液氮致裂时间对煤样力学性能、渗透性与致裂机理的影响

为研究液氮致裂时间对煤样的力学性能和渗透率的影响,利用自主研发的WYS-800三轴瓦斯渗流试验装置及声发射检测系统,对4组不同液氮致裂时间处理的煤样分别进行三轴力学渗流试验并采集声发射信号,对三轴力学渗流试验中各组煤样的力学性能、渗透率的变化进行了分析,描述了声发射信号的特征;根据沸腾换热理论、一维圆柱导热理论、热应力理论分析了致裂机理,计算了不同致裂时间下产生的热应力,通过数据拟合揭示了平均温度降、平均热应力、初始渗透率与致裂时间的关系。研究结果表明:①液氮致裂时间对煤样的力学性能产生不同影响,抗压强度和弹性模量随致裂时间的增加呈现先减小后增大的趋势,泊松比则呈现先增大后减小的趋势,煤样三轴加载时轴向应力-轴向应变曲线的阶段性演化具有明显差异,与力学参数的改变相关。②不同液氮致裂时间煤样在三轴加载过程中的渗透率均呈U型变化,煤样的初始渗透率、最小渗透率、试验测得最大渗透率随致裂时间的增加而增大,致裂30 min时增幅分别为119.05%、437.5%、146.49%;声发射信号在压密和弹性阶段不活跃,主要产生于屈服阶段和破坏阶段,致裂后煤样的声发射振铃计数峰值产生于破坏点附近,均大于20000次。③煤样与液氮之间的膜态沸腾换热系数为570.4 W/(m2·K),煤样平均温度降与致裂时间相关,对平均热应力和初始渗透率起主导作用,致裂30 min时煤样内部产生的平均温度降可达213.63 K,平均热应力可达5.850 MPa。④液氮处理后煤样的初始渗透率与平均温度降之间呈线性关系,与致裂时间呈负指数分布关系。改变参数取值,可推广至其他类似处理的煤样或实际生产评估。

Mapping Daily Temperature and Precipitation in the Qilian Mountains of Northwest China

Daily meteorological data are the critical inputs for distributed hydrological and ecological models. This study modified mountain microclimate simulation model （MTCLIM） with the data from 19 weather stations, and compared and validated two methods （the MTCLIM and the modified MTCLIM） in the Qilian Mountains of Northwest China to estimate daily temperature （i.e., maximum temperature, minimum temperature） and precipitation at six weather stations from i January 2000 to 31December 2009. The algorithm of temperature in modified MTCLIM was improved by constructing the daily linear regression relationship between temperature and elevation, aspect and location information. There are two steps to modify the MTCLIM to predict daily precipitation： firstly, the linear regression relationship was built between annual average precipitation and elevation, location, and vegetation index; secondly, the distance weight for measuring the contribution of each weather station on target point was improved by average wind direction during the rainy season. Several regression analysis and goodness-of-fit indices （i.e., Pearson＇s correlation coefficient, coefficient of determination, mean absolute error, root-mean-square error and modelingefficiency） were used to validate these estimated values. The result showed that the modified MTCLIM had a better performance than the MTCLIM. Therefore, the modified MTCLIM was used to map daily meteorological data in the study area from 2000 to 2009. These results were validated using weather stations with short time data and the predicted accuracy was acceptable. The meteorological data mapped could become inputs for distributed hydrological and ecological models applied in the Qilian Mountains.

Asian climate change under 1.5-4 ℃ warming targets

Based on simulations of 18 CMIP5 models under three RCP scenarios, this article investigates changes in mean temperature and precipitation and their extremes over Asia in the context of global warming targets of 1.5-4 ℃, and further compares the differences between 1.5 ℃ and 2 ℃ targets. Results show that relative to the pre-industrial era, the mean temperature over Asia increases by 2.3 ℃, 3.0 ℃, 4.6 ℃, and 6.0 ℃ at warming targets of 1.5 ℃, 2 ℃, 3 ℃, and 4 ℃, respectively, with stronger warming in high latitudes than in low latitudes. The corresponding enhancement in mean precipitation over the entire Asian region is 4.4%, 5.8%, 10.2%, and 13.0%, with significant regional differences. In addition, an increase in warm extremes, a decrease in cold extremes, and a strengthening in the variability of amounts of extreme precipitation are projected. Under the 1.5 ℃ target, compared with the climate under the 2 ℃ target, the mean temperature will be lower by 0.5-1 ℃ over Asia; the mean precipitation will be less by 5%-20% over most of Asia, but will be greater by about 10%-15% over West Asia and western South Asia; extreme high temperatures will be uniformly cooler throughout the Asian region, and the warming in extreme low temperatures will decrease significantly in high latitudes of Asia; extreme precipitation will be weaker over most of Asia but will be stronger over West Asia and western South Asia. Under the 1.5 ℃ and 2 ℃ warming targets, the probability of very hot weather （anomalies greater than 1σ, σ is standard deviation）, extremely hot weather （anomalies greater than 3or）, and extremely heavy precipitation （anomalies greater than 3σ） occurring will increase by at least once, 10%, and 10%, respectively, compared to the reference period （1861-1900）.

Historical and Future Climatic Change Scenarios for Temperature and Rainfall for Iraq

The world is facing a big challenge of climatic change, mainly due to increasing concentrations of GHGs （greenhouse gases） in the atmosphere. Many researches indicated that the climate change occurred disproportionately on developing countries such as MENA （Middle East and North Africa） countries. The climatic model CGCM3.1 （T47） 2 is used in this research to explain the changes in average temperatures and the rainfall on the MENA region with special emphases on Iraq. Historical records （1900-2009） and future （2020-2099） were studied and compared; each period was divided to four sub-periods of thirty years. The results showed that the average monthly temperature for the four historical periods fluctuated between the lowest and highest value as follows： 9.2-32.9, 10.3-32.7, 9.3-32.8 and 8.6-33.9 （℃）. The rainfall for historical periods kept on the same distribution during the past 109 years, and fluctuated between the lowest and highest value of 21.3 mm and 37.6 mm with an average that reached up to 26.51 mm. For the future period, the maximum average monthly temperature reached up to 37.41 （℃） during June and minimum average monthly temperature reached up to 4.24 （℃） during January. The average monthly temperature fluctuated giving a clear impression that the future portends a higher temperature. The average monthly rainfall, for the future period, fluctuated between the lowest and highest value of 12.91 mm and 20.63 mm with an average that reached 16.84 mm which represent a reduction percentage of about 36.47% relative to the historical record of rainfall for the sanae months.

Wavelet Analysis and Nonparametric Test for Climate Change in Tarim River Basin of Xinjiang During 1959-2006

Using wavelet analysis,regression analysis and the Mann-Kendall test,this paper analyzed time-series(1959-2006) weather data from 23 meteorological stations in an attempt to characterize the climate change in the Tarim River Basin of Xinjiang Uygur Autonomous Region,China.Major findings are as follows:1) In the 48-year study period,average annual temperature,annual precipitation and average annual relative humidity all presented nonlinear trends.2) At the 16-year time scale,all three climate indices unanimously showed a rather flat before 1964 and a detectable pickup thereafter.At the 8-year time scale,an S-shaped nonlinear and uprising trend was revealed with slight fluctuations in the entire process for all three indices.Incidentally,they all showed similar pattern of a slight increase before 1980 and a noticeable up-swing afterwards.The 4-year time scale provided a highly fluctuating pattern of periodical oscillations and spiral increases.3) Average annual relative humidity presented a negative correlation with average annual temperature and a positive correlation with annual precipitation at each time scale,which revealed a close dynamic relationship among them at the confidence level of 0.001.4) The Mann-Kendall test at the 0.05 confidence level demonstrated that the climate warming trend,as represented by the rising average annual temperature,was remarkable,but the climate wetting trend,as indicated by the rising annual precipitation and average annual relative humidity,was not obvious.

Changes in Climate Factors and Extreme Climate Events in South China during 1961-2010

Daily climate data at 110 stations during 1961-2010 were selected to examine the changing characteristics of climate factors and extreme climate events in South China. The annual mean surface air temperature has increased significantly by 0.16℃ per decade, most notably in the Pearl River Delta and in winter. The increase rate of the annual extreme minimum temperature (0.48℃ per decade) is over twice that of the annual extreme maximum temperature (0.20℃ per decade), and the increase of the mean temperature is mainly the result of the increase of the extreme minimum temperature. The increase rate of high-temperature days (1.1 d per decade) is close to the decrease rate of low-temperature days (-1.3 d per decade). The rainfall has not shown any significant trend, but the number of rainy days has decreased and the rain intensity has increased. The regional mean sunshine duration has a significant decreasing trend of -40.9 h per decade, and the number of hazy days has a significant increasing trend of 6.3 d per decade. The decrease of sunshine duration is mainly caused by the increase of total cloud, not by the increase of hazy days in South China. Both the regional mean pan evaporation and mean wind speed have significant decreasing trends of -65.9 mm per decade and -0.11 m s-1 per decade, respectively. The decrease of both sunshine duration and mean wind speed plays an important role in the decrease of pan evaporation. The number of landing tropical cyclones has an insignificant decreasing trend of -0.6 per decade, but their intensities show a weak increasing trend. The formation location of tropical cyclones landing in South China has converged towards 10-19°N, and the landing position has shown a northward trend. The date of the first landfall tropical cyclone postpones 1.8 d per decade, and the date of the last landfall advances 3.6 d per decade, resulting in reduction of the typhoon season by 5.4 d per decade.

Zonal Differences in Correlation Patterns Between Soil Organic Carbon and Climate Factors at Multi-extent

Studying the relationship between climate factors and soil organic carbon （SOC） is vitally important. However, how SOC responses to climate （temperature and precipitation） at cohesive extents is poorly studied. Two transects of approximately the same length （transect P and transect T） were selected to examine the variation of SOC content in relation to mean annual temperature （MAT） and mean annual precipitation （MAP）. The coefficients of partial correlation between SOC density and MAT （Rt） and MAP （Rp） were determined to quantify the relationships between SOC density and the two climate factors. The results indicated that for transect T, Rt was statistically significant once the extent level was greater than or equal to two fundamental extent units, while for transect P, Rp showed statistical significance only at extent levels which were greater than two fundamental extent traits. At the same extent levels but in different transects, Rts exhibited no zonal difference, but Rps did once the extent level was greater than two fundamental extent units. Therefore, to study the relationship between SOC density and different climate factors, different minimum extent levels should be ex- amined. The results of this paper could deepen the understanding of the impacts that SOC pool has on terrestrial ecosystem and global carbon cycling.

Simulation of Climate Change Scenarios for Phu Luong Watershed in Northern Viet Nam

The purpose of this paper is to apply ＂LARS-WG （Long Ashton Research Station--Weather Generator）＂ model to simulate the climate change scenarios for Phu Luong watershed in northem Viet Nam. Results indicated that LARS-WG adequately predicted precipitation and temperature with R2 = 0.80 and 0.73, respectively. Likewise, p-value of F test = 0.062 and p-value of t test = 0.885 for precipitation, meanwhile, for temperature are 0.092 and 0.564 at 0.05 level of significance, respectively. Moreover, results also stated that mean annual precipitation increases 1.62%, 2.17% and 3.96% and mean annual temperature increases 0.6 ℃, 0.8 ℃ and 1.05 ℃ in 2020, 2030 and 2040, respectively, with respect to those from baseline periods. This study also showed that LARS-WG model was used successfully for Viet Nam＇s watershed conditions.

Patterns of Soil ^(15)N and Total N and Their Relationships with Environmental Factors on the Qinghai-Tibetan Plateau

The patterns of soil nitrogen （N） isotope composition at large spatial and temporal scales and their relationships to environmental factors illustrate N cycle and sources of N, and are integrative indicators of the terrestrial N cycle and its response to global change. The objectives of this study were： i） to investigate the patterns of soil N content and natural abundance of 15N （δ15N） values in different ecosystem types and soil profiles on the Qinghai-Tibetan Plateau; ii） to examine the effects of climatic factors and soil characteristics on the patterns of soil N content and soil δ15N values; and iii） to test the relationship between soil δ15N values and soil C/N ratios across ecosystems and soil profiles. Soil profiles were sampled at 51 sites along two transects 1 875 km in length and 200 km apart and distributed in forest, meadow and steppe on the Qinghai-Tibetan Plateau. Each site was sampled every 10 cm from a soil depth of 0 to 40 cm and each sample was analyzed for soil N content and δ15N values. Our results indicated that soil N and 515N values （0-40 cm） in meadows were much higher than in desert steppe. Soil N decreased with soil depth for each ecosystem, while variations of soil ~15N values along soil profiles were not statistically significant among most ecosystems but for mountain meadow, lowland meadow, and temperate steppe where soil δ15N values tended to increase with soil depth. The parabolic relationship between soil δ15N values and mean annual precipitation indicated that soil δ15N values increased with increasing precipitation in desert steppe up to 500 mm, and then decreased with increasing precipitation across all other ecosystems. Moreover, the parabolic relationship between δ15N values and mean annual temperature existed in all individual ecosystem types. Soil N and δ15N values （0-0 cm） increased with an increase in soil silt and clay contents. Furthermore, a threshold of C/N ratio of about 11 divided the parabolic relationship between soil δ15N values and soil C/N ratios into positive （C/N 〈 11） and negative （C/N 〉 11） parts, which was valid across all ecosystems and soil profiles. The large explanatory power of soil C/N ratios for soil δ15N values suggested that C and N concentrations, being strongly controlled by precipitation and temperature, were the primary factors determining patterns of soil δ15N on the Qinghai-Tibetan Plateau.

Are There Differences in the Response of Natural Stand and Plantation Biomass to Changes in Temperature and Precipitation?A Case for Two-needled Pines in Eurasia

A comparative discussion of the advantages and disadvantages of natural stands and plantations,including in terms of their productivity and stability,began from the moment of the first forest plantings and continues to this day.In the context of the progressive replacement of natural forests by plantations due to deforestation,the question of how will change the carbon storage capacity of forest cover when replacing natural forests with artificial ones in a changing climate becomes extremely relevant.This article presents the first attempt to answer this question at the transcontinental level on a special case for two-needled pine trees(subgenus Pinus L.).The research was carried out using the database compiled by the authors on the single-tree biomass structure of forest-forming species of Eurasia,in particular,data of 1880 and 1967 of natural and plantation trees,respectively.Multi-factor regression models are calculated after combining the matrix of initial data on the structure of tree biomass with the mean January temperature and mean annual precipitation,and their adequacy indices allow us to consider them reproducible.It is found that the aboveground and stem biomass of equal-sized and equal-aged natural and plantation trees increases as the January temperature and precipitation rise.This pattern is only partially valid for the branches biomass,and it has a specific character for the foliage one.The biomass of all components of plantation trees is higher than that of natural trees,but the percent of this excess varies among different components and depends on the level of January temperatures,but does not depend at all on the level of annual precipitation.A number of uncertainties that arose during the modeling process,as well as the preliminary nature of the obtained regularities,are noted.

Regional Diferences in the Efect of Climate and Soil Texture on Soil Organic Carbon

The agricultural soil carbon pool plays an important role in mitigating greenhouse gas emission ana unaerstanamg the son orgamc carbon-climate-soil texture relationship is of great significance for estimating cropland soil carbon pool responses to climate change. Using data from 900 soil profiles, obtained from the Second National Soil Survey of China, we investigated the soil organic carbon （SOC） depth distribution in relation to climate and soil texture under various climate regimes of the cold northeast region （NER） and the warmer Huang-Huai-Hai region （HHHR） of China. The results demonstrated that the SOC content was higher in NER than in HHHR. For both regions, the SOC content at all soil depths had significant negative relationships with mean annual temperature （MAT）, but was related to mean annual precipitation （MAP） just at the surface 0-20 cm. The climate effect on SOC content was more pronounced in NER than in HHHR. Regional differences in the effect of soil texture on SOC content were not found. However, the dominant texture factors were different. The effect of sand content on SOC was more pronounced than that of clay content in NER. Conversely, the effect of clay on SOC was more pronounced than sand in HHHR. Climate and soil texture jointly explained the greatest SOC variability of 49.0% （0-20 cm） and 33.5% （20-30 cm） in NER and HHHR, respectively. Moreover, regional differences occurred in the importance of climate vs. soil texture in explaining SOC variability. In NER, the SOC content of the shallow layers （0-30 cm） was mainly determined by climate factor, specifically MAT, but the SOC content of the deeper soil layers （30-100 cm） was more affected by texture factor, specifically sand content. In HHHR, all the SOC variability in all soil layers was predominantly best explained by clay content. Therefore, when temperature was colder, the climate effect became stronger and this trend was restricted by soil depth. The regional differences and soil depth influence underscored the importance of explicitly considering them in modeling long-term soil responses to climate change and predicting potential soil carbon sequestration.