Improving Heat-Related Health Outcomes in an Urban Environment with Science-Based Policy

Ground Urban Heat Island: Strengthening the Connection Between Spaceborne Thermal Observations and Urban Heat Risk Management

As urbanization progresses under a changing climate, urban populations face increasing threats from chronically higher heat exposures and more frequent extreme heat events. Understanding the complex urban thermal exposure patterns becomes crucial for effective heat risk management. The spatial advantage of satellite thermal observations positions surface urban heat islands (SUHI) as a primary measure for such applications at the city scale. However, satellite-inherent biases pose considerable uncertainties. To improve the representation of human-relevant heat exposure, this study proposes a simple but effective satellite-based measure- ground urban heat island (GUHI), focusing solely on radiant temperatures from urban ground elements. Leveraging ECOSTRESS land surface temperature product and radiation-based statistical downscaling, diurnally representative GUHIs were evaluated over NYC. The findings reveal that overall GUHI is consistently warmer than SUHI diurnally. However, GUHI exhibits complex spatial contrasts with SUHI, primarily influenced by vegetation coverage. Various indicators associated with urban structures and materials were examined, showing important but dissimilar roles in shaping the spatial dynamics of GUHI and SUHI. This study highlights the value of satellite thermal observations compared to air temperature while addressing uncertainties in widely adopted practices of using them. By improving the depiction of human-related urban heat patterns from Earth observations, this research offers valuable insight and more reliable measures to address the urgent requirements for urban heat risk management globally.

Moving from adaptation capacities to implementing adaptation to extreme heat events in urban areas of the European Union: Introducing the U-ADAPT! research approach

Extreme Heat Events (EHE) are a major concern for many urban areas worldwide and are considered as one of the deadliest natural hazards globally. Climate change and socioeconomic trends (exposure and susceptibility) are expected to exacerbate the risk of urban heat stress. Several urban areas have recently declared a climate emergency and initiated the adaptation process, but progress is still patchy, uncoordinated, and of varied quality. The main constraint is the lack of mechanisms for monitoring and reporting adaptation strategies, not allowing the supervision and evaluation of the adaptation process. The EU-funded project U-ADAPT! (Urban-Adaptation) focuses on the concrete expression of adaptation to evaluate the current implementation and effectiveness of adaptation measures and strategies to reduce Heat Disaster Risk (HDR), moving the emphasis from the study of vulnerability, resilience, and potential adaptation (adaptation capacity) of communities to the actual depth and pace of the past and current adaptation process. In this article, we discuss the theoretical support and design of the project and set the base for next project stages, which ultimately aims to create a unique interdisciplinary framework and a replicable multidimensional indicator on adaptation to EHE that empower European Union citizens to demand a safe and sustainable environment and hold institutions accountable for the adaptation process to current and upcoming risks.

Potential overall heat exposure reduction associated with implementation of heat mitigation strategies in Los Angeles

We analyzed two historical extreme heat events in Los Angeles to explore the potential of increasing vegetative cover and surface solar reflectance (albedo) to reduce total exposure (indoor and outdoor) to dangerously hot conditions. We focus on three population subgroups, the elderly, office workers, and outdoor workers, and explore the extreme case where each subgroup does not have functioning air conditioning in their residences. For each heat event, we conducted atmospheric model simulations for a control case and four mitigation cases with varying levels of increased albedo and vegetation cover. Simultaneously, we conducted building simulations of representative residential buildings that lacked mechanical air conditioning. These simulations factored in both the indirect cooling effects associated with neighborhood implementation of mitigation strategies and the direct effects of high albedo roofing on the individual buildings. From both the atmospheric and building models, we exported hourly values of air temperature and dew point temperature, and used this information in combination with various scenarios of occupant behavior to create profiles of individual heat exposure. We also gathered heat-mortality data for the two heat events and developed a synoptic climatology-based relationship between exposure and excess mortality. This relationship was then applied to the scenarios in which albedo and canopy cover were increased. The results suggest that improvements in indoor thermal conditions are responsible for a sizable portion of the health benefit of large-scale implementation of heat mitigation strategies.

Observational Evidence of Neighborhood Scale Reductions in Air Temperature Associated with Increases in Roof Albedo

The effects of neighborhood-scale land use and land cover (LULC) properties on observed air temperatures are investigated in two regions within Los Angeles County: Central Los Angeles and the San Fernando Valley (SFV). LULC properties of particular interest in this study are albedo and tree fraction. High spatial density meteorological observations are obtained from 76 personal weather-stations. Observed air temperatures were then related to the spatial mean of each LULC parameter within a 500 m radius “neighborhood” of each weather station, using robust regression for each hour of July 2015. For the neighborhoods under investigation, increases in roof albedo are associated with decreases in air temperature, with the strongest sensitivities occurring in the afternoon. Air temperatures at 14:00–15:00 local daylight time are reduced by 0.31 °C and 0.49 °C per 1 MW increase in daily average solar power reflected from roofs per neighborhood in SFV and Central Los Angeles, respectively. Per 0.10 increase in neighborhood average albedo, daily average air temperatures were reduced by 0.25 °C and 1.84 °C. While roof albedo effects on air temperature seem to exceed tree fraction effects during the day in these two regions, increases in tree fraction are associated with reduced air temperatures at night.

The Urban Heat Island: Implications for Health in a Changing Environment

PURPOSE OF REVIEW

The Urban Heat Island (UHI) is a well-studied phenomenon, whereby urban areas are generally warmer than surrounding suburban and rural areas. The most direct effect on health from the UHI is due to heat risk, which is exacerbated in urban areas, particularly during heat waves. However, there may be health benefits from warming during colder months. This review highlights recent attempts to quantitatively estimate the health impacts of the UHI and estimations of the health benefits of UHI mitigation measures.

RECENT FINDINGS

Climate change, increasing urbanisation and an ageing population in much of the world, is likely to increase the risks to health from the UHI, particularly from heat exposure. Studies have shown increased health risks in urban populations compared with rural or suburban populations in hot weather and a disproportionate impact on more vulnerable social groups. Estimations of the impacts of various mitigation techniques suggest that a range of measures could reduce health impacts from heat and bring other benefits to health and wellbeing. The impact of the UHI on heat-related health is significant, although often overlooked, particularly when considering future impacts associated with climate change. Multiple factors should be considered when designing mitigation measures in urban environments in order to maximise health benefits and avoid unintended negative effects.

Biometeorology for cities

Improvements in global sustainability, health, and equity will largely be determined by the extent to which cities are able to become more efficient, hospitable, and productive places. The development and evolution of urban areas has a significant impact on local and regional weather and climate, which subsequently affect people and other organisms that live in and near cities. Biometeorologists, researchers who study the impact of weather and climate on living creatures, are well positioned to help evaluate and anticipate the consequences of urbanization on the biosphere. Motivated by the 60th anniversary of the International Society of Biometeorology, we reviewed articles published in the Society's International Journal of Biometeorology over the period 1974-2017 to understand if and how biometeorologists have directed attention to urban areas. We found that interest in urban areas has rapidly accelerated; urban-oriented articles accounted for more than 20% of all articles published in the journal in the most recent decade. Urban-focused articles in the journal span five themes: measuring urban climate, theoretical foundations and models, human thermal comfort, human morbidity and mortality, and ecosystem impacts. Within these themes, articles published in the journal represent a sizeable share of the total academic literature. More explicit attention from urban biometeorologists publishing in the journal to low- and middle-income countries, indoor environments, animals, and the impacts of climate change on human health would help ensure that the distinctive perspectives of biometeorology reach the places, people, and processes that are the foci of global sustainability, health, and equity goals.