新疆伊犁地区现代气候特征与300 a来的干湿变化规律

在现代实测资料分析和利用树木年轮对伊犁地区３１４ａ降水重建研究的基础上，通过与历史资料在时间上的对比以及与中亚、中国东部和北疆地区小冰期以来气候变化模式在空间上的对比分析，发现３００ａ来伊犁地区的气候变化不仅具有冷与湿、暖与干相对应的特点，而且偏干年出现的频率多于偏湿年。在气候的干湿波动中，湿润期变短，而干旱期相对增长，反映了该区３００ａ来气候与北疆其它地区类似。

Drying Shrinkage of Cement-Based Materials Under Conditions of Constant Temperature and Varying Humidity

Currently,deformations along the central axis of specimens were usually measured under fixed environmental conditions. Seldom were the effects of environmental factors on the drying-shrinkage deformation of cement-based ma-terial considered. For this paper,the drying-shrinkage deformation at different w/b ratios and different additions to mor-tars was investigated under different environments at a temperature of 20 ℃ and humidity ranging from 100% to 50%. The specimens were cured in water for 28 days before measurement. The results illustrate that mortar shows much less shrinkage under various drying conditions when a lower w/b ratio is adopted. With a decrease in relative humidity the speed of drying-shrinkage becomes gradually lower. The addition of silica fume reduces the drying-shrinkage of mortar under higher relative humidity,because the pore structure of mortar with silica fume becomes more refined. The addi-tion of fly ash increases the total porosity and the volume of coarse pores in the mortar. The drying-shrinkage of mortar under different conditions increases with the addition of more of fly ash.

DRY-WET EVOLUTION IN GUANGDONG PROVINCE DURING LAST 500 YEARS

Based on the historical records in Guangdong Province during the last 500a, the moist index sequence was reconstructed and analyzed by the correlation analysis, wavelet analysis and the power spcctrum analysis. The resuits indicate that： 1 ） The El Nino events have evident correlations with the droughts happened in the west and north of Guangdong Province, which intensified the dryness and wetness distribution patterns in these areas in a certain degree. 2） Good correspondence relations exist among the moist index sequence, Greenland ice core oxygen isotope record and the winter-half-year temperature sequence in the eastern China, which showed pattern of moisture and temperature. 3） By applying the wavelet analysis to deal with icities are revealed, among which some can be attributed to the solar activities. At monsoon （especially the East Asian monsoon） activity and the human activity may an apparent monsoonal disposal the data, several apparent period. the same tithe, the ENSO event, also have some influences on the periodicities of the climatic changes in Guangdong Province. 4） Guangdong will persist in dry period before 2040 （±5 years） though some little waterlogged period will also exist in this interval, and after that great floods maybe take place in Guangdong. We think that the variety range of the dryness and wetness has increasing tendency in Guangdong Province in future several even hundred years.

Changes of Dry-wet Climate in the Dry Season in Yunnan(1961-2007)

Factor analysis was used to investigate the changes of dry-wet climate in the dry season in Yunnan during 1961-2007 based on observed data from 15 stations.Three common factors were extracted from the 9 climatic factors.The results showed that the dry-wet climate has evidently changed since the early 1960s.The general trends in the changes of drywet climate were described as slight decrease in humidity and gradual enhancement in drought intensity.The climate during 1960s-1980s was under weak-medium drought.But since early 1990s,dry conditions have markedly strengthened and continued due to uneven temporal distribution of rainfall and climate warming.

Law of Water Content Change in Subgrade Soil Under Action of Dry-Wet Cycle

Due to the influence of the groundwater level,the internal humidity of the subgrade changes and the stability of the subgrade is affected. The main purpose of this paper is to obtain a reliable model of subgrade soil water content variation under the action of dry-wet cycle through sensor readings. Thus,an indoor soil column model test system is designed,and the readings of the sensors are used to determine the changing law of moisture field in the subgrade soil. The sensor readings indicate that the water content gradually decreases along the height of the soil column,and the water in the upper part of the soil column continuously loses,while the water in the lower part migrates upward to supplement. With the increase of dry-wet cycle index,the water holding capacity of soil decreases,and the soil surface gradually cracks and tends to rupture.

Wet-dry changes in the borderland of Shaanxi,Gansu and Ningxia from 1208 to 1369 based on historical records

More than 240 items of historical records containing climatic information were retrieved from official historical books, local chronicles, annals and regional meteorological disaster yearbooks. By using moisture index and flood/drought （F/D） index obtained from the above information, the historical climate change, namely wet-dry conditions in borderland of Shaanxi Province, Gansu Province and Ningxia Hui Autonomous Region （BSGN, mainly included Ningxialu, Hezhoulu, Gongchanglu, Fengyuanlu and Yan＇anlu in the Yuan Dynasty） was studied. The results showed that the climate of the region was generally dry and the ratio between drought and flood disasters was 85/38 during the period of 1208-1369. According to the frequencies of drought-flood disasters, the whole period could be divided into three phases. （1） 1208-1240： drought dominated the phase with occasional flood disasters. （2） 1240-1320： long-time drought disasters and extreme drought events happened frequently. （3） 1320-1369： drought disasters were less severe when flood and drought disasters happened alternately. Besides, the reconstructed wet-dry change curve revealed obvious transition and periodicity in the MongoI-Yuan Period. The transitions occurred in 1230 and 1325. The wet-dry change revealed 10- and 23-year quasi-periods which were consistent with solar cycles, indicating that solar activity had affected the wet-dry conditions of the study region in the Mongol-Yuan Period. The reconstructed results were consistent with two other study results reconstructed from natural evidences, and were similar to another study results from historical documents. All the above results showed that the climate in BSGN was characterized by long-time dry condition with frequent severe drought disasters during 1258 to 1308. Thus, these aspects of climatic change, might have profound impacts on local vegetation and socio-economic system.

Impact of Wetland Change on Local Climate in Semi-arid Zone of Northeast China

Wetlands are sensitive to climate change, in the same time, wetlands can influence climate. This study analyzed the spa- rio-temporal characteristics of wetland change in the semi-arid zone of Northeast China from 1985 to 2010, and investigated the impact of large area of wetland change on local climate. Results showed that the total area of wetlands was on a rise in the study area. Although natural wetlands （marshes, riparians and lakes） decreased, constructed wetlands （rice fields） increased significantly, and the highest in- crease rate in many places exceeded 30%. Anthropogenic activities are major driving factors for wetland change. Wetland change pro- duced an impact on local climate, mainly on maximum temperature and precipitation during the period of May-September. The increase （or decrease） of wetland area could reduce （or increase） the increment of maximum temperature and the decrement of precipitation. The changes in both maximum temperature and precipitation corresponded with wetland change in spatial distribution. Wetland change played a more important role in moderating local climate compared to the contribution of woodland and grassland changes in the study area. Cold-humid effect of wetlands was main way to moderating local climate as well as alleviating climatic wanning and drying in the study area, and heterogeneity of underlying surface broadened the cold-humid effect of wetlands.

Observed dryness and wetness variability in Shanghai during 1873-2005

Dryness and wetness variations on different time scales in Shanghai were analyzed using the Standardized Precipitation Index （SPI） based on monthly precipitation data for 1873-2005. The SPI on scales of 3, 6, 12 and 24 months has been calculated. The SPI on 3, 6, 12 and 24 months present 4 wet periods prevailed during 1873-1885, 1904-1923, 1938-1960 and 1983-2005, and 3 dry episodes during 1886-1903, 1924-1937 and 1961-1982. Significant periods of higher wavelet power in the SPI-24 months occurred on the time scales of 2-7-year band in around 1880-1890, 1910-1950 and 1970-1990, and at 8-15-year band in 1920-1960 and 1965-2000 respectively. Periodicities in the SOl and ENSO indices are similar to those in SPI-24 months with little difference, namely, in the SPI-24 months, there are significant periods at the 2-7- and 8-15-year bands during 1930-1940. The periodicity components in individual SPI-24 months, SOl and ENSO indices are more complicated, showing the wetness and dryness variability in Shanghai is controlled by more than one physical factors. The research results indicate that the Shanghai area has experienced dryness and wetness variability on different time scales during the past 133 years.

Shrinking and Drying up of Baiyangdian Lake Wetland:A Natural or Human Cause?

The shrinking and drying up of wetlands in arid and semiarid areas of China have been widely observed in the recent years, but there has been no consensus on whether the aggravation is caused by human activities or by global climate warming. For a better understanding of the cause, this study investigates the dynamic changes of Baiyangdian Lake wetland over the last 40 years. It is shown that since the 1980s, Baiyangdian Lake has suffered from an insufficient water input and shrunk considerably. By using SPSS 11.0, this study urines a detailed Analysis on the signifficance of the effects of the possible driving factors for the degradation. It is identified that the North China Plain has been warrnin~ up significantly in recent years, which causes a significant reduction in the precipitation and inflow to the lake. Although human disturbances such as the irrigation and storage of water in reservoirs do not play a decisive role, they accelerate the degradation and their effects should be minimized.

Spatio-temporal variation of the wet-dry conditions from 1961 to 2015 in China

As an important part of the regional environment, the wet-dry climate condition is determined by precipitation and potential evapotranspiration （expressed as ETo）. Based on weather station data, this study first calculated ETo by using the FAO56 Penrnan-Monteith model. Then, the dryness index K （ratio of ETo to precipitation） was used to study the spatio-temporal variation of the wet-dry condition in China from 1961 to 2015; moreover, dominant climatic factors of the wet-dry condition change were discussed. The annual precipitation and ETo of the Qinling-Huaihe line were close to a balance （K≈1.0）. The annual precipitation in most areas exceeded the ETo in the south of this line and the east of Hengduan Mountains （K〈0.0）, where the climate is wet. Furthermore, the precipitation in the northwest inland areas of China, where the climate is dry, was markedly lower than ETo （K≥4.0）. The overall annual K of China fluctuated around the 55-year mean and its linear trend was not significant. However, a relatively wet period of about 10 yr （1987-1996） was recorded. The overall annual K of China showed strong cyclicality on the time scale of 3, 7-8, 11 and 26-28 yr, and regional differences of the annual K trends and cyclicality were large. The degrees of wetness in the Northwest China and western Qinghai-Tibet Plateau were substantially increased, whereas the degrees of dryness in the Yunnan-Guizhou Plateau, Sichuan Basin, and Loess Plateau were markedly increased. The linear trend of the annual K in most regions of China was not significant, and the annual K of most areas in China showed strong cyclicality on the 8-14 yr time scale. Precipitation was the dominant factor of wet-dry condition change in most areas, especially in North China, where the annual K change was highly correlated with precipitation.