Intensity Of Heat Waves Research Articles

Increasing Intensity of Extreme Heatwaves: The Crucial Role of Metrics

AbstractIn weather and climate applications, a wide range of commonly employed heatwave intensity indices relies either on cumulative or averaged values of temperature‐based variables. In this study, by comparing four different heatwave intensity indices applied to reanalysis data we show that metrics based on cumulative or averaged values lead to important differences in the detection of the most intense events of the period 1950–2021. This suggests that particular attention is needed when using the two families of metrics for assessing heatwave intensity. Indices based on cumulative values should be preferred over the ones relying on temporal averages, better allowing for the comparison of events of different length. Under these considerations, one of the considered cumulative indices is used for characterizing heatwaves of the period 1950–2021, showing that heatwaves that were unlikely before 1986 have become almost 10 times more frequent and up to three times more intense during recent times.

Organismal effects of heat in a fixed ecological niche: Implications on the role of behavioral buffering in our changing world

Increasingly frequent and intense heatwaves generate new challenges for many organisms. Our understanding of the ecological predictors of thermal vulnerability is improving, yet, at least in endotherms, we are still only beginning to understand one critical component of predicting resilience: exactly how do wild animals cope with sub-lethal heat? In wild endotherms, most prior work focuses on one or a few traits, leaving uncertainty about organismal consequences of heatwaves. Here, we experimentally generated a 2.8°C heatwave for free-living nestling tree swallows (Tachycineta bicolor). Over a week-long period coinciding with the peak of post-natal growth, we quantified a suite of traits to test the hypotheses that (a) behavioral or (b) physiological responses may be sufficient for coping with inescapable heat. Heat-exposed nestlings increased panting and decreased huddling, but treatment effects on panting dissipated over time, even though heat-induced temperatures remained elevated. Physiologically, we found no effects of heat on: gene expression of three heat shock proteins in blood, muscle, and three brain regions; secretion of circulating corticosterone at baseline or in response to handling; and telomere length. Moreover, heat had a positive effect on growth and a marginal, but not significant, positive effect on subsequent recruitment. These results suggest that nestlings were generally buffered from deleterious effects of heat, with one exception: heat-exposed nestlings exhibited lower gene expression for superoxide dismutase, a key antioxidant defense. Despite this one apparent cost, our thorough organismal investigation indicates general resilience to a heatwave that may, in part, stem from behavioral buffering and acclimation. Our approach provides a mechanistic framework that we hope will improve understanding of species persistence in the face of climate change.

Vulnerability of Affordable Housing to Global Warming in South Africa: Case Study of a Masonry House in Johannesburg

Global warming is expected to lead to longer and more intense heatwaves, which will have negative environmental and socioeconomic impacts around the world. South Africa is projected to experience significant warming, with surface temperatures possibly increasing by up to 3 °C by mid-century. This warming trend has implications for architecture, as the demand for cooling in buildings could rise dramatically. However, socioeconomic conditions in developing countries may limit the use of air conditioning to mitigate indoor overheating. In South Africa, research has shown that government provided low-cost housing structures are thermally inefficient, with temperatures occasionally exceeding outdoor levels. Residents often rely on natural ventilation and personal actions to cope with heat. However, the effects of climate change may render these strategies insufficient if energy poverty and housing improvement are not addressed. This study aims to examine the impact of global warming on a high mass, naturally ventilated, affordable housing structure in Johannesburg, South Africa. Measured operative temperature data from a long-term experimental study, alongside adaptive temperature limits to evaluate overheating, highlight the vulnerability of indoor spaces without adequate insulation and/or thermal mass. The results underscore concerns about the performance of low-cost and affordable housing in warmer future climates in the South African interior.

Impacts of marine heat extremes on bivalves

As the global ocean continues to experience the consequences of an increase in the frequency and intensity of heat waves, the trend is expected to persist into the 21st century, with a projected tripling of heat waves by 2040. This phenomenon poses a significant threat to marine ecosystems and the survival of marine organisms, including the ecologically and economically vital bivalves. Bivalves are vulnerable to harm from heat stress at various levels of biological organization, and their growth can be negatively impacted by high temperatures, potentially leading to mass mortalities and posing a threat to ecosystem quality and food security. In light of these concerns, this review aims to provide a comprehensive examination of the effects of heat stress on bivalves. It summarizes the physiological and biochemical changes that bivalves undergo in response to extreme heat events and offers an overview of the strategies they employ to mitigate their impacts. A better understanding of the underlying mechanisms of bivalve responses to heat stress is crucial in order to fully appreciate the impact of these events on these organisms. This review synthesizes the current knowledge on heat stress in bivalves and highlights the importance of further research in this area. By providing a comprehensive overview of the physiological and biochemical changes that bivalves experience during heat stress and the strategies they use to mitigate its impact, this review aims to support the development of more effective approaches to minimize heat stress in bivalves.

Linkages of unprecedented 2022 Yangtze River Valley heatwaves to Pakistan flood and triple-dip La Niña

In July-August 2022, Yangtze River Valley (YRV) experienced unprecedented hot summer, with the number of heatwave days exceeding climatology by four standard deviations. The heatwaves and associated severe droughts affected about 38 million people and caused devastating economic losses of about five billion US dollars. Here we present convergent empirical and modelling evidence to show that the record-breaking Pakistan rainfall, along with the 2022 tripe-dip La Niña, produces anomalous high pressure over YRV, causing intense heatwaves. The La Niña-induced second-highest sea surface temperature gradient in the equatorial western Pacific suppresses western Pacific convection and extends the subtropical high westward. More importantly, the tremendous diabatic heating associated with the unprecedented Pakistan rainfall reinforces the downstream Rossby wave train, extending the upper-level South Asia High eastward and controlling the entire YRV. The overlay of the two high-pressure systems sustains sinking motion and increases solar radiation reaching the ground, causing recurrent heat waves.

The dose makes the poison: The longer the heat lasts, the lower the temperature for functional impairment and damage

Climate change increases the intensity and duration of heatwaves. Heat limits for plants are commonly determined by a 30-minute test. This neglects the effect of heat-dose (intensity x exposure-duration) on heat limits, which has been poorly studied. Heat limits for dysfunction (PSII efficiency) and damage were measured after exposure to various heat-doses (34–64 °C x 1–512 min) for five alpine species. The ecological significance of heat-dose was tested based on measured natural heat episodes. With increasing exposure-duration heat limits for 5% damage decreased by 11.2–17.5 K. The same was found for PSII dysfunction, but on average at 7.4 K lower temperatures. Exposure-duration and LT50 followed a slightly species-specific, but logarithmic relationship. This seems very useful for modelling. Natural heat episodes lasted longer than 30 min which questions the 30-minute test. Comparison of natural heat load with the dose-dependent heat limits highlighted that adult trees are safe, but small plants are at high risk for prolonged PSII dysfunction, and even heat damage. Heat responses are not triggered by a single threshold temperature but dose-dependent. The logarithmic relationship found makes it possible to shorten test procedures, extrapolate the response for fully hardened plants and overall more accurately model their heat damage risk in future.

Frequent heatwaves limit the indirect growth effect of urban vegetation in China

The positive indirect growth effects of urban vegetation (IGE-UV) are widespread in urban environments and are influenced by climatic and anthropogenic factors. However, we still have a poor understanding of whether and how heatwaves affect the IGE-UV. Here, we explore the impacts of different heatwave characteristics on the IGE-UV during different seasons in China. We find that the heatwave frequency limits the IGE-UV more strongly than the heatwave intensity. Moreover, the limiting effect is more pronounced in early autumn than in late spring and summer due to the time-lag and time-accumulation effects. Relatively high cumulative heat, low cumulative soil moisture, high cumulative vapor pressure deficit, and high solar radiation during frequent heatwaves may be influential factors limiting the IGE-UV, among which the increased solar radiation is the most important. Our results deepen the understanding of urban vegetation growth in extreme climatic contexts, and are thus important for promoting sustainable urban development.

Beating the heat: military training and operations in the era of global warming.

Global climate change has resulted in an increase in the number and intensity of environmental heat waves, both in areas traditionally associated with hot temperatures and in areas where heat waves did not previously occur. For military communities around the world, these changes pose progressively increasing risks of heat-related illnesses and interference with training sessions. This is a significant and persistent "noncombat threat" to both training and operational activities of military personnel. In addition to these important health and safety concerns, there are broader implications in terms of the ability of worldwide security forces to effectively do their job (particularly in areas that historically already have high ambient temperatures). In the present review, we attempt to quantify the impact of climate change on various aspects of military training and performance. We also summarize ongoing research efforts designed to minimize and/or prevent heat injuries and illness. In terms of future approaches, we propose the need to "think outside the box" for a more effective training/schedule paradigm. One approach may be to investigate potential impacts of a reversal of sleep-wake cycles during basic training during the hot months of the year, to minimize the usual increase in heat-related injuries, and to enhance the capacity for physical training and combat performance. Regardless of which approaches are taken, a central feature of successful present and future interventions will be that they are rigorously tested using integrative physiological approaches.

Increasing heatwave with associated population and GDP exposure in North China

AbstractTwenty‐seven CMIP6 models were grouped into three ensembles based on the simulated performance of heatwaves in North China during present‐day (1995–2014), and future changes in the duration and intensity of heatwaves were projected under SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5. The selected three ensembles showed consistent projections: both the duration and intensity of heatwaves would increase significantly, with the greatest under SSP5‐8.5. Besides, the heatwave growth in 2081–2100 would double in 2041–2060, except for SSP1‐2.6, where heatwaves would be similar in both periods. For the spatial distribution, the duration (intensity) would increase more in southern (western) parts of North China. Combining heatwaves with population and GDP, future heat exposures would concentrate on urban areas and the tertiary industry. For example, the 2041–2060 population exposure would reach 3.2–5.6 times the current level, with contributions from the urban population ranging from 55% to 60%. The GDP exposure would hit tens to hundreds of times the current level, with the tertiary sector replacing the secondary sector as the leading industry in North China, producing the major contribution and facing significant heat‐related risks. Overall, there will be significant heat‐related impacts under SSP5‐8.5, about 1.5–3.0 fold of those under SSP1‐2.6 and SSP2‐4.5. The urban and tertiary sectors would suffer greater risks relative to the rural and other industries. Our results reinforced the need to minimize global emissions and develop strategic plans to mitigate heat impacts under high‐emission scenarios, especially for urban areas and the tertiary industry, requiring great attention to climate adaptation.

Acceleration of the Onset Speeds of Heat Waves Over East China by Upwind Flash Droughts

AbstractThe summer temperatures in 2022 have exceeded historical records over the Northern Hemisphere, leading to compound extreme events of droughts and heat waves (HWs) with rapid intensification. This type of compound extreme event has raised unprecedented social concerns. Previous studies have found that upwind droughts can enhance the intensity of HWs through advected sensible heat, but how the droughts affect the onset speed of HWs remains unclear, which is key to HW early warning. By using a Lagrangian model to track the air mass trajectory during the HWs, here we show that upwind droughts enhance 21% of the HWs over East China, and the upwind droughts with faster onset speeds (i.e., flash droughts) have a greater impact on HWs than the slowly evolving droughts. The strong negative soil moisture anomaly caused by a persistent anticyclone increases sensible heating, leading to the increases of total sensible heat and atmospheric boundary layer height over East China. Meanwhile, the rapid onset of flash drought is accompanied by the intensified anticyclone and rapid accumulation of advected sensible heat, and these increase the HW onset speed. Compared with the antecedent upwind slow droughts, the antecedent upwind flash droughts and the associated anticyclone accelerate the HW onset speed by 43% significantly. Our research shows that flash drought is a critical precursor for an extreme HW in the downwind region.

Interactions between the summer urban heat islands and heat waves in Beijing during 2000–2018

The coexistence of urban heat islands (UHIs) and heat waves (HWs) enhances the stress on human society. The HWs can be classified into pure daytime type (daytime HWs), pure nighttime type (nighttime HWs), and compound daytime-nighttime type (compound HWs). However, the interactions between UHI and three HWs types and their mechanisms, using the regional climate model incorporated with the local climate zone (LCZ), are less known. In this study, the regional climate model ALARO-SURFEX (incorporated with LCZs) was used to estimate the UHI and energy balance before, during, and after three types of HWs during 2000–2018. Our results indicate that: (1) All types of HWs enhance the nighttime UHI during the HW period. The compound HWs and daytime HWs enhanced UHI of both daytime and nighttime, while the nighttime HWs suppressed daytime UHI. (2) The enhancement effects of the compound HWs on the UHI are caused by raising the urban-rural differences in sensible heat (H) and ground heat flux (GF), and decreasing urban-rural differences in latent heat (LE). The enhancement of daytime HWs on UHI is triggered by increased urban-rural differences in H and declined that in LE. But nighttime HWs altered the daytime UHI by less urban-rural differences in net radiation (RN). (3) The daytime HWs predominantly increase the nighttime UHI in the LCZ1, LCZ2 and LCZ4. (4) The historical urbanization increased the compound HW intensity from 0.65 °C (Miyun, LCZ7) to 2.47 °C (Changping, LCZ3), and the compound HWs' frequency from 1 time (Shijingshan, LCZ7) to 7 times (Daxing, LCZ2).

Current and projected patterns of warming and marine heatwaves in the Southern Indian Ocean

The Southern Indian Ocean (20–120°E, 70–30°S) hosts an exceptional biodiversity that contributed to the inscription of the French and Australian natural reserves on the UNESCO World Heritage List. This region is a “hot spot” for ocean heat uptake and already experiences intense marine heat waves (MHW), as evidenced in 2011/2012 over the Kerguelen Plateau. In the coming decades, this region is also expected to face supplemental anthropogenic warming, depending on future greenhouse gas emissions, with unknown consequences for its marine ecosystems. Here, we present a regional analysis of ocean warming and MHW based on the analyses of historical observations and Coupled Model Intercomparison Project Phase 6 (CMIP6) climate projections. Consistent with observations over the last decades, we find an intensification through the 21st century of surface warming and MHW over a band located between 40°S and 55°S within the Antarctic Circumpolar Current region. CMIP6 models also project much faster climate velocities (i.e. the speed and direction at which isotherms drift in the wake of climate change) in the mesopelagic (200–1000 m) than at the surface (0–200 m). Lastly, a comparison between the two Shared Socioeconomic Pathways (SSP1-2.6 and SSP2-4.5) analysed in this study shows much larger changes in the second half of the 21st century for the higher emission scenario. These results suggest that the subantarctic islands will probably be mostly affected by warming and MHW under both scenarios, although committing to SSP1-2.6 could substantially alleviate the pressure on ecosystems in the long term. This study also highlights the need to consider a tri-dimensional environment that may evolve at different paces when designing efficient conservation measures.

Future population exposure to heatwaves in 83 global megacities

Global warming leads to more frequent and intense heatwaves, putting urban populations at greater risk. Previous related studies considered only surface air temperature or one or two Shared Socioeconomic Pathways (SSPs) and were limited to specific regions. Moreover, no research focused on heatwave exposure in highly-populated global megacities facing severe threats. This study is the first to project future population exposure to heatwaves in 83 global megacities by 2100 using fine-resolution data, suitable indices reflecting human comfort in heatwaves by incorporating temperature and humidity, and a future population exposure projection and analysis framework. The results show that (1) the global frequency of extreme heatwave events and average change rate in each megacity sequentially increase from SSP1-2.6 to SSP5-8.5, and the change rate is generally larger in megacities in the Southern Hemisphere; (2) the increases in heatwave exposure are greatest under SSP370, and the change rates are generally larger for megacities in Southern Asia; (3) there is a high degree of inequality (Gini of 0.6 to 0.63) in future heatwave exposure globally, with the highest inequality under SSP5-8.5 and the lowest under SSP3-7.0; (4) the average exposure, increase rate, and change are highest in low-income megacities and lowest in high-income megacities. The distribution of exposure is the most balanced in middle-income megacities and the least balanced in high-income megacities; and (5) population growth contributes more to the change in exposure than total warming in high-income megacities under SSP1-2.6, and total urban warming contributes much more than population growth in all other cases. Every effort should be made to avoid the SSP3-7.0 scenario and pursue sustainable and rational urban economic development. Mumbai, Manila, Kolkata, and Jakarta warrant particular attention due to their rapid exposure growth. Additionally, policymakers and urban planners must focus on improving sustainable development planning for megacities in southern Asia and low-income megacities.

Climate change will exacerbate population exposure to future heat waves in the China-Pakistan economic corridor

The China-Pakistan Economic Corridor (CPEC) is a climate change-sensitive region, facing frequent and intense heat waves (HWs). The CPEC is expected to experience a simultaneous increase in population and temperature in the coming decades, which could exacerbate human exposure to future HWs. However, it is unknown how much of the population would likely be exposed to HWs in the CPEC under changing climate. This study used the Coupled Model Inter-comparison Project 6 (CMIP6) models and population projections to estimate population exposure to daytime, nighttime, and compound HWs in the CPEC during 2071–2100, relative to 1985–2014 under four Shared Socioeconomic Pathways (SSPs). The results indicate that the study region will probably experience the highest number of nighttime HWs, followed by daytime and compound HWs in the northern, southwestern, and southern parts of the CPEC. The largest population would likely be exposed in the eastern and southwestern CPEC under SSP3-70|SSP3, followed by SSP5-8.5|SSP5, SSP2-4.5|SSP2, and SSP1-2.6|SSP1. The results reveal that the climatic and interactive effects could significantly escalate the population exposure to future HWs in the CPEC. The probability of 2015-HWs-like events and population exposure to such extremes would probably be higher in the eastern CPEC. The return period of 2015-HW-like events would decrease, which indicates their frequent occurrence under the selected SSPs. The findings of the study highlight the need for urgent actions to limit greenhouse gas emissions and to adopt effective adaptation measures in order to avoid the negative consequences of HWs on the local population in the future.

Average and extreme heatwaves in Europe at 0.5–2.0 °C global warming levels in CMIP6 model simulations

European heatwaves at the 0.5, 1.0, 1.5 and 2.0 ^circC global warming levels above the pre-industrial temperature are examined using bias-corrected daily-mean temperature data from 60 simulations performed with 25 global climate models (GCMs). A heatwave event is defined here to consist of at least three consecutive days above the 90th percentile of summer daily-mean temperatures and a break of 1 day is allowed. At the 2.0 ^circC global warming level compared with 0.5 ^circC, the multi-GCM mean annual count of heatwave days is projected to be three to fourfold in northern and more than sixfold in southern Europe. The total annual heatwave extremity index, or the sum of exceedings above the threshold temperature over all the heatwave days, becomes approximatively fourfold in the north and tenfold in the south. In central Europe, the date of the strongest heatwave of year is delayed by about 1 week. By concatenating the bias-corrected output data of all the GCM runs, 1200-year samples were created from which probabilities of occurrence of the strongest heatwaves can be determined very robustly under all four warming levels. An intense heatwave occurring once in 10 years at the 0.5 ^circC warming level has an annual probability of about 50% in northern and 80–90% in southern Europe under 2.0 ^circC. Corresponding probabilities for 100-year heatwaves would be nearly 20% in the north and about 60% in the south. Finally, we discuss factors that explain the stronger increase in heatwave duration and extremity in the south than north.

Projecting the excess mortality due to heatwave and its characteristics under climate change, population and adaptation scenarios.

Heatwaves have significant adverse effects on human health. The frequency, duration, and intensity of heatwaves are projected to increase dramatically, in the context of global warming. However, there are few comprehensive assessments of the health impact of heatwaves considering different definitions, and their characteristics under climate change scenarios. We aimed to compare future excess mortality related to heatwaves among different definitions under climate change, population, and adaptation scenarios in China and further explore the mortality burden associated with heatwave characteristics. Daily data during 2010-2019 were collected in Guangzhou, China. We adopted nine common heatwave definitions and applied quasi-Poisson models to estimate the effects of heatwaves and their characteristics' impact on mortality. We then projected the excess mortality associated with heatwaves and their characteristics concerning climate change, population, and adaptation scenarios. The relative risks of the nine common heatwave definitions ranged from 1.05 (95% CI: 1.01, 1.10) to 1.24 (95% CI: 1.13, 1.35). Heatwave-related excess mortality will consistently increase in the future decades considering multiple heatwave definitions, with more rapidly increasing rates under the Shared Socioeconomic Path5-8.5 and non-adaptability scenarios. Regarding heatwave characteristics, the intensity is the main factor involved in the threat of heatwaves. The increasing trend of characteristic-related mortality burden is similar to that of heatwaves, and the mortality burden caused by the duration of the heatwaves was the largest among all characteristics. This study provides a comprehensive picture of the impact of heatwaves and their characteristics on public health under various climate change scenarios, population changes, and adaptive assumptions. The results may provide important public health implications for policymakers in planning climate change adaptation and mitigation policies, and implementing specific plans.

Heatwaves Risk Perception and Knowledge-Empirical Evidence from Pakistan

Introduction:Heatwaves are the leading weather-related causes of deaths globally. Since the mid 20th century, the frequency and intensity of heatwaves has increased with recent reports projecting a substantial warming in temperature extremes by the end of the 21st century.Method:In this cross-sectional study, we attempted to assess public perception and knowledge on heatwaves. Data was collected across Pakistan among a sample of people aged 18 years and above using an online survey questionnaire. Health Belief Model (HBM) constructs were used to assess risk perception using a total of 14 statements while knowledge was measured using 12 statements. The Unadjusted Odd Ratio (UOR) and Adjusted Odd Ratio (AOR) of 95% Confidence Intervals (CI) were employed through binary logistic regression. A total of twelve variables were included in the model (11 categorical and 1 continuous).Results:Out of the 686 participants, the majority of the people (57.73) showed high heatwaves risk perception and a high level of heatwave knowledge (59.91). The results of the multivariate regression model (AOR) showed that participants within the Secondary and/or higher Secondary (Grade 9th to Grade 12th) were less likely (OR=0.304) perceiving heatwaves risk compared to the reference group (Basic/Elementary Level i.e., (Grade 1st to Grade 8th)). As the number of participants who lives with others and who heard about heatwaves increases, the participants are more likely to perceive high heatwaves risk. For instance, participants who lives with others and have heard about heatwaves perceived heatwaves risk 1.982 and 1.816 times higher respectively than those who live alone and those who have not heard about heatwaves before.Conclusion:HBM can be useful in designing interventions aimed at increasing people’s adaptive behaviors during heat waves. This study provides useful insights to the policymakers across Pakistan in understanding the public’s perception that can lead to informed decision-making.

Climate change-induced ecosystem disturbance: a review on sclerophyllous and semi-deciduous forests in Tunisia.

According to the sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC), global climate change is now unequivocal. Tunisia, like many other countries, has been affected by climate changes, including rising temperatures, intense heatwaves, and altered precipitation regimes. Tunisia's mean annual temperatures has risen about +1.4 °C in the twentieth century, with the most rapid warming taking place since the 1970s. Drought represents a primary contributing factor to tree decline and dieback. Long-term drought can result in reduced growth and health of trees, thereby increasing their susceptibility to insect pests and pathogens. Reported increases in tree mortality point toward accelerating global forest vulnerability under hotter temperatures and longer, more intense droughts. In order to assess the effect of these climate changes on the current state of forest ecosystems in Tunisia and their evolution, an investigative study was required. Here, we review the current state of knowledge on the effects of climate change on sclerophyllous and semi-deciduous forest ecosystems in Tunisia. Natural disturbance during recent years, as well as the adaptability and resilience of some forest species to climate change, were surveyed. The Standardized Precipitation Evapotranspiration Index (SPEI) is a multi-scalar drought index based on climate data that has been used to analyse drought variability. The SPEI time scale analysis showed a negative trend over the 1955-2021 period in Tunisian forest regions. In 2021, Tunisia lost 280 km2 of tree cover to fires, which is equivalent to 26% of the total lost area between 2008 and 2021. Changing climate conditions have also affected phenological parameters, with an advance in the start of the green season (SOS) of 9.4 days, a delay at the end of the green season (EOS) of 5 days, with a consequent extended duration of the green season (LOS) by an average of 14.2 days. All of these alarming findings invite us to seek adaptation strategies for forest ecosystems. Adapting forests to climate change is therefore a challenge for scientists as well as policymakers and managers.

Thermoregulatory and Renal Responses to Simulated Heatwaves in Younger and Older Adults

The frequency, intensity, and duration of heat waves are projected to increase in the coming decades. Older adults have impaired heat-dissipating capabilities and are at a greater risk for heat-related morbidity and mortality. Many hospitalizations and deaths in this population during heat waves are due to renal complications. Indeed, age-related reductions in kidney function, altered fluid regulation, and impaired thermoregulation, may place the elderly at an increased risk for heat-related renal complications. Purpose: Therefore, we tested the hypothesis that aging augments heatwave-induced renal stress. Methods: We assessed core temperature, mean skin temperature, whole-body sweat loss, and estimated glomerular filtration rate (eGFR) via serum creatinine in healthy older (8 Female/7 Male; 70±4 years) and younger (6 Female/7 Male; 29±4 years) adults exposed to three hours of 1) very hot and dry (DRY: 47ºC, 10% relative humidity) and 2) hot and humid (HUMID: 41ºC, 40% relative humidity) heatwave conditions on different days (random order). To simulate activities of daily living, participants performed seven 5-minute periods of light exercise (~3 METS; metabolic heat production: Old: 2.98±0.42; Young: 2.96±0.34 W/kg) dispersed across the heat exposure. Additionally, participants consumed 3 mL/kg/hr of tap-temperature water to maintain euhydration. We analyzed data from each heatwave condition independently using linear mixed effect models with main effects of time (pre and post) and group (Older and Younger) or unpaired t-tests, as appropriate. Repeated measures correlation was used to determine any relation between the change (Δ) in core temperature and Δ eGFR across both heatwave conditions. Results: Following exposure to DRY, older adults had greater increases in core temperature (Older: Δ 1.46±0.42, Younger: Δ 0.74±0.28ºC, interaction p<0.01), but no difference in mean skin temperature increases (Older: Δ 2.09±1.31, Younger: Δ 1.73±0.48ºC, interaction p=0.404) or whole body sweat loss (Older: 1479±391, Younger: 1556±542 mL, p=0.661). In addition, following DRY, eGFR decreased in older but increased in younger adults (Older: Δ -4.3±5.9; Younger: Δ 4.12±4.75 mL/min/1.73 m2, interaction p<0.01). Following exposure to HUMID, older adults had greater increases in core temperature (Older: Δ 1.09±0.29, Younger: Δ 0.55±0.28ºC, interaction p<0.01) and mean skin temperature (Older: Δ 2.43±1.05, Younger: Δ1.37±1.13ºC, interaction p=0.018), but no difference in whole body sweat loss (Older: 979±304, Younger: 1011 ± 269 mL, p=0.774). eGFR increased in younger, but not older, adults (Older: Δ 0.30±4.01, Younger: Δ 6.16±3.37 mL/min/1.73 m2, interaction p<0.01) following HUMID. There was a significant negative relation between Δ core temperature and Δ eGFR (r=-0.48, p<0.01). Conclusion: These preliminary data suggest that older individuals exhibit greater increases in core temperature during heatwave exposures that may contribute to reducedrenal function. Supported by NIH R01AG069005 (CGC), F32HL154559 & K01HL160772 (JCW), and F32HL154565 (LNB). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Unequal exposure to heatwaves in Los Angeles: Impact of uneven green spaces.

Cities worldwide are experiencing record-breaking summer temperatures. Urban environments exacerbate extreme heat, resulting in not only the urban heat island but also intracity variations in heat exposure. Understanding these disparities is crucial to support equitable climate mitigation and adaptation efforts. We found persistent negative correlations between daytime land surface temperature (LST) and median household income across the Los Angeles metropolitan area based on Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station observations from 2018 to 2021. Lower evapotranspiration resulting from the unequal distribution of vegetation cover is a major factor leading to higher LST in low-income neighborhoods. Disparities worsen with higher regional mean surface temperature, with a $10,000 decrease in income leading to ~0.2°C LST increase at 20°C and up to ~0.7°C at 45°C. With more frequent and intense heat waves projected in the future, equitable mitigation measures, such as increasing surface albedo and tree cover in low-income neighborhoods, are necessary to address these disparities.