How Blackouts during Heat Waves Amplify Mortality and Morbidity Risk.

The recent concurrence of electrical grid failure events in time with extreme temperatures is compounding the population health risks of extreme weather episodes. Here, we combine simulated heat exposure data during historical heat wave events in three large U.S. cities to assess the degree to which heat-related mortality and morbidity change in response to a concurrent electrical grid failure event. We develop a novel approach to estimating individually experienced temperature to approximate how personal-level heat exposure changes on an hourly basis, accounting for both outdoor and building-interior exposures. We find the concurrence of a multiday blackout event with heat wave conditions to more than double the estimated rate of heat-related mortality across all three cities, and to require medical attention for between 3% (Atlanta) and more than 50% (Phoenix) of the total urban population in present and future time periods. Our results highlight the need for enhanced electrical grid resilience and support a more spatially expansive use of tree canopy and high albedo roofing materials to lessen heat exposures during compound climate and infrastructure failure events.

A microscale three-dimensional model of urban outdoor thermal exposure (TUF-Pedestrian).

Urban street design choices relating to tree planting, building height and spacing, ground cover, and building façade properties impact outdoor thermal exposure. However, existing tools to simulate heat exposure have limitations with regard to optimization of street design for pedestrian cooling. A microscale three-dimensional (3D) urban radiation and energy balance model, Temperatures of Urban Facets for Pedestrians (TUF-Pedestrian), was developed to simulate pedestrian radiation exposure and study heat-reducing interventions such as urban tree planting and modifications to building and paving materials. TUF-Pedestrian simulates the spatial distribution of radiation and surface temperature impacts of trees and buildings on their surroundings at the sub-facet scale. In addition, radiation absorption by a three-dimensional pedestrian is considered, permitting calculation of a summary metric of human radiation exposure: the mean radiant temperature (TMRT). TUF-Pedestrian is evaluated against a unique 24-h observational dataset acquired using a mobile human-biometeorological station, MaRTy, in an urban canyon with trees on the Arizona State University Tempe campus (USA). Model evaluation demonstrates that TUF-Pedestrian accurately simulates both incoming directional radiative fluxes and TMRT in an urban environment with and without tree cover. Model sensitivity simulations demonstrate how modelled TMRT and directional radiative fluxes respond to increased building height (ΔTMRT reaching -32 °C when pedestrian becomes shaded), added tree cover (ΔTMRT approaching -20 °C for 8 m trees with leaf area density of 0.5 m2 m-3), and increased street albedo (ΔTMRT reaching + 6 °C for a 0.21 increase in pavement albedo). Sensitivity results agree with findings from previous studies and demonstrate the potential utility of TUF-Pedestrian as a tool to optimize street design for pedestrian heat exposure reduction.

Compound Climate and Infrastructure Events: How Electrical Grid Failure Alters Heat Wave Risk.

The potential for critical infrastructure failures during extreme weather events is rising. Major electrical grid failure or "blackout" events in the United States, those with a duration of at least 1 h and impacting 50,000 or more utility customers, increased by more than 60% over the most recent 5 year reporting period. When such blackout events coincide in time with heat wave conditions, population exposures to extreme heat both outside and within buildings can reach dangerously high levels as mechanical air conditioning systems become inoperable. Here, we combine the Weather Research and Forecasting regional climate model with an advanced building energy model to simulate building-interior temperatures in response to concurrent heat wave and blackout conditions for more than 2.8 million residents across Atlanta, Georgia; Detroit, Michigan; and Phoenix, Arizona. Study results find simulated compound heat wave and grid failure events of recent intensity and duration to expose between 68 and 100% of the urban population to an elevated risk of heat exhaustion and/or heat stroke.

PanoMRT: Panoramic infrared thermography to model human thermal exposure and comfort.

As summer heat waves become the new normal worldwide, modeling human thermal exposure and comfort to assess and mitigate urban overheating is crucial to uphold livability in cities. We introduce PanoMRT, an open source human-biometeorological model to calculate Mean Radiant Temperature (TMRT), Physiologically Equivalent Temperature (PET), and the Universal Thermal Climate Index (UTCI) from thermal equirectangular 360° panoramas and standard weather information (air temperature, relative humidity, wind speed). We validated the model for hot, dry, clear summer days in Tempe, Arizona, USA with in-situ observations using a FLIR Duo Pro R thermal camera on a rotating arm and the mobile human-biometeorological instrument platform MaRTy. We observed and modeled TMRT and thermal comfort for 19 sites with varying ground cover (grass, concrete, asphalt), sky view factor, exposure (sun, shade), and shade type (engineered, natural) six times per day. PanoMRT performed well with a Root Mean Square Error (RMSE) of 4.1 °C for TMRT, 2.6 °C for PET, and 1.2 °C for UTCI, meeting the accuracy requirement of ±5 °C set in the ISO 7726 standard for heat and cold stress studies. RayMan reference model runs without measured surface temperature forcing reveal that accurate longwave radiative flux estimations are crucial to meet the ±5 °C threshold, particularly for shaded locations and during midday when surface temperatures peak and longwave modeling errors are largest. This study demonstrates the importance of spatially resolved 3D surface temperature data for thermal exposure and comfort modeling to capture complex longwave radiation exposure patterns resulting from heterogeneity in built configuration and material radiative and thermal properties in the built environment.

Targeted implementation of cool roofs for equitable urban adaptation to extreme heat.

Cities are facing the twin pressures of greenhouse gas driven climatic warming and locally induced urban heating. These pressures are threatening populations that are sensitive to extreme heat due to sociodemographic factors including economic means. Heat-reducing infrastructure adaptation measures such as reflective "cool" materials can reduce urban temperatures. Here we examine the needs-based equity implications associated with heat-reducing cool roofing in Maricopa County, Arizona through application of high-resolution urban-atmospheric simulations. We simulate heatwave conditions and evaluate the air temperature reduction arising from uniform cool roof implementation (i.e., the entire urbanized county), and contrast results against simulated cooling impacts of needs-based targeted cool roof implementation in sociodemographically heat sensitive areas. We find that installing cool roofs uniformly, rather than in a targeted fashion, provides on average 0.66 °C reduction in the highest heat sensitivity area and 0.39 °C temperature reduction in the lowest heat sensitivity area due in part to a higher roof area density in the heat sensitive area. Targeting cool roof implementation yields 0.45 °C cooling in the most sensitive areas compared to 0.22 °C cooling in the least sensitive areas, meaning that needs-based targeted cool roofs in high sensitivity areas provide more relief than cool roofs targeted at low sensitivity areas, thus providing more cooling where it is most needed. Needs-based targeted implementation has the dual benefits of concurrently producing more than twice as much cooling and reducing heat exposure for the largest absolute number of individuals in the densely populated, highly heat sensitive areas. Targeting cool roof implementation to high heat sensitivity areas, however, does not achieve thermally equal temperatures in Maricopa County because the high sensitivity areas were substantially warmer than low sensitivity areas prior to implementation. This study illustrates the utility of a new "Targeted Urban Heat Adaptation" (TUHA) framework to assess needs-based equity implications of heat-reducing strategies and underscores its importance by examining the impacts of cooling interventions across sociodemographically heterogeneous urban environments.

Impact of Ontario's Harmonized Heat Warning and Information System on emergency department visits for heat-related illness in Ontario, Canada: a population-based time series analysis.

INTERVENTION: Ontario's Harmonized Heat Warning and Information System (HWIS) brings harmonized, regional heat warnings and standard heat-health messaging to provincial public health units prior to periods of extreme heat. RESEARCH QUESTION: Was implementation of the harmonized HWIS in May 2016 associated with a reduction in emergency department (ED) visits for heat-related illness in urban locations across Ontario, Canada? METHODS: We conducted a population-based interrupted time series analysis from April 30 to September 30, 2012-2018, using administrative health and outdoor temperature data. We used autoregressive integrated moving average models to examine whether ED rates changed following implementation of the harmonized HWIS, adjusted for maximum daily temperature. We also examined whether effects differed in heat-vulnerable groups (≥65 years or <18 years, those with comorbidities, those with a recent history of homelessness), and by heat warning region. RESULTS: Over the study period, heat alerts became more frequent in urban areas (6 events triggered between 2013 and 2015 and 14 events between 2016 and 2018 in Toronto, for example). The mean rate of ED visits was 47.5 per 100,000 Ontarians (range 39.7-60.1) per 2-week study interval, with peaks from June to July each year. ED rates were particularly high in those with a recent history of homelessness (mean rate 337.0 per 100,000). Although rates appeared to decline following implementation of HWIS in some subpopulations, the change was not statistically significant at a population level (rate 0.04, 95% CI: -0.03 to 0.1, p=0.278). CONCLUSION: In urban areas across Ontario, ED encounters for heat-related illness may have declined in some subpopulations following HWIS, but the change was not statistically significant. Efforts to continually improve HWIS processes are important given our changing Canadian climate.

RéSUMé: INTERVENTION: Le système d'avertissement et d'information de chaleur harmonisé pour l'Ontario (SAIC) transmet des alertes régionales harmonisées sur la chaleur et des messages normalisés sur la chaleur et la santé aux unités de santé publique provinciales, avant les périodes de chaleur extrême. QUESTION DE RECHERCHE: La mise en œuvre du SAIC harmonisé en mai 2016 a-t-elle été associée à une réduction des visites aux urgences pour des maladies liées à la chaleur dans les zones urbaines de l'Ontario, au Canada? MéTHODES: Nous avons effectué une analyse de séries chronologiques interrompues basée sur la population du 30 avril au 30 septembre, 2012­2018, en utilisant des données administratives sur la santé et la température extérieure. Nous avons utilisé des modèles autorégressifs à moyenne mobile intégrée pour examiner si le taux de visites des urgences avait changé après la mise en œuvre du SAIC harmonisé, ajusté pour tenir compte de la température maximale quotidienne. Nous avons également examiné si les effets différaient pour les groupes vulnérables à la chaleur (≥65 ans ou <18 ans, les personnes ayant des comorbidités et les personnes avec un passé récent de sans-abri), et selon la région d'alerte de chaleur. RéSULTATS: Au cours de la période d'étude, les alertes de chaleur sont devenues plus fréquentes dans les zones urbaines (6 événements déclenchés entre 2013 et 2015 et 14 événements déclenchés entre 2016 et 2018 à Toronto, par exemple). Le taux moyen de visites aux urgences était de 47,5 pour 100 000 Ontariens (de 39,7 à 60,1) par intervalle de deux semaines, avec des pointes chaque année en juin et juillet. Le taux de visites aux urgences était particulièrement élevé chez les personnes avec un passé récent de sans-abri (taux moyen de 337,0 pour 100 000). Malgré une baisse du taux après la mise en œuvre du SAIC dans certaines sous-populations, le changement n'était pas statistiquement significatif au niveau de la population (taux 0,04, IC 95 % : -0,03 à 0,1, p=0,278). CONCLUSION: Dans les zones urbaines de l'Ontario, le nombre de consultations aux urgences pour des maladies liées à la chaleur a diminué dans certaines sous-populations après la mise en place du SAIC, mais le changement n'était pas statistiquement significatif. Les efforts visant à améliorer continuellement les processus du SAIC sont importants compte tenu de l'évolution du climat canadien.

Evaluating the association between extreme heat and mortality in urban Southwestern Ontario using different temperature data sources.

Urban areas have complex thermal distribution. We examined the association between extreme temperature and mortality in urban Ontario, using two temperature data sources: high-resolution and weather station data. We used distributed lag non-linear Poisson models to examine census division-specific temperature-mortality associations between May and September 2005-2012. We used random-effect multivariate meta-analysis to pool results, adjusted for air pollution and temporal trends, and presented risks at the 99th percentile compared to minimum mortality temperature. As additional analyses, we varied knots, examined associations using different temperature metrics (humidex and minimum temperature), and explored relationships using different referent values (most frequent temperature, 75th percentile of temperature distribution). Weather stations yielded lower temperatures across study months. U-shaped associations between temperature and mortality were observed using both high-resolution and weather station data. Temperature-mortality relationships were not statistically significant; however, weather stations yielded estimates with wider confidence intervals. Similar findings were noted in additional analyses. In urban environmental health studies, high-resolution temperature data is ideal where station observations do not fully capture population exposure or where the magnitude of exposure at a local level is important. If focused upon temperature-mortality associations using time series, either source produces similar temperature-mortality relationships.

Micrometeorological determinants of pedestrian thermal exposure during record-breaking heat in Tempe, Arizona: Introducing the MaRTy observational platform.

We report the first set of urban micrometeorological measurements for assessment of pedestrian thermal exposure during extreme heat in a dry climate. Hourly measurements of air temperature, humidity, wind speed and six-directional shortwave and longwave radiation were recorded with a mobile human-biometeorological station (MaRTy) from 10:00 to 21:00 local time, June 19, 2016, at 22 sites that include diverse microscale urban land cover. Sky view factor (SVF) and 360° pervious and impervious view factors for each location were calculated from six-directional fisheye photographs. Mean radiant temperature (TMRT) was determined using the six-directional method. Three-dimensional radiation budgets were decomposed into directional weighted shortwave and longwave radiation components to create a distinct TMRT profile for each site and determine the main drivers of TMRT and thermal exposure. Air temperature peaked locally at 48.5 °C, with a maximum TMRT of 76.4 °C at 15:00 MST in an east-west building canyon. Longwave radiation measured by laterally-oriented sensors dominated the TMRT budget, suggesting the importance of cooling vertical surfaces adjacent to pedestrians. Lateral shortwave radiation contributions were most spatially and temporally variable across TMRT profiles, reflecting the diverse shade conditions. The largest radiation fluxes contributing to TMRT were particularly sensitive to shade and secondarily to ground cover. Trees reduced afternoon TMRT up to 33.4 °C but exhibited a clear TMRT increase of up to 5 °C after sunset; during daytime, trees generated ground cover-dependent longwave radiant cooling or warming. Replacement of impervious with pervious ground cover cooled TMRT at all measurement times, even under dense tree shade. While recent work has found that adaptation cannot offset projected urban air temperature increases, outdoor thermal exposure depends on additional micrometeorological variables, including shortwave and longwave radiation, indicating the need and the opportunity to create pedestrian spaces that are radiantly cool within the context of future urban heat.

The urban energy balance of a lightweight low-rise neighborhood in Andacollo, Chile.

Worldwide, the majority of rapidly growing neighborhoods are found in the Global South. They often exhibit different building construction and development patterns than the Global North, and urban climate research in many such neighborhoods has to date been sparse. This study presents local-scale observations of net radiation (Q * ) and sensible heat flux (Q H ) from a lightweight low-rise neighborhood in the desert climate of Andacollo, Chile, and compares observations with results from a process-based urban energy-balance model (TUF3D) and a local-scale empirical model (LUMPS) for a 14-day period in autumn 2009. This is a unique neighborhood-climate combination in the urban energy-balance literature, and results show good agreement between observations and models for Q * and Q H . The unmeasured latent heat flux (Q E ) is modeled with an updated version of TUF3D and two versions of LUMPS (a forward and inverse application). Both LUMPS implementations predict slightly higher Q E than TUF3D, which may indicate a bias in LUMPS parameters towards mid-latitude, non-desert climates. Overall, the energy balance is dominated by sensible and storage heat fluxes with mean daytime Bowen ratios of 2.57 (observed Q H /LUMPS Q E )-3.46 (TUF3D). Storage heat flux (ΔQ S ) is modeled with TUF3D, the empirical objective hysteresis model (OHM), and the inverse LUMPS implementation. Agreement between models is generally good; the OHM-predicted diurnal cycle deviates somewhat relative to the other two models, likely because OHM coefficients are not specified for the roof and wall construction materials found in this neighborhood. New facet-scale and local-scale OHM coefficients are developed based on modeled ΔQ S and observed Q * . Coefficients in the empirical models OHM and LUMPS are derived from observations in primarily non-desert climates in European/North American neighborhoods and must be updated as measurements in lightweight low-rise (and other) neighborhoods in various climates become available.