Daily Heat Research Articles

New insights of designing thermal insulation and heat storage of Chinese solar greenhouse in high latitudes and cold regions

The demand for the quality and yield requirements of crops in high latitudes and cold regions is increasing. The traditional structure design of the Chinese solar greenhouse (CSG) can't meet the needs of over-winter production of warm-season crops, the thermal insulation and heat storage capacity of the CSG need to be further improved. This paper proposed an innovative theory of designing the thermal insulation and heat storage of the CSG that divided into independent heat collection-release system, independent heat storage system and independent thermal insulation system. A novel CSG was designed and built in the Shenyang area, experimentally tested and analyzed the application performance in winter. The results showed that the minimum nighttime air temperature with the novel CSG was 10.1 °C on average during seven continuous days of the coldest temperatures and overcast weather. The maximum temperature difference between inside and outside the novel CSG increased to 38 °C in winter. The average daily heat collection ratio for the five coldest and overcast days was 73.4%. This paper can provide new sights and theoretical guidance for the design of the thermal insulation and heat storage of the CSG in high latitudes and cold regions.

Heat warnings, mortality, and hospital admissions among older adults in the United States.

Heat warnings are issued in advance of forecast extreme heat events, yet little evidence is available regarding their effectiveness in reducing heat-related illness and death. We estimated the association of heat warnings and advisories (collectively, "alerts") issued by the United States National Weather Service with all-cause mortality and cause-specific hospitalizations among Medicare beneficiaries aged 65 years and older in 2,817 counties, 2006-2016. In each county, we compared days with heat alerts to days without heat alerts, matched on daily maximum heat index and month. We used conditional Poisson regression models stratified on county, adjusting for year, day of week, federal holidays, and lagged daily maximum heat index. We identified a matched non-heat alert day for 92,029 heat alert days in 2,817 counties, or 54.6% of all heat alert days during the study period. Contrary to expectations, heat alerts were not associated with lower risk of mortality (RR: 1.005 [95% CI: 0.997, 1.013]). However, heat alerts were associated with higher risk of hospitalization for fluid and electrolyte disorders (RR: 1.040 [95% CI: 1.015, 1.065]) and heat stroke (RR: 1.094 [95% CI: 1.038, 1.152]). Results were similar in sensitivity analyses additionally adjusting for same-day heat index, ozone, and PM2.5. Our results suggest that heat alerts are not associated with lower risk of mortality but may be associated with higher rates of hospitalization for fluid and electrolyte disorders and heat stroke, potentially suggesting that heat alerts lead more individuals to seek or access care.

Emission and spatialized health risks for trace elements from domestic coal burning in China

Residential coal combustion (RCC) emission exhibited obvious daily variation, while no real-time estimation of air pollutants from RCC has been reported, as the shortages of corresponding activity dataset and emission factors with high time resolution. A real-time monitoring platform for RCC emission was established. Hourly emission factors of 18 typed of TEs from eleven kinds of chunk coals and nine kinds of honeycomb coals burning in China were obtained. The monthly and hourly coal consumption amounts were calculated with reference and our field survey. Then the hourly TEs emission inventories from RCC were established in China. GEOS-Chem and Risk Quotients Models were utilized to map the spatialized health risks of hazardous elements, including the gridded hazard index and carcinogenic risk. The result indicated that the EFs of TEs would be underestimated if the tests only consider flaming conditions. Cu, K, Ca, Zn, and Co were the top five elements from RCC, with corresponding emission amounts as 1397.7, 1054.0, 676.0, 623.5 and 420 tons in 2017, respectively. K, Ti, Fe, Sn, and Sb showed hourly peak values under flaming dominated periods, accounting for 48.2%, 45.9%, 31.8%, 42.8%, and 33.8% of their daily emissions. Other elements (e.g., V, Co, As, Hg and Pb) exhibited higher emissions under smoldering dominated period in nighttime, accounting for 22.2%, 32.9%, 27.6%, 34.7%, and 28.4% of their daily emissions. TEs emission from RCC closely follows the habits of human daily cooking and heating activity. The national HI were lower than the acceptable level (HI ≤ 1) except Sichuan Province (up to 1.2). Higher carcinogenic risks (≥1 × 10-6) occurred in parts of Sichuan, Shanxi, Hunan and Hubei, which were up to 2.0 × 10-5. The high-resolution TEs emission inventories could be useful for future modeling works on the formation and evolution of air pollution and are helpful for human exposure assessment.

The effects of intermittent feeding and cold water on welfare status and meat quality in broiler chickens reared under daily heat stress.

This study was aimed to determine the effects of feeding type (ad libitum: AF and intermittent: IF) and water temperature (normal: NW and cold: CW) treatments on welfare status and meat quality in fast-growing broiler chickens reared under daily heat stress between 22 and 42 days of age. The chickens' panting rate and rectal temperature were determined at 4, 5, and 6 weeks of age and twice a week in 3 female and 3 male chickens in each pen. Welfare traits such as foot pad dermatitis (FPD), hock burn (HB), breast burn (BB), and leg problems (LP) were examined individually at 42 days of age. At day 43, 3 male and 3 female chickens per pen were randomly selected and slaughtered after an 8-h fasting period; pH and color (lightness (L*), redness (a*), and yellowness (b*)) of breast and thigh meat were determined. AF × C W chickens had significantly higher panting rates at all ages than the other groups (P < 0.05). While FPD and LP were not affected by feeding type and water temperature treatments, interaction effects on HB and BB were found significant (P < 0.05). The HB and BB levels were the lowest in AF × NW chickens (P < 0.05). While treatments did not change to any color traits in breast meat (P > 0.05), interactions significantly affected the yellowness (b*) value in the thigh (P < 0.05). In conclusion, management practices such as IF and CW in fast-growing broilers could not completely reduce the undesirable effects of heat stress on some welfare and meat quality traits, and in some cases, even caused more negativity.

Simulation research on distributed energy system based on coupling of PV/T unit and wind-to-heat unit

With people's pursuit of high-quality life, building energy consumption is increasing. To expand the development and utilization of renewable energy in building energy supplement, a novel distributed energy system based on PV/T unit and wind-to-heat unit coupling is proposed. The PV/T unit, wind turbine, heat pump, ground heat source, and energy storage device, are combined together to generate heat and electricity. Different operational modes of the system under different conditions around one year are established. The mathematical model of the system is introduced. The solar-to-thermal conversion performances of a new PV/T collector are simulated under different working conditions. As the key component of wind-to-heat unit, the performance of the twin-screw compressor is investigated by simulation with various parameters. Finally, the applicability of the system is analyzed through a case study in Northeast China. The averaged heating power of the system is 184.45 kW, and the average generating power is 127.66 kW. The daily heat supply and the daily power generation are about 1.59 × 104 MJ and 1.28 × 103 kW·h, respectively, which can meet the building load of three villas. By the simulation results, the novel system is proved to be an effective choice to achieve the aim of multiple types of renewable energy combined heating.

Control-oriented thermal network models for predictive load management in Canadian houses with on-Site solar electricity generation: application to a research house

This paper presents a methodology for development of control-oriented thermal RC network models for optimized HVAC load management in typical electrically heated single-family two-storey detached houses in Québec, assuming that there are three zones and it is equipped with photovoltaics and battery storage. Using data from an unoccupied research house, two 3rd order RC networks are developed and calibrated. One model (3C6R network) assumes that each floor is a separate thermal zone, and the other model (3C7R network) assumes that the south-facing zone and the north-facing zone of the building are separate zones. Application of model predictive control with both developed models results in an average 12.1% reduction in the daily heating load, 19.8% reduction in the total daily electricity imported, 68.1% reduction in the peak demand, 67.0% reduction in the energy cost, and 13.4% increase in the self-consumption of on-site generated solar electricity compared to a traditional reactive controller.

Experimental characterization of a water/rock thermocline cold thermal energy storage for optimization of condenser cooling

The concept of a cTES (for cold Thermal Energy Storage) is experimentally investigated in this paper. It aims at demonstrating its technical relevancy, for arid regions, in improving the efficiency of a dry cooled turbine's condenser. Gain is realized by postponing total or part of the daily heat exhausted from the condenser and shifting the release of the remaining heat during the night-time when the ambient temperatures are lower. The global system consists in a 13 m3 dual-media water/rock thermocline TES connected to a 110 kW heat source and a 100 kW dry cooler. Experiments have been first conducted to validate the thermal storage behavior in well-controlled operations. Then, the thermal storage has been connected in parallel with the dry cooler to highlight the global behavior of the “dry cooler / cTES” cooling system under different operation's conditions. Results confirm that the cTES is able to compensate the performances loss of the dry cooler during daytime in case of high ambient temperature and to evacuate heat and to store cold during nigh-time. The control of the cTES is simple, characterized by continuous and smooth transitions from one mode to another and without discontinuities in performances and operations.

Empirical evaluation of energy profiles of thermally-efficient homes with smart energy systems and controls

Smart control technologies are beginning to be deployed in homes to optimise heating and alter the timing of domestic energy demand to enable residential demand side response (DSR). This paper presents before (baseline phase) and after (control phase) evaluation of the monitored indoor temperature and energy demand during the heating season in 10 new-build dwellings, each of which received a 5kWh electro-chemical battery and smart control to enable shifting of heating energy demand. The dwellings had air source heat pumps (ASHP) and 2kWp solar photovoltaic (PV) panels, and were located in a social housing estate in Barnsley, England. For eight dwellings, heat pump electricity use per heating degree day was found to decrease by 10% and narrow baseline peaks were suppressed during the control phase. Daily mean grid electricity import and heat pump electricity use in the peak period (4pm – 7pm) were measured as 4.0 kWh and 1.4 kWh during the control phase as compared to 3.8kWh and 1.3 kWh for the baseline phase. However the use of a flat tariff (single-rate) meant that battery charging-discharging capability was not fully utilised. Time-of-use tariff would further enhance cost savings associated with the change in the timing of energy demand.

Performance Comparison of CPC based solar installations at different locations in India and analysis of variation pattern

Currently the industrial heat demand is met by using expensive fossil fuels. Exclusive use of solar energy is not feasible due to the fluctuating pattern of solar radiation intensity. Solar hybridization with the existing heating system can be an appropriate solution to meet the process heat requirement of many industries. Concentrator Solar Thermal (CST) technologies can generate the medium temperature heat required for industrial processes. The present study was undertaken with an objective of comparing and analyzing the designed performance of the solar fields using the Compound Parabolic Concentrator (CPC) technology against the actual measured performance values for boiler feed water preheating application at two different locations in India. The optical efficiency of the CPC collector, 64.8%, obtained when tested as per part 5 of IS 16648:2017 was used for designing the solar fields as per the daily heat requirement. The performance of the installations at both the locations was monitored for a period of five months. The observed variation in the performance of each installation than the designed performance was compared and analyzed for the causes. The average variation in designed and measured performance was in the range of 9.0% to 9.8% for location 1 and 2 respectively, attributing to heat rejection from the collector attachments and fluid transfer lines, dust effect on the absorber and reflector of CPC, instrument’s uncertainty, other losses due to shadow effect, vacuum loss from the tubes, dislocation of tubes, heat removal and usage pattern etc. The reasons of the losses from both the fields were of the similar nature, which should be taken into account to design a solar thermal system to achieve predicted performance near to the designed performance. Preheating of boiler feed water is one of the potential applications of solar CPC technology.

Revisiting heat energy consumption modeling: Household production theory applied to field experimental data

This paper offers new insights on utility-driven heat energy consumption derived from using an interdisciplinary modeling framework that is based on Becker's household production theory. The research question addressed is whether economic aspects affect short-term, less conscious behavior in the same way as long-term, more conscious behavior. From the investigation, new insights on the usefulness of price-based energy policy measures targeting heat energy consumption are gained. The household production model proposed for analyzing residential heat energy demand integrates economic, engineering and behavioral elements. Comparative statics enables an interdisciplinary integration of price- and income functions to cover economic influences on heat energy (service) consumption, the production function to cover technical influences, and the utility-based choice architecture to cover utility maximization influences. Based on a functional representation of the theories, a panel data model of heat energy consumption is estimated. The empirical analysis is based on data from 60 adjacent apartments in South-West Germany. We find empirical evidence that the price elasticity of demand is only statistically significant when using yearly aggregated data. This result provides evidence that occupants apparently do not act much based upon energy price levels when following their daily home heating routine. In less frequent considerations, as e.g. according to their yearly billing cycles, occupants adjust their heat energy consumption in response to the fuel price changes noticed on the energy bill. Furthermore, in relation to the other influences on heat energy consumption, we find that the price impact is less pronounced than the impact of comfort conditions. Therefore, a CO2 price on heat energy might set the right incentives to invest in more energy-efficient heating technology, but hardly alter comfort-taking or rebound effects.

Numerical study and thermal evaluation of a triple glass window under Mexican warm climate conditions

The conjugate heat transfer in a triple glass window (TG) is presented to determine the air-gap width that improves its thermal performance under a warm Mexican climate. Five different air-gap widths (Hc = 6, 10, 14, 18, and 22 mm), 4 mm of thickness for each glass, and 80 cm in height are considered. Hourly climatic data of the coldest and the warmest day of Merida were used to assess the thermal behavior of the TG, and the results were compared against a double glass (DG) and a singles glass window (SG). A validated numerical code based on the Finite Volume Method was developed to model the windows. We found that an air-gap width of 10 mm reduces the hourly heat flux to the indoor during the warmest day up to 17.7 and 38.7 % compared to the DG and SG, respectively. Moreover, the daily total heat flux, electricity cost, and CO2 emission on the TG are up to ≈ 40% lower than an SG, respectively. Therefore, we recommended a TG to improve the thermal performance on windows under weather conditions of Merida, Yucatan.

Heat stress, labour productivity and adaptation in Europe—a regional and occupational analysis

Labour exposure to heat stress driven by climate change will increase significantly with the rising global temperatures. Under heat stress, workers have to reduce work intensity and take longer breaks from work to prevent occupational illness and injuries. This study explores how the global warming and the resulting increase in heat stress can directly affect productivity of workers and indirectly impact upon the broader economy. Occupational statistics for 269 European regions are combined with daily heat stress indicator derived from a set of high-resolution climate scenarios. The novel approach, enabled by using a set of published exposure-response functions, assesses workers productivity losses differentiated by occupations. A macro econometric model of the European economy is then used to asses implications of change in productivity in monetary terms. The study finds that, compared to nowadays, productivity of labour can be 1.6% lower in Europe in 2080s, with a clear geographical gradient showing that southern and eastern regions are much more affected (e.g. up to 5.4% productivity loss in Greece). Furthermore, regions where the dominant occupations have relative lower earnings would also experience higher productivity loses. The analysis also focuses on the potential role of adaptation to reduce the productivity and economic losses, via air conditioning and a preliminary assessment of the potential of wearable robotics, which can reduce damages by 30%–40%.

Applicability of Heat Index for Effective Heatwave Response

Damage caused by heatwaves has been increasing recently worldwide. As climate change led by global warming progresses, heatwaves are projected to cause the most damage. Thus, it is very important to issue an appropriate heatwave advisory so that one can be prepared for it. Considering that the degree of heat experienced by people differs depending on the difference in humidity between regions with similar summer temperatures, it is necessary to evaluate whether the issuance of a heatwave warning using only the daily maximum temperature is appropriate. This study intends to examine the applicability of the heat index considering both temperature and humidity for effective heatwave response. First, the agreement between the occurrences of heatwaves and heat-related illness, where the occurrence is decided by the daily maximum temperature and daily maximum heat index, was evaluated. The results show that when the daily maximum heat index was applied as a criterion for issuing a heatwave warning, the coincidence with the occurrence of heat-related illness was more than two times higher than when the daily maximum temperature was applied. Next, on evaluating the prediction accuracy of the heat index according to the prediction-related leading time, the accuracy of the heat index was noted to be higher than that of the temperature for all the leading times; the highest accuracy was shown at the leading time of 10 hours (NSE = 0.7196; CORR = 0.8698). Based on the results of this study, it is necessary to consider using a heat index that contains both temperature and humidity elements to issue a heatwave warning. Furthermore, to establish regional standards for heatwave warnings, the relationship between heatwave characteristics and meteorological factors should be first analyzed using long-term data from various observation points.

Performance Studies and Energy-Saving Analysis of a Solar Water-Heating System

This paper proposed an experimental test: the solar water-heating system was been monitored for a whole year to analyze collector performance in an actual operation process. Heat-collecting efficiency, heating capacity, power consumption, and heat required were analyzed theoretically. Results showed that solar irradiance and ambient temperature were positively correlated with heat collection efficiency, and the daily average heat collection efficiency was up to 56.63%. In winter, the auxiliary heat source consumed the most power, almost all of which bears the heat of users. The heat collection in summer met the demand for hot water, and the guarantee rate of solar energy could reach 100%. The energy saving properties and CO2 emission reduction were analyzed. This system had a significant effect on the energy-saving effect and environmental protection. The analysis showed that the hot-water system can fully meet the design requirements under the condition of relatively sufficient solar energy, and can operate stably, which has a certain guiding significance for the design and application of large-scale solar hot-water systems.

Associations between PM2.5 and term low birth weight in a North Carolina cohort and effect modification by extreme heat events

BACKGROUND AND AIM: Low birth weight (LBW) can be an indicator for poor health outcomes, including neonatal mortality, and may be caused by environmental exposures. Previously, exposure to high ambient temperatures was linked with increased odds of LBW, while results looking at fine particulate matter (PM₂.₅) exposure have been mixed. Our objective is to determine if a relationship exists between PM₂.₅ exposure during pregnancy and term LBW and then to see if that relationship is modified by concurrent exposure to extreme heat events. METHODS: We used North Carolina birth registry data linked to exposure data using geocoded addresses obtained from the birth records (2002-2015) for live, full-term (≥37 weeks gestation), singleton births (n=1,280,064). LBW was defined as weighing 2,500g. PM₂.₅ concentrations were obtained using EPA’s CMAQ downscaler and were averaged over trimester and entire pregnancy. Extreme heat events were defined as a census-tract specific daily maximum heat index 95th percentile for at least 2 consecutive days. We computed census-tract specific 95th percentiles using heat index data for the summer months (1981–2010). For inclusion in a trimester analysis, portions of that trimester had to occur between May-September. We estimated risk differences (RD) and 95% confidence intervals (CI) with interaction terms for total number of extreme heat events during the corresponding exposure period, adjusting for Medicaid and maternal age. RESULTS:We observe generally null relationships between PM₂.₅ and term LBW for all trimesters (RD per 10,000 [95% CI]) ranged from -1 [-8, 6] to 1 [-5, 6]) and the pregnancy (1 [-5, 8]). These results persisted when extreme heat events were included as an interaction term (Pregnancy:1 [-5, 8]). CONCLUSIONS:Preliminary analyses did not indicate a relationship between PM₂.₅ and term LBW or effect measure modification by extreme temperature days. This abstract does not reflect CDC, ATSDR, or EPA policy. KEYWORDS: Air pollution, birth outcomes, particulate matter, climate, environmental epidemiology

Changing heat impacts on mortality and implications for mitigation planning in New York City

BACKGROUND AND AIM: Heat mitigation planning requires careful characterization of the adverse impacts of temperature on health outcomes. New York City (NYC) has used observed temperature-mortality relationships to revise the city’s heat advisory trigger threshold, but such assessment must be ongoing as temperatures rise. METHODS: We analyzed 5-year rolling periods of weather and mortality data for May-September, 1997-2017 in NYC to estimate changes in cumulative relative risks (CRR) with up to 3-day lag and attributable deaths over time using both the extreme heat event (EHE) day indicator (0/1) for NYC’s heat advisory threshold (=35°C for two days or =38°C for any duration) and a continuous daily maximum heat index (or maximum temperature when heat index was unavailable), or MAX, using quasi-Poisson distributed lag non-linear models. For MAX, we used the median for the entire period (28°C) as reference, estimated CRRs at 37°C (median temperature of days above 35°C), compared to EHE CRR, and estimated attributable deaths for all days above 28°C. RESULTS:CRRs for both EHE and MAX have been comparable and stable (~1.08) in the recent decade and lower than in earlier periods (~1.10). The number of EHE days were stable over the study period (~10 days/year), while non-EHE summer days (28°C to less than 35°C) have been increasing (57 days in 1997-2001 vs. 74 days in 2013-2017). The estimated attributable deaths for MAX mirror the warming climate, increasing since 1997, and surpassing those for EHE in recent years (267 MAX vs 94 EHE for 2013-2017). CONCLUSIONS:Estimated excess deaths due to non-EHE days are larger than those for EHE days and increasing. In NYC, where the overall air conditioning prevalence is greater than 90%, near-term heat mitigation should focus on addressing inequities in air conditioning and energy insecurity in the most-impacted communities along with other structural heat mitigation strategies beyond emergency response. KEYWORDS: temperature, mortality, extreme heat, attributable deaths, heat mitigation

Associations between Heat Index and Child Emergency and Hospital Visits in New York City

BACKGROUND AND AIM: Emerging literature has documented heat-related impacts on child health, yet few studies have evaluated the effects of heat among children of different age groups or compared emergency department (ED) with hospitalization risks, which may serve to indicate morbidity severity. We examine the differing associations between maximum heat index (a metric that combines maximum temperature and relative humidity) and risk of ED visits and hospitalizations among children by age group. METHODS: We used New York Statewide Planning and Research Cooperative System (SPARCS) data on children aged 0-18 years admitted to EDs (n = 2,252,550) and hospitals (n = 228,006) during the warm months (May-September) from 2005 to 2011. Using a time-stratified, case-crossover design, we estimated the risk of ED visits and hospitalizations associated with daily heat index for children of all ages and by age group. Heat index was modeled using distributed lag functions accumulated over lag 0 to 5 days using a linear term for ED visits and a piecewise linear term above the threshold of 90F for hospitalization. RESULTS:The average maximum heat index over the study period was 84.4F (range 48F-135F). Heat index conferred an increased risk of ED visits for children of all age groups, with the strongest effect observed among children 0-4, followed by those 13-18 and 5-12 years. For hospitalizations, an elevated risk was observed when heat index exceeded a threshold of 90F, and the effect was found only among adolescents 13-18 years. CONCLUSIONS:Heat impacts on child morbidity differ between ED visits and hospitalizations and by age groups. Young children, as well as older children and adolescents, are sensitive to heat effects. Our findings underscore the importance of focusing on children and adolescents in targeting heat illness prevention and emergency response activities, especially as global temperatures continue to rise. KEYWORDS: Temperature, Children and adolescents, Emergency department, Hospitalization, New York City

Effects of oxygen concentration during incubation and broiler breeder age on embryonic heat production, chicken development, and 7-day performance

Older breeder flocks produce eggs with a relatively larger yolk and thereby a higher nutrient availability than young breeder flocks. To optimise nutrient utilisation and embryonic development throughout incubation and posthatch period, embryos originating from older breeder flocks may require a higher oxygen availability. The current study investigated effects of broiler breeder flock age and incubational oxygen concentration on embryonic metabolism and chicken development until 7-day posthatch. Similar sized eggs of a young (28–32 week) or old (55–59 week) Cobb 500 breeder flock were incubated at one of three oxygen concentrations (17%, 21% or 25%) from day 7 of incubation until 6 h after emergence from the eggshell. Posthatch, chickens were reared until 7 days of age. Egg composition at the start of incubation, heat production during incubation, and embryo or chicken development at embryonic day (ED)14 and ED18 of incubation, 6 h after hatch and day 7 posthatch were evaluated. An interaction was found between breeder age and oxygen concentration for yolk-free body mass (YFBM) at ED18. A higher oxygen concentration increased YFBM in the old breeder flock, whereas no difference was found between 21 and 25% oxygen in the young breeder flock. Yolk size was larger in the old compared to the young flock from ED0 until 6 h after hatch. Breeder flock age did not affect YFBM at ED14 and 6 h after hatch nor daily embryonic heat production, but there were some effects on relative organ weights. Chickens of the old compared to the young breeder flock showed a higher weight gain at day 7, but at a similar feed conversion ratio (FCR). A higher oxygen concentration during incubation stimulated embryonic development, especially between 17% and 21% of oxygen, in both flock ages. Although this growth advantage disappeared at 7 days posthatch, a low oxygen concentration during incubation resulted in a higher FCR at 7 days posthatch. Results indicated that breeder flock age seemed to influence body development, with an advantage for the older breeder flock during the posthatch period. Oxygen concentrations during incubation affected body development during incubation and FCR in the first 7 days posthatch. Although an interaction was found between breeder flock age and oxygen concentration at ED18 of incubation, there was no strong evidence that nutrient availability at the start of incubation (represented by breeder flock ages) affected embryo and chicken development at a higher oxygen concentration.

Physical connection of sensible and ground heat flux

Characterizing physical relationships between the sensible, latent and ground heat flux at the Earth surface is of crucial importance in studying the global energy, water, and carbon cycles. Here we demonstrate an analogy between the daily mean turbulent heat transfer in the atmospheric surface layer and conductive-advective heat transfer in soil. This finding, in conjunction with temperature continuity at the land–atmosphere interface, uncovers a physical linkage between sensible and ground heat flux. The proposed relationship and its ramification for estimation of latent heat flux are validated based on daily averaged data from six AmeriFlux eddy covariance stations in North America over a wide range of land covers and climate regimes.

Long-term trend of heat waves and potential effects on phytoplankton blooms in Lake Qiandaohu, a key drinking water reservoir.

Global warming is increasing the frequency and duration of heat waves, which is defined as when air temperature exceeds a threshold for more than specific consecutive days. Ecosystem around the globe will be impaired by heat waves just like the exposures to dangerously high temperatures as a public health threat to human. However, the knowledge of the response of lake and reservoir ecosystem to heat waves is largely unknown although it has been argued that climate warming may increase the incidence of harmful algal blooms. We examined the long-term trend of heat waves and how the variability of phytoplankton biomass responds to lake heat waves on a deep reservoir (Lake Qiandaohu). Long-term (1980–2020) meteorological observation in the lake watershed showed a significant warming trend of 0.36 °C per decade for the yearly average of daily average air temperature and the yearly average of daily maximum air temperature of 18.32 °C was observed in 2016. Meanwhile, a significant increasing number of heat wave events lasting longer was observed, and Lake Qiandaohu suffered an unusually severe lake heat wave in summer 2016. Significant correlations were found between the yearly average of daily maximum air temperature and heat days, heat wave events, and heat wave days. Nuisance phytoplankton bloom was found in Lake Qiandaohu by high frequency observation and remote sensing monitoring in summer 2016. Remote sensing estimation from two Landsat 8 Operational Land Imager (OLI) images showed that the average chlorophyll a (Chla) was 7.45 ± 4.89 μg/L on July 18 before heat wave and 18.96 ± 0.98 μg/L on August 19 during the heat wave. Two heat wave events lasting from July 20 to August 2 and August 11 to 26 with average surface water temperature of 29.93 and 31.99 °C promoted two marked phytoplankton blooms with average Chla concentrations of 11.75 ± 4.08 and 10.53 ± 1.65 μg/L in the central lake region, respectively, as evidenced by high-frequency buoy data. These findings suggest that heat waves are likely to yield an increased threat of harmful algal bloom in freshwater ecosystems. With lake heat waves projected to increase in frequency, duration, and spatial extent with global climate change, more studies are needed to improve our understanding of lake heat waves and their potential effects on the species, communities, frequency of phytoplankton bloom, and also help providing advanced schemes of water quality management.