of a compacted clay liner (CCL) exposed to different constant elevated waste temperatures (CETs) in the absence and presence of two heat reduction techniques, respectively. Rockwool insulation layers with varying thicknesses and galvanized steel cooling pipes with varying flowrates were introduced separately as the two heat reduction techniques. Introduction of both techniques led to a significant attenuation of the temperature rise and desiccation experienced by the CCL in the face of different CETs. An increase in rockwool thickness increments led to a progressive reduction of CCL temperature, while an increase in flow rate under turbulent condition did not have a significant influence on the temperature and desiccation reduction of the CCL. Nevertheless, the present study certainly highlights the potential of the two proposed heat reduction techniques to minimize desiccation and consequently increase the service life of CCLs exposed to different elevated temperatures in MSW landfills.

Integrative Remote Sensing Approaches Using Generative Adversarial Networks for Urban Heat Island Analysis and Mitigation

Integrative Remote Sensing Approaches Using Generative Adversarial Networks for Urban Heat Island Analysis and Mitigation

Highly inhomogeneous interactions between background climate and urban warming across typical local climate zones in heatwave and non-heatwave days

Abstract Urban heat island (UHI) in conjunction with heatwave (HW) leads to exacerbation of thermal stress in urban areas. Prior research on UHI and HW has predominantly concentrated on examining the thermal conditions at the surface and near-surface, with few investigations extending to the radiative and dynamical interactions of UHI and HW, particularly with a focus on the inhomogeneities across local climate zones (LCZs). Here, we analyse the temperature disparity between HW and non-HW conditions across LCZs in the Sydney area by quantifying the contributions of individual radiative and dynamical processes using the coupled surface-atmosphere climate feedback-response analysis method (CFRAM). Three moist HW events in 2017, 2019, and 2020 are simulated using the Weather Research and Forecasting (WRF) model coupled with the single-layer urban canopy model (SLUCM). It is found that the maximum surface and 900 hPa temperature difference between HW and non-HW days may reach up to 10 K, with the increased net solar radiation during HWs being comparable to the typical level of anthropogenic heat flux in urban areas. It is also found that the reduction of clouds, the presence of vapour, and the increase of sensible heat contribute to the warming effect to various degrees, with the contribution of clouds being the most dominant. Conversely, the generation of dry convection and the increase of latent heat flux lead to cooling effects, with the latter being more dominant and capable of causing up to 10 K surface temperature difference between LCZ1 (compact high-rise) and LCZ9 (sparsely built). The differences in the contributions of climate feedback processes across different LCZs become more evident during more severe and humid HWs. These findings underscore the necessity of implementing LCZ-tailored heat mitigation strategies.

Physiological and behavioral indicators of water buffaloes with access to heat mitigation resources in a grazing system during the hot season in the subtropics

Water buffaloes are increasingly being raised in similar way to dairy cows, in grazing systems frequently deprived of shade and water for immersion. This study aimed to evaluate the effects of different heat mitigation resources, 1) only shade and 2) shade plus water for immersion, on the behavioral repertoire and physiological characteristics of female grazing buffaloes in the subtropics during the hot season. Twenty buffaloes (Bubalus bubalis), including calves, heifers and non-lactating cows were allocated throughout the hot season (from December 2021 to April 2022) in a grazing system with two different heat mitigation resources (treatments): only shade (SH) and shade plus water for immersion (SHW). Diurnal behavioral repertoire was recorded every 15 days, individually and focally, at every 5 minutes for 12 hours per day. Heart rate (HR; beats/min), respiration rate (RR; breaths/min), rectal temperature (RT; °C) and panting score were also measured. Buffaloes reduced grazing time especially with THI above 75. Buffaloes at SHW spent more time grazing and lying than SH buffaloes (P < 0.05). Cows and heifers had higher ruminating (P < 0.05) and standing time (P < 0.05) compared with calves. Physiological variables did not differ (P > 0.05) between treatments (SH vs. SHW) and were positively correlated with air temperature and THI (P < 0.05). HR was higher for heifers (59.6) and calves (63.5) than for cows (53.3; P < 0.05). RT tended to be higher for heifers (38.4) and calves (38.3) than for cows (38.1; 0.05 < P < 0.10). However, respiration rate did not differ across buffalo categories (P > 0.05). Panting behavior was not reported throughout the observation days (panting score = 0). When both heat mitigation resources, shade and water for immersion were available, buffaloes preferred water for immersion to mitigate the effects of heat stress. Regardless animal category, buffaloes were able to maintain physiological variables within the normal range, indicating that providing shade and/or water for immersion, as environmental enrichment resources for thermoregulation, is suitable for heat stress mitigation in water buffaloes throughout the hot season in the subtropics.

Radiometric characterization of daytime luminescent materials directly under the solar illumination

The materials efficiently emitting photoluminescence (PL) under solar irradiation could find broad applications in passive radiative cooling of buildings, urban heat mitigation, and solar energy harvesting. In this work, we discuss the limitations of common laboratory characterization of such materials (using tunable light sources or solar simulators) and propose a methodology for direct outdoor characterization of PL efficiency under full solar irradiation. A simple, portable radiometry setup with an integrating sphere is described, and its capability of rapid determination of the spectral distribution of the absorbed and emitted power, as well as the overall PL power efficiency and quantum yield, is demonstrated. By characterization of three materials developed for daytime radiative cooling applications, we reveal deviations of obtained parameters caused by the replacement of the real solar irradiation by that of solar simulators. The described method is suitable for studies of long-term stability, photo-induced degradation, or thermal effects.

Scale effect on the relationship between urban landscape patterns and land surface temperature

Great efforts have been made to examine the linkages between land surface temperature (LST) and urban landscape patterns (ULPs), which, however, focus on a single spatial scale and linear relationships. This study aims to examine the influence range of four key ULP indicators on LST, namely sky view factor (SVF) and three indices of built-up area, greens, and blue spaces. The analyses are conducted at street block level in 38 big cities in China, and leverage a multiscalar approach to investigate change patterns of indicators within multiple buffer zones and identify the buffer distance that yields the greatest influence. Results reveal that (1) the greatest local impacts are produced within 0−150 m buffer zones in most cities for all key ULP metrics; (2) the maximum impacts of most indicators in summer are greater than other seasons; and (3) the influence magnitude of key ULP indicators increase after considering scale effect, and the influence of SVF varies significantly across cities. Results suggest that the consideration of maximum influence ranges of ULP indicators can better explain LST spatial variations. Our findings offer evidence on the local impact of ULPs on LST and contribute to urban design in urban heat mitigation.

A WRF-UCM-SOLWEIG framework for mapping thermal comfort and quantifying urban climate drivers: Advancing spatial and temporal resolutions at city scale

The capability to evaluate city-scale outdoor thermal comfort is crucial for understanding the public's experience of heat stress, especially during heat waves. Nevertheless, there remains a methodological gap in accurately mapping thermal comfort with high spatial and temporal resolutions in complex urban environment and in quantifying the contributions of various urban climate drivers, such as sky view factors and tree canopy fraction. To bridge this gap, we propose an innovative WRF-UCM-SOLWEIG framework that couples a mesoscale model with an urban microclimate model. Specifically, it integrates the Weather Research and Forecasting model coupled with the urban canopy model (WRF-UCM) and the Solar and Longwave Environmental Irradiance Geometry model (SOLWEIG). This framework is then applied to a densely populated tropical city in China, to quantify the impact of urban climate drivers on the Universal Thermal Climate Index (UTCI). The results reveal a significant diurnal variation in the impact of urban morphology. Notably, the most significant drivers affecting daytime UTCI are the impervious surface fraction and the tree canopy fraction, with maximum Pearson's correlation coefficients of 0.80 and -0.70, respectively. These findings suggest that urban heat mitigation strategies should prioritize on reducing impervious surfaces and enhancing shade management, alongside expanding urban forestry measures.

Investigating the efficacy of a fast urban climate model for spatial planning of green and blue spaces for heat mitigation

Problems caused by urban heat have prompted the exploration of urban greenery and blue spaces for heat mitigation. Various numerical models can simulate heat-related processes, but their use as support-tools to urban planners remains underexplored, particularly at the city-scale, due to high computational demand and complexity of such models. This study investigates the spatial relationships between urban heat, urban form and urban green and blue spaces with the fast climate model TARGET (The Air-temperature Response to Green/blue-infrastructure Evaluation Tool), which only requires minimal inputs of standard meteorological data, land cover and building geometry data. Using the City of Zurich as our case study, we: (i) validated the TARGET model against air temperature measurements from private sensor networks, (ii) performed a sensitivity analysis to identify key variables affecting urban heat, and (iii) investigated urban heat relationships with blue-green cover at locations frequented by pedestrians. Presence of urban green and blue spaces across the region shows potential for reducing local air temperatures by up to 5.2 °C (with urban forest). Investigating this relationship at different locations in the city revealed key districts that should potentially be targeted for reduction of pedestrian heat-impacts, due to their high pedestrian traffic, fewer green and blue spaces and high daytime air temperatures. Our results not only provide insights into the cooling effect of different amounts of green and blue features in the urban environment, but also demonstrates the application and integration potential of simplified models like TARGET to support the planning of more liveable future cities.

Surface and canopy urban heat island disparities across 2064 urban clusters in China

The vast majority of urban heat island (UHI) studies are now derived from surface temperatures, substituting for the original air temperature-based definition. The disparities in hourly surface-canopy UHI effects (SUHI, CUHI) and the contrasting mechanisms are currently poorly understood. Here, we use high-resolution hourly LST and air temperature data from 2064 urban clusters in China to estimate SUHI and CUHI intensities and their driving mechanisms during the summer and winter of 2022. Across all urban clusters, we find that SUHI is on average ten times higher than the CUHI in the summer (0.97 VS. 0.09 °C) yet nearly triple that in the winter (0.30 VS. 0.11 °C), with SUHI exceeding CUHI in 91.5 % and 65.7 % of urban clusters, respectively. Seasonal and hourly analyses on SUHI/CUHI confirm typically opposite hysteresis variations (magnitude, peak, and timing of occurrence) and more correlated surface-canopy UHIs patterns during the night. We further demonstrate that SUHI magnitude can be largely explained by biophysical factors, urban attributes, and climate contexts, whereas CUHI interferes with additional constraints linked to ground-air energy transfer and advective dissipation. The improvement of urban greenery aids summer cooling efficiently in equatorial and boreal regions, while albedo measures are relevant in mitigating nocturnal warming in arid regions. Our findings support multiple technologies as ideas for urban three-dimensional UHIs (surface, canopy and boundary) and energy mechanisms, and the urgent need for ambitious urban heat mitigation strategies to minimize future climate change impacts.

Simulating the impact of ventilation corridors for cooling air temperature in local climate zone scheme

Climate change and urbanization are impacting urban microclimates, necessitating careful consideration in urban ventilation planning. However, there remains uncertainty regarding the identification and examination of urban ventilation corridors (VCs), and their mechanisms for urban heat mitigation. This study combined ENVI-met and the least-cost path (LCP) algorithm to simulate the VCs within the local climate zone (LCZ) scheme, with Guangzhou as an example. The results show that (1) VCs constructed using the LCP method are primarily distributed along vegetation and rivers, bypassing high-temperature aggregation in high-density/high-rise building areas; (2) The cooling effect of VCs varies across different LCZs, influenced by factors such as land use, vegetation, building, and topography. (3) In low-density, low-rise LCZs, VCs significantly reduce temperatures by about 0.23°C, while in high-density, high-rise LCZs, the cooling effect is weaker, with a reduction of only around 0.01°C. This study highlights the importance of preserving hydrological system and optimizing green space layout to enhance urban ventilation thus mitigate heat accumulation.

Impact of urban spatial dynamics and blue-green infrastructure on urban heat islands: A case study of Guangzhou using Local Climate Zones and predictive modeling

Amidst mounting concerns regarding health risks associated with excessive carbon emissions, attention has turned to the heat mitigation ability of blue-green infrastructure (BGI). BGI offers heat mitigation through transpiration cooling, effectively countering the urban heat island (UHI) effect while facilitating energy conservation and carbon reduction. This study adopted the InVEST model to assess the spatial pattern of UHI and heat mitigation service based on the Local Climate Zone (LCZ) classification, along with quantifying the energy savings in Guangzhou for 2019. The results revealed that the UHI effect exhibited greater intensity in the southwest built-up area. Compact Lowrise (LCZ-3) and Heavy Industry (LCZ-10) areas demonstrated higher UHI intensity, while Water (LCZ-G) and Dense Trees (LCZ-A) areas showcased the highest heat mitigation index (HMI) and optimal cooling capacities. Three urban development scenarios were devised to simulate the UHI distribution, heat mitigation capacity, and energy savings by 2025, using the CA-Markov model. In comparison to the Baseline scenario, the Environmental Protection scenario showed a modest 3.67 % decrease in the built-up area, but a noteworthy increase in HMI and energy saving, by 21.2 % and 6.6 % respectively. This scenario can serve as a reference pathway for urban energy conservation and sustainable development.

Spatio-Temporal Heterogeneity of the Urban Heat Effect and Its Socio-Ecological Drivers in Yangzhou City, China

Rapid urbanization and land-use changes may affect the intensity of urban heat islands (UHIs). However, research on the eastern Chinese city of Yangzhou is lacking. Using land cover data and the InVest Urban Cooling model, this study evaluated the spatiotemporal heterogeneity of the UHI effect from 1990 to 2020 and its socioecological drivers in Yangzhou City. Landscape pattern indices such as patch area (CA), percentage of landscape (PLAND), number of patches, patch density, and aggregation index were created using Fragstats 4.2 software. Several social indicators, such as gross domestic product (GDP), night-light index, and population density, were considered to explore their correlation with UHI indicators. During the past three decades, rapid urbanization in Yangzhou has intensified the UHI effect, with the cooling capacity (cc park) and heat mitigation index (HMI) decreasing by ~9.6%; however, the mixed air temperature (T air) has increased by 0.14 °C. The main heat island areas are concentrated in southern Yangzhou, including the Hanjiang and Guangling districts, and have expanded over time. T air was positively correlated with GDP, night-light index, and population density. Moreover, for the impervious land use type, cc park and HMI were negatively correlated with CA and PLAND (p &lt; 0.01). This study contributes to a deeper understanding of the dynamics of UHIs and provides valuable insights for policymakers, urban planners, and researchers striving to create sustainable and climate-resilient cities in Yangzhou.

Exploring maladaptive patterns of small-scale green roofs through evaluation in a capacity of heat mitigation: A case study in seoul

Climate change leads to more frequent and intense heat waves, exposing urban populations to extreme heat conditions and significant health risks. Many cities are adopting Nature-based Solutions (NbS) to mitigate urban heat, with green roofs emerging as a widely recognized NbS. Although numerous green roof projects are implemented on a small scale, research on the effectiveness of small-scale green roofs on an urban scale is limited, making it challenging to identify the critical factors for both maladaptation and success. Therefore, we assessed the cooling potential of 18 small-scale green roofs in Seoul, Republic of Korea. This comparative study that adopted a multi-site approach examined the cooling capacity of green roofs to reduce surface temperature and identified characteristics of effective and ineffective green roofs. We utilized a developed difference-in-differences method to improve causal inference, effectively isolating the effects of individual green roofs from background climate change. The multi-site comparative approach and more robust causal inference methods improved our understanding of the effects of small-scale green roofs. The findings of this study indicate that three out of 18 green roofs were statistically significant maladaptation cases with an increase in LST. This evidence can help an urban planner reduce ineffectiveness and enhance effective adaptation practices. Our proposed method is expected to support government projects, especially those with limited budgets, in efficiently managing urban heat and reducing trial and error.

Micro-Urban Heatmapping: A Multi-Modal and Multi-Temporal Data Collection Framework

Monitoring microclimate variables within cities with high resolution and accuracy is crucial for enhancing urban resilience to climate change. Assessing intra-urban characteristics is essential for ensuring satisfactory living standards. This paper presents a comprehensive methodology for studying urban heat islands (UHIs) on a university campus, emphasizing the importance of multi-modal and multi-temporal data collection. The methodology integrates mobile surveys, stationary sensor networks, and drone-based thermal imaging, providing a detailed analysis of temperature variations within urban microenvironments. The preliminary findings confirm the presence of a UHI on the campus and identify several hotspots. This comprehensive approach enhances the accuracy and reliability of UHI assessments, offering a cost-effective, fine-resolution approach that facilitates more effective urban planning and heat mitigation strategies.

The Occupational Heat Exposure-related Symptoms Prevalence and Associated Factors Among Hospitality Industry Kitchen Workers in Ethiopia: Wet Bulb Globe Temperature

BackgroundOccupational heat stress caused by excessive environmental heat gain disrupts thermoregulatory mechanisms and harm workers' health and productivity. Kitchens are known for their thermal risks; however, research on heat stress in kitchen is limited. This study aimed to bridge this knowledge gap by assessing, the prevalence of heat-stress-related symptoms, and associated factors among kitchen workers in Gondar City, Ethiopia. MethodsThis institutional-based cross-sectional study (April to June 2023) evaluated heat stress among hospitality kitchen workers in Ethiopia. Heat exposure was measured using hygrometers. A simple random sample of 605 participants completed a survey and data was exported to Statistical Package for Social Science version 26. To assess strength and direction an adjusted odds ratio with 95% confidence interval (CI) was employed. A p-value of less than 0.05 was utilized to identify significant associations. ResultsOver the last 6 months 67.1% (95% CI: 63.0, 71.1), of the participants reported heat-stress symptoms. Multivariable analysis revealed that age ≥40 years [AOR: 2.28; 95% CI (1.08, 4.82)], high workload [AOR: 1.89; 95% CI (1.04, 3.49)], poor heat mitigation practice [AOR: 2.39; 95% CI (1.58, 3.59), wood fuel [AOR: 2.60; 95% CI (1.54, 4.40)], improper ventilation [AOR: 3.28; 95% CI (1.56, 6.87)], and higher heat index value [AOR: 2.15; 95% CI (1.35, 3.42)] were factors significatly associated with heat stress related symptoms. ConclusionThis study identified a high prevalence of heat–stress-related symptoms among kitchen workers. Mitigation strategies include improved ventilation, cooling, advanced building designs, and heat reduction technologies. Future research should utilize standard heat-stress assessment tools.

Measuring and monitoring tree cover and plant canopy height in Pune city, India

Global datasets often fall short in estimating tree cover areas outside the forest tracts, particularly in urban areas. This limitation poses a challenge for accurately estimating tree cover outside forests (ToF) and understanding their contribution to ecosystem services. In the context of increasing population pressure and unsustainable urbanization in Indian cities, regional-level tree cover and canopy height estimations are crucial for evaluating the impact of ToF on various ecosystem services, including carbon sequestration, climate change adaptation, biodiversity hotspots, groundwater recharge, soil conservation, flood control, urban heat mitigation, and psychological and emotional well-being. This technical note outlines a rapid and cost-effective methodology for assessing tree canopy cover and height, specifically tailored for ToF estimation, offering a valuable tool for addressing these socio-urban environmental challenges and enabling sustainable land use planning.

Prioritizing social vulnerability in urban heat mitigation.

We utilized city-scale simulations to quantitatively compare the diverse urban overheating mitigation strategies, specifically tied to social vulnerability and their cooling efficacies during heatwaves. We enhanced the Weather Research and Forecasting model to encompass the urban tree effect and calculate the Universal Thermal Climate Index for assessing thermal comfort. Taking Houston, Texas, and United States as an example, the study reveals that equitably mitigating urban overheat is achievable by considering the city's demographic composition and physical structure. The study results show that while urban trees may yield less cooling impact (0.27 K of Universal Thermal Climate Index in daytime) relative to cool roofs (0.30 K), the urban trees strategy can emerge as an effective approach for enhancing community resilience in heat stress-related outcomes. Social vulnerability-based heat mitigation was reviewed as vulnerability-weighted daily cumulative heat stress change. The results underscore: (i) importance of considering the community resilience when evaluating heat mitigation impact and (ii) the need to assess planting spaces for urban trees, rooftop areas, and neighborhood vulnerability when designing community-oriented urban overheating mitigation strategies.