Humid Heat Research Articles

Effect of ice slurry ingestion on thermoregulatory responses during fixed-intensity cycling in humid and dry heat.

This study examined the thermoregulatory response and ergogenic effects of ice slurry (ICE) ingestion in hot environments with high and low relative humidity (RH). Eight males completed four trials in a crossover manner in dry (DRY: 34.7 ± 0.2°C, 38 ± 2%RH) and humid heat (HUM: 34.8°C ± 0.2°C, 80 ± 1%RH). They ingested 8.0g·kg-1 of ICE (0.0°C) or 37.5°C water (CON) during 30min before exercise, and three aliquots (3.2g·kg-1) of ICE or CON during 45-min cycling at 50%[Formula: see text]O2peak, followed by cycling to exhaustion at 80%[Formula: see text]O2peak (TTE). Body core temperature (Tcore), mean skin temperature (Tsk), heart rate (HR), thermal comfort, thermal sensation and rating of perceived exertion (RPE) were measured. Relative to CON, ICE improved TTE by 76.5 ± 96.5% in HUM and 21.3 ± 44.9% in DRY (p = 0.044). End-exercise Tcore was lower in ICE versus CON in DRY (37.8 ± 0.4°C versus 38.1 ± 0.3°C, p = 0.005) and HUM (38.8 ± 0.4°C versus 39.3 ± 0.6°C, p = 0.004). ICE decreased HR, heat storage and heat strain index only in DRY (p < 0.001-0.018). ICE improved thermal sensation and comfort in DRY and HUM (p < 0.001-0.011), attenuated RPE in HUM (p = 0.012) but not in DRY (p = 0.065). ICE tended to benefit performance in humid heat more than in dry heat. This is likely due to the reduced extent of hyperthermia in dry heat and the relative importance of sensory inputs in mediating exercise capacity.

Thermal exchanges, physiological responses and productive performance of Guinea Fowl (Numidia meleagris) subjected to different air temperatures.

The objective of this research was to evaluate the thermal exchanges, physiological responses, productive performance and carcass yield of Guinea Fowl confined under thermoneutral conditions and under thermal stress. For the experiment, 96 animals were confined in 8 experimental boxes of 1 m2 of area, each, divided in equal numbers and placed inside two distinct climatic chambers, where the birds were distributed in a completely randomized design, with two treatments (air temperatures of 26 and 32°C, respectively). For the collection of physiological responses and carcass yield 16 birds were evaluated and for the collection of data on feed and water consumption and productive responses, 48 birds per treatment were evaluated. The environmental variables (air temperature (AT), air relative humidity and wind speed), temperature and humidity index (THI), heat exchanges, physiological responses (respiratory rate, surface temperature, cloacal temperature and eyeball temperature), feed (FC) and water (WC) consumption and production responses (weight gain, feed conversion index and carcass yield) of the birds were evaluated. With the elevation of the AT, it could be noticed that the THI went from a thermal comfort condition to an emergency condition, where the birds lost part of their feathers, increased all physiological responses evaluated, and consequently, reduced by 53.5% the amount of heat dissipated in the sensible form and increased by 82.7% the heat losses in the latent form, increasing also the WC. ATs of up to 32°C did not significantly affect the productive performance and carcass yield of the guinea fowl.

Humid Heat Equally Impairs Maximal Exercise Performance in Elite Para-Athletes and Able-Bodied Athletes.

This study aimed to compare the impact of hot-humid environmental conditions on performance outcomes, thermoregulatory responses, and thermal perception during exercise between elite para- and able-bodied (AB) athletes. Twenty elite para-athletes (para-cycling and wheelchair tennis) and 20 elite AB athletes (road cycling, mountain biking, beach volleyball) performed an incremental exercise test in a temperate environment (mean ± SD, 15.2°C ± 1.2°C; relative humidity, 54% ± 7%) and a hot-humid environment (31.9°C ± 1.6°C, 72% ± 5%). Exercise tests started with a 20-min warm-up at 70% of maximal heart rate, after which power output increased by 5% every 3 min until volitional exhaustion. Time to exhaustion was shorter in hot-humid versus temperate conditions, with equal performance loss for para- and AB athletes (median (interquartile range), 26% (20%-31%) vs 27% (19%-32%); P = 0.80). AB athletes demonstrated larger exercise-induced increases in gastrointestinal temperature (T gi ) in hot-humid versus temperate conditions (2.2 ± 0.7 vs 1.7 ± 0.5, P < 0.001), whereas T gi responses in para-athletes were similar between conditions (1.3 ± 0.6 vs 1.3 ± 0.4, P = 0.74). Para- and AB athletes showed similar elevations in peak skin temperature ( P = 0.94), heart rate ( P = 0.67), and thermal sensation score ( P = 0.64) in hot-humid versus temperate conditions. Elite para-athletes and AB athletes demonstrated similar performance decrements during exercise in hot-humid versus temperate conditions, whereas T gi elevations were markedly lower in para-athletes. We observed large interindividual variation within both groups, suggesting that in both para- and AB athletes, personalized heat mitigation plans should be developed based on individual thermal testing.

Increased heat risk in wet climate induced by urban humid heat.

Cities are generally warmer than their adjacent rural land, a phenomenon known as the urban heat island (UHI). Often accompanying the UHI effect is another phenomenon called the urban dry island (UDI), whereby the humidity of urban land is lower than that of the surrounding rural land1-3. The UHI exacerbates heat stress on urban residents4,5, whereas the UDI may instead provide relief because the human body can cope with hot conditions better at lower humidity through perspiration6,7. The relative balance between the UHI and the UDI-as measured by changes in the wet-bulb temperature (Tw)-is a key yet largely unknown determinant of human heat stress in urban climates. Here we show that Tw is reduced in cities in dry and moderately wet climates, where the UDI more than offsets the UHI, but increased in wet climates (summer precipitation of more than 570 millimetres). Our results arise from analysis of urban and rural weather station data across the world and calculations with an urban climate model. In wet climates, the urban daytime Tw is 0.17 ± 0.14 degrees Celsius (mean ± 1 standard deviation) higher than rural Tw in the summer, primarily because of a weaker dynamic mixing in urban air. This Tw increment is small, but because of the high background Tw in wet climates, it is enough to cause two to six extra dangerous heat-stress days per summer for urban residents under current climate conditions. The risk of extreme humid heat is projected to increase in the future, and these urban effects may further amplify the risk.

Environmental and thermoecological comparative assessment of improved humid air waste heat recovery configurations

This paper provides a comprehensive assessment of the humid air turbine-based waste heat recovery system with respect to different flow configurations in the air saturator. The novelty of this work is to provide a holistic approach to the environmental and thermoecological assessment of Maistosenko cycle-based waste heat recovery units by considering three configurations of air saturator namely, counter-flow, cross-flow, and mixed-flow configuration. In other words, the assessment is carried out to evaluate the performance improvements while comparing the environmental as well as thermoecological perspectives. This provides a broader and wholesome perspective allowing a wider application of these configurations, especially in different climatic conditions experiencing varying ambient temperatures. The ambient temperature is particularly important when air is used as working fluid and routed in three different configurations within the heat recovery unit i.e., air saturator. The addition of humidity in the air saturator tends to improve the performance of bottoming cycle depending on the air direction within the saturator which has a counter, cross and mixed flow configurations. Moreover, ambient or dead state temperature is considered one of the influencing parameters on the performance of considered heat recovery configurations. With the rising ambient temperatures up to 50 °C, owing to intensive heat waves and sustained droughts; the performance indicators of power generation units indicate as much as 25% reduction in the sustainability index along with 10% lowering of energy and exergy efficiencies. In this regard, the flow configuration and efficiency of air saturators become critically important especially as a heat recovery unit while working in intense operating conditions. The results have suggested that counter configuration can offer the highest among of net-work marking 51.9 MW whereas the cross-flow configuration can mark only 49.78 MW. Thermoecological assessment has suggested that the ambient temperature of this type of powerplant can be less than 40 °C. It is concluded that the optimal configuration is counter-flow configuration for the waste heat recovery in gas turbines based upon second law and thermoecological assessment.

Critical Environmental Limits for Human Thermoregulation in the Context of a Changing Climate.

Human-caused climate change has increased the average temperature of the Earth by over 1°C since the 19th century with larger increases expected by 2100 due to continued human influence. This change in mean ambient temperature has had nonlinear effects, resulting in more high temperature extremes, i.e., heat waves, that have increased in frequency, duration, and magnitude. Additional occurrences of humid heatwaves have significantly affected human health due to the physiological strain associated with a relative inability for evaporative cooling. Inability to efficaciously cool the body, whether during passive heat exposure or physical activity, not only leads to elevated core temperatures but also places strain on the cardiovascular system, often exacerbating age-related co-morbidities. As part of the PSU HEAT (Pennsylvania State University - Human Environmental Age Thresholds) Project, a progressive environmental strain protocol has been developed to determine critical environmental limits - combinations of ambient temperature and humidity -- associated with uncompensable heat stress and intractable rises in core temperature (Tc). These human heat balance thresholds, well below those originally theorized by climatologists, have been surpassed in recent heatwaves and be exceeded on a more regular basis in the future, providing additional impetus to the urgency of adaptative measures and climate change mitigation.

Large humidity effects on urban heat exposure and cooling challenges under climate change

Many urban climates are characterized by increased temperature and decreased relative humidity, under climate change and compared to surrounding rural landscapes. The two trends have contrasting effects on human-perceived heat stress. However, their combined impact on urban humid heat and adaptation has remained largely unclear. Here, we use simulations from an earth system model to investigate how urbanization coupled with climate change affects urban humid heat stress, exposure, and adaptation. Our results show that urban humid heat will increase substantially across the globe by 3.1 °C by the end of the century under a high emission scenario. This projected trend is largely attributed to climate change-driven increases in specific humidity (1.8 °C), followed by air temperature (1.4 °C)—with urbanization impacts varying by location and of a smaller magnitude. Urban humid heat stress is projected to be concentrated in coastal, equatorial areas. At least 44% of the projected urban population in 2100, the equivalent of over 3 billion people worldwide, is projected to be living in an urban area with high humid heat stress. We show a critical, climate-driven dilemma between cooling efficacy and water limitation of urban greenery-based heat adaptation. Insights from our study emphasize the importance of using urban-explicit humid heat measures for more accurate assessments of urban heat exposure and invite careful evaluation of the feasibility of green infrastructure as a long-term cooling strategy.

Ultrastable and highly efficient CsPbBr3 composites achieved by dual‐matrix encapsulation for display devices

AbstractPerovskite nanocrystals (NCs) with high stabilities and excellent optical performances are crucial for display applications. However, to date, perovskite emitters with both high photoluminescence (PL) quantum yield (PLQY) and high stabilities under harsh synergistic humidity–heat–light aging conditions have not been reported. The promising high‐temperature solid‐state sintering with single oxide matrices cannot ensure high PLQY and synergistic aging stabilities of perovskites. Herein, both the PLQY and overall (thermal, moisture, and photo) stabilities of all‐inorganic perovskite (CsPbBr3) NCs are improved by dual‐matrix encapsulation, which is accomplished by in situ crystallization of CsPbBr3@Cs4PbBr6 nanocomposites in silica molecular sieve (MS) templates via advanced solid‐state synthesis a using precisely controlled molar ratio of precursor components and cooling rates. The Cs4PbBr6 matrix effectively passivates the surfaces of CsPbBr3 NCs, and the MS matrix insulates CsPbBr3@Cs4PbBr6 from the external environment. The resulting CsPbBr3@Cs4PbBr6/MS composites exhibit the highest PLQY (&gt;90%) among those of the solid‐state perovskite NCs and significant stabilities against water, heat, and blue light irradiation, maintaining more than 80% of their initial PL intensities after being aged for 1000 h under synergistic high‐humidity (85%), high‐temperature (85°C), and strong blue light irradiation (350 mW cm−2) conditions. To the best of our knowledge, these CsPbBr3@Cs4PbBr6/MS composites represent the most stable perovskite emitters under synergistic humidity–heat–light aging conditions. The liquid crystal display backlight module fabricated using these stable composites demonstrates a wide color gamut of 131% of the National Television Standards Committee standard. We speculate that this dual‐matrix encapsulation can be used for industrial mass production.image

Comparative Efficacy of Humidifiers for Noninvasive Infant Respiratory Support

Abstract Delivery of cold, dry air to infants while supporting their breathing can lead to hypothermia in addition to irritating and damaging their sensitive nares and negatively impacting outcomes with these therapies. In high resource settings, electric heated humidifiers are used to mitigate this problem. In many resource-constrained settings, passive nonelectric bubbling humidifiers are instead used. We here compare the efficacy of conventional electric heated humidification, custom-built low cost heated humidification, passive nonelectric bubbling humidification and a control of no humidification. In a hospital patient room (temperature 22 °C, humidity 50%), the temperature and humidity delivered to a simulated patient lung via a BC161-10 Fisher Paykel bubble continuous positive airway pressure (CPAP) system were measured with conventional electric heated humidification, low cost custom-built heated humidification, passive bubbling humidification and no humidification. (Delivered CPAP: 5 cm H2O; flowrate varied from 4 to 8 liters per minute (LPM) in 2 LPM increments.) As the flowrate was varied from 4 to 8 LPM, delivered relative humidity (standard deviation) with each humidifier was as follows: control 10% (3.6%), passive bubbler 44% (3.7%), custom-built humidifier 67% (1.7%), electric heated humidifier 91% (0.86%). Delivered temperature with the electric heated humidifier was 38 °C (0.21 °C) versus 33 °C for all other setups. Conventional electric heating humidification is more effective than passive bubbling humidification, and the custom-built low cost humidifier provides an intermediate degree of humidification. Through further improvement of this concept with a heated inspiratory circuit and sensor based control of the heating element, an effective yet low cost solution heating humidification could be developed.

Evaluation of production performance of Binjharpuri cattle of Odisha

Binjharpuri, a dual purpose indigenous breed of Odisha is commonly reared for its various advantages, viz. optimum milk production in low input management system, excellent draft ability in hot humid climate condition and heat resistance ability. In the present study, attempt was made to evaluate production performance along with influence of non- genetic effects such as location, lactation order and season of calving on production traits of binjharpuri cattle. The overall average least square means along with standard error for lactation milk yield, average daily milk yield, peak yield, lactation length and dry period were found to be 974.490±6.788 kg, 3.557±0.023 kg, 4.633±0.021 kg, 274.444±1.249 days and 121.913±0.611 days, respectively. Location had highly significant effect on lactation milk yield, average daily milk yield, lactation length and dry period, whereas non-significant effect on peak yield. Lactation order too had highly significant effect on the traits considered under study. Season of calving had highly significant effect on lactation milk yield, average daily milk yield; significant effect on lactation length whereas non-significant effect on peak yield and dry period. Significant influence of non-genetic factors and significant variations in traits under study is suggestive that remarkable improvement in the Binjharpuri cattle populace can be targeted through better management and by nurturing effective breeding strategies.

Study on erosion and stability of the ecological slope

Rainfall is the main influencing factor causing slope erosion, landslide, and instability in loess; thus, it is vital to comprehend the process of rainfall erosion on various slope surfaces and water penetration inside the slope. In this paper, the loess sample is from Heifangtai in Gansu Province, and triaxial shear tests were conducted on loess with roots under varying water contents to evaluate the slope-reinforcing impact of roots. The slope surface erosion process was analyzed using a soil moisture sensor and matric suction meter to monitor the variation of matric suction in the middle slope and slope foot in response to varying precipitation levels. The numerical simulation approach is utilized to analyze the fluctuation of slope stability under the effect of varying rainfall intensities and humid heat, and the analytical solution of the safety factor is compared to the model solution. The results indicate that the shortest generation time for bare slope runoff is 6 min, whereas the greatest generation time for the Bermuda grass slope is 12 min; the shorter the period, the less water penetration and the simpler it is to reach the slope erosion stage. The slope’s rise increases runoff velocity, strengthening water resistance on the slope surface. When the test slope is 30°, the maximum mass of scouring sediment on the bare slope is 15.2 g from 24 to 36 min, compared to 14.7 g from 24 to 36 min when the test slope is 60°. The amount of scouring reduces as the slope increases. The slope safety factor declined from 3.51 to 2.84 after 24 h of heavy rain, and the loss rate accelerated as the rainfall intensity increased.

Contrasting impacts of dry versus humid heat on US corn and soybean yields

The impact of extreme heat on crop yields is an increasingly pressing issue given anthropogenic climate warming. However, some of the physical mechanisms involved in these impacts remain unclear, impeding adaptation-relevant insight and reliable projections of future climate impacts on crops. Here, using a multiple regression model based on observational data, we show that while extreme dry heat steeply reduced U.S. corn and soy yields, humid heat extremes had insignificant impacts and even boosted yields in some areas, despite having comparably high dry-bulb temperatures as their dry heat counterparts. This result suggests that conflating dry and humid heat extremes may lead to underestimated crop yield sensitivities to extreme dry heat. Rainfall tends to precede humid but not dry heat extremes, suggesting that multivariate weather sequences play a role in these crop responses. Our results provide evidence that extreme heat in recent years primarily affected yields by inducing moisture stress, and that the conflation of humid and dry heat extremes may lead to inaccuracy in projecting crop yield responses to warming and changing humidity.

Diverging Global Dry and Humid Heat Responses to Modern Irrigation

Abstract The moderating influence of irrigation on dry heat extremes is well established, but the effect of irrigation on humid heat is more uncertain. Here, we study the impact of modern irrigation on both dry and humid heat-wave occurrences during the boreal summer using the NASA GISS Earth System Model (ModelE) with and without present-day irrigation. We show that the presence of modern irrigation reduces the total number of dry heat waves in most land areas, especially in arid and temperate regions. In contrast, humid heat waves occur more frequently under modern irrigation, especially in the Mediterranean Sea region, northern Africa, southern Africa, and the Middle East. Present-day irrigation reduces dry heat extremes by favoring latent heating over sensible heating and lowering surface solar radiation by increasing total cloud cover. Meanwhile, modern irrigation drives increases in humid heat through increases in specific humidity and precipitation. Notably, the reduction in dry heat is mostly localized over irrigated grid cells while humid heat increases both in locally irrigated areas and remote (nonirrigated) regions because of widespread increases in humidity associated with irrigation. Our results suggest that irrigation may amplify humid heat, even in nonirrigated areas, highlighting the importance of improving our understanding of both local and remote effects of the irrigation forcing on climate hazards.

GSDM-WBT: global station-based daily maximum wet-bulb temperature data for 1981–2020

Abstract. The wet-bulb temperature (WBT; TW) comprehensively characterizes the temperature and humidity of the thermal environment and is a relevant variable to describe the energy regulation of the human body. The daily maximum TW can be effectively used in monitoring humid heat waves and their effects on health. Because meteorological stations differ in temporal resolution and are susceptible to non-climatic influences, it is difficult to provide complete and homogeneous long-term series. In this study, based on the sub-daily station-based HadISD (Met Office Hadley Centre Integrated Surface Database) dataset and integrating the NCEP-DOE reanalysis dataset, the daily maximum TW series of 1834 stations that have passed quality control were homogenized and reconstructed using the method of Climatol. These stations form a new dataset of global station-based daily maximum TW (GSDM-WBT) from 1981 to 2020. Compared with other station-based and reanalysis-based datasets of TW, the average bias was −0.48 and 0.34 ∘C, respectively. The GSDM-WBT dataset handles stations with many missing values and possible inhomogeneities, and also avoids the underestimation of the TW calculated from reanalysis data. The GSDM-WBT dataset can effectively support the research on global or regional extreme heat events and humid heat waves. The dataset is available at https://doi.org/10.5281/zenodo.7014332 (Dong et al., 2022).

Linkages between Amplified Quasi-Stationary Waves and Humid Heat Extremes in Northern Hemisphere Midlatitudes

Abstract Humid heat extremes, taking account of both temperature and humidity, have adverse impacts on society, particularly on human health. It has been suggested that quasi-stationary waves (QSWs) with anomalously high amplitudes contribute to the occurrence of near-surface precipitation extremes and temperature extremes in the midlatitudes of the Northern Hemisphere. However, little attention has been paid to the linkages between amplified QSWs and humid heat extremes. Using the ERA5 dataset, we identify amplified QSWs of zonal wavenumbers 5–7 (Wave 5–7) in summer months from 1979 to 2020. These amplified QSWs show clear circumglobal wave patterns horizontally and nearly barotropic structure vertically. Linking amplified Wave 5–7 to wet-bulb temperature (WBT) extremes, we find that amplified QSWs preferentially induce prominently prolonged WBT extremes in specific regions: north-central North America for amplified Wave 5; western United States, south-central Asia, and eastern Asia for amplified Wave 6; and western Europe and the Caspian Sea region for amplified Wave 7. Analyses of physical processes indicate that, accompanied by the amplification of Wave 5–7, the changes in horizontal temperature advection, adiabatic heating associated with descending motion, downward solar radiation, moisture transport and moisture flux convergence, and surface latent heat fluxes largely account for the increase in persistence of WBT extremes. Significance Statement In the context of climate change, humid heat extremes exhibit different changes and impacts from high-temperature extremes, but the physical processes that may cause them remain unclear. This study aims to explore the atmospheric dynamic processes leading to the concurrence of humid heat extremes, which may exacerbate the risk from heat stress in today’s interconnected world. In specific regions over the Northern Hemisphere midlatitudes, durations of humid heat extremes are found to be elevated simultaneously by amplified quasi-stationary waves. We further identify the physical connections between amplified quasi-stationary waves and humid heat extremes over targeted regions. This would help in better understanding the role of changing atmospheric circulations in the humid heat extremes.

Induction and decay of seasonal acclimatization on whole body heat loss responses during exercise in a hot humid environment with different air velocities.

Whether whole body heat loss and thermoregulatory function (local sweat rate and skin blood flow) are different between summer and autumn and between autumn and winter seasons during exercise with different air flow in humid heat remain unknown. We therefore tested the hypotheses that whole body sweat rate (WBSR), evaporated sweat rate, and thermoregulatory function during cycling exercise in autumn would be higher than in winter but would be lower than in summer under hot-humid environment (32 C, 75% RH). We also tested the hypothesis that the increase of air velocity would enhance evaporated sweat rate and sweating efficiency across winter, summer, and autumn seasons. Eight males cycled for 1 h at 40% V̇o2max in winter, summer, and autumn seasons. Using an electric fan, air velocity increased from 0.2 m/s to 1.1 m/s during the final 20 min of cycling. The autumn season resulted in a lower WBSR, unevaporated sweat rate, and a higher sweating efficiency compared with summer (all P ≤ 0.05) but WBSR and unevaporated sweat rate in autumn were higher than in winter and thus sweating efficiency was lower when compared with winter only at the air velocity of 0.2 m/s (All P ≤ 0.05). Furthermore, evaporated sweat rate and core temperature (Tcore) were not different among winter, summer, and autumn seasons (All P > 0.19). In conclusion, changes in WBSR across different seasons do not alter Tcore during exercise in a hot humid environment. Furthermore, increasing air velocity enhances evaporated sweat rate and sweating efficiency across all seasons.

Urban Heat Island High Water-Vapor Feedback Estimates and Heatwave Issues: A Temperature Difference Approach to Feedback Assessments

The goal of this paper is to provide an initial assessment of water-vapor feedback (WVF) in humid urban heat island (UHI) environments based on temperature difference data. To achieve this, a novel temperature difference WVF model was developed that can analyze global and UHI local temperature difference data. Specifically, the model was applied to a comparative temperature literature study of similar cities located in humid versus dry climates. The literature study found that the daytime UHI ΔT was observed to be 3.3 K higher in humid compared to dry climates when averaged over thirty-nine cities. Since the direct measurement of WVF in UHI areas could prove challenging due to variations in the temperature lapse rates from tall buildings, modeling provides an opportunity to make a preliminary assessment where measurements may be difficult. Thus, the results provide the first available UHI ΔT WVF model assessment. The preliminary results find local water-vapor feedback values for wet-biased cities of 3.1 Wm−2K−1, 3.4 Wm−2K−1, and 4 Wm−2K−1 for 5 °C, 15 °C, and 30 °C UHI average temperatures, respectively. The temperature difference model could also be used to reproduce literature values. This capability helps to validate the model and its findings. Heatwave assessments are also discussed, as they are strongly affected by UHI water-vapor feedback and support the observation that humid regions amplify heat higher than UHIs in dry regions, exacerbating heatwave problems. Furthermore, recent studies have found that urbanization contributions to global warming more than previously anticipated. Therefore, cities in humid environments are likely larger contributors to such warming trends compared to cities in dry environments. These preliminary modeling results show concern for a strong local UHI water-vapor feedback issue for cities in humid environments, with results possibly over a factor of two higher than the global average. This assessment also indicates that albedo management would likely be an effective way to reduce the resulting WVF temperature increase.

Physiological responses of Holstein calves and heifers carrying the SLICK1 allele to heat stress in California and Florida dairy farms.

Inheritance of the SLICK1 allele of the prolactin receptor gene improves thermotolerance of lactating Holstein cows under humid heat stress conditions. The aim of this study was to investigate whether pre- and postweaning Holstein heifers carrying the SLICK1 allele would show physiological responses indicative of higher tolerance to heat stress in high- and low-humidity climates. A total of 101 heifer calves of two age groups heterozygous for the SLICK1 allele and 103 wild-type half-siblings were evaluated during July 2020 in 3 dairy farms in central California and 2 in south Florida. Dry bulb temperature and relative humidity data were recorded during evaluation and used to calculate the temperature-humidity index (THI). Physiological measurements were obtained between 1600 and 1900 h in California, and 1200 and 1400 h in Florida and included rectal temperature, respiration rate, skin temperature, and sweating rate. Data were analyzed via Generalized Linear Mixed Models including the main effects of genotype, state, group, sire, farm within state, and interactions, with THI included as a covariate. The correlations between THI and dependent variables were analyzed via linear regression. The average 24-h THI was higher in Florida compared with California (90 vs. 72, respectively); the main driver of the higher THI in Florida was the high relative humidity (average 85.6% in Florida vs. 36.7% in California). In Florida, the rectal temperature of slick calves was 0.4°C lower than non-slick calves (39.5 ± 0.1 vs 39.9 ± 0.1°C); no differences were detected between slick and non-slick calves in California. Regardless of genotype, heifer calves in Florida had higher respiration rate, higher rectal and skin temperatures, and lower sweating rate than in California. This study is the first to evaluate physiological responses of calves carrying the SLICK1 allele under heat stress conditions in different climates. Our findings demonstrate that the presence of this allele is associated with lower rectal temperatures in pre- and post-weaning Holstein females. According to the physiological parameters evaluated, calves raised in Florida appeared to be under more severe heat stress; in those conditions, the SLICK1 allele was advantageous to confer thermotolerance as evidenced by lower rectal temperature in slick animals.

Autonomic thermoregulatory responses and subjective thermal perceptions upon the initiation of thermal behavior among resting humans in hot and humid environment

BackgroundWhile thermoregulatory behavior is critical for maintaining homeostasis, our knowledge of behavioral thermoeffectors in humid heat is limited compared to the control of autonomic thermoeffectors. The predictions that the frequency and duration of intensified humid heat events are expected to increase in the coming years underline this shortcoming. Therefore, this study aims to elucidate the activation of autonomic thermoregulatory responses and subjective thermal perceptions upon deciding to initiate thermal behavior in a hot and humid environment.MethodsTen young male adults participated in an experimental trial where local cooling was permitted at any time during the behavioral assessment during passive exposure to humid heat. The air temperature and relative humidity were kept at 33^{circ }C and 80%, respectively. Skin temperatures, core body temperature (T_{text {core}}), and skin blood flow (forearm, upper arm, and upper back) were obtained 120 s preceding thermal behavior. Local sweat rate (forearm and upper arm) and subjective thermal perceptions (neck and whole-body) upon thermal behavior initiation were also recorded.ResultsMean skin temperature ({overline{mathrm {T}}}_{text {sk}}) and T_{text {core}} increased prior to thermal behavior initiation (p= 0.002; p= 0.001). An increase in mean body temperature ({overline{mathrm {T}}}_{text {body}}) was also observed (p < 0.001). However, the initiation of thermal behavior is not preceded by an increase in skin blood flow (pge 0.154) and local sweat rate (pge 0.169). An increase in thermal discomfort and skin wetness perception was observed (ple 0.048; ple 0.048), while thermal sensation did not differ from the baseline (pge 0.357).ConclusionThese findings suggest that when given the opportunity to behaviorally thermoregulate in a hot and humid environment, changes in skin blood flow and sweat rate are not required for thermal behavior to be initiated in resting humans. Moreover, an increase in {overline{mathrm {T}}}_{text {sk}} and T_{text {core}}, which appears to cause an increase in thermal discomfort, precedes thermal behavior. In addition, an increase in {overline{mathrm {T}}}_{text {body}} leading up to thermal behavior initiation was observed, suggesting that changes in {overline{mathrm {T}}}_{text {body}} rather than {overline{mathrm {T}}}_{text {sk}} and T_{text {core}} alone mediate thermal behavior in humid heat. Collectively, the results of this study appear to support the hypothesis that the temporal recruitment of autonomic thermoeffectors follows an orderly manner based on their physiological cost.

Evaluation of Bioclimatic Discomfort Trend in a Central Area of the Mediterranean Sea

Effects of climate change are perceived in ever larger areas of the planet. Heat waves occur with increasing frequency, constituting a risk to the population, especially for the most sensitive subjects. Preventive information to the population on the characteristics of the phenomenon and on the behavior to be supported is the means to reduce the health risks. To monitor the intensity of heat and the physiological discomfort perceived by humans, there are indices based on the perception of meteorological parameters such as temperature and relative humidity. In this work, by applying the Thom Discomfort Index (TDI), the first bioclimatic characterization of the provinces that make up Sicily, a Mediterranean region defined as a hotspot for climate change, was performed by the authors. The nonparametric Mann–Kendall test was applied to the daily values of the TDI in all provinces in order to verify the presence of significant trends. The test results highlighted the existence of increasing trends, especially in the months of August and September, when the TDI value undergoes a significant increase due not only to high temperatures, as one might expect, but above all to a high humidity rate. When these two meteorological parameters reach certain values, the physiological discomfort from humid heat represents a risk to the population.