Extreme Heat Days Research Articles

Low-carbon consumption in extreme heat in eastern China: Climate change anxiety as a facilitator or inhibitor?

With the planet warming, extreme heat events are becoming increasingly frequent and hazardous. At the same time, reducing carbon emissions from consumer activities is crucial for addressing global warming. This study aims to explore how extreme heat affects low-carbon consumption behaviors (LCB), leading to a more comprehensive understanding of the relationship between climate change and human behavior. Guided by resource scarcity theory and the general strain theory. The laboratory experiment used the recall paradigm to induce extreme heat experiences (Study 1, n = 198), and we found that extreme heat impacts LCB through climate change anxiety: cognitive climate change anxiety tends to increase low-carbon behaviors, while affective climate change anxiety inhibits low-carbon behaviors. The field experiments conducted on actual extreme heat days with simulated purchasing decision-making methods (Study 2, n = 203) further confirmed the laboratory findings. An inverted U-shaped relationship between climate change anxiety and LCB was also revealed. In summary, the current study reveals the differential impact of cognitive and affective climate anxiety on LCB. This finding provides new insights for understanding the complex psychological mechanisms of extreme climate events on consumer behavior, which could also serve as an operational basis for intervention design and policy making.

Changing climate risks for high-value tree fruit production across the United States

Abstract Climate change poses growing risks to global agriculture including perennial tree fruit such as apples that hold important nutritional, cultural, and economic value. This study quantifies historical trends in climate metrics affecting apple growth, production, and quality, which remain understudied. Utilizing the high-resolution gridMET dataset, we analyzed trends (1979-2022) in several key metrics across the U.S. – cold degree days, chill portions, last day of spring frost, growing degree days (GDD), extreme heat days (daily maximum temperature >34°C), and warm nights (daily minimum temperatures >15°C). We found significant trends across large parts of the U.S. in all metrics, with the spatial patterns consistent with pronounced warming across the western states in summer and winter. Yakima County, WA, Kent County, MI, Wayne County, NY—leading apple-producers—showed significant decreasing trends in cold degree days and increasing trends in GDD and warm fall nights. Yakima county, with over 48,870 acres of apple orchards, showed significant changes in five of the six metrics - earlier last day of spring frost, fewer cold degree days, increasing GDD over the overall growth period, and more extreme heat days and warm nights. These trends could negatively affect apple production by reducing the dormancy period, altering bloom timing, increasing sunburn risk, and diminishing apple appearance and quality. Large parts of the U.S. experience detrimental trends in multiple metrics simultaneously that indicate the potential for compounding negative impacts on the production and quality of apples and other tree fruit, emphasizing the need for developing and adopting adaptation strategies.

Heat Waves and Adverse Health Events Among Dually Eligible Individuals 65 Years and Older

Extensive research has found the detrimental health effects of heat waves. However, a critical gap exists in understanding their association with adverse health events among older dually eligible individuals, who may be particularly susceptible to heat waves. To assess the association between heat waves and adverse health events among dually eligible individuals 65 years and older. This retrospective time-series study assessed the association between heat waves in warm months from 2016 to 2019 and zip code tabulation area (ZCTA)-day level adverse health events. Dually eligible individuals 65 years and older who were continuously enrolled in either a Medicare fee-for-service plan or a Medicare Advantage plan with full Medicaid benefits from May to September in any given year were identified. All ZCTAs in the US with at least 1 dually eligible individual in each study year were included. Data were analyzed from September 2023 to August 2024. Heat waves, defined as 3 or more consecutive extreme heat days (ie, days with a maximum temperature of at least 90 °F [32.2 °C] and in the 97th percentile of daily maximum temperatures for each ZCTA during the study period). Daily counts of heat-related emergency department visits and heat-related hospitalizations for each ZCTA. The study sample included 5 448 499 beneficiaries 65 years and older in 28 404 ZCTAs across 50 states and Washington, DC; the mean (SD) proportion of female beneficiaries and beneficiaries 85 years and older in each ZCTA was 66% (7%) and 20% (8%), respectively. The incidence rate for heat-related emergency department visits was 10% higher during heat wave days compared to non-heat wave days (incidence rate ratio [IRR], 1.10; 95% CI, 1.08-1.12), and the incidence rate of heat-related hospitalizations was 7% higher during heat wave days (IRR, 1.07; 95% CI, 1.04-1.09). There were similar patterns in other adverse health events, including a 4% higher incidence rate of death during heat wave days (IRR, 1.04; 95% CI, 1.01-1.07). The magnitude of these associations varied across some subgroups. For example, the association between heat waves and heat-related emergency department visits was statistically significant only for individuals in 3 of 9 US climate regions: the Northwest, Ohio Valley, and the West. In this time-series study, heat waves were associated with increased adverse health events among dually eligible individuals 65 years and older. Without adaptation strategies to address the health-related impacts of heat, dually eligible individuals are increasingly likely to face adverse outcomes.

Increased Stillbirth Rates and Exposure to Environmental Risk Factors for Stillbirth in Counties with Higher Social Vulnerability: United States, 2015-2018.

Exposure to unfavorable environmental conditions during pregnancy, such as extreme heat and air pollution, has been linked to increased risk of stillbirth, defined as fetal mortality at or after 20 weeks' gestation, however no studies have examined its association with social vulnerability. We examined associations between county-level stillbirth rates, environmental risk factors for stillbirth, and social vulnerability in the United States. This ecologic study linked county-level data from three nationwide datasets on stillbirths (National Vital Statistics System), environmental conditions (North American Land Data Assimilation System and Environmental Protection Agency), and social vulnerability (Centers for Disease Control and Prevention/Agency for Toxic Substances and Disease Registry Social Vulnerability Index). Poisson and negative binomial models were fit to the variables and produced rate ratios to estimate associations among stillbirth rates, environmental risk factors, and social vulnerability. Social vulnerability was positively associated withn stillbirth rates, annual average number of extreme heat days, and ambient concentration of particulate matter ≤ 2.5μm in diameter (PM2.5). The average number of days that ozone and PM2.5 each exceeded regulatory standards were not associated with stillbirth rates or social vulnerability. A positive association between average annual PM2.5 concentration and stillbirth rates was detected; no other significant associations between environmental risk factors and stillbirth rates were observed. We found evidence of associations between social vulnerability and stillbirth rates, and between social vulnerability and environmental risk factors for stillbirth at the county level. Further research could inform understanding of how social vulnerability impacts the relationship between environmental exposures and stillbirth risk.

Projections of Extreme Temperature–Related Deaths in the US

ImportanceExtreme heat in the US is increasing due to climate change, while extreme cold is projected to decline. Understanding how extreme temperature along with demographic changes will affect population health is important for devising policies to mitigate the health outcome of climate change.ObjectiveTo assess the burden of extreme temperature–related deaths in the contiguous US currently (2008-2019) and estimate the burden in the mid–21st century (2036-2065).Design, Setting, and ParticipantsThis cross-sectional study used historical (1979-2000) daily mean temperatures to calculate monthly extreme heat (>97.5th percentile value) and extreme cold days (<2.5th percentile value) for all contiguous US counties for 2008 to 2019 (current period). Temperature projections from 20 climate models and county population projections were used to estimate extreme temperature–related deaths for 2036 to 2065 (mid–21st century period). Data were analyzed from November 2023 to July 2024.ExposureCurrent monthly frequency of extreme heat days and projected mid–21st century frequency using 2 greenhouse gas emissions scenarios: Shared Socioeconomic Pathway (SSP)2-4.5, representing socioeconomic development with a lower emissions increase, and SSP5-8.5, representing higher emissions increase.Main Outcomes and MeasuresMean annual estimated number of extreme temperature–related excess deaths. Poisson regression model with county, month, and year fixed effects was used to estimate the association between extreme temperature and monthly all-cause mortality for older adults (aged ≥65 years) and younger adults (aged 18-64 years).ResultsAcross the contiguous US, extreme temperature days were associated with 8248.6 (95% CI, 4242.6-12 254.6) deaths annually in the current period and with 19 348.7 (95% CI, 11 388.7-27 308.6) projected deaths in the SSP2-4.5 scenario and 26 574.0 (95% CI, 15 408.0-37 740.1) in the SSP5-8.5 scenario. The mortality data included 30 924 133 decedents, of whom 15 573 699 were males (50.4%), with 6.3% of Hispanic ethnicity, 11.5% of non-Hispanic Black race, and 79.3% of non-Hispanic White race. Non-Hispanic Black adults (278.2%; 95% CI, 158.9%-397.5%) and Hispanic adults (537.5%; 95% CI, 261.6%-813.4%) were projected to have greater increases in extreme temperature–related deaths from the current period to the mid–21st century period compared with non-Hispanic White adults (70.8%; 95% CI, −5.8% to 147.3%).Conclusions and RelevanceThis cross-sectional study found that extreme temperature–related deaths in the contiguous US were projected to increase substantially by mid–21st century, with certain populations, such as non-Hispanic Black and Hispanic adults, projected to disproportionately experience this increase. The results point to the need to mitigate the adverse outcome of extreme temperatures for population health.

The effect of extreme temperatures on evictions

Using data on evictions in the United States, we estimate the relationship between temperature and eviction filings. We find that extreme heat days result in a statistically significant increase in filings, while extreme cold days do not have the same relationship. To explain these findings, we show that residential energy expenditures are more sensitive to extreme heat than extreme cold, and that energy assistance programs in the United States prioritize funding for heating rather than cooling. These findings suggest that relative to today, future climate change scenarios with more hot days and fewer cold days will increase eviction filings without other policy or private adaptation.

Extreme Heat, Functional Disability, and Social Isolation: Risk Disparity Among Older Adults.

This study examines how functional disability worsens among older adults exposed to extreme heat, particularly those socially isolated. Analyzing data from over 35,000 older adults aged 50 or older from the Health and Retirement Study from 1996-2018, this study found that more frequent exposure to extreme heat is associated with an increase in the number of instrumental activities of daily living (IADL) that older adults find difficulty in performing over time. This heat-related disability progression is greater among those living alone and not working. However, findings indicate that maintaining contact with children and receiving higher levels of support from friends can alleviate the risk of IADL disability progression amidst extreme heat days for older adults with limited social relationships at home and work. By examining various aspects of social isolation and their nuanced effects, this study underscores the need for social support and assistance for older adults during extreme heat.

Impacts of Local Circulations on Ozone Pollution in the New York Metropolitan Area: Evidence From Three Summers of Observations

AbstractElevated surface ozone levels are often detected in the New York metropolitan area during summertime. Moreover, surface ozone in this region exhibits sharp spatial gradients and distinctive diurnal cycles under the influence of complex boundary layer circulations induced by the intricate coastal geometry. This study examines how surface ozone is impacted by local circulations spatially and temporally under different temperature scenarios (all summer days, hot summer days, and extreme heat days) with the help of cluster‐based meteorological conditions during the summertime of 2017–2019. The most polluted days are found to be highly associated with hot sea breeze days with weak background flow. When sea breeze development in the New York Bight is delayed and its penetration north is intercepted by the dominant westerlies during hot summer days, daily maximum 8‐hr average ozone (DMA8) in some ozone hot spots of New York City (NYC) and the south shore of Connecticut (CT) typically drops 9–10 ppb under comparable temperature levels. The average regional decrease of DMA8 for NYC and coastal CT is 6.7 and 8.3 ppb, respectively. Furthermore, we conclude that a change in early morning meridional wind direction is the most critical meteorological characteristic in controlling sea breeze onset type and helping modulate ozone exceedances in the region during extreme hot days when ozone exceedances are expected to be very common. The conclusion is further demonstrated with two case studies during the Long Island Sound Tropospheric Ozone Study 2018 field campaign.

Generative design of walkable urban cool spots using a novel heuristic GAN×GAN approach

Enhancing pedestrian-level outdoor thermal comfort (OTC) and walkability in urban environments is vital for mitigating thermal risks induced by global warming. This study introduces walkable urban cool spots (WUCS), a novel concept which incorporates pedestrian walkability into the design of thermally comfortable urban street blocks. The methodology combines OTC simulation, pedestrian walkability analyses, and surrogate models based on integrated generative adversarial networks (GAN×GAN)-enhanced genetic generative design (GGD) approach. And maximize the design metrics of WUCS through the multi objective optimization algorithm in GGD. The method is tested in To Kwa Wan, an urban renewal area in Hong Kong. Results demonstrate that it can efficiently identify high-performing WUCS solutions, with proportion of WUCS areas increasing from 53.3 % to 74 %, and the number of walkable urban cool spots increasing by 51 %. The average universal thermal climate index (UTCI) in high walkability areas decreasing from 31.7 °C to 30.5 °C, and total average UTCI during extreme heat days dropping from 31.73 °C to 31.22 °C. This research thus contributes an efficient design tool for enhancing both pedestrian-level OTC and walkability in urban environments.

Performance Under Fire: Older Adult Cognitive Risks and Protections Under Heat Strain.

Although extreme heat events disproportionately affect older adults and the importance of cognition is known, research examining older adult cognition under heat stress is limited. This study examines the relationship between risk/protective factors and heat strain on older adult cognition, employing a social-ecological model. Retrieved from the 1996-2016 waves of the Health and Retirement Study, our study used older adults aged 50 and older and their spouses residing in the United States. Individual-fixed effects models estimated changes in cognition as measured by fluid and crystallized intelligence scores in response to extreme heat days. This study further estimated interactions of extreme heat with protective/risk factors for cognition (i.e., education, physical activity, social engagement, and genetic risk for Alzheimer's disease). Our results demonstrated that extreme heat days were associated with fluid but not crystallized intelligence scores. Educational attainment, mild physical activity, and social contacts with children moderated this relationship. Furthermore, Alzheimer's disease polygenic scores moderated the correlation between extreme heat days and crystallized intelligence scores. An increasing frequency of extreme heat events and an aging population globally highlight the need for policies and interventions building resiliency in older adults. Actions promoting the protective modifiable behaviors to older adult cognition identified by our study can lead to healthier individuals and communities.

Increasing concurrent exposure of global breadbaskets to reproductive heat extremes

Abstract In recent years, circumglobal heatwaves are becoming increasingly frequent, motivating concerns about the concurrent exposure of global breadbaskets to heat extremes during crop reproductive periods. Here we project the likelihood of concurrent exposure of global breadbaskets of staple crops to widespread reproductive heat extremes. We find that circumglobal reproductive extreme heat exposure would be an agriculturally relevant climate feature in the coming decades. By 2028‒2057 (with approximately 2 oC warming above preindustrial levels), the probability of major breadbaskets of the world concurrently enduring at least 5 days of reproductive extreme heat over more than half of their croplands in a typical year is projected to rise from virtually unlikely to 0.43 for maize, 0.27 for wheat, 0.33 for rice and soybean. While as of 2050‒2079 (with approximately 3 oC warming above preindustrial levels), these probabilities would grow rapidly to 0.91, 0.83, 0.87, and 0.80, respectively. Should such dramatic increases in circumglobal reproductive extreme heat exposure occur, they could pose substantial stress on food production and agricultural adaptation, particularly when coinciding with agricultural droughts.

Exposure to Ambient Heat and Risk of Spontaneous Abortion: A Case-Crossover Study.

Few epidemiologic studies have examined the association of ambient heat with spontaneous abortion, a common and devastating pregnancy outcome. We conducted a case-crossover study nested within Pregnancy Study Online, a preconception cohort study (2013-2022). We included all participants reporting spontaneous abortion (N = 1,524). We defined the case window as the 7 days preceding the event and used time-stratified referent selection to select control windows matched on calendar month and day of week. Within each 7-day case and control window, we measured the mean, maximum, and minimum of daily maximum outdoor air temperatures. We fit splines to examine nonlinear relationships across the entire year and conditional logistic regression to estimate odds ratios (ORs) and 95% confidence interval (CI) of spontaneous abortion with increases in temperature during the warm season (May-September) and decreases during the cool season (November-March). We found evidence of a U-shaped association between outdoor air temperature and spontaneous abortion risk based on year-round data. When restricting to warm season events (n = 657), the OR for a 10-percentile increase in the mean of lag 0-6 daily maximum temperatures was 1.1 (95% CI: 0.96, 1.2) and, for the maximum, 1.1 (95% CI: 0.99, 1.2). The OR associated with any extreme heat days (>95th county-specific percentile) in the preceding week was 1.2 (95% CI: 0.95, 1.5). Among cool season events (n = 615), there was no appreciable association between lower temperatures and spontaneous abortion risk. Our study provides evidence of an association between high outdoor temperatures and the incidence of spontaneous abortion.

Mean Summer Land Temperatures in the Southern California Coastal Zone: Connections With Ocean Processes

AbstractThe cooling effect of the ocean on the Southern California coastal zone is investigated using a high‐resolution (4‐km) gridded surface meteorological data set (gridMET) of daily maximum temperature (Tmax), with focus on summer mean conditions, taken as the July–August–September (JAS) average. An empirical orthogonal function analysis reveals a coastal mode of JAS temperature covariability, distinct from a more energetic inland mode, that captures Tmax averaged across the Southern California coastal plain. The coastal mode temperature correlates significantly with, and has similar amplitude to, regional sea surface temperature (SST). High (low) summer land and sea surface temperatures, as well as inversion layer temperature differences, are associated with decreases (increases) of northerly coastal wind speeds and coastal cloudiness. The number of extreme heat days on land increases as regional SST increases (4.3 days °C−1), with heat wave days 10 times more likely during peak warm versus cool coastal mode years. The coastal zone was notably warmer and heat wave days peaked during the well documented marine heat wave events of 2014/15 and 2018 off Southern California. The marine variability associated with the coastal mode also has strong expression off the Baja California peninsula, presumably due to strong covarying winds in that area. As in previous studies, higher ocean temperatures are attributed to weaker summer winds, with associated reductions in ocean surface heat loss, coastal upwelling, and cloudiness.

Assessing the extended‐range forecast skills of the extreme heat events over South China based on three S2S models

AbstractThis paper assesses the extended‐range forecast skills of the extreme heat events (EHEs) over South China based on three subseasonal‐to‐seasonal models (European Centre for Medium‐Range Weather Forecasts [ECMWF], National Centers for Environmental Prediction [NCEP], and China Meteorological Administration [CMA]). Overall, ECMWF has the best skill, NCEP the second and CMA the poorest. The predicting skills of EHEs depend on the predicting skills of relevant circulation. Cases studies (June 4–6, 1999, August 19–29, 2009, and August 3–5, 2010) show that the three models generally predict circulation anomalies weaker than observation, leading to the misses of some extreme heat days (EHDs). In these cases, ECMWF is able to well predict the influence of tropical circulation, capture the major characteristics of mid‐latitude circulation but with a slower propagating speed. NCEP could capture the main signals of tropical (mid‐latitude) circulation, but with slower propagating speed (slower propagating speed, deviated direction or more northward location). CMA might produce some EHDs but is derived from the circulation anomaly with the wrong origin or location. Therefore, ECMWF could predict the EHEs most accurately, NCEP could reasonably predict the formation of EHEs and tend to have more delayed predictions, while CMA has the poorest skill due to the false origins of anomalies. These results suggest potential ways to improve the current models' extended‐range forecast skills.

Association of Psychiatric Emergency Visits and Warm Ambient Temperature during Pregnancy: A Time-Stratified Case-Crossover Study.

Acute exposure to high ambient temperature and heat waves during the warm season has been linked with psychiatric disorders. Emerging research has shown that pregnant people, due to physiological and psychological changes, may be more sensitive to extreme heat, and acute exposure has been linked to increased risk of pregnancy complications; however, few studies have examined psychiatric complications. Our objective was to examine the association between acute exposure to warm ambient temperatures and emergency department (ED) visits for mental disorders during pregnancy. A time-stratified case-crossover design with conditional logistic regression was performed on psychiatric ED visits for pregnant patients in North Carolina, from May to September 2016 to 2019. Daily average ambient temperature was the main exposure and was linked to daily visits by maternal zip code of residence for prenatal mood and anxiety disorders (PMAD), severe mental illness (SMI), mental disorder of pregnancy (MDP), suicidal thoughts (SUIC), and any psychiatric disorder (Any). Effect modification by trimester, residential segregation, economic segregation, urbanicity, and availability of greenspace was also investigated. Each increase in same-day exposure to warm ambient temperature on case days was associated with an increase in incidence rate ratio (IRR) for any psychiatric disorder [IRR = 1.07; 95% confidence interval (CI): 1.01, 1.14] including anxiety (IRR = 1.14; 95% CI: 1.00, 1.30), bipolar disorder (IRR = 1.28; 95% CI: 0.98, 1.67), and suicidal thoughts (IRR = 1.28; 95% CI: 1.00, 1.65) compared to control days. In general, the associations were strongest for warm season temperatures on the same day of exposure or for temperatures averaged over the 3 or 6 d preceding the ED visit. The greatest risk of an incident ED admission for PMAD (RR = 1.20; 95% CI: 1.04, 1.39), particularly for anxiety (RR = 1.30; 95% CI: 1.07, 1.59), and any psychiatric disorder (RR = 1.17; 95% CI: 1.07, 1.28) occurred following cumulative exposure to hot temperatures the week before admission. Higher psychiatric burden from temperature was observed in urban areas and on extreme heat days. For this pregnant population in the southeastern United States, short-term exposure to high ambient temperatures during the warm season was associated with a greater risk of ED visits for an array of psychiatric disorders. Findings show that climate-related increases in ambient temperature may contribute to psychiatric morbidity in pregnant people. https://doi.org/10.1289/EHP13293.

Effects of Coexposure to Air Pollution from Vegetation Fires and Extreme Heat on Mortality in Upper Northern Thailand.

Background: understanding the effects of coexposure to compound extreme events, such as air pollution and extreme heat, is important for reducing current and future health burdens. This study investigated the independent and synergistic effects of exposure to air pollution from vegetation fires and extreme heat on all-cause mortality in Upper Northern Thailand. Methods: we used a time-stratified case-crossover study design with a conditional quasi-Poisson model to examine the association between mortality and coexposure to air pollution due to vegetation fire events (fire-PM2.5) and extreme heat. Extreme heat days were defined using the 90th and 99th percentile thresholds for daily maximum temperature. Results: we observed a significant positive excess risk of mortality due to independent exposure to fire-PM2.5 and extreme heat, but not an interactive effect. All-cause mortality risk increased by 0.9% (95% confidence interval (CI): 0.1, 1.8) for each 10 μg/m3 increase in fire-PM2.5 on the same day and by 12.8% (95% CI: 10.5, 15.1) on extreme heat days (90th percentile) relative to nonextreme heat days. Conclusion: this study showed that exposure to PM2.5 from vegetation fires and extreme heat independently increased all-cause mortality risk in UNT. However, there was no evidence of a synergistic effect of these events.

Ten tips on how to care for your CKD patients in episodes of extreme heat.

Climate change is responsible for ≈75% of extreme heat events throughout the world. Heat events are associated with an increased risk for acute kidney injury, which contributes to the development of chronic kidney disease (CKD) and cardiovascular events. Patients with CKD are especially vulnerable to heat stress for a variety of reasons. A disproportionate percentage of patients with CKD live in poverty; experience homelessness, mental illness or disabilities; work outside or are elderly, all demographics that overlap with populations most susceptible to episodes of extreme heat. Therefore, it is reasonable to conclude that exposure to episodes of extreme heat can lead to the progression of CKD and increases morbidity and mortality. Given these concerns, clinicians must be prepared to promptly recognize complications of heat in CKD patients and to help patients appropriately acclimate. We propose the following tips for clinicians to effectively care for their CKD patients during extreme heat days.

Beliefs and behaviors associated with the first named heat wave in Seville Spain 2022

Heat waves pose a substantial and increasing risk to public health. Heat health early warning systems (HHEWSs) and response plans are increasingly being adopted to alert people to the health risks posed by days of extreme heat and recommend protective behaviors. However, evidence regarding the effectiveness of HHEWSs remains limited. We examined the impact of heat wave naming on heat-related beliefs and behaviors to ascertain the potential effectiveness of heat wave naming as a heat health risk communication and management tool. Specifically, we surveyed members of the public exposed to the proMETEO Sevilla HHEWS messaging campaign which in the summer of 2022 applied a name to heat waves considered to pose the greatest risk to public health. During the heat season we evaluated, the proMETEO Sevilla HHEWS campaign applied a name to one heat wave, heat wave “Zoe”. Our analysis of the post-survey of 2022 adults indicated that the 6% of participants who recalled the name Zoe unaided reported greater engagement in heat wave safety behaviors and more positive beliefs about naming heat waves and their local governments’ heat wave response. These results provide initial evidence for potential utility in naming heat waves as part of HHEWSs and HAPs.

Residential electricity demand on CAISO Flex Alert days: a case study of voluntary emergency demand response programs

Abstract The California Independent System Operator (CAISO) utilizes a system-wide, voluntary demand response (DR) tool, called the Flex Alert program, designed to reduce energy usage during peak hours, particularly on hot summer afternoons when surges in electricity demand threaten to exceed available generation resources. However, the few analyses on the efficacy of CAISO Flex Alerts have produced inconsistent results and do not investigate how participation varies across sectors, regions, population demographics, or time. Evaluating the efficacy of DR tools is difficult as there is no ground truth in terms of what demand would have been in the absence of the DR event. Thus, we first define two metrics that to evaluate how responsive customers were to Flex Alerts, including the Flex Period Response, which estimates how much demand was shifted away from the Flex Alert period, and the Ramping Response, which estimates changes in demand during the first hour of the Flex Alert period. We then analyze the hourly load response of the residential sector, based on ∼200 000 unique homes, on 17 Flex Alert days during the period spanning 2015–2020 across the Southern California Edison (SCE) utility’s territory and compare it to total SCE load. We find that the Flex Period Response varied across Flex Alert days for both the residential (−18% to +3%) and total SCE load (−7% to +4%) and is more dependent on but less correlated with temperature for the residential load than total SCE load. We also find that responsiveness varied across subpopulations (e.g. high-income, high-demand customers are more responsive) and census tracts, implying that some households have more load flexibility during Flex Alerts than others. The variability in customer engagement suggests that customer participation in this type of program is not reliable, particularly on extreme heat days, highlighting a shortcoming in unincentivized, voluntary DR programs.

Effectiveness of novel artificial seabird nest modules for reducing ambient temperature transfer in a warming climate

AbstractArtificial habitat for cavity nesting birds can provide excellent opportunities for research and conservation efforts but may expose species to the negative impacts of warming ambient temperatures with climate change. Artificial nest boxes have been successfully used to monitor the breeding activity of the Cassin's auklet (Ptychoramphus aleuticus), a small burrow‐nesting seabird, on Southeast Farallon Island (SEFI) since 1971. Mean monthly ambient air temperatures on SEFI during the summer months have increased at an annual rate of roughly 0.03°C from 1971 to 2022, along with an increase in the number of extreme heat days and average maximum temperature, confirming a warming trend at this seabird colony. Given a projected increase in global temperature, we assessed the effectiveness of traditional wooden nest boxes vs. newer ceramic modules at buffering external ambient air temperatures in normal and extreme heat days across a gradient of microclimates on SEFI. Results from fitting linear mixed effects models indicated that, on average, internal temperatures of wooden and ceramic nests (of comparable size and shape) exhibited similar rates of deviation from ambient air temperature of approximately 0.15°C, even during extreme heat events. Ceramic modules did keep nest chambers cooler by approximately 1.2°C than wooden boxes during extreme events at the warmer, drier southern location of the island. Our results can help guide future efforts to design artificial nests that can effectively provide habitat for seabirds as ambient temperatures increase.