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Frost is one of the most frequent, intense, and influential agrometeorological disasters that occurs frequently in Northeast China. The study of the spatiotemporal changes of ground frost is of great significance for farmers and policymakers in Northeast China, as it can inform decisions related to crop selection, planting schedules, and the development of regional climate adaptation plans. In this study, the spatiotemporal changes of frost indices (last spring frost (LSF), first fall frost (FFF), and frost-free period (FFP)) in Northeast China were analyzed from 1961 to 2020. Then, we investigated the mutation characteristics of the frost indices and their correlation with geographical factors. The results revealed that (1) the LSF, FFF, and FFP in Northeast China were concentrated at 120–140 DOY, 260–280 DOY, and 110–170 days, respectively. The spatial distribution of frost indices exhibited significant spatial heterogeneity. (2) The LSF, FFF, and FFP showed significant trends of advancement, delay, and extension, with trends of −1.94 days/10 a, 1.72 days/10 a, and 4.21 days/10 a, respectively. (3) More than 80% of the LSF, FFF, and FFP of the sites showed trends of advancement, delay, and extension, with greater variability in the central part of Heilongjiang Province. (4) The FFF and FFP experienced an abrupt change in the late 1990s. (5) The correlation between latitude and LSF, FFF, and FFP was the strongest, with correlation coefficients of 0.77, −0.79, and −0.78, respectively. This study provides a comprehensive understanding of the changing characteristics of ground frost indices that impact agricultural production in Northeast China against the backdrop of climate change. The findings hold significant scientific value in guiding the adaptation of agricultural production layouts in Northeast China to the evolving climatic conditions. [ABSTRACT FROM AUTHOR]

The permafrost in Northeast China is experiencing rapid degradation due to the influence of climate change and human activities, profoundly impacting the local ecological environment and engineering construction. Understanding the spatiotemporal dynamics of long-term permafrost in this region is crucial; however, systematic research on this topic remains scarce. This study combines meteorological station data, MODIS land surface temperature (LST) datasets, and borehole locations to apply the surface frost number (SFn) model. This approach enables the simulation and estimation of the spatial distribution and changes in the area of the surface frost number without vegetation effects (SFnv) and permafrost temperature (PT) in Northeast China from 1971 to 2020. The area of the SFnv > 0.49 within the permafrost region decreased substantially from approximately 44.353 × 104 km2 to 19.909 × 104 km2 between 1971 and 2020, with a notable change in 1988. The area of permafrost calculated using PT < 0 was slightly smaller, declining from 39.388 × 104 km2 to 29.852 × 104 km2. There was also a significant increase in the area with PT ranging from −1 °C to 0 °C, indicating a decline in permafrost stability. Approximately 10.926 × 104 km2 of stable permafrost has been transformed into semi-stable and unstable permafrost. Moreover, from 1982 to 2020, the NDVI was negatively correlated with the area of stable permafrost and positively correlated with the area of transitional or unstable permafrost. Vegetation cover decreased as transitional or unstable permafrost degraded. These findings provide valuable information for permafrost research and engineering development in cold regions, as well as for future planning and adaptation strategies. [ABSTRACT FROM AUTHOR]

Fruit tree frost, an agricultural meteorological disaster primarily occurring in spring, severely impacts the growth and development of trees and fruit set. Therefore, exploring the temperature change rules of fruit trees during frost events is of considerable importance. This study used a T40 unmanned aerial vehicle (UAV) as the test vehicle based on the air disturbance frost prevention principle. The airflow field change pattern of the UAV was explored using the computational fluid dynamics simulation method, and the reliability of the multi-rotor UAV in frost prevention was verified using field tests. Setting the UAV height at 6.0 m above the ground and the rotor speed at 1000 r min−1, it was found that under the conditions of the inverse temperature phenomenon, the temperatures of different altitude layers will eventually converge to a stable value when the UAV down-rotating airflow is disturbed, which could be completed rapidly within 20 s. The results of the field test also showed that when the fruit trees reached the critical temperature of frost at the flowering stage, UAV intervention could have a substantial effect on the warming of the near-surface layers, whose warming amplitude was in the range of 2.5 °C–3 °C. This study provides a reliable method for mitigating frost, which serves as an important theoretical and guiding basis for improving agricultural frost disasters in China. • A multi-rotor UAV is used to test frost protection performance on fruit trees. • The temperature field characterizations are obtained. • The anti-frost effectiveness of UAV intervention is confirmed. [ABSTRACT FROM AUTHOR]

The occurrence of early spring and late frost damage brought severe challenges to the production of walnuts in China, seriously affecting their growth, development, yield and revenue. In order to clarify the harmful characteristics and influencing mechanisms of late frost on walnuts in China, the influencing factors of the degree of damage caused by late frost on walnuts, as well as the changes in physiological and biochemical indicators and molecular mechanisms in response to low temperature stress were reviewed. It was found that research on physiological changes focused on the three aspects including cell membrane system (relative conductivity), antioxidant system (malondialdehyde, superoxide dismutase, peroxidase and catalase) and osmoregulation substances (soluble sugars, soluble protein and proline), in addition, the expression levels of genes such as JrPAL, JrJAZ, JrGRAS, JrICE1, JrCBF/JrDREB1, JrCOR, JrWRKY, JrDHN, JrGST, and JrPUB were induced by low temperature stress. And prospects were put for future research directions, which provided scientific basis for further exploring the response mechanism of walnuts to late frost damage and adopting effective production measures. [ABSTRACT FROM AUTHOR]

Frost events are a climatic phenomenon of great severity, exerting profound impacts on agricultural production and human endeavours. From 1961 to 2017, China experienced a reduction in frost days (FDs) and elongation of frost‐free periods (FFPs) across most regions. Many factors contribute to the variation of frost events, highlighting the urgent need to scrutinize the intrinsic factors driving these climatic frost events' inter‐annual and interdecadal fluctuations. This work analysed the temporal and spatial attributes of FDs and FFPs, using statistical methods to dissect daily minimum temperature data collected from ground observation stations from 1961 to 2017. The results reveal a declining trajectory in annual FDs and an ascending trend in FFPs. However, the interannual and interdecadal variations do not consistently align with the climatological course. The spatial distribution of the first four modes of EOF exhibits a persistent variation, north–south, monopole and east–west pattern for FDs and FFPs. In comparison, the modes of FFPs exhibit many complexities and diversities. Moreover, this study considers geographical location, altitude and proximity to the ocean, as well as atmospheric circulation factors, including circulation indices, ocean indices and other relevant indices, to elucidate their influence on frost events. In conjunction with the role of greenhouse gases in propelling global warming, we elucidate that the intensity of the Atlantic–European polar vortex, the area of the Indian Ocean warm pool, and the spatial positioning and extent of the subtropical high emerge as preeminent internal oscillations instigating interdecadal shifts in frost events. This study provides valuable scientific insights into the formation mechanisms and evolving patterns of frost events. [ABSTRACT FROM AUTHOR]

Frost damage to winter wheat during stem elongation frequently occurred in the Huang-Huai plain of China, leading to considerable yield losses. Minimum Stevenson screen temperature (STmin) and minimum grass temperature (GTmin) have long been used to quantify frost damage. Although GTmin has higher accuracy than STmin, it is limited in application due to the lack of data. Therefore, this study aimed to select appropriate environmental variables to estimate GTmin, as well as to quantify the frost damage. Shangqiu, a frost-prone winter wheat area in the central Huang-Hui plain, was selected as the study area. From the descriptive statistics of ST, air relative humidity (RH), wind speed (WS), cloud fraction (CF), and volumetric soil water content (VWC) during temperature decreasing and increasing, seven variables significantly correlated with GTmin were selected, including STmin, maximum reduction of ST (RST), maximum increase of ST (IST), minimum RH during temperature increasing (RHmin), WS at STmin occurrence (WS), minimum VWC during temperature decreasing (VWCmin), and nightly CF. Multiple linear regression (MLR), support vector regression (SVR), random forest (RF), and K-nearest neighbor (KNN) were adopted for estimating GTmin based on the various combinations of the variables. Results showed the more variables, the higher the accuracy for the MLR and SVR. However, this pattern was not always true for the KNN and RF. The KNN based on STmin, RST, IST, RHmin, and WS achieved the highest accuracy, with R2 of 0.9992, RMSE of 0.14 ℃, and MAE of 0.076 ℃. The overall classification accuracy for frost damage identified by the estimated GTmin reached 97.1% during stem elongation of winter wheat from 2017 to 2021. The integrated frost stress (IFS) index calculated by the estimated and measured GTmin maintained high linear fitting accuracy. The KNN with fewer variables demonstrated good applicability at the regional scale. [ABSTRACT FROM AUTHOR]

Late spring frost stress is one of the major environmental limiting factors for apricot in the warm zone in China. Investigation of frost exposure of apricot is of particular interest for estimating the frost risk, thus representing the potential damage for apricot production. In this study, daily minimum temperature (Tmin), disaster and phenological data of apricot from 1981 to 2020 in the warm zone were integrated to explore the temperature threshold on apricot at young fruit, facilitating the assessment of apricot frost exposure (E) under the background of climate warming. The daily Tmin was firstly extracted according to the historical disaster records, to identify the per‐ and ongoing weather conditions of the low‐temperature events. The overall accuracy and Receiver Operating Characteristics curve (ROC) were combined to identify the trigger threshold of apricot frost. 1.9°C was identified as the apricot frost trigger threshold in regional assessment, with relatively higher correct rate for disaster (90.2%) and lower incorrect rate for none‐disaster (23.4%). An area under the ROC curve (AUC) of 0.88 was obtained, demonstrating a good performance of Tmin as the trigger factor in discriminating between apricot frost and no frost. High frequency of days suffered from apricot and frost exposure at young fruit were mainly found in the northwestern and middle parts of the region, with frequencies of more than 2 days and E more than 3. Regional days suffered from apricot frost and E were found to have a negative trend with slope −0.0317 and −0.789, respectively, whereas the northwest and middle part of the study region were found to have an increasing trend. The results can provide technical and theoretical support for targeted apricot frost detection and risk assessment, and measures for apricot frost prevention and mitigation can be implemented according to the threshold‐based results. [ABSTRACT FROM AUTHOR]

Frequent occurrences of late spring frost disaster create severe agricultural/forest damage, even given the background of global warming. In the warm temperate zone of China, which is the largest planting area for fresh apricot, late spring frost disaster has become one of the major meteorological hazards during flowering. To prevent cold weather–induced apricot frost disaster and reduce potential losses in related fruit economic value, it is vital to establish a meteorological indicator for timely and accurate identification of cold weather process–based apricot frost disaster, to provide support for timely apricot frost monitoring and warning in late spring. In this study, daily minimax temperature ( T min ) and apricot frost disaster data during flowering were combined to establish meteorological identification indicators of apricot frost based on cold weather processes. A process-based apricot frost model f (D , T cum) was firstly constructed, and characteristics of T cum (accumulated harmful temperature) were explored under different D (duration days) based on the representation of historical apricot frost processes. Thresholds for the T cum for apricot frost in 1, 2, 3, 4, and more than 5 days of apricot frost process were determined as − 1.5, − 2.9, − 4.4, − 5.8, and − 7.3 °C, respectively. Validation results by reserved independent disaster samples were generally consistent with the historical records of apricot frost disasters, with 89.00% accuracy for indicator-based identification results. Typical process tracking of the proposed identification indicator to an apricot frost event that occurred in North Hebei during April 3–9, 2018, revealed that the indicator-based identification result basically coincides with the historical disaster record and can reflect more detailed information about the apricot frost process. [ABSTRACT FROM AUTHOR]

Meteorological disasters (MDs), including drought, flood, hail, low temperature and frost (LTF), are causing severe damage to human life and economic development in China. Mapping the distribution of MDs and induced losses at fine spatial resolution across the whole country is helpful for disaster control. Based on the officially published records and yearbooks, the spatiotemporal variations in MD frequency at prefecture-level city scale and disaster-induced losses at provincial scale during 2011–2019 were analyzed. The result showed that there were average 1416.9 MD events every year at prefecture-level city scale. Flood and hail disasters dominated from April to September, while LTF disasters dominated from December to February. Drought disasters were mainly distributed at the second terrain step and North China Plain; frequency of flood disasters in the south part of China was higher than that in the north part of China, especially in the upper and middle reaches of Yangtze River basin; while the north part of China experienced higher frequency of hail and LTF than the south part. Cities on the second terrain step of China experienced the largest MD frequency because of the combination of disaster-causing factors and hazard-bearing body. Disaster loss analysis results showed that drought disasters had the severest effects on cropland because of the highest average covered and failed area of cropland among four MDs. Hunan, Hubei and Sichuan provinces experienced higher values of covered population and direct economic losses, while coastal provinces experienced less exposure to MDs. The results of this study can help optimal allocation of disaster mitigation and adaptive measures at both country and regional scales. [ABSTRACT FROM AUTHOR]

• Determine amount, frequency, and duration of dew/hoar frost using weighing lysimeters. • Compare characteristics of dew/hoar frost between Artemisia ordosica and bare soil. • Dew provides 30% of water for Artemisia ordosica during extreme drought periods. Dew and hoar frost are important water resources in arid and semi-arid regions. However, knowledge of the characteristics of dew/hoar frost formation in the typical shrub canopy of Northwestern China and its importance for vegetation survival is still not clear as it is difficult to observe. In this study, we investigated dew/hoar frost formation characteristics under both Artemisia ordosica and bare soil conditions based on weighing lysimeters in Mu Us Sandy Land, Northwest of China. The results show that dew and hoar frost occurred 214 days for Artemisia ordosica and 162 days for bare soil. The hoar frost formation mainly occurs from October to March, while dew formation occurs every month. The amount of hoar frost was 19.6 mm under Artemisia ordosica condition and 17.4 mm under bare soil condition, and the amount of dew was 27.5 mm of Artemisia ordosica and 18.4 mm of bare soil. The most common daily amount of dew/hoar frost is between 0 and 0.2 mm, which accounts for 60.7 % and 52.5 % of dew/hoar frost formation days for the Artemisia ordosica and bare soil conditions, respectively. The results from boosted regression tree analysis indicated that relative humidity had the greatest influence on dew/hoar frost formation. During soil drought periods (July 15 to August 18, 2021), the soil water content of Artemisia ordosica kept constant at 0.061 cm3/cm3, while the soil water content of bare soil was dropped at the rate of 0.00135 (cm3/cm3)/d. The ratio of dew amount of Artemisia ordosica to rainfall amount was 42.1 %. Despite the small amount of dew, it serves as a frequent and important supplementary water source for the ecosystem. This study provided valuable insights into dew/hoar frost formation, especially its importance for vegetation survival. [ABSTRACT FROM AUTHOR]

Demand for medium sand has increased greatly with increasing infrastructure construction items. The shortage of construction sand resources has become a serious problem in many districts. It not only increases the engineering cost, and the overexploitation of river sand and mountain as medium sand also brings a series of serious environment problems. There are abundant desert sand (DS) resources in western China. If DS resources can be used to substitute medium sand to produce desert sand concrete (DSC), which was suitable for engineering practice, the environment can be improved and engineering cost can be reduced. Although many researchers had focused on the mechanical performance of DSC, there were few documents on the frost resistance of DSC. Frost resistance experiments of DSC with 50% desert sand replacement ratio (DSRR) and ordinary concrete (OC) were performed in this paper. Influence of freeze-thaw cycles on the mechanical properties of OC and DSC was analyzed. Experimental results showed that, with increasing freeze-thaw cycles, the damage, peak strain, and porosity increased, while elastic modulus, Poisson's ratio, and peak stress declined, the stress-strain curves tended to be flat. Under the same condition of freeze-thaw cycles, the frost resistance of DSC with 50% DSRR was higher than that of OC. Constitutive model of DSC after different freeze-thaw cycles was formulated. The results predicted by constitutive model agreed well with experimental results, which can provide technical support for DSC engineering practice. [ABSTRACT FROM AUTHOR]

Face slab concrete suffers from serious frost damage in the cold regions in China. How to improve the frost resistance of face slab concrete in cold regions is one of the important issues in concrete-faced rockfill dam (CFRD) design and construction. The results in this paper indicate that the frost resistance of concrete can be improved by adding fly ash, fiber, MgO and shrinkage-reducing admixtures (SRAs), and their efficiencies are in the following sequence: (fly ash + fiber) > fiber > fly ash > MgO > SRA. The incorporation of 0.8 kg/m3 polyvinyl alcohol (PVA) fiber and 20 wt.% fly ash together enhances the compressive strength and tensile capacity of concrete by 6–7% at the late age, whereas the addition of 6 wt.% MgO or 1 wt.% SRA reduces the compressive strength and tensile capacity by about 4–10% at various ages. The D s of concrete added with fly ash, fiber, MgO and SRA is within the range of 2.619–2.796. The frost resistance of concrete correlates linearly with the air void parameters, pore structures and D s . The utilization of fly ash and/or PVA fiber refines and optimizes the pore structure, thus increasing D s and improving the frost resistance. On the contrary, MgO and SRA in this study are less effective in refining the pores than PVA fiber and fly ash, thereby producing smaller D s and relatively weaker frost resistance. [ABSTRACT FROM AUTHOR]

Runoff patterns are crucial to determine the hydrological response to climate change, especially in a seasonal frost area. In this study, multi-time runoff responses to meteoric precipitation for the period from July 2014 to June 2016 and the period from 1955 to 2010 were obtained to identify different runoff patterns in the Songhua River basin, northeast China, based on six stations. Two distinctly different runoff responses are exhibited: a periodic one in response to precipitation in the Nen River and a constant one in the Second Songhua River under different scales. Stable isotopes in the plain with diverse characteristics also supported these runoff patterns. What is more, gradual runoff relatively less sensitive to precipitation in the Second Songhua Rive was attributed to upstream dam constructions. Furthermore, the Second Songhua River contributes more water to the main stream during January to March at the seasonal scale and in the 2000s at the annual scale, with low precipitation during those periods. This study could have implications for water management in the Songhua River basin. [ABSTRACT FROM AUTHOR]

At present, the tunnel design specifications in China do not provide a clear and systematic intelligent evaluation system of tunnel frost damage in cold regions. Based on the research results of 122 seasonal frozen soil tunnels in high-latitude areas of China, four key influencing factors of geohydrology, temperature, surrounding rock, and engineering measures were determined, the intelligent fuzzy comprehensive evaluation model was established, the weights of all factors were considered, and the intelligent evaluation technology system of tunnel frost damage in cold areas had been put forward. Meanwhile, the rationality of the intelligent model was verified by a specific engineering case. The research suggests that the intelligent evaluation model of tunnel frost damage proposed in this paper can accurately describe the relationship of influencing factors of tunnel frost damage in cold areas, the weight of each influencing factor is calculated by using analytic hierarchy process, and the main risk sources of tunnel frost damage in cold areas are found out. The intelligent evaluation model is an efficient and practical method for Intelligent prediction of frost damage. By using the subordinate function method, the improvement from qualitative analysis to quantitative index calculation is realized. The blindness of engineering analogy construction is avoided, and the scientificity and accuracy of renovation measures for frost damage have been improved. At the same time, the research results provide a theoretical basis for the improvement of the intelligent evaluation system of tunnel frost damage in cold regions. [ABSTRACT FROM AUTHOR]

The degradation of natural rocks due to severe environmental conditions can influence their durability over an extended period of time. This research aims to investigate the long-term durability or disintegration rate of rocks used as construction materials under severe climatic conditions using frost damage action, and the deterioration rate was assessed using mathematical decay function approach. The mathematical model assumes an initial order operation and gives purposeful properties for the deterioration rate of rocks due to frost action. For this reason, six different limestone types used as building materials were quarried from limestone mine in China and subjected to a series of laboratory tests to determine the mineralogical, petrographical, physical, and mechanical characteristics. Then, 50 cycles of frost damage process was performed, and after each 10 cycles, the unconfined compressive strength, point load strength, and Schmidt rebound were determined. The disintegration rate or integrity loss characteristics of each rock type were assessed using the mathematical decay function approach parameters. This approach proved that the disintegration rate varies for the rocks of the same type especially which were extracted from the same areas, the rock durability under frost damage conditions can be estimated with good accuracy, the parameters of this model saved a lot of time and provided important practical features to assess a rapid durability, and hence, there is no need to carry out the frost damage test which is slow and consumes time. [ABSTRACT FROM AUTHOR]

It has been widely recognized that loess has a low stability and permeability, and it is susceptible to a sudden decrease in total volume or collapse upon wetting. When the railway subgrade was under the dynamic trainload, the loess subgrade was prone to instability and liquefaction. Bao Zhong railway is a key railway for Guyuan city, in Ningxia province of China, which is an important city of the Belt and Road. Due to the influence of large-area flood irrigation on the farmland, the subgrade had a degree of settlement. The settlement had not been alleviated after three treatments, which seriously affected the safety of the train. For this reason, cement, Modified Phospho Gypsum (MPG) and MPG-cement were used to reinforce the subgrade loess, and the unconfined compressive strength test, permeability test and freeze-thaw cycle test were carried out. Then the compressive strength, impermeability and frost resistance of the three were analyzed and compared. The results indicate that the compressive strength of the MPG-cement modified loess is higher than that of the cement modified loess, but lower than that of the MPG modified loess. However, the coefficient of permeability for the MPG-cement modified loess has an opposite result, and the MPG-cement modified loess specimens have the best frost resistance. In addition, the mechanism of MPG-cement modified loess is discussed. It is found that cement and MPG have two hydration reactions with water in loess. Ettringite, the hydration reaction product, which not only fills the pores, restricts the movement of the soil particles, but also acts as a connecting soil particle in the soil particles. Therefore, the strength of the modified loess continues to increase, and the physical properties of the modified loess are improved. [ABSTRACT FROM AUTHOR]

The Yangtze River region is the main production area for famous, high-quality tea in China. Radiation frost frequently occurs in this region, especially in the early spring during calm and clear nights, and it causes substantial damage to crops, which leads to huge economic losses for tea growers. The formation of frost is difficult to experimentally control due to the complexity and variability of the agro-micrometeorological environment. The objective of this study was to evaluate an artificial radiation frost chamber based on the temperature difference between leaf and air dew point, which was designed for advanced frost-related research. Micro-meteorological data and the frost formation process were monitored in an experimental tea field during typical radiation frost nights to mimic declining temperatures that are consistent with nature. The radiation frost chamber model and main parameters were determined by theoretical calculations and computational fluid dynamics (CFD) simulation. A frost-forming experiment was conducted to evaluate the performance of the frost chamber. The observation results showed that the greatest temperature difference between leaf and air dew point (Tdiffer) was −2.3 °C. The simulation results showed that the desublimation cooling rate of the air vapor was greater than sublimation, and the Tdiffer should be greater than −3.2 °C, which could cause frost to easily form on the leaf. The performance testing results showed that leaf temperature slowly declined after a rapid decrease, which is similar to the natural condition, which results in noticeable frost formation on the leaf. [ABSTRACT FROM AUTHOR]

Increased soil frost associated with winter climate change could have immediate and carry-over effects on biological processes in high-altitude forest soils, but the nature of these processes remain poorly understood. We conducted a snow-exclusion experiment to investigate the immediate and cross-seasonal effects of increased soil frost on soil CO 2 efflux and biological activity in a subalpine spruce forest on the eastern Tibetan Plateau, China. The increased frost reduced soil CO 2 efflux by ∼15 and ∼19% in the winters of 2015/2016 and 2016/2017, respectively. Increased frost also tended to decrease soil basal respiration, the amount of microbial phospholipid fatty acids and the activities of enzymes involved in soil carbon cycling during the winters. Winter soil nitrogen availabilities were higher in the snow-exclusion treatment than in the control plots. However, these effects did not carry over to the following growing season. Our results suggest that increased frost reduces winter soil respiration by direct environmental effects (e.g. soil temperature) and indirect biological processes (e.g. microbial biomass and activity), whereas increased frost did not induce any cross-seasonal effects. These findings underscore the ecological importance of seasonal snowpack and microbe-associated carbon processes in subalpine forests where winter snowfall is decreasing substantially. • Increased frost reduced soil microbial biomass and enzyme activity in winter. • Increased frost reduced soil respiration in winter. • Increased frost unaffected biological processes in the snow-free growing season. [ABSTRACT FROM AUTHOR]

Background: Both Pharmacopoeia of the People's Republic of China and the ancient Chinese herbal formulas recorded that mulberry leaves collected after frost had good quality. However, the reason has not yet been fully elucidated. Objective: We investigated the effect of frost on the accumulation of flavonoids and antioxidant activities of mulberry leaves. Materials and Methods: Liquid chromatography-mass spectrometry and high-performance liquid chromatography were used to analyze chemical components and determine the content of five flavonol glycosides from mulberry leaves collected before and after frost, respectively. Antioxidant activities of the same mulberry leaves were evaluated by total antioxidant capacity (TAC), Fe2+ equivalent (FeE), reducing power (RP), 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay, and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) free radical scavenging assay. Results: Ten compounds were identified as flavonol glycosides exception of chlorogenic acid. Quantitative analysis showed that content of isoquercitrin, astragalin, and kaempferol-3-O-(6''-acetyl)-β-D-glucopyranoside reached a maximum of 3.05 mg/g, 0.70 mg/g, and 0.69 mg/g after Frost's Descent, respectively. Moreover, the lowest value of flavonol glycosides appeared in August. The antioxidant activities were also found to have the same tendency. The maximum value of TAC, FeE, RP, DPPH and ABTS were 64.3 rutin equivalent (RE) mg/g, 46.2 RE mg/g, 31.3 RE mg/g, 22.5 RE mg/g and 26.7 RE mg/g, respectively, in November. They were 1.4 times, 1.4 times, 1.6 times, 1.6 times, and 1.9 times of the minimum values, respectively, in August. There was a significantly and positively correlation between antioxidant activities and content of flavonol glycosides (P < 0.01). Conclusion: Frost is beneficial to the accumulation of flavonol glycosides and the improvement of antioxidant activities of mulberry leaves. [ABSTRACT FROM AUTHOR]

Frost exposure and poor pollination are great challenges for the cultivation of perennial orchard systems such as apples, whose adaptive capacity to climate impacts is limited. Unfortunately, such climatic risks remained largely unexplored due to the complexity in future climate predictions, uncertainties in apple phenological simulations, and difficulties in quantifications of risks of late-spring frost and poor pollination. Here, focusing on the main apple production Sub-regions I–IV (i.e., the Loess Plateau, the Bohai Bay, the Southwest Cool Highland, and Xinjiang) in China, we used an ensemble of seven phenological models to estimate changes in apple first flowering and fruit-setting. Based on phenological sensitivity window proposed, we evaluated the late-spring frost risk and climatic risk of poor pollination based on two individual indices developed for these two kinds of meteorological risks. The phenology model ensemble was driven by climatic data derived from an ensemble of 27 global climate models (GCMs) from CMIP6 to simulate apple phenology in two periods of 2021 − 2060 (Near Future) and 2061 − 2100 (Far Future) under two climate scenarios of SSP245 and SSP585. Model ensemble could largely improve phenology prediction accuracy. Our results also confirmed the general earlier occurrence of apple phenological stages and the shortening of phenological sensitive windows. The first flowering advanced about 0.19 − 0.32 d∙y-1 and fruit-setting advanced about 0.24 − 0.47 d∙y-1. Although the shortening of phenological sensitivity window might decrease frost frequency in some regions and reduce the general risk of late-spring frost (e.g. in Sub-region II), the increase of frost intensity could offset this kind of alleviation and even exacerbate frost risks in Sub-regions I and IV. Finally, except for Sub-region III and a few sites in Sub-regions I and IV, shifts in climatic risks of poor pollination in spatial contrasts were lower than late-spring frost risk. This highlighted late-spring frosts would be more possibly the reason for apple yield or quality losses than the unfavorable climatic pollination conditions under climate change. Model ensemble provides a realistic assessment for quantifying future risks of late spring frost and poor pollination in apple production systems, and helps to identify urgent meteorological risks and provide options for apple production systems in response to climate change. [Display omitted] • Model ensemble approach improved the accuracies in apple phenophase prediction. • Apple phenophase is advanced while phenological sensitive window is shortened. • Warming may not reduce frost due to discrepancies in frost intensity & frequency. • Change of pollination risk is small in most regions of China under climate change. [ABSTRACT FROM AUTHOR]

Frost events in spring pose a serious threat to wheat production in China. These events coincide with late vegetative stages and reproductive development, which are sensitive to frost stress. To understand the spatio-temporal pattern of spring frost and its impact on winter wheat yield, we calculated the accumulated frost degree-days (AFDD) as an index for frost risk affecting yield. Additional indices to characterize the spring frost risk included accumulated frost days and temperature-drop-rate. These indices were calculated for the growth period from stem elongation to flowering with historical data collected from 161 stations across the main winter wheat growing area in China from 1981 to 2009. Frost risk is smaller in the cooler northern and warmer southern regions than in the central winter wheat growing region of China. Huang-Huai Subregion (HHS) has the greatest frost duration, intensity and suffers the largest yield losses due to spring frost. Frost risk during stem elongation to flowering has not been significantly decreased in the winter wheat-growing regions of China under climate warming. While rising temperature reduces frost events in general, it also accelerates wheat phenology which increases the risk of spring frost. Quantifying future trends and impacts of spring frost damage on wheat production will be critical for developing appropriate adaptation and mitigation strategies for food availability in China and other regions of the world affected by frost. [ABSTRACT FROM AUTHOR]

To cope with tunnel frost damage, studies on prevention methods are routinely conducted to improve environmental protection and energy saving. Based on field investigations, the main available thermal insulation methods and their application are discussed and analysed in this paper. The results show that passive measures, such as a thermal insulation layer or door, cannot completely avoid frost damage. Construction investment of the electric heat tracing (EHT) system is lower at the early stage, but a large investment in operation and pollution problems are needed in the later period. As renewable, clean and environmentally friendly primary energy, geothermal energy can realize energy-saving and emission-reduction. Furthermore, our research team proposed the optimization design method for tunnel heat insulation and anti-freezing by using geothermal energy and presented the challenges for future applications of the ground-source heat pump (GSHP) system in tunnels. The results regarding energy conservation from this review can provide useful technical support in design, operation and management of tunnels in cold regions. [ABSTRACT FROM AUTHOR]

• Phenology dynamics and frost risk of apples were investigated under climate change. • Apples phenophase expect to advance, but the advance rate would be slower. • Frost frequency expects to decrease, while frost intensity expects to increase. • The larger advance in apple phenophase, the more frost risk is expected. Changes in apple phenology associated with climate change have attracted extensive attention. However, it is poorly known whether the phenological dynamics responding to climate change would increase the severity and frequency of frost in apple trees. Here, we investigated the variation of phenophase (budburst and fruit-setting) and the frost risk for apple trees in the Loess Plateau combined with phenology models driven by Global Climate Models (GCMs) under two emission scenarios (SSP2-RCP4.5 and SSP5-RCP8.5 for two time periods 2050s and 2090s, respectively). The results showed that apple budburst and fruit-setting are expected to be advanced to varying degrees, but the rate of advance is decreasing (budburst 0.04–0.14 d∙y−1, fruit-setting 0.12–0.22 d∙y−1). The combinations of high emission scenarios and 'far' time periods (SSP5-RCP8.5, 2090s) in budburst and fruit-setting advance larger than conservative emission scenarios and 'near' time periods (SSP2-RCP4.5, 2050s). Furthermore, although frost frequency is expected to decrease about 0.09–0.36 d under both SSP2-RCP4.5 and SSP5-RCP8.5, frost intensity tends to increase about 0.004–0.008 °C·d−1 (except SSP5-RCP8.5, 2090s). Due to the different directions of changes in frequency and intensity of frost under future time periods, overall frost risk showed regional differences. The unchanged or decreased frost risk distributed in the northern and southern areas of the study areas, while the increased frost risk mainly distributed across the central areas of the study areas. Finally, the advancement of two phenophase was disproportionately related to frost risks in the geographic distributions. Areas with large advance in phenophase were themselves expected to be at greater frost risk. Our findings will help to promote local preventative interventions for reasonably reducing the risk of late spring frosts in future climate warming scenarios. [Display omitted] [ABSTRACT FROM AUTHOR]

Frost damage during flowering is recognized as one of the most serious agro-meteorological disasters affecting apple production in Shaanxi province, a typical apple producing area in China. Quantitative assessments of flowering frost damage to apple yield are critical for the development of strategies on mitigating yield losses, but have been rarely conducted. For the first time, our study used the process-based STICS model and statistical methods based on Lagrange interpolation method to assess the impacts of frost damage during flowering on apple yield at five study sites over the past three decades. Four canopy temperature thresholds were set as 0 °C, − 2 °C, − 5 °C, and − 35 °C for 0, 10%, 90%, and 100% frost damage on fruit number, respectively. The study results showed that STICS could effectively simulate the phenology and yield of apple, with the simulation errors less than 15%. Simulated yield losses caused by frost damage during flowering by STICS model were consistent with that estimated by statistical methods. Average yield loss due to frost damage during flowering estimated by STICS model was 6.35–29.27% in frost years during past three decades at five study sites. In general, both the frost occurrence days and intensities were the highest in the recent ten years. Our study provides a method to quantitatively assess the impacts of frost damage during flowering on apple yield for the prevention and mitigation of frost disasters in apple production. • Crop model and statistical method were cross-validated to assess frost damage. • STICS could effectively simulate the flowering frost damage to apple yield. • Flowering frost was most serious in recent 10 years during past three decades. [ABSTRACT FROM AUTHOR]

Flood, drought, hail, low temperature and frost disasters from low temperature and frost (DLTF), and snowstorm are the five main meteorological disasters (MDs) in China. Based on the collection of historical documents during 1950-2013 and official records between 2012 and 2013, this paper analyzed the temporal trends of affected area induced by MDs during 1950-2013 and the spatiotemporal characteristics of disaster frequency in recent 2 years in China. Besides, the direct economic losses and deaths caused by MDs were further discussed at a provincial level. Results showed that the affected area of MDs, especially flood, drought and DLTF significantly increased during the past 60 years. Flood was the most frequent disaster in China during 2012 and 2013, followed by hail. Spatial patterns of disaster frequency showed that there were more frequent floods in the middle and lower reaches of the Yellow River and the Yangtze River basin, droughts in central and southwest China, hails in north, northwest and southwest China, DLTFs and snowstorms in north, northwest China and individual areas in south China. However, the economic losses caused by MDs were higher in economically developed provinces, and the deaths were higher in mountain regions. Additionally, flood was the major disasters type that contributing to the most losses in most regions of China. These results play an important theoretical guiding role in meteorological disaster prediction, disaster prevention and reduction in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dew/hoar frost can be distinguished by leaf wetness sensor and air temperature. • The differences in dew duration on and below canopy depended on plant species. • Sky view factor and shading effects were main factors leading to the differences. • Dew can be an important water supply during sharp declines of soil water. Dew and hoar frost are important sources of water available in dryland ecosystems in arid and semi-arid areas, however, little is known about the quantitative characteristics of dew/hoar frost on the canopies and underlying surfaces of typical shrubs in Northwest China. Few studies have examined the ecological relevance of dew/hoar frost to drought. We conducted an observational experiment regarding the frequency, duration, and amount of dew/hoar frost on both canopies and underlying surfaces of the Artemisia ordosica (AO) and Salix psammophila (SP)—two common species in northern China—using leaf wetness sensor (LWS) in a desert shrubland in Northwest China from May to December 2015. Potential dew/hoar frost was estimated using the Penman–Monteith (P–M) equation, while measuring meteorological parameters. Results showed that dew/hoar frost exhibited a significant diurnal variation that occurred mainly between 20:00 and 09:00 the following day, while peaking at about 04:00–06:00 (i.e., before dawn). The monthly mean duration of dew/hoar frost was longer in November and December, and shorter in May and June. Eighty percent of daily dew values were within 0–0.4 mm d−1. For SP, the durations of dew and hoar frost were both longer on the canopy than on the underlying surface. For AO, however, the duration of dew was longer and that of hoar frost was shorter on the canopy than on the underlying surface. The P–M equation may underestimate dew/hoar frost during cold times with higher wind speed. Dew may be an important water supply, especially during two periods of sharp declines of soil water during the long (the period > one month) and short term (the period < one month) droughts (equal to 63.77 and 96.18% of rainfall, respectively). Our findings suggest that AO is more conducive to the formation of dew/hoar frost than SP, and dew/hoar frost can serve as a sustainable significant water resource during periods of drought, especially in desert areas. [ABSTRACT FROM AUTHOR]

Based on annual minimum air temperature, the minimum ground temperature, cloudiness, air pressure, wind velocity in Lianyungang City during 1971 -2010 and sounding geopotential height, wind direction, dew point and temperature at related stations, using mathematical stepwise regression method and SPSS statistical software, short-term prediction equations of daily minimum air temperature and daily minimum ground temperature at the observation station were established. According to the relationships between frost and temperature, ground temperature, based on local frost forecast standard, the short-term forecast equation was used to judge if frost occurred in Lianyungang City. Via real-time weather monitoring , accurate and fine forecast and early warning, short-term objective forecast business system of frost in Lianyungang was established for a full range of effective service. [ABSTRACT FROM AUTHOR]

Based on day-to-day minimal ground temperatures in 1961-2010 from 62 meteorological stations in Shanxi province, the variation characteristics of Shanxi's first frost were analyzed. The results show: Shanxi's average first frost date was October 7, and the first frost date of the north was generally earlier than the south;the average first frost date had obvious negative correlations with altitude and latitude, and the correlation coefficients were respectively -0.85 and -0.82. M-K mutation test shows that the first frost date of most meteorological stations had mutations from 1961 to 2010, mainly in the years from 1981 to 2000, and the mutation year of the central area was generally later than the north and the south; the mutation year had negative correlations with altitude and latitude, and the correlation coefficients were respectively -0.45 and -0.51. The first frost dates of most stations had a delaying trend. Specifically, the large delaying scope region was located in the north and the mid-east, and the large advancing scope region was located in the south and the south central. The changing trend had negative correlations with altitude and latitude, and the correlation coefficients were respectively -0.30 and -0.37.Probabilities of the mild, the moderate and the severe first frost were 62%-82%,6%-26% and 4%-22%, respectively, and the maximum probabilities appeared in the south central & northeast, the central & north central and the west & north central.Correlation of altitude with first frost tends to be volatile upon frost grade and latitude has bigger impacts on first frost probabilities. [ABSTRACT FROM AUTHOR]

The uneven frosting on air source heat pumps' (ASHPs) outdoor coils is undesired product, as it comes with additional defrosting energy consumption and may aggravate the frosting consequence. Homogenizing the uneven frosting may help suppressing frosting. In this study, visual experiments were conducted to clarify a typical uneven frosting phenomenon. It was observed that the air inlet side of ASHPs' outdoor coils escaped from frosting, whereas frost built up on the outlet side. To clarify the air temperature/relative humidity ( RH ) conditions that would cause such uneven frosting, the frosting plot was depicted. On the frosting plot, most of the frosting region was occupied by the uneven frosting region. Homogenizing the uneven frosting may shrink the uneven frosting region, and thereby reduce the chance of frosting. To study the anti-frosting potential of homogenizing uneven frosting, a semi-experimental model was developed. The model calculations demonstrated that, by homogenizing the uneven frosting, the maximal air temperature causing frosting would reduce about 2.5 °C, and the minimal RH causing frosting would increase about 10%. In China, after homogenizing the uneven frosting, it was found that the annual frosting duration in the severe cold zone and the cold zone would be reduced by 30% to 50%; in the hot summer and cold winter zone and the mild zone be reduced by 50% to 80%; and in the hot summer and warm winter zone may achieve frosting-free. [ABSTRACT FROM AUTHOR]

Abstract: In cold region, precipitation, air temperature and snow cover significantly influenced soil water and heat transfer, and thus freezing–thawing processes of active soil layer. On the basic of physical processes of water and heat balances and their transfers in the snow covered soil, a water-heat coupling model for snow cover and its underlying soil layers was established in this paper. Numerical solution of the model was conducted by a full-implicit finite volume method. Observation data of snow cover depth, soil water content and active soil depth at two typical sites in the northeast of Three-River Source Region of China were selected for model calibration and validation. The results indicate that the model can capture soil freezing–thawing processes at the two sites. Simulated results reveal that variations of soil water content, soil temperature and soil freezing depth depend on climate conditions of air temperature, precipitation and snow cover as well. In comparison of the simulated results at two sites, we know that thick snow cover hinders temperature transfer from air to soil, resulting in prolonging the time lag between air and soil temperatures, decreasing variations of soil temperature and soil water content and reducing soil freezing depths of active soil. [Copyright &y& Elsevier]

Observations from 550 surface stations in China during 1961-2000 are used to evaluate the skill of seven global coupled climate models in simulating extreme temperature and precipitation indices. It is found that the models have certain abilities to simulate both the spatial distributions of extreme climate indices and their trends in the observed period. The models' abilities are higher overall for extreme temperature indices than for extreme precipitation indices. The well-simulated temperature indices are frost days (Fd), heat wave duration index (HWDI) and annual extreme temperature range (ETR). The well-simulated precipitation indices are the fraction of annual precipitation total due to events exceeding the 95th percentile (R95T) and simple daily intensity index (SDII). In a general manner, the multi-model ensemble has the best skill. For the projections of the extreme temperature indices, trends over the twenty-first century and changes at the end of the twenty-first century go into the same direction. Both frost days and annual extreme temperature range show decreasing trends, while growing season length, heat wave duration and warm nights show increasing trends. The increases are especially manifested in the Tibetan Plateau and in Southwest China. For extreme precipitation indices, the end of the twenty-first century is expected to have more frequent and more intense extreme precipitation. This is particularly visible in the middle and lower reaches of the Yangtze River, in the Southeast coastal region, in the west part of Northwest China, and in the Tibetan Plateau. In the meanwhile, accompanying the decrease in the maximum number of consecutive dry days in Northeast and Northwest, drought situation will reduce in these regions. [ABSTRACT FROM AUTHOR]

Soil heat and moisture processes are interconnected, especially during low temperatures. To examine the interaction between soil temperature and moisture under freeze-thaw cycles, a physical process-based model (CoupModel) coupled with uncertainty analysis was applied to 3-year measurements under seasonal frost conditions from a site in the black soil belt of northeast China. The uncertainty in parameters and measurements was described by general likelihood uncertainty estimation (GLUE). To identify the degree of linkage between soil temperature and moisture, three criteria were applied to them separately or together. The most sensitive parameters among 26 site-specific parameters were closely related to soil heat, soil evaporation and freeze-thaw processes. Soil temperature was simulated with less uncertainty than soil moisture. Soil temperature measurements had the potential to improve model performance for soil water content, whereas soil moisture measurements demonstrated a trade-off effect when finding a model with good performance for both temperature and moisture. During winter conditions the uncertainty ranges of soil temperature were most pronounced, probably because of the greater complexity of soil properties during the freeze-thaw process and the uncertainty caused by snow properties. The largest uncertainty ranges of both soil water content and soil water storage were found mainly in the deep soil layers. The simulated surface heat fluxes are an important output of the model and it is of great value to compare them with the results from regional climate models and micrometeorological measurements. [ABSTRACT FROM AUTHOR]

In January and February 2010, heavy sea ice formed along the coast of the Bohai Sea and the northern Yellow Sea, China. Intertidal organisms were subjected to serious freezing stress. In this study, we investigated the freezing tolerance of the upper intertidal economic seaweed Porphyra yezoensis. The maximum photochemical efficiency of PS II ( F/ F) in undehydrated thalli remained high after 24 h at −2°C and that in dehydrated thalli decreased in a proportion to thallial water loss. F/ F dropped sharply after 24 h at −20°C, regardless of absolute cellular water content (AWC). The F/ F in frozen thalli recovered rapidly at 0-20°C. A wide range of water loss in the thalli enhanced their tolerance to freezing. F/ F values in undehydrated thalli dropped sharply after 3 d at −2°C or 10 d at −20°C while those in dehydrated thalli (20-53% AWCs) remained at high levels after 9 d at −2°C or 30 d at −20°C. These results indicate that P. yezoensis has high freezing tolerance by means of dehydration during the ebb tide and rapid recovery of F/ F from freezing. A strategy of P. yezoensis industry to avoid heavy loss during freezing season is discussed based on these findings. [ABSTRACT FROM AUTHOR]

Abstract: The China–Russia Crude Oil Pipeline (CRCOP) faces significant challenges due to differential frost heaving and thaw settlement resulting from significant variations of oil temperatures along the pipeline. Oil temperature distribution along the pipeline during the long-term operation period is a very important factor in pipeline foundation design under future climate warming and various frozen soil conditions. It is important for the assessment and prediction of differential frost heave and thaw settlement of the pipeline foundations soils, forecasting the development of the seasonal and inter-annual frozen and thawed cylinders around the operating pipeline, stress–strain analysis of the pipeline, and mitigation of subsequent frost hazards. A quasi three-dimensional computational model was developed to predict the oil temperature along the pipeline. It was verified by analytic solutions of the minimum oil temperatures along the route provided by the Daqing Oilfield Engineering (DOE) Co. The oil temperatures were predicted and analyzed for two proposed annual oil flow rates of 15million tons (0.3mbpd) and 30million tons (0.6mbpd) with and without mitigative measures (only pipe insulation was considered here) during the operation period. Also, the inter-annual variations of oil temperature at key typical locations were investigated to understand the impact of climate warming. The results indicated that the maximum oil temperature cools southwards, but the minimum oil temperature warms southwards (with the inlet oil temperatures from −6 to +10°C). However, the average annual oil temperature decreases southwards in the northern part of the pipeline, then it starts to slowly increase. The amplitudes of oil temperature change will decrease southwards. Oil temperatures will slightly increase with elapsing time due to the imposed boundary conditions of climate warming. The oil temperatures with a lower flow rate vary more significantly than that with a higher flow rate because the oil temperature with a low flow rate is more affected by the thermal regime of the surrounding soils and the external environments. Insulation around the pipeline tends to reduce the oil temperature variations along the pipeline during pipeline operation period. Therefore, pipe insulation can effectively reduce the development of frozen and thawed cylinders in the permafrost zone. The phase change of water in soils around the pipeline has a distinct influence on the oil temperature during the freeze–thaw transition periods. The oil temperature tends to be equal to the ambient ground temperature around the pipeline with southward distance and with elapsing operation time. The pipeline oil temperature is controlled by the incoming oil temperature and the surrounding ground temperature before the equalization. It would be mainly controlled by the ground temperature around the pipeline afterwards. [Copyright &y& Elsevier]

Abstract: The proposed China–Russia Crude Oil Pipeline (CRCOP) will be subjected to strong frost heave and thaw settlement of the surrounding soil as it traverses permafrost and seasonally frozen ground areas in Northeastern China. The freezing–thawing processes, the development of the maximum frozen cylinder in taliks and thawed cylinder in permafrost areas, and the variations in the maximum freezing depths under the pipeline in taliks and thawing depths in different permafrost regions near Mo''he station, the first pumping station in China, were studied in detail using numerical methods in this paper. The inlet oil temperature at Mo''he station was assumed to vary from 10 to −6°C in a sine wave form during the preliminary design phase. Research results showed that the freezing–thawing processes of soils surrounding the buried pipeline had distinct differences from those in the undisturbed ground profile in permafrost areas. In summer, there was downward thawing from the ground surface and upward and downward thawing from the pipeline''s surface once the temperature of the oil rose above 0°C. In winter, downward freezing began from the ground surface but upward and downward cooling of the cylinder around the pipeline didn''t begin until the temperature of the oil dropped below 0°C. However, in the undisturbed ground profile, downward thawing from the ground surface occurred in summer and downward freezing from the ground surface and upward freezing from the permafrost table occurred in winter. The maximum thawing depths and thawed cylinder around the pipeline in warm permafrost enlarged with elapsing time and decreasing water content of the soils. In taliks, the maximum freezing depths and frozen cylinder around the pipeline kept shrinking with elapsing time and increasing water content of the soils. The freezing–thawing processes and development of the thawed and frozen cylinders around the pipeline were muted by any insulation layer surrounding the pipeline. Insulation had better thermal moderating on the heat exchange between the pipeline and the surrounding soils during the early operating period. But its role slowly weakened after a long-term operating. Research results will provide the basis for assessment and forecasting of engineering geological conditions, analysis of mechanical stability of the pipeline, foundation design, and pipeline construction and maintenance. [Copyright &y& Elsevier]

Abstract: The impact of salt on asphalt binders was first studied through basal experiments of binders. The complex influence of freeze–thaw cycles and salt on strength, volume and weight of three types of asphalt mixtures was then investigated through freeze–thaw tests. Test results indicate that salt has a significant effect on the low temperature performance of asphalt binders; Freeze–thaw is a main influencing factor when the percentage of salt is less than 3%, and the erosion effect of salt accelerates the failure of asphalt mixtures when the percentage of salt is more than 3%. The damage of asphalt mixtures is initiated by ice expansion load and accelerated by the interfacial damage between asphalt and aggregate or fracture of asphalt mortar. It can therefore be concluded that different types of asphalt mixtures have fixed residual lives after a number of freeze–thaw cycles. Freeze–thaw cycles, salinity, percent air void, asphalt property and 4.75mm percent passing are main factors having an influence on freeze–thaw strength. [Copyright &y& Elsevier]

Natural frost during stem elongation of winter wheat is one of the most destructive weather-related events in the Huang-Huai plain of China. Early prediction for yield loss helps to guide the timely implementation of a post-frost management strategy. Currently, frost stress indices calculated using the minimum Stevenson screen temperature (ST) only consider the effects of low temperature and duration of frost damage, exhibiting a limited ability for the early prediction of yield loss. Therefore, this study aimed to propose a new index to improve the accuracy of early prediction for yield loss. In this study, Shangqiu was selected for a survey during 2015–2019 where we proposed a method to calculate the percent yield difference (PYD) based on samples of wheat collected during the reproductive stage. In addition, we considered the impact of the compensation of regenerated tillers on PYD. An integrated frost stress (IFS) index was proposed based on the hourly minimum grass temperature (GT) at the regional scale. The IFS index integrated the influence of low temperature, duration, and developmental progress of winter wheat on frost damage and was compared with two accumulated frost degree-days (AFDD) indices to predict PYD. Frost reduced the grain number per ear and grain yield significantly (p < 0.05), and reduced ear number and 1000-grain weight to a lesser extent. The average PYD reached 18.3% in 2018, followed by 11.2% in 2015, 4.2% in 2016, and 1.8% in 2017. Regenerated tillers contributed to yield only if the PYD increased to a certain extent. Compensation by regenerated tillers for PYD in 2018 was only 2.8% and 0.4% in the experimental field and non-experimental fields, respectively, without significant impact (p > 0.05) on the PYD. Compared with the AFDD indices, the IFS index improved the accuracy of early prediction for PYD significantly, with the lowest root mean square error (RMSE) of 6.4%, which showed the advantage of considering the developmental progress and the hourly GT. The IFS, which adopted a critical temperature of − 3 ℃, produced the best calibration model, with the highest interpretation rate of 69.5% for variation in PYD. Although the calibration model did not show the highest accuracy in the validation, its fitted line was closest to the 1:1 line, which indicated the smallest deviation of predicted PYD from measured PYD. This research demonstrated the potential of the IFS index calculated by hourly GT data to evaluate frost damage to winter wheat during stem elongation, which will help guide site-specific, post-frost management. • An integrated frost stress (IFS) index based on hourly minimum grass temperature was proposed. • The IFS integrated low temperature, frost duration, and developmental progress of winter wheat. • The IFS with a temperature of − 3 ℃ yielded the best accuracy for predicting percent yield difference. [ABSTRACT FROM AUTHOR]

China is a large country in terms of coal production and consumption. The fly ash and slag produced by thermal power plants pose a great threat to the environment. To reduce the adverse effects of fly ash and slag on the environment, a mixture of slag and macadam stabilized with cement and fly ash was prepared as pavement base material. Compaction tests, unconfined compressive strength tests, splitting strength tests, frost resistance tests, and ultrasonic tests were performed on the mixture. The results show that with an increase in slag replacement rate, the unconfined compressive strength and splitting strength decreased. However, the adverse influence of the slag replacement rate on unconfined compressive strength and splitting strength of specimens gradually weakened with increasing curing time. The frost resistance of the mixture first increased and then decreased with an increase in the slag replacement rate. When cement content was 5% and the slag replacement rate was 50%, the frost resistance of the mixture was the best. Regression analysis of the ultrasonic test showed that the ultrasonic test can effectively characterize the strength of the mixture and the internal damage degree under freeze–thaw cycles. In conclusion, the slag replacement rate of the mixture is recommended to be ~50%, which has preferable mechanical and frost resistance performance. [ABSTRACT FROM AUTHOR]

This paper presents the impacts of frazil ice jams on the variation in water level at the Hequ Reach of the Yellow River in China. Based on both field observations and experimental studies, it is found that both the evolution of frazil ice jams and the associated variation in water level depend upon an interesting interaction between hydraulic variables during the ice-jammed period. In particular, the critical Froude number governing the formation of river ice jams and their upstream propagation is about 0.09. The water level during ice-jammed periods depends not only on the slope of the water surface and the water level under open-water conditions with the same discharge, but also on the length of the ice jam and the ice concentration in the water. Moreover, the field investigations show that the thickness of river ice strongly influences the variation in water level during ice-jammed periods. Empirical relationships are derived to quantify the relationship between the highest water level during ice periods and related physical parameters. To confirm the field results, and to explore the influence of ice discharge on the variation in water level, experimental studies were also conducted. These results confirm that the ice concentration plays a key role in the variation in water level and the jam thickness. Given the complexity of the jamming processes, surprisingly good agreement is observed between field and experimental investigations. [ABSTRACT FROM AUTHOR]

This paper presents a case history study of a tunnel in the cold plateau region of China. It describes the permafrost distribution of the mountain in which the tunnel is located and the observed air and surrounding rock temperatures in and outside the tunnel. By comparing these measured temperatures, it is found that the effect of the thermal insulation doors, installed at both ends of the tunnel, raises the air temperature in the tunnel higher than the antisnow shelter installed at both ends of the tunnel. The thermal insulation doors are thought to be better than the antisnow shelters in preventing the tunnel from being damaged by frost action. [ABSTRACT FROM AUTHOR]

With the increase in the frequency of extreme weather events in recent years, apple growing areas in the Loess Plateau frequently encounter frost during flowering. Accurately assessing the frost loss in orchards during the flowering period is of great significance for optimizing disaster prevention measures, market apple price regulation, agricultural insurance, and government subsidy programs. The previous research on orchard frost disasters is mainly focused on early risk warning. Therefore, to effectively quantify orchard frost loss, this paper proposes a frost loss assessment model constructed using meteorological and remote sensing information and applies this model to the regional-scale assessment of orchard fruit loss after frost. As an example, this article examines a frost event that occurred during the apple flowering period in Luochuan County, Northwestern China, on 17 April 2020. A multivariable linear regression (MLR) model was constructed based on the orchard planting years, the number of flowering days, and the chill accumulation before frost, as well as the minimum temperature and daily temperature difference on the day of frost. Then, the model simulation accuracy was verified using the leave-one-out cross-validation (LOOCV) method, and the coefficient of determination (R2), the root mean square error (RMSE), and the normalized root mean square error (NRMSE) were 0.69, 18.76%, and 18.76%, respectively. Additionally, the extended Fourier amplitude sensitivity test (EFAST) method was used for the sensitivity analysis of the model parameters. The results show that the simulated apple orchard fruit number reduction ratio is highly sensitive to the minimum temperature on the day of frost, and the chill accumulation and planting years before the frost, with sensitivity values of ≥0.74, ≥0.25, and ≥0.15, respectively. This research can not only assist governments in optimizing traditional orchard frost prevention measures and market price regulation but can also provide a reference for agricultural insurance companies to formulate plans for compensation after frost. [ABSTRACT FROM AUTHOR]

• Three adjusting methods suitable for district heating using ASHPs are proposed. • Energy loss corrections of frosting and on–off are adopted in the simulation model. • Power consumption increment caused by the correction of frosting reaches 3.85–17.41%. • Energy loss ratio of on–off declines from 3.19% to 0.68% with heating area increase. • Energy-saving potential of pump reaches 80.97–86.46% in different adjusting methods. Air source heat pump (ASHP) has been used in Northern China for district heating. However, few investigations on its regulating methods have been conducted till now. To increase the energy-saving effect of AHSPs, a simulation model, which considered the energy loss caused by frosting and on–off, was developed in this paper. Based on this model, three combination regulating modes suitable for district heating using ASHPs as heating source were proposed. Then the heating performance of ASHPs used for district heating in seven cities was investigated using this model. Results showed that both the energy loss corrections of frosting and on–off have evident impacts on the power consumption and seasonal coefficient of performance (SCOP). Owing to the energy loss correction of frosting, the power consumption of ASHP unit is increased by 3.85%–17.41%, and meanwhile SCOP is decreased by 3.72%–14.83%. The influence of the energy loss of on–off decreases gradually with the increase of heating area. In the three regulating modes, the power consumption of ASHP unit changes slightly, while the energy saving rate of water pump can reach 80.97%–86.46%. When the pitch of buried pipe was 300 mm, ASHP can meet the heating demand in all the three regulating modes. [ABSTRACT FROM AUTHOR]

Frost damage frequently occurs in cold-region tunnels due to temperature changes, posing risks to the structural stability and traffic safety. Therefore, temperature variations and its distribution in tunnels are crucial factors that have to be considered. Temperature measurements were conducted in the Xing'anling tunnel in northeast China from 2016 to 2019 to investigate the spatiotemporal characteristics of the temperature field. An equation to determine frost depth based on the Stephen's method was established to evaluate the influence of different factors on frost depth. The sensitivity of frost depth to different influencing factors was investigated using system stability analysis. The results showed that mean annual temperature inside the Xing'anling tunnel has gradually increased from 2016 to 2019 due to global warming. Freezing front was characterized by three stages based on the freezing rate, i.e., the fast freezing stage, transitional freezing stage, and stable freezing stages. The maximum frost depth ranged from 1.5 to 5.1 m without an insulating layer covering the lining, and a lag of about 2 months was observed with air temperature. Along the length of the entire tunnel, four stages of frost depth were observed, namely, fluctuations and a decrease, a steady decrease, fluctuations and an increase, and a steady increase. Frost depth exhibited an asymmetrical distribution to the length of the entire tunnel. Temperature parameters had the largest influence on frost depth, followed by water parameters and thermal parameter. Density parameters had relatively little influence on frost depth. • Temperature field measurements in a long highway tunnel were conducted for a long term in cold regions. • Distribution characteristics of the tunnel temperature along depth and length were revealed. • Characterized stages of freezing front over time on the basis of freezing rate were classified. • Influencing factors on frost depth were analyzed to determine its change laws and sensitivities in cold-region tunnels. [ABSTRACT FROM AUTHOR]

The applicability of common defrost technologies depends on how easy it is for air source heat pumps to frost under local climate conditions. At the same time, the degree of frost formation of the air source heat pumps outdoor units are mainly affected by local climatic conditions. Therefore, this study proposes the concept of frosting degree hours, which is used to specifically characterize the impact of climatic conditions on air source heat pumps frost. In order to make the analysis and calculation of the frosting degree hours more accurate, this study carried out the collection of the actual operation data of the air source heat pumps in winter in many cities in China. Through the selection and analysis of the actual operating data, the data fitting method was used to analyze the different variables and the characteristic temperature difference between the evaporation temperature and the outdoor dry bulb temperature of systems with different power types was obtained. Finally, according to the analysis of the frosting degree hours under different characteristic temperature differences, combined with the frost characteristics of air source heat pumps of different power types in 275 cities in China, the climatic division was performed. This can provide a reference for the climate-adaptive design of air source heat pumps and the development of defrost control strategies. [ABSTRACT FROM AUTHOR]

Vegetation phenology and photosynthetic primary production have changed simultaneously over the past three decades, thus impacting the velocity of vegetation greenup (Vgreenup) and withering (Vwithering). Although climate warming reduces the frequency of frost events, vegetation is exposed more frequently to frost due to the extension of the growing season. Currently, little is known about the effect of frost during the growing season on Vgreenup and Vwithering. This study analyzed spatiotemporal variations in Vgreenup and Vwithering in Northeast China between 1982 to 2015 using Global Inventory Modeling and Mapping Studies Normalized Difference Vegetation Index (GIMMS 3g NDVI) data. Frost days and frost intensity were selected as indicators to investigate the influence of frost during the growing season on Vgreenup and Vwithering, respectively. Increased frost days during the growing season slowed Vgreenup and Vwithering. The number of frost days had a greater impact on Vwithering compared to Vgreenup. In addition, Vgreenup and Vwithering of forests were more vulnerable to frost days, while frost days had a lesser effect on grasslands. In contrast to frost days, frost intensity, which generally decreased during the growing season, accelerated Vgreenup and Vwithering for all land cover types. Changes in frost intensity had less of an impact on forests, whereas the leaf structure of grasslands is relatively simple and thus more vulnerable to frost intensity. The effects of frost during the growing season on Vgreenup and Vwithering in Northeast China were highlighted in this study, and the results provide a useful reference for understanding local vegetation responses to global climate change. [ABSTRACT FROM AUTHOR]

• NNVAI is proposed to indicate winter wheat damage caused by a single frost event. • Growth-stage-specific relations between NNVAI and frost features were explored. • Winter wheat is sensitive to different features of frost at different growth stages. • Developed monitoring framework to do two-phase assessment of winter wheat damage. Frost events pose a threat to normal development of winter wheat and increase risk of production loss, even given the context of global warming. On the Huang-Huai-Hai Plain (HHHP), which is the largest region of winter wheat cultivation in China, frost damage has become one of the major meteorological catastrophes. In recent years, both frequency of occurrence and severity of frost events in this region have exhibited an upward trend. For timely and accurate monitoring of single-event frost damage of winter wheat, this study developed a frost-monitoring framework that considers the processes of the evolution of a frost event and the response of winter wheat, as well as the lag between them. The framework adopts a NDVI valley area index (NVAI) to represent the gradual response process of winter wheat to frost. In this framework, the normalized NVAI (NNVAI) is used to indicate the degree of damage, and a two-phased damage assessment (i.e., T1 and T2) is adopted to resolve the contradiction between the urgency of obtaining information on frost severity, the spatial distribution of frost damage, and the delayed response process of winter wheat to frost. Using prediction models based on historical statistics, assessment at the T1 stage estimates the possible damage after the end of the frost, and assessment at the T2 stage evaluates the actual damage caused by frost when the winter wheat has recovered. Application of the proposed framework to a frost event that occurred on the HHHP during March 4–9, 2018 revealed that the average absolute percentage error between actual and predicted damage across the entire region was 33 %. Moreover, the prediction of damage was made 13 days ahead of the occurrence of actual damage. Thus, the framework could provide guidance to enable action to be taken to reduce the impact of frost. The proposed monitoring framework fully considers the processes of the evolution of a frost event and the response of winter wheat to frost, and it learns potential patterns from historical frost events to provide early prediction of potential frost damage. Consequently, the framework is considered suitable for wide practical application. [ABSTRACT FROM AUTHOR]

The effect of spring snowmelt infiltration in a seasonal soil frost area on groundwater recharge was evaluated by systematically monitoring meteorological factors, soil temperature and humidity, groundwater table and temperature, electrical conductivity, and the value of δ18O in a small field site over a 2-year period. The variation of soil temperature and humidity, groundwater table during the freezing period, and the snowmelt period respectively, as well as their correspondence to the relevant environmental factors, and the influencing factors of the permeability of frozen layer were analyzed. The results showed that the evaluation of precipitation infiltration in seasonal soil frost areas should be divided into three stages: a non-freezing period, a freezing period, and a snowmelt period. Snow is the main form of precipitation during the freezing period, and groundwater cannot be recharged. During the snowmelt period of spring, the snow cover that accumulated during the freezing period infiltrates together with rainfall and has a significant effect on groundwater recharge. The general precipitation infiltration process occurs after the frozen soil thaws completely. These research results can improve the accuracy of groundwater recharge calculations for snowmelt infiltration in the seasonal soil frost area of Northeast China and provide a scientific basis for the evaluation and management of regional water resources. [ABSTRACT FROM AUTHOR]

The article focuses on the discovery of a hybrid soil erosion phenomenon as identified by freeze-thaw action, wind and water alternations in a complex environmental system. Natural soil erosion processes are known to be caused by single natural agent such as water, wind, gravity or freeze-thaw alternation. This hybrid erosion phenomenon is caused by fluvialoaeolian interactions. It is explained as freeze-thaw-action induced erosion process during winter and spring and thawing and wind interactions during late spring. This unique phenomenon was observed in the Songnen Plains, northeastern China which is affected deeply by Siberian climate regime.