Future Heat Waves Research Articles

Extreme weather and societal impacts in the eastern Mediterranean

Abstract. Gaining a holistic understanding of extreme weather, from its physical drivers to its impacts on society and ecosystems, is key to supporting future risk reduction and preparedness measures. Here, we provide an overview of the state of the art, knowledge gaps and key open questions in the study of extreme weather events over the vulnerable eastern Mediterranean. This region is situated in a transition zone between subtropical and mid-latitude climates. The large-scale atmospheric circulation and its interaction with regional synoptic systems (i.e., Cyprus Lows, Red Sea Troughs, Persian Troughs, “Sharav” Lows) and high-pressure systems mainly govern extreme weather. Complex orographic features further play an important role in the generation of extreme weather. Most extreme weather events, including heavy precipitation, cold spells, floods and windstorms, are associated with Cyprus Lows or active Red Sea Troughs, whereas heat waves are related with either Persian Troughs and sub-tropical high-pressure systems in summer or the Sharav Low during springtime. In future decades, heat waves and droughts are projected to significantly increase in both frequency and intensity. Changes in heavy precipitation may vary in sign and magnitude depending on the scale, severity and region of interest. There are still relatively large uncertainties concerning the physical understanding and the projected changes of cold spells, windstorms and compound extremes, as these types of events received comparatively little attention in the literature. We further identify knowledge gaps that relate to the societal impacts of extreme weather. These gaps mainly relate to the effects extreme weather may have on mortality, morbidity and infrastructure in the eastern Mediterranean. Research is currently limited in this context, and we recommend strengthening the database of analyzed case studies. We trust that this can only be suitably accomplished by inter-disciplinary and international regional collaboration (in spite of political unrest).

Prediction of Indoor Environmental Quality Using a Regression Model for Educational Buildings in Hot Arid Climate: A Case Study in the Al-Najaf Technical Institute – Iraq

In hot climates, achieving a good indoor environmental quality (IEQ) in existing buildings is important especially with climate change challenges as future heat waves will increase in frequency, duration, and intensity. In educational buildings, there is much more focus on the IEQ parameters and the interactions among them that need to be in line with the continuously changing learning environment. This study assesses the IEQ parameters (represented by noise, temperature and humidity) at three selected campus areas (lecture rooms of an administrative department building (LR), main hall of a management department building (MH) and a central library building (CL)) at the Al-Najaf Technical Institute (NTI), Al-Najaf City, Iraq, for the period from May to December 2019. A statistical analysis using a multi-linear regression model was performed to determine the relationship between the selected IEQ parameters and explain the noise level behavior as a function of the temperature and relative humidity. The research indicated that the noise levels and temperature values exceeded the maximum standard limits in all buildings reflecting the displeasing sound and heating quality within the studied areas, while the readings for relative humidity within each building environment complied with standards. Moreover, for both LR and MH buildings (R2 ≥ 0.8, significance F ≤ 0.01), the noise values were satisfactorily modeled by temperature and relative humidity highlighting the interactions between temperature, humidity and noise under consistent conditions. However, the results for the CL building (R2 = 0.6, significance F = 0.1) showed no relationship between the IEQ parameters, highlighting the fact that this building is exposed to unsteady conditions (an irregular number of people using this building during the daytime) resulting in a high variation of data measurements. The current results demonstrate that detailed modeling can be helpful to predict IEQ parameters depending on other known parameters in buildings. The results of the predictive model aligned with the directly measured data. Therefore, its performance is equally effective, but with a significant reduction in cost and time consumed.

Internal thermal mass for passive cooling and ventilation: adaptive comfort limits, ideal quantities, embodied carbon

How effective is naturally ventilated internal thermal mass for obviating air-conditioning, mitigating heatwaves and storing carbon in buildings? This study combines detailed climate model outputs with scaling rules for optimizing internal thermal mass coupled with buoyancy ventilation. It identifies regions where this passive design strategy is most effective during future heatwaves and determines how much internal thermal mass each person needs to stay comfortable in these regions, with a special focus on Canada. Results suggest that naturally ventilated internal thermal mass is likely to become less effective due to future global heating. Regions where internal thermal mass will no longer be sufficient to obviate air-conditioning and where it can still play a significant role in hybrid cooling are identified. By comparing the ideal per capita thermal mass quantities in different regions, it is found that biomass-based materials require approximately 3.5 times the volume of cementitious materials to perform equivalently, if thermal proportions for surface area and thickness are respected. Finally, an analysis of the per capita embodied carbon of these ideal internal thermal mass quantities is undertaken, suggesting a fair functional unit to compare thermal mass materials. <em><strong>Practice relevance</strong></em> High-resolution Canadian maps and lower-resolution global maps are developed in this study to allow practitioners to distinguish between areas where internal thermal mass should be sufficient to obviate air-conditioning and where supplementary cooling is needed. Ideal per capita quantities of different thermal mass materials are given for each region, with guidelines for how to distribute this thermal mass internally in walls, floors and ceilings, and how the surface area and thickness of the thermal mass scales with the thermal properties of the material and the per capita heat loads and ventilation and temperature damping requirements. As such, this study suggests how thermal mass materials can be compared fairly in terms of performance and embodied carbon at the preliminary stages of design.

Future Changes of Summer Heat Waves Over Urban Agglomerations in Eastern China Under 1.5°C and 2.0°C Global Warming

Extreme hot events have increased evidently under global warming, particularly in the urban areas. This study aims to explore the detailed features of future changes in summer heat waves (HWs) over three major urban agglomerations (Beijing Tianjin Hebei, BTH; Yangtze River Delta, YRD; Pearl River Delta, PRD) in eastern China under 1.5 and 2.0°C warming scenario by using the Weather Research and Forecasting model (WRF) with the updated land cover data for China (ChinaLC), which is also coupled with urban canopy model. Based on the future projection results from Community Earth System Model (CESM) under the Representative Concentration Pathway (RCP) 4.5, dynamic downscaling with high-resolution WRF has been performed to project the future changes in frequency, duration and intensity of summer HWs in urban agglomerations under 1.5 and 2.0°C warming scenarios respectively. Compared with the historical period, it is found that both the summer HWs indices and the HWs affected areas all increase significantly under 1.5 and 2.0°C warming scenarios. The increasing rates of the three HWs indices are above 50% under 1.5°C warming situation, and 70% for 2.0°C warming scenario, with the increasing rate of HWs intensity even exceeding 200%. It is noted that an additional 0.5°C warming from 1.5 to 2.0°C can produce much larger impact on the future HWs changes in YRD, with the HWs intensity increased by 75.5% from 1.5 to 2.0°C warming scenarios. It is further found that the changes of HWs indices in urban area is much higher than that of non-urban areas under 1.5 and 2.0°C warming, indicating that the urban areas will face higher risk of heat-related illness or environments than suburban or rural areas in the future. Our results can provide further scientific support for the mitigation and adaption strategy for the future HWs risk in mega-cities.

Resident lobsters dominate food competition with range-shifting lobsters in an ocean warming hotspot

Species redistributions are one of the most prevalent changes observed in oceans worldwide due to climate change. One of the major challenges is being able to predict temperature-driven changes to species interactions and the outcome of these changes for marine communities due to the complex nature of indirect effects. In the ocean-warming hotspot of south-east Australia, the ranges of many species have shifted poleward. The range of the eastern rock lobster Sagmariasus verreauxi has extended into warming Tasmanian waters inhabited by the resident southern rock lobster Jasus edwardsii, which may lead to increased competitive interactions between the species. Using video monitoring, we investigated how the 2 species compete for food at current (18°C), future (21°C) and future heatwave (24°C) summer temperatures. Behavioural competition occurred in 80% of experiments, during which J. edwardsii won 84% of competitive interactions and showed more aggressive behaviour at all temperatures. This indicates that resident J. edwardsii is not only more dominant in direct food competition than the range-shifting S. verreauxi but, surprisingly, also sustains competitive dominance beyond its physiological thermal optimum under predicted future ocean warming and heatwave scenarios.

Feeling the Heat: Mortgage Lending and Central Bank Options

Extreme heat periods due to the changing climate are having a negative impact on many areas of the economy. In our study, we look at how much US mortgage lending is originated in the areas that are most vulnerable to future heat waves, and what central bank and supervisory authority actions could mitigate the resulting risk. From our results, we see that proportionally more lending flows into the areas that are likely to be most exposed to heat in the future. Population and economic output are relatively higher in these areas, and thus climate risk is less of a factor in lending decisions. However, lenders reject proportionately slightly more mortgage applications in the counties that are expected to be the hottest. Central bank and supervisory authority measures to support climate objectives are therefore of key importance. These could include, for example, central bank asset purchase programmes to support sustainable construction, especially in areas vulnerable to climate change, or the development of collateral management along similar lines. Coordination between the different authorities is also important because of the limitations of central bank actions.

A Stepwise-Clustered Simulation Approach for Projecting Future Heat Wave Over Guangdong Province

A heat wave is an important meteorological extreme event related to global warming, but little is known about the characteristics of future heat waves in Guangdong. Therefore, a stepwise-clustered simulation approach driven by multiple global climate models (i.e., GCMs) is developed for projecting future heat waves over Guangdong under two representative concentration pathways (RCPs). The temporal-spatial variations of four indicators (i.e., intensity, total intensity, frequency, and the longest duration) of projected heat waves, as well as the potential changes in daily maximum temperature (i.e., Tmax) for future (i.e., 2006–2095) and historical (i.e., 1976–2005) periods, were analyzed over Guangdong. The results indicated that Guangdong would endure a notable increasing annual trend in the projected Tmax (i.e., 0.016–0.03°C per year under RCP4.5 and 0.027–0.057°C per year under RCP8.5). Evaluations of the multiple GCMs and their ensemble suggested that the developed approach performed well, and the model ensemble was superior to any single GCM in capturing the features of heat waves. The spatial patterns and interannual trends displayed that Guangdong would undergo serious heat waves in the future. The variations of intensity, total intensity, frequency, and the longest duration of heat wave are likely to exceed 5.4°C per event, 24°C, 25 days, and 4 days in the 2080s under RCP8.5, respectively. Higher variation of those would concentrate in eastern and southwestern Guangdong. It also presented that severe heat waves with stronger intensity, higher frequency, and longer duration would have significant increasing tendencies over all Guangdong, which are expected to increase at a rate of 0.14, 0.83, and 0.21% per year under RCP8.5, respectively. Over 60% of Guangdong would suffer the moderate variation of heat waves to the end of this century under RCP8.5. The findings can provide decision makers with useful information to help mitigate the potential impacts of heat waves on pivotal regions as well as ecosystems that are sensitive to extreme temperature.

Planetary albedo decline over Northwest India contributing to near surface warming

The increase in frequency and severity of heat waves during the pre-monsoon season (March–May) over Northwest India in recent decades is alarming. This study investigates the causative mechanism for warming through the forcing induced by planetary albedo changes over Northwest India, a hotspot for land-cover change. We use satellite-measured planetary albedo (α) and satellite-derived land-use-land-cover (LULC) data to estimate the impact of LULC changes from 2001 to 2018 on α and the associated radiative forcing. Over Northwest India, significant area under native land-cover, viz., barren, shrub and grass-lands, has been converted to cropland. The associated land-cover-induced changes have perturbed the radiation-budget by modifying the absorption of shortwave radiation, thereby contributing to the pronounced reduction of α as observed over this region. The diurnal-mean α has decreased by 0.016 ± 0.001 from 2001 to 2018 during pre-monsoon season which dominates α-decrease during the annual cycle over this region and contributes to the overall decreasing trend over India. Conversion of barren and shrub-lands to cropland is observed to be the greatest contributor to the α-decrease as compared to other land-cover changes. The radiative forcing due to decline in diurnal-mean α over Northwest India from 2001 to 2018 is highest during pre-monsoon at 5.99 ± 0.34 W/m2. This α-induced forcing averaged over the global land surface (0.02 W/m2) is equivalent to the corresponding direct forcing from rise in atmospheric methane concentrations during this period. We find an enhancement in near-surface heating to be associated with change in α; the decreasing trend in α during pre-monsoon has substantially enhanced near-surface extreme effective temperatures by 3.15 ± 2.61 K thus far and may further lead to more extreme heatwaves in future. Further, our findings highlight a decreasing (warming) and increasing (cooling) trend in clear-sky planetary albedo respectively over Northwest India and coastal regions, suggesting that sudden climate change could occur if one forcing dominates over the other.

Predators mitigate the destabilising effects of heatwaves on multitrophic stream communities.

Amidst the global extinction crisis, climate change will expose ecosystems to more frequent and intense extreme climatic events, such as heatwaves. Yet, whether predator species loss-a prevailing characteristic of the extinction crisis-will exacerbate the ecological consequences of extreme climatic events remains largely unknown. Here, we show that the loss of predator species can interact with heatwaves to moderate the compositional stability of ecosystems. We exposed multitrophic stream communities, with and without a dominant predator species, to realistic current and future heatwaves and found that heatwaves destabilised algal communities by homogenising them in space. However, this happened only when the predator was absent. Additional heatwave impacts on multiple aspects of stream communities, including changes to the structure of algal and macroinvertebrate communities, as well as total algal biomass and its temporal variability, were not apparent during heatwaves and emerged only after the heatwaves had passed. Taken together, our results suggest that the ecological consequences of heatwaves can amplify over time as their impacts propagate through biological interaction networks, but the presence of predators can help to buffer such impacts. These findings underscore the importance of conserving trophic structure, and highlight the potential for species extinctions to amplify the effects of climate change and extreme events.

Heatwave fatalities in Australia, 2001–2018: An analysis of coronial records

Historically, heatwaves are Australia's most destructive natural hazard in terms of loss of life. This study analyses statistics of fatalities associated with heatwaves in Australia from 2001 to 2018 as noted by a Coroner. At least 473 heat-related deaths were reported to a Coroner during the period of research, of which 354 occurred during heatwave conditions and, of these, 244 within buildings. Most indoor heatwave fatalities occurred in older housing stock. There was no overall trend in the number or rate of fatalities but, rather, a record of generally low numbers with periodic excursions into very high numbers. Almost two-thirds (63%) of heatwave fatalities occurred during two severe heatwave years: 2009 and 2014. The record was dominated by male fatalities. The risk of dying in a heatwave increased with age, socio-economic disadvantage, social isolation, geographical remoteness, the presence of disabilities (physical or mental) and some prescribed medications and the absence or non-use of air conditioning or other building heat protection. Other risk factors and behaviours were examined and recommendations to decrease future heatwave deaths suggested.

Development of Heatwave Probability Prediction Model Based on Recurrent Neural Network: A Case of Seoul Metropolitan Government

Recently, the incidence of heat waves has increased due to climate change, and the resultant mortalities and socio-economic damage are also increasing in Korea. Hence, emphasis has been placed on research examining heatwaves and their effects. Predicting the probability of heatwave in advance is very important from the perspective of disaster risk management; however, related studies have been insufficient so far. Therefore, in this study, the probability of future heatwave onset was predicted using daily scaled past weather data for Seoul Metropolitan Government. For the analysis, models based on recurrent neural networks (RNN, LSTM, GRU) were used, which are suitable for analyzing time-series data. Upon evaluating the performance of the GRU model, which was selected as the optimized model, no overfitting problem was observed. The prediction accuracy of the model was high as it demonstrated a reproduction of 78% and 86% of actual heatwave days during the validation and test process, respectively. Therefore, this model can be used by each local government to coordinate an efficient response to heat waves.

Temperature and Patterns of Occurrence and Abundance of Key Copepod Taxa in the Northeast Pacific

The Northeast Pacific is a highly heterogeneous and productive ecosystem, yet it is vulnerable to climate change and extreme events such as marine heat waves. Recent heat wave induced die-offs of fish, marine mammals, and seabirds in the Gulf of Alaska were associated with the loss of large, lipid-rich copepods, which are a vital food resource for forage fishes. The critical and temperature sensitive role of copepods in this ecosystem motivates our investigation into the impacts of temperature on copepod occurrence, abundance, and phenology. Here, we pair long term in situ copepod data from Continuous Plankton Recorder surveys with satellite temperature data to determine the influence of water temperature on three key copepod taxa: Neocalanus plumchrus, Calanus pacificus, and Oithona spp. Through the use of linear models and thermal threshold methods, we demonstrate that N. plumchrus is most vulnerable to warming and future marine heat waves in this region. Linear models demonstrate that N. plumchrus abundance is negatively related to temperature, and thermal threshold methods reveal that N. plumchrus has an upper thermal threshold of 11.5°C for occurrence, and 10.5°C for abundance. Additionally, examining N. plumchrus abundance before and during the 2014–2016 marine heat wave demonstrates reduced species abundance during past warming events. Oithona spp. and C. pacificus appear to be less vulnerable to warm temperatures. However, their presence will not be sufficient to supplement the loss of the larger-bodied and lipid-rich N. plumchrus. Our findings demonstrate the power of using long-term in situ data to determine thermal tolerances, and suggest the need to further examine the potential resilience of N. plumchrus to climate change.

Rapid rises in the magnitude and risk of extreme regional heat wave events in China

Increasing occurrence of extreme heat waves poses serious risks to human society and ecosystems. Past studies generally examined the changes in heat wave characteristics at individual stations or grid points; however, a heat wave typically appears as a regional event being continuous in time and space. Using an objective identification technique for distinguishing regional extreme events and a metric for measuring regional heat wave magnitude (i.e., an integrated index that accounts for heat wave intensity, duration, and spatial extent), this study revealed an approximate doubling in both the frequency and the magnitude of regional heat wave events observed over 1960–2018 in China. The identified top three regional heat wave events occurred in the summers of 2013, 2017, and 2003, respectively. Fine-resolution multimodel climate projections suggest that China will experience regional heat wave events with magnitude exceeding the 2013 heat event on a regular basis by 2030 under a business-as-usual scenario (RCP8.5). Compared to a 2 °C warming level, 1.5 °C warming could halve the expected occurrence of future severe regional heat wave events with magnitude similar to or slightly greater than the record-breaking one in 2013.

The missing exposure-outcome link: “equivalent” outdoor ambient temperatures for assigning heat-health effects to individual-level temperature exposures in three U.S. cities

BACKGROUND AND AIM: Heat-health epidemiologic studies often lack information on key determinants of exposure, including occupation, housing, and air conditioning, at the individual or parcel (home) level. Therefore, effect estimates specific to people in subgroups defined by various combinations of these determinants are often not available. We derived subgroup estimates from modeled individually-experienced temperatures (IETs) during 10 days around a past city-specific extreme heat event for three U.S. cities of varying climates: Atlanta, Georgia (hot-humid), Detroit, Michigan (temperate), and Phoenix, Arizona (hot-dry). METHODS: IETs were previously estimated for 2.5 million people in the three cities using modeled data: parcel-linked population microdata, housing-specific indoor temperatures, temporospatially-varying outdoor ambient temperatures, and time activity patterns. To each of the IETs we linked the daily outdoor ambient temperatures as measured at the regional airport—the temperature exposure often used in heat-health studies. We then fit a mixed-effects regression model to predict this often-used temperature exposure, ‘equivalent’ outdoor airport temperature, based on IET and housing type, demographics, air conditioning, and person-specific random effects. Using the equivalent temperatures, we assigned risk ratios (RRs, for increases in outdoor airport temperature) from existing literature on mortality, emergency department visits, and preterm births to each person-day and estimated attributable burdens (using age/race/sex) health event counts. RESULTS:The equivalent temperatures, RRs, and attributable burdens, by design, differed between population subgroups due to variability in indoor and outdoor temperature exposure. For example, heat-associated deaths were 150% higher among Blacks vs. Whites in Atlanta and 40% higher in Detroit. Emergency department visits were 19%, 13%, and 25% higher in Atlanta, Detroit, and Phoenix, respectively, among those without vs. with air conditioning. CONCLUSIONS:When IETs are known, these person-specific equivalent temperatures can be used to estimate subgroup and spatially-varying heat-health burdens for resource allocation for future heat waves and environmental and energy justice policies. KEYWORDS: climate change, indoor temperature exposure, urban heat island, climate vulnerability, extreme weather preparedness

Rapidly Increasing Chance of Record-Shattering Heat Extremes

A new study warns that we need to expect and prepare for unprecedented heat waves in the near future.

Ollie Jay: managing heat, improving health

Ollie Jay: managing heat, improving health

The future of our suburbs: Analyses of heatwave vulnerability in a planned estate

AbstractPlanned estates may be a solution to housing demand and affordability in high growth regions. As a result, planned estate research has tended to focus on privatisation, social engineering of communities by developers, and social polarisation. Heatwave research has focused on measuring and mitigating the impact of such events on disadvantaged communities. However, these two research streams have not been combined to examine how planned estate residents may be vulnerable to heatwaves. We address that gap by considering past, current, and future heatwave impacts; identifying underlying processes governing the vulnerability of planned estates to heatwaves; and reflecting on the implications for the sustainability of planned estates in relation to future heatwave risk. We adopt a mixed‐methods approach using the case of the Jordan Springs estate in Western Sydney, Australia, and that work is underpinned by systems approaches embedded in sustainability science. We find that Jordan Springs is physically vulnerable to heatwaves due to characteristics in its built environment. Human vulnerability is complex: rooted in multiscalar socio‐economic and systemic processes both internal and external to the estate. We suggest resilience be increased to improve estate liveability and sustainability by retrofitting the built environment, improving urban greening, broadening consumer awareness, and modifying development processes.

Heat wave magnitude over India under changing climate: Projections from CMIP5 and CMIP6 experiments

AbstractAtmospheric warming is expected to increase the magnitude and frequency of extreme climatic events namely floods, droughts, heat waves, and so on. Thus, the present study attempts to answer the following research questions; (i) What are the possible implications on future heat wave events due to the projected temperature? (ii) What are the expected changes in heat wave properties under different classifications of heat wave events under different climate scenarios? (iii) Whether the future projection of heat wave events differ significantly under CMIP5 and CMIP6 experiments over India? To answer the above questions, the present study uses the bias‐corrected future projections of maximum temperature (Tmax) from 26 GCMs that is, 13 from CMIP5 and 13 from CMIP6 experiments. In addition, two RCPs (4.5 and 8.5) under CMIP5 and four SSPs (126, 245, 370, and 585) under CMIP6 scenarios are considered. The Heat Wave Magnitude Index (HWMI) is used to characterize the heat wave over India. The essential findings from the study indicate that the Tmax anomaly is likely to increase (SSP126 &lt; SSP245 &lt; SSP370 &lt; SSP585 and RCP4.5 &lt; RCP8.5) in future causing more intense, high frequency, and long duration heat wave events over India. Presently unaffected large regions of southern, northeast, and western parts are expected to be severely affected by heat wave events. More intense heat wave events are likely to occur under RCP8.5 scenario as compared to SSP585 scenario. The percentage of affected area is projected to increase significantly from SSP126 to SSP585 under extreme and very extreme heat wave events. Under RCP8.5 scenario, the average duration of heat wave events for very extreme, and super extreme classifications is significantly higher than SSP585 scenario. Our findings suggest the paramount necessity of adaptation strategies to address the adverse consequences of foreseen heat wave events.

Electric fan use for cooling during hot weather: a biophysical modelling study

In hot weather, electric fans can potentially provide effective cooling for people, with lower greenhouse gas emissions and cost than air conditioning. However, international public health organisations regularly discourage fan use in temperatures higher than 35°C, despite little evidence. We aimed to determine humidity-dependent temperature thresholds at which electric fans would become detrimental in different age groups. We used biophysical modelling to determine the upper humidity-dependent temperature thresholds at which fan use would become detrimental (ie, worsen heat stress) for healthy young adults (aged 18-40 years), healthy older adults (aged ≥65 years), and older adults taking anticholinergic medication. We also obtained hourly environmental data for the period Jan 1, 2007, to Dec 31, 2019, for 108 populous cities to determine the number of days fan use would be effective for cooling, standardised to a 31-day hot weather month. We established simplified temperature thresholds for future fan use recommendations on the basis of temperatures below which fan use would never have been detrimental between Jan 1, 2007, and Dec 31, 2019, across all prevailing levels of ambient humidity. According to our model, fan use would have been beneficial on 30·0 (96·6%) of 31 hot weather days for healthy young adults and 29·4 (94·9%) of 31 hot weather days for both older adults and older adults taking anticholinergic medication between Jan 1, 2007, and Dec 31, 2019. Adherence to the current WHO recommendation of fan use below temperatures of 35°C only, fan use would have been recommended on 27·2 days (87·7%) of 31 hot weather days. According to our simplified thresholds for fan use (at temperatures <39·0°C for healthy young adults, <38·0°C for healthy older adults, and <37·0°C for older adults taking anticholinergic medication), fan use would have been recommended on 29·6 (95·5%) of 31 hot weather days in healthy young adults, 29·4 (94·8%) days in healthy older adults, and 28·8 (93·0%) days in older adults taking anticholinergic medication between Jan 1, 2007, and Dec 31, 2019. Electric fan use, particularly for healthy young adults, would not have worsened heat stress on the majority of study days between 2007 and 2019. Our newly proposed thresholds for fan use provide simple guidelines that improve future heatwave fan use recommendations. None.

Heat waves in spring from Senegal to Sahel: Evolution under climate change

AbstractThis study analyses the long‐term (1950–2100) observed and projected changes in springtime (March–May) heat waves (HWs) in West Africa under climate change. To that end, 28 climate models participating to the fifth Coupled Model Intercomparison Project (CMIP5) are considered, after a statistical post‐correction of their biases. A multi‐scale approach is proposed, covering the Sahel, Senegal, and three thermally‐coherent zones within Senegal. HWs are defined as a sequence of at least three consecutive days above a moving 95th percentile of current temperature distributions. Climate change over Senegal translates into a general shift of the whole statistical distribution towards higher temperature values, with a general stability in the shape of the distribution. Ongoing mean warming could reach +5°C in 2100 under RCP8.5 scenario, implying that coastal Senegal could experience then a mean climate comparable to the hinterland parts today. HWs have increased in intensity, frequency and duration across Sahel and Senegal over the past years, such intensification being higher on recent decades. Future HWs over all regions present intrinsic properties that radically differ from those observed so far. The severity and length of HWs displayed stationary conditions until the late 1990s, but started increasing since then. Projected changes show marked and rapid increase in these variables, the amplitude of which is primarily RCP‐dependent, and secondarily region‐dependent. For both metrics, the largest changes occur over hinterland Senegal and Sahel. There, under RCP8.5 and after the 2070s, the whole spring season could be considered as a permanent HW lasting 3 months. Along the coast, by contrast, average temperatures are both weaker and more variable, causing more frequent threshold crossings and limiting the duration of HWs. The multi‐scale approach used here highlights contrast within Senegal, which constitutes important information for public policy decision‐makers and its inhabitants in terms of adaptation to climate change.