Based on the daily data of temperature and precipitation of 108 meteorological stations in Southwest China from 1960 to 2009, we calculate the monthly and yearly surface humid indexes, as well as the extreme drought frequency. According to the data, the temporal and spatial characteristics of the extreme drought frequency in inter-annual, inter-decadal, summer monsoon period and winter monsoon period are analyzed. The results are indicated as follows. (1) In general, the southwestern Sichuan Basin, southern Hengduan Mountains, southern coast of Guangxi and northern Guizhou are the areas where the extreme drought frequency has significantly increased in the past 50 years. As for the decadal change, from the 1960s to the 1980s the extreme drought frequency has presented a decreasing trend, while the 1990s is the wettest decade and the whole area is turning wet. In the 2000s, the extreme drought frequency rises quickly, but the regional differences reduce. (2) During summer monsoon period, the extreme drought frequency is growing, which generally occurs in the high mountains around the Sichuan Basin, most parts of Guangxi and “the broom-shaped mountains” in Yunnan. It is distinct that the altitude has impacts on the extreme drought frequency; during winter monsoon period, the area is relatively wet and the extreme drought frequency is decreasing. (3) During summer monsoon period, the abrupt change is observed in 2003, whereas the abrupt change during winter monsoon period is in 1989. The annual extreme drought frequency variation is a superposition of abrupt changes during summer monsoon and winter monsoon periods. The departure sequence vibration of annual extreme drought frequency is quasi-5 years and quasi-12 years.

Variation of δ18O in precipitation is a physical process of evaporation and condensation and closely related to various factors, such as latitude, altitude, distance from coast, seasonal variation and precipitation amount, and have characteristics of regular change. According to isotope data in precipitation and meteorological data obtained from upper, middle and lower reaches of the Yellow River Basin, spatial and temporal variation characteristics of isotope in precipitation was analyzed. The relationship between stable isotopes in precipitation and temperature, as well as precipitation amount, reveal the changing regularity of stable isotopes in precipitation over the Yellow River Basin. The results indicate that the seasonal variations of stable isotopes in precipitation have different features in the upper, middle and lower reaches of the Yellow River Basin, with enrichment of stable isotopes in summer and depletion in winter for the upper reaches, and opposite features present in the middle and lower reaches. The spatial distribution shows that stable isotopes in precipitation tends to decrease from upper reaches to lower reaches generally, with significant fluctuation and the extremum area. Different reaches of the Yellow River have different isotope process, and the altitude effect and circulation of internal continent affect stable isotopes in precipitation significantly in the upper reaches, while stable isotopes in the middle and lower reaches are influenced by monsoon system and local factors. Analysis of local meteoric water line and correlation of d-excess in precipitation with vapor pressure suggests that rainfall events undergo secondary evaporation accompanied by isotope fractionation during rain drops descent from the cloud base to the ground.

Based on the daily meteorological data from 116 meteorological stations in the Yangtze River basin of China in 1961-2011, and by using the Penman-Monteith method recommended by the FAO, this paper calculated the potential evapotranspiration in the basin. In the meantime, the methods of inverse distance-weighted interpolation, Mann-Kendall mutation test, Morlet wavelet analysis, and rescaled range analysis were adopted to study the spatiotemporal variation patterns of the potential evapotranspiration. In recent 51 years, the inter-annual change tendency rate of the potential evapotranspiration in the whole basin was -0.34 mm·a-1. Spatially, the potential evapotranspiration had an increased trend after an initial decrease from west to east. Temporally, the potential evapotranspiration presented an obvious increasing trend in autumn, but a decreasing trend in spring, summer, and winter, with an overall tendency of summer autumn spring winter. The M-K mutation test and Morlet wavelet analysis showed that the yearly potential evapotranspiration mutation happened around 1980, and the departure sequence vibration of the potential evapotranspiration frequency was primary quasi 12 years and secondary quasi 4 years. The rescaled range analysis showed that except precipitation, all the test climate factors had the same variation trend with the potential evapotranspiration as that in the past.

Based on the daily precipitation data from 19 stations in Shaanxi Province during 1960-2011,and by using the methods of inverse distance weighted interpolation,climate tendency coefficient,M-K mutations inspection,Morlet wavelet analysis,correlation analysis,synthetic analysis,and R/ S analysis,this paper analyzed the variation characteristics of intra-annual precipitation concentration degree and concentration period and their variation tendency in the Province.In 1960-2011,the intra-annual precipitation concentration degree in the Province ranged from 0.44 to 0.66,and presented the spatial distribution characteristics of being higher in the south and north but lower in the middle part.The intra-annual precipitation concentration period ranged from 18.32-22.37 ten days,and showed comparatively small regional difference.The intra-annual precipitation concentration degree presented an increasing trend,while the intra-annual precipitation concentration period displayed an advanced tendency.The variation trends of the intra-precipitation concentration degree and concentration period all existed obvious regional differences.A decreasing abrupt variation in the intra-annual precipitation concentration degree occurred in 1974,while the postponed abrupt variation of the intra-annual precipitation concentration period happened in 1962.The variations of the intra-annual precipitation concentration degree and concentration period did not have a fixed cycle,but various cycle scales nested each other,showing stronger partial characteristics of time and frequency.In the whole province,the annual precipitation was positively correlated with intra-annual precipitation concentration degree,and also,positively correlated with intra-annual precipitation concentration period except in Hengshan of northern Shaanxi.Both in waterish and in water deficient years,the spatial distribution of intra-annual precipitation concentration degree displayed the characteristics of being higher in the south and north but lower in the middle part,while the spatial distribution of intra-annual precipitation concentration period had a greater difference.The variation tendency of the intra-annual precipitation concentration degree and concentration period in the future would keep the same with that in the past 52 years.

According to the meteorological data of 35stations in North China Plain from 1962to 2011,this study analyzed the variation characteristics of the extreme drought frequency in inter-annual,inter-decadal and its impact factors by using linear tendency estimate,inverse distance weighted interpolation,M—K mutations test and so on.The results are indicated as follows:The extreme drought frequency in North China Plain decreased in the past 50years with a rate of 0.013 5times per year.The changes of extreme drought frequency in spring and summer were consistent with that of all year around,but contrary changes were showed in autumn and winter.The areas where the year-round extreme drought frequency presented increasing trend were distributed scatteredly in the researched area.The extreme drought frequency in North China Plain showed a positive departure in 1962—1969and 1980s,but it was negative departure in other decades.At spatial scale,the areas where extreme drought occurred frequently expanded decade by decade from 1962 to 1989,but they shrunk obviously since 1990s.The areas where extreme drought frequency was comparatively low expanded significantly since 1990sand which covered nearly all the North China Plain since 2000.In recent 50years,the year-round extreme drought frequency in North China Plain changed abruptly in 2003 and the abrupt change in spring,summer,autumn,winter occurred in 1993,1998,1987,2002,respectively.The extreme drought frequency showed a positive correlation with sunshine duration,average wind speed,potential evaporation,average temperature,while it showed a negative correlation with precipitation and relative humidity.

The temporal distribution of precipitation has many effects on water resource uses.The non-uniform distribution of precipitation is the main cause of flood and drought disaster in the monsoon climate zone.Based on the daily precipitation data in flood period(June to September) of 72 stations in the Yellow River Basin from 1960 to 2011,the change rules of precipitation concentration degree in the flood period during these past 51 years in this area and the quantitative relationship between precipitation concentration degree and flood and drought index were analyzed by methods of EOF,Morlet wavelet analysis,etc.The results indicate that,the distribution of precipitation is obviously non-uniform.The non-uniform characteristics and concentration degree of precipitation in the northeast of the area and the effects of precipitation concentration degree are especially obvious on flood and drought disaster,and so flood and drought disasters caused by extreme strong precipitations should be watched out with extra vigilance;while the precipitation in the west of the area is relatively less,which aggravates the drought of the west.The precipitation concentration period shows an advancing trend from northeast to southwest.Mid-July is the main period of precipitation concentration and have inter-annual and inter-decadal change characteristics.

Based on stable isotope data of precipitations and lakes on the Tibetan Plateau and Tianshan-Altay areas,contributions of secondary evaporation and evaporative vapors to local precipitations are estimated.(1) The stable isotope data show that values of both δ18O and d-excess decreases from Hetian to Altay in summer monsoon(June to September),suggesting that in the area secondary evaporation has a greater effect in summer monsoon,while in Tibetan plateau area the stable isotope composition of hydrogen and oxygen increases along the water vapor trajectory in both summer monsoon and winter monsoon(October to May),contributed mainly by evaporative vapors from surface water bodies throughout the year.(2) The estimation of evaporation rate indicates that in Tianshan-Altay area the secondary evaporation happens at all times,and it has greater effect in summer monsoon,with rates from 13% to 20% and an average rate of 16.7%,and less effect in winter monsoon,with an average rate of 4.3%.(3) Using a vapor contribution rate model,contributions from moisture advection,evaporative vapors from surface water bodies,and transpiration from plants are calculated.Moisture advection generally contributes the biggest part,greater than 50%,while evaporative vapors contribute the smallest part,with an overall rate of 10%.Transpiration has a contribution rate in between.

According to the meteorological observation data of 72 stations from 1960 to 2010 in the Huanghe (Yellow) River Watershed, China, the long-term variations of potential evapotranspiration, calculated in the modified Penman-Monteith model of Food and Agriculture Organization of the United Nations, were presented, as well as the meteorological causes for the decrease of potential evapotranspiration were discussed. Since 1960, temperature has risen significantly and potential evapotranspiration a decreasing trend, which indicated the existence of “Evaporation paradox” in the Huanghe River Watershed. This phenomenon was not consistent spatially or temporally with the increase of temperature, potential evapotranspiration decreased in spring, summer and winter, mainly over most parts of Shanxi and Henan, and some parts of Gansu, Ningxia, Inner Mongolia, and Shaanxi. During the recent half century, the trends of temperature and potential evapotranspiration were negatively correlated at most of the stations, while precipitation and potential evapotranspiration exhibited a contrary trend. Calculated in multiple regressions, the contribution to potential evapotranspiration change of related meteorological factors was discussed, including mean pressure, maximum and minimum temperature, sunshine hours, relative humidity and average wind speed. The decrease of wind speed in the Huanghe River Watershed may be the dominating factor causing potential evapotranspiration decreasing.

Using monthly mean temperature and monthly mean precipitation data from 25 weather stations in the upper Yellow River from 1960 to 2008, climatic linear trend, moving average, accum ulated variance and R/ S analysis methods were used to study the climatic changing trend. The main findings were summarized as follows ： （ 1 ） Annual and seasond temperatures presented different degree of increasing trend, since the nineties of the 20th century it was more obvious, and with the trend of the most prominent winter heating in upper Yellow River from 1960 to 2008. （2） Precipitation was more in the 1960s, then gradually reduced, since 2000 it was significantly increased, and there existed significant difference change trend of the four seasons. In spring and summer precipitation changes were less, autumn showed decreasing trends, winter showed increasing trend but there were not statistically significant. （3） Compared with the previous studies, we found temperatures was increasing, precipitation showed reduceing trendy. On this basis, using the R/S analysis the climate trend forecast results showed that temperature and .precipitation. has obvious Hurst phenomenon, and the future climate change trend is same with the past 49 years.

Based on the data of 72 meteorological stations in the Yellow River Basin from 1960 to 2010,this paper analyzed the changing trends in potential evapotranspiration and air temperature,and the main factors affecting the decrease of potential evapotranspiration.It also discussed the existence of the"evaporation paradox"(the contract between expectation and observation of evaporation).The results are indicated in the following aspects.(1)In the past 51 years,the air temperature increased significantly and the potential evapotranspiration decreased,therefore the evaporation paradox actually existed in the Yellow River Basin.(2) The"evaporation paradox"is not consistent spatially or temporally:as the temperature increased,potential evapotranspiration decreased in spring,summer and winter over most parts of Shanxi and Henan,and some parts of Gansu,Ningxia,Inner Mongolia,and Shaanxi. In the past 51 years,the changing trend of potential evapotranspiration is not significant from 1960 to 1979,and the changing trends of temperature and the potential evapotranspiration were negatively correlated at most of the stations.(3)In the past 51 years,the changing trends of annual,summer and autumn precipitation are not obvious,and the precipitation and potential evapotranspiration exhibit a contrary trend.(4)In terms of the contribution rate of meteorological elements change to potential evapotranspiration change,a significant decrease of wind speeds in the 51 years is the dominating factor leading to the decrease of potential evapotranspiration in the Yellow River Basin.

This paper summarized the main advances in soil water isotopes by reviewing the influential factors on the changes in soil water stable isotopes,spatial and temporal variation and water transformation and cycle processes at the soil-plant-atmosphere interface.Isotopes had obvious advantages in the investigation of soil water movement,rainfall infiltration and soil evaporation and could clarify the macro and micro characteristics and movement of soil water.This paper also indicated the current problems and the future focus in soil water isotope study and prospected the application of the isotope technology or method in the soil water.

Based on the observed data of stable isotopes in precipitation and meteorological statistics at Urümqi (1986-2003), Zhangye (1986-2003), and Hotan (1988-1992) from IAEA/WMO, the precipitation equation of arid region in Northwest China was calculated through the regression analysis, and the characteristics of stable isotopic in precipitation, as well as the correlation between stable isotopic and meteorological records, were analyzed. The water vapor source of the three sites was tracked by the HYSPLIT4. 9 model, and water vapour transmission regime of arid region in Northwest China was established, while the record of delta18O in cryosphere was discussed. Results showed that the precipitation equation of deltaD = 7.24 delta18O + 1.96 per thousand indicates intense evaporation; delta18O values at Urümqi, Zhangye and Hotan fluctuates at -20.58 per thousand- -5.4 per thousand, -18.58 per thousand- -2.46 per thousand and -20.33 per thousand- -0.01 per thousand, respectively. The delta18O value is low in winter and high in summer, but the values of d-excess is on the contrary; The spatial distribution shows that delta18O value at Zhangye is highest, followed by Hotan, and the lowest is at Urümqi; The highest of d-excess value is at Urümqi, followed by Hotan, the lowest is at Zhangye; The temperature effect of delta18O in precipitation is significant with the correlation coefficients of 0.85, 0.81 and 0.86, respectively, and the rainfall effect does not exist; The modeled trajectory of vapor source showed there are two main paths all the year, which are from the Atlantic Ocean via Westerlies and the Arctic region, respectively, influence by different vapor sources, the seasonality of delta18O values lower in winter, higher in summer; In addition, according to the cryospheric environment, the correlation between delta18O in snow pack or ice core and the corresponding meteorological station record was significant, which reflects the variation of temperature efficiently.