Number Of Hot Days Research Articles

Spatially differentiated effects of local moisture deficit and increased global temperature on hot extreme occurrences

This study compares the relative importance of global temperature change and local moisture deficit in influencing the frequency of hot extremes on a global scale. For the first time, the wavelet decomposed GRACE terrestrial water storage is applied in examining the relationship between soil moisture (θ) and the number of hot days in the hottest month (NHD). It reveals stronger θ-NHD relationships over larger areas than the selected commonly used soil moisture proxies (i.e., standardised precipitation index and a GLDAS model-derived product). During 1985–2015, local moisture deficit played a more important role in influencing hot extreme occurrences in the regions with relatively flat topography, thick soil and where inter-annual rainfall variability is large. They cover an area 1.6 times larger than the areas (e.g., mountain ranges, deserts) where the global temperature change has posed a stronger influence. Under a continuing increase of greenhouse gas forcing, global actions in reducing emissions will support combating the expansion of hot extremes. However, this study shows that necessary attention should also be directed to mitigating the moisture deficit exacerbating hot extremes, e. g., through regional adaptive land management.

The 2021 European Heat Wave in the Context of Past Major Heat Waves

AbstractThe past two decades in Europe have been characterized by numerous major heat waves, with record‐breaking temperatures reported also during the summer of 2021. While most previous studies on heat waves were based on land‐only datasets (station or gridded), we use the ERA5 reanalysis to capture also heat wave characteristics over water bodies. An up‐to‐date list of major European heat waves since 1950 is presented, and the 2021 heat wave is evaluated in this long‐term context. This event was record‐breaking in length at the European scale, and in many other aspects (spatial extent, magnitude) comparable to the 2003 and 2010 major heat waves. The summer of 2021 was unprecedented over Europe according to the number of hot days (63) and the earliest start of a major heat wave (June 19), while the 2019 heat wave with record‐breaking temperatures across Western Europe stands out as to its intensity. Another recent major heat wave in 2018 ranked fourth in terms of magnitude. The spatial pattern in occurrence of the most severe heat wave since 1950 in individual parts of Europe is dominated by the 2003 (Western Europe), 2010 (Eastern Europe), 2018 (Scandinavia), and 2021 (Mediterranean) major heat waves. Overall, 83% of the domain area experienced the most severe heat wave in the past two decades (2002–2021), which demonstrates a rapidly changing summer climate in Europe.

Assessing heat index changes in the context of climate change: A case study of Hanoi (Vietnam)

Air temperature and humidity have a great impact on public health, leads to heat stress. The US National Weather Service uses temperature and relative humidity to build a heat index (HI) as a metric to identify the thresholds for heat stress as felt by the public. Under climate change conditions and especially in hot humid weather during summer, the number of hot days in Hanoi has increased in recent times. Subsequently, the heat index is rising in both number of occurrences and level of intensity leading to increasing temperature stress on people’s health. The daily heat index for the future was simulated using maximum daily temperature and minimum daily relative humidity based on climate change scenarios. Maximum daily temperature was provided by the climate change model, while minimum daily relative humidity was estimated from the following: maximum daily temperature, mean daily temperature and daily rainfall. Results show that in the future, the heat index will increase by 0.0777°C/year in the RCP 4.5 scenario and 0.08°C/year in the RCP 8.5 scenario. Number of weeks with heat at danger tends to increase to 5.5 weeks/5 year for scenario RCP 4.5, and it is 6 weeks/5 years under RCP 8.5 scenario. In particular, the number of days of heatstroke over a 30-year period (from 1991 to 2020) amounted to only 4, that is an average of 0.13 days of the year, which represents a very rare weather phenomenon in the past. In contrast, under an RCP 4.5 scenario in the future over a 30-year period, the average number of days per year will be 2, 57 days; while the average number of days per year under an RCP 8.5 scenario would be 3, 87 days. This phenomenon will be mainly concentrated in the months of June, July, and August. Projections of this type are a key tool for communities working out how they will adapt to heat stress in the context of climate change.

Current and future risks of drought-induced mortality in Pinus radiata plantations in New South Wales, Australia

ABSTRACT Drought is a regular feature of Australian landscapes, and its intensity and frequency are likely to increase in a changing climate. Land managers are grappling with managing the impacts of drought, with large-scale die-offs occurring more frequently in forests globally. Drought-induced tree mortality has caused major impacts in Pinus radiata plantations in New South Wales, Australia, with extended drought, heatwaves and pest and disease attacks all recognised as predisposing, inciting or contributing factors. The extent and severity of drought-induced tree mortality has been mapped across the Pinus plantation estate in New South Wales annually since 1996. In this study, we used this long-term empirical data to develop a model of drought risk for P. radiata plantations. Using random forest, we identified site index, annual temperature, annual rainfall, elevation and increasing number of hot days (above 20°C and 35°C) as the influencing variables associated with drought-induced tree mortality. We then used this model to look at the risk of drought-induced tree mortality under climate-change scenarios in 2050 and 2070. Although forest managers already understand the drought risk in their estates, we developed an empirical model and produced GIS layers at high resolution (100 m) to assist in more accurately and effectively managing drought. The accuracy and precision of our model (overall accuracy 89.2%, kappa 0.75) enables forest managers to include it in their decision-making in the management of the potential impacts of drought on the current plantation estate (e.g. via modified silvicultural regimes) as well as in the future (e.g. modified silvicultural regimes or planting drought-tolerant genotypes).

Heat Policies and AC Availability in US Prison Systems

BACKGROUND AND AIM Climate change will increase the number of hot days and heatwaves leaving incarcerated populations particularly vulnerable to extreme heat due to their lack of agency and control over their heat exposure. Previous prison heat policy analysis has not utilized Heat Index to provide context for the implementation of policies or had access to air-conditioning data. We aimed to examine the coverage and gaps of US prison system heat policies and air-conditioning access. METHODS Prison heat policies were identified using 52 prison system (50 states, DC, and Federal Bureau of Prisons) websites and complemented by state legislation. Heat policies were analyzed using the National Weather Service’s (NWS) Heat Index Calculator on maximum reported temperature values. Facility-level air-conditioning data for 18 prison systems were public or received through public records requests by UCLA’s COVID-19 Behind Bars, with facility function, capacity, and heat risk collected from federal, state, and the Intercept’s Climate and Punishment datasets. RESULTS Half of the prison systems had publicly-available heat policies (n=52), of which 81% included temperature values (n=21). 64% of heat indices using maximum indoor temperature (n=14) would be classified as "caution” and 63% of heat indices using temperatures when respite resources would be provided (e.g. extra water) (n=8) were classified as "extreme caution” by the NWS assuming 50% relative humidity. 18% of facilities (n=374) lacked AC access completely. Among these, 55% of non-air-conditioned facilities (41,000 operational capacity) are at "severe or extreme heat risk”. Overall, 23% of facilities whose function includes serving heat-sensitive populations (n=202), lack any air-conditioning despite their heat risk. CONCLUSIONS This study emphasizes the need for national correctional temperature policies and air-conditioning requirements to protect the thermal health of those who live and work in carceral facilities. KEYWORDS environmental justice built environment prison

Dictyocaulus viviparus bulk tank milk seropositivity is correlated with meteorological variables

Control of infections with Dictyocaulus viviparus is difficult due to its volatile epidemiology. In the absence of predictive models, ‘vigilance and treatment’ is today’s mainstay for control. In order to evaluate the potential of predictive model development to support a more preventative approach, this longitudinal study aimed at understanding the influence of weather factors on D. viviparus bulk tank milk antibody ELISA results. Bulk tank milk samples were analysed with a Major Sperm Protein-based ELISA (expressed as an optical density ratio) twice monthly on 717 Flemish dairy farms during the grazing season (April–October) in 2018. Meteorological data of the sampled farms were obtained at 1 km spatial scale using the ALARO-SURFEX climate model. A mixed effects model showed that the bulk tank milk optical density ratio was significantly associated with the month of sampling, evapotranspiration, temperature and its quadratic term, the number of hot days and the number of rainy days in the 7–8 weeks prior to sampling. There were significant farm effects involved. The model’s accuracy to predict bulk tank milk optical density ratio infection status was 80%, while optical density ratios were generally overestimated by 38%. Inclusion of the previous (2-week-old) optical density ratio values increased accuracy to 86% and reduced the mean square error. We conclude that meteorological parameters have a predictive value for bulk tank milk optical density ratio results, while further research should evaluate model improvements through the addition of herd management factors as well as confirm the predictive power through external validation in additional farms and years.

Monitoring Heat Extremes across Central Europe Using Land Surface Temperature Data Records from SEVIRI/MSG

The frequency and intensity of extreme hot events have increased worldwide, particularly over the past couple of decades. Europe has been affected by unprecedented mega heatwaves, namely the events that struck Western Europe in 2003 and Eastern Europe in 2010. The year 2018 was also reported as an unusually hot year, with record-breaking temperatures in many parts of Europe during spring and summer, associated with severe and unusual wildfires and significant crop losses in central and northern Europe. We show the ability of Land Surface Temperature (LST), retrieved from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard Meteosat Second Generation (MSG) to monitor heat extremes, using the 2018 European event as a showcase. The monitoring approach relies on monthly anomalies performed as departures from the median and the monthly number of hot days (NHD), both computed for satellite LST derived from MSG and MODIS, and for 2 m air temperature (T2m) from ERA5 reanalysis, using as threshold the 90th percentiles. Results show strong monthly LST anomalies during the spring and summer of 2018 extending over central and north Europe. Over a vast region in Central and Northern Europe, LST reached the last 15 years high record. Moreover, those outstanding warm LSTs persisted for more than four months. Results obtained using MODIS LST and ERA5 T2m show similar patterns, which, although slightly less intense, corroborate the exceptionality of the heat extremes observed over central and northern Europe during 2018. The spatial pattern of the number of monthly record high anomalies over the MSG observations period clearly depicts the regions in Northern and Central Europe affected by the complex phenomena that occurred in 2018, which resulted from the combined effect of an extreme heatwave in spring and summer with extensive dry conditions. Therefore, the results highlighted the suitability of MSG LST to evaluate and monitor heat extremes alone or combined with dry and bright conditions and prompts the potential of other climate data records from geostationary satellites to characterize these climate extremes that could become the norm in the near future over central and northern Europe.

National-Scale Assessment of Climate Change Impacts on Two Native Freshwater Fish Using a Habitat Suitability Model

Climate change, which has the potential to alter water flow and temperature in aquatic environments, can influence the freshwater fish habitat. This study used an ecological habitat suitability model (EHSM), which integrates hydraulic (water depth and velocity) and physiologic (water temperature) suitability, to investigate the impact of climate change on two native freshwater fish species (Zacco platypus and Nipponocypris koreanus) in South Korea. The model predicted that in 2080 (2076–2085), the decrease in average ecological habitat suitability (EHS) will be higher for N. koreanus (19.2%) than for Z. platypus (9.87%) under the representative concentration pathway (RCP) 8.5 scenario. Under the same condition, EHS for Z. platypus and N. koreanus at 36.5% and 44.4% of 115 sites, respectively, were expected to degrade significantly (p < 0.05). However, the habitat degradation for Z. platypus and N. koreanus was much lower (7.8% and 10.4%, respectively) under the RCP 4.5 scenario, suggesting a preventive measure for carbon dioxide emission. Partial correlation analysis indicated that the number of hot days (i.e., days on which the temperature exceeds the heat stress threshold) is the variable most significantly (p < 0.05) related to EHS changes for both species. This study suggests that the EHSM incorporating the effect of water temperature on the growth and heat stress of fish can be a promising model for the assessment of climate change impacts on habitat suitability for freshwater fish.

Climate Impact and Model Approaches of Blue-Green Infrastructure Measures for Neighborhood Planning

Nowadays, most cities deal with the problem of “Urban Heat Islands”. Especially existing city districts cannot easily be adapted. In this paper, the effects of blue-green infrastructure elements (BGI) on air and surface temperature in courtyards are examined, based on on-site measurements and simulations. Recognizable effects on the temperature were observed: BGI lower the number of hot days in the courtyard, including a faster air temperature drop at night, but water elements increase the number of tropical nights due to their heat capacity. Model simulations with PALM-4U proved to be useful to analyze the effects of BGI on the microclimate. Besides analyzing existing structures, the effects of planned measures can be quantified by simulation. However, for this application, needs of improvement were recognized to evaluate the influence of BGI on the microclimate more realistically. For decision support, standard indicators such as the number of tropical nights and hot days are not differentiated enough to quantify specific climate stress of urban residents. It is suggested to consider summer days additionally, percentiles could be used instead of fixed thresholds and the entire course of the year should play a role in the evaluation of the elements and urban design.

Impacts of mean climate and extreme climate indices on soybean yield and yield components in Northeast China

Soybean is an important oil crop in China, and the national focus of soybean production is in Northeast China. In order to achieve high-stable yield, it is crucial to acknowledge the impacts of mean climate and extreme climate indices on soybean yield and yield components. In this study, based on the weather data from 61 counties from 1981 to 2017 in Northeast China, we assessed the impacts of mean climate and extreme climate indices on soybean observed yield and simulated yield. Mean climate include effective growing degree days (GDD10), precipitation (Pre), and solar radiation (SR); extreme climate indices include the number of cool days during seed-filling period (C15), the number of cool days during 15 days before anthesis (C17), the number of hot days (H30), maximum amount of 5 Day accumulated precipitation (P5), and consecutive dry days (CDD)). We used the DSSAT-CROPGRO-Soybean model to identify the main yield components for soybean. The results showed that observed soybean yield reduced by 3.57% due to the collective changes in the eight study climate indices. Increases in GDD10, decreases in Pre, and decreases in SR caused a 3.96%, −3.89%, and − 0.48% change in soybean yield, respectively. Decreases in C15 and C17 led to a 5.36% increase in soybean yield; increases in H30, P5, and CDD caused a 5.75%, 0.30%, and 1.14% reduction in soybean yield, respectively. By comparing the response of observed and simulated soybean yield to climate indices (excluding P5) in the DSSAT-CROPGRO-Soybean model, we identified the key yield components for soybean as the number of pods and seed weight. The negative impacts on the number of pods and seed weight were mainly attributed to changes in Pre and H30 from anthesis to podding and during seed-filling period. Our results could be used to assist the local soybean community adapt to climate change.

Intercomparison of Local Warming Trends of Shanghai and Hong Kong Based on 120-Year Temperature Observational Data

Using surface air temperature observations from 1901 to 2020, this study compared the warming trends of Shanghai and Hong Kong over a period of 120 years. The statistical results reveal the following: (1) The average temperatures of the two cities underwent fluctuating increases during the past 120 years, with linear warming rates of 0.23 °C/decade in Shanghai and 0.13 °C/decade in Hong Kong. (2) The fluctuation ranges of maximum temperature in the two cities were considerably higher than those of mean temperature. Moreover, in both cities, the annual mean maximum temperature decreased during a phase of more than a decade. The fluctuation ranges of minimum temperature were smaller, whereas the linear increases were higher than those for the mean temperature. (3) The diurnal temperature ranges (DTRs) of the two cities decreased; a certain phase of the decreases in DTR in the two cities was caused by decreases in the maximum temperature. (4) At a certain stage of urban development, owing to the shading effect of new high-rise buildings, the solar shortwave radiation reaching the Earth’s surface decreased, and anthropogenic heat generated by the energy consumption of buildings and urban human activities at that time was not sufficient to make up for the reduced shortwave radiation. This result may have led to the declines in the maximum temperature experienced by both cities. (5) Currently, the number of hot days and extremely hot days in the two cities has increased significantly compared with that a century ago, indicating that climate warming has an adverse impact on human settlements.

Extreme Hot Weather Has Stronger Impacts on Avian Reproduction in Forests Than in Cities

Climate change and urbanisation are among the most salient human-induced changes affecting Earth’s biota. Extreme weather events can have high biological impacts and are becoming more frequent recently. In cities, the urban heat island can amplify the intensity and frequency of hot weather events. However, the joint effects of heat events and urban microclimate on wildlife are unclear, as urban populations may either suffer more from increased heat stress or may adapt to tolerate warmer temperatures. Here, we test whether the effects of hot weather on reproductive success of great tits (Parus major) are exacerbated or dampened in urban environments compared to forest habitats. By studying 760 broods from two urban and two forest populations over 6 years, we show that 14–16 days-old nestlings have smaller body mass and tarsus length, and suffer increased mortality when they experience a higher number of hot days during the nestling period. The negative effects of hot weather on body mass and survival are significantly stronger in forests than in urban areas, where these effects are dampened or even reversed. These results suggest that urban nestlings are less vulnerable to extreme hot weather conditions than their non-urban conspecifics. This difference might be the result of adaptations that facilitate heat dissipation, including smaller body size, altered plumage and reduced brood size. Alternatively or additionally, parental provisioning and food availability may be less affected by heat in urban areas. Our findings suggest that adaptation to heat stress may help birds cope with the joint challenges of climate change and urbanisation.

Cooling Effects Revealed by Modeling of Wetlands and Land‐Atmosphere Interactions

AbstractWetlands are important ecosystems—they provide vital hydrological and ecological services such as regulating floods, storing carbon, and providing wildlife habitat. The ability to simulate their spatial extents and hydrological processes is important for valuing wetlands' function. The purpose of this study is to dynamically represent the spatial extents and hydrological processes of wetlands and investigate their feedback to regional climate in the Prairie Pothole Region (PPR) of North America, where a large number of wetlands exist. In this study, we incorporated a wetland scheme into the Noah‐MP land surface model with two major modifications: (a) modifying the subgrid saturation fraction for spatial wetland extent and (b) incorporating a dynamic wetland storage to simulate hydrological processes. This scheme was evaluated at a fen site in central Saskatchewan, Canada and applied regionally in the PPR with 13‐year climate forcing produced by a high‐resolution convection‐permitting model. The differences between wetland and no‐wetland simulations are significant, with increasing latent heat and evapotranspiration while suppressing sensible heat and runoff in the wetland scheme. Finally, the dynamic wetland scheme was applied in the Weather Research and Forecasting (WRF) model. The wetlands scheme not only modifies the surface energy balance but also interacts with the lower atmosphere, shallowing the planetary boundary layer height and promoting cloud formation. A cooling effect of 1–3°C in summer temperature is evident where wetlands are abundant. In particular, the wetland simulation shows reduction in the number of hot days for >10 days over the summer of 2006, when a long‐lasting heatwave occurred. This research has great implications for land surface/regional climate modeling and wetland conservation, especially in mitigating extreme heatwaves under climate change.

Projected Air Temperature Extremes and Maximum Heat Conditions Over the Middle-East-North Africa (MENA) Region

This study analyzes projected heat extremes over the Middle-East–North Africa (MENA) region until the end of the twenty-first century with a number of temperature indices based on absolute values and thresholds to describe hot conditions. We use model projected daily near-surface air (2-m) temperature (T_mathrm{{max}} and T_mathrm{{min}}) to derive the indices for the period 1980–2100. The data were taken from 18 CMIP5 models combining historical (1980–2005) and scenario runs (2006–2100 under RCP2.6, RCP4.5, and RCP8.5 pathways). Results show a domain-wide projected warming for all emission scenarios. Our findings for a business-as-usual pathway indicate excessive warming of more than 8 ^circ C in the northern part of the domain (south Europe) for the annual warmest day (TXx) and night (TNx). In the hottest parts of the domain record high temperatures reached 50 ^circ C in the recent past, which could increase to at least 56 ^circ C by the end of the century, while temperatures over 50 ^circ C are expected to occur in a large part of the MENA region. A significant increase is projected in the number of hot days (TX >40^circ C) and nights (TN >30 ^circ C) all over the region. For the period of 2071–2100 excessive hot days and nights will become the normal during summer in large parts of the MENA with some locations expected to exceed 180 and 100 days, respectively. Calculations of the corresponding heat index suggest that several areas across the MENA region may reach temperature levels critical for human survival.

Summer hot extremes and antecedent drought conditions in Australia

AbstractThe compound occurrence of extreme weather and/or climate events can cause stronger negative impacts than the individual events, and its frequency is increasing in several regions of the world. In this work, the effect of antecedent drought conditions on hot extremes during the months of December–February in Australia was analysed for two periods (1979–2019 and 1950–2019). The standardized precipitation evapotranspiration index (SPEI) and the indices number of hot days (NHD) and number of hot nights (NHN) were used to assess drought and extreme temperature events. While the link between dry and heat events is more important in the north in February, in December and January it is strong in the east coast. When temporal lags of 1–3 months are considered, there is a strong correlation between SPEI and NHD/NHN for the concurrent month on most of the study area. For the previous 1–3 months, the area and the correlation values decreased, but consistent spatial patterns were obtained for each month, namely negative correlations on the southwest and southeast in December, and the east in February. Tropical areas showed large areas of correlation between SPEI and NHN, including for the previous 3 months, whereas temperate climates showed the smaller area of correlation with NHN, including at the concurrent month. Significant correlations obtained for lead times longer than 1 month, namely with night heat extremes, point to a predictive ability in several regions of Australia. Moreover, the correlation coefficients obtained using the more recent period (1979–2019) show similar spatial patterns, but with higher values than for the 1950–2019 period. The results highlight the prospect of an early prediction of hot summer extremes in regions affected by drought in spring.

Projections of changes in maximum air temperature and hot days in Poland

AbstractThe aim of the study was to determine changes in maximum air temperature (Tmax) in summer, and occurrence of hot days in the period 1966–2020, as well as to forecast the direction and rate of changes in near and far future. The research showed an increase in Tmax in the summer season. In the analysed period, the changes intensified over the last 20 years, as suggested by, among others, the occurrence of the 10 warmest years in the study period, mostly after 2000. According to model projections, an increase in Tmax will be recorded both in the near and far future. The consequence of the current increase in Tmax has been an increase in the frequency of hot days. Further increase in the number of hot days in Poland is projected for the upcoming decades. The smallest changes are projected for areas with most intensive changes in Tmax, and the largest in areas with moderate changes in the Tmax.

Climate change projections for Greece in the 21st century from high-resolution EURO-CORDEX RCM simulations

We present an updated assessment of projected climate change over Greece in the near future and at the end of the 21st century, focusing on near surface temperature, precipitation, and related heat (Hot Days and Tropical Nights), cold (Frost Days), and drought (Consecutive Dry Days) climate indices. The analysis is based on an ensemble of 11 high-resolution EURO-CORDEX regional climate model (RCM) simulations covering the historical period 1950–2005 and the future period 2006–2100 under the influence of a strong, a moderate, and a no mitigation Representative Concentration Pathway (RCP2.6, RCP4.5 and RCP8.5). The statistical robustness of climate change signal is also assessed. Our results strongly point towards a warmer future for Greece under all the examined RCPs. Under RCP8.5, annual near surface temperature is projected to increase on average by 1.6 °C in the near future and 4.3 °C at the end of the century. As a consequence of warming, the number of hot days and tropical nights in a year is projected to increase significantly and the number of frost days to decrease. In addition, the future will be possibly drier. Statistically robust results for precipitation changes are found only for the end-of-the-century period under RCP8.5. Precipitation is generally projected to decrease under RCP8.5 by −16% and the number of consecutive dry days in a year to increase by 15.4 days (30%) at the end of the century.

Radial growth decline of white spruce (Picea glauca) during hot summers without drought: preliminary results from a study site south of a boreal forest border

If the modern climate trend continues for an additional 20–40 years, forests along the southern border of Canadian taiga may shift into new ranges of annual temperature and precipitation that are similar to the modern climate of central New York State, United States. Here we investigate the possible future response of white spruce (Picea glauca (Moench) Voss) to a warmer climate by studying trees planted 90 years ago near the southern limit of their climate tolerance in central New York, 300 km south of the boreal forest where this species is prevalent. We employed high-frequency recording dendrometers to determine radial growth phenology of six mature white spruce trees during 2013–2017. The results demonstrate significant reductions in the length of radial growth periods inversely proportional to the number of hot days with air temperature exceeding 30 °C. During years with very hot summers, the start of radial growth began about 3 days earlier than the 2013–2017 average. However, in those same years, the end of radial growth was also about 17 days earlier resulting in a shorter (70 days versus 100 days) radial growth season. Abundant (350–500 mm) summer precipitation, which resulted in soil moisture values of 20%–30%, allowed us to dismiss drought as a factor. Instead, a likely cause of reduced radial growth was mean temperature that exceeded optimal growth ranges, exacerbated by temperature extremes in ranges that lead to photoinhibition. The latter case was evident in the two warmest growing seasons (2013 and 2017), marked by extended periods of high daytime temperature (>30 °C) followed by early cessation of radial growth independent of seasonal precipitation.

Variations of high temperature from 1961 to 2019 in Liaoning Province, China.

Better understanding of the changes in high-temperature would be helpful for improving the monitoring of hot extremes and mitigating their impacts towards a sustainable regional development. Based on the data of daily maximum temperature, relative humidity, and wind speed from 23 meteorological stations in Liaoning Province in summer (June to August) during 1961 to 2019, we analyzed the variations of daily maximum temperature (Tx), daily maximum apparent temperature (AT), and heat wave events (3 consecutive days ≥35 ℃). The effects of meteorological variables on daily maximum apparent temperature were examined by the grey relational analysis method. The results showed that the average Tx (AT) of all stations was 26.19 (27.35), 28.29 (31.13), and 28.14 (31.08) ℃, respectively, while the average trends in Tx (AT) was 0.17 (0.38), 0.20 (0.35), and 0.17 (0.28) ℃·(10 a)-1, respectively, in June, July and August during 1961 to 2019. The average AT and its trends in each month were larger than the Tx. From June to August, there was significant negative correlation between Tx (AT) and its climate tendency rate, indicating that the range of warming in the area with low Tx and AT was larger than that in the area with high values. We should therefore pay more attention to the protection against high temperature in the low value area of Tx and AT in summer. From June to August, the average number of hot days with AT ≥ 35 ℃ was 0.85 d·a-1, with an average increase rate of 0.20 d·(10 a)-1. Hot days were signifi-cantly more in June and July than in August. The area with more hot days was mainly located in the west of Liaoning, and the area with less hot days was mainly located in the south and coastal areas. The number of heat wave events was 0.071 times per year, which was large in western Liaoning. There was no high temperature heat wave event in the southern and coastal areas of Liaoning. The correlation analysis showed that the AT in June was strongly associated with relative humidity, while AT in July and August had the closest relationship with Tx. Therefore, the importance of relative humidity on the monitoring and forecasting of high temperature and hot weather cannot be ignored.

Assessment of Seasonal Variability of Extreme Temperature in Mainland China under Climate Change

Some studies have suggested that variations in the seasonal cycle of temperature and season onset could affect the efficiency in the use of radiation by plants, which would then affect yield. However, the study of the temporal variation in extreme climatic variables is not sufficient in China. Using seasonal trend analysis (STA), this article evaluates the distribution of extreme temperature seasonality trends in mainland China, describes the trends in the seasonal cycle, and detects changes in extreme temperature characterized by the number of hot days (HD) and frost days (FD), the frequency of warm days (TX90p), cold days (TX10p), warm nights (TN90p), and cold nights (TN10p). The results show a statistically significant positive trend in the annual average amplitudes of extreme temperatures. The amplitude and phase of the annual cycle experience less variation than that of the annual average amplitude for extreme temperatures. The phase of the annual cycle in maximum temperature mainly shows a significant negative trend, accounting for approximately 30% of the total area of China, which is distributed across the regions except for northeast and southwest. The amplitude of the annual cycle indicates that the minimum temperature underwent slightly greater variation than the maximum temperature, and its distribution has a spatial characteristic that is almost bounded by the 400 mm isohyet, increasing in the northwest and decreasing in the southeast. In terms of the extreme air temperature indices, HD, TX90p, and TN90p show an increasing trend, FD, TX10p, and TN10p show a decreasing trend. They are statistically significant (p < 0.05). This number of days also suggests that temperature has increased over mainland China in the past 42 years.