Pan evaporation, as a measurement of atmospheric evaporative demand, has traditionally been used for agricultural water management. The changing trend of pan evaporation also attracts attentions from the hydrological community worldwide due to its indicative meaning in hydrological cycles. In this study, the changing trend of pan evaporation in China over the past 50 years was analyzed by using Mann-Kendall test method. The results show that there is a decreasing trend in most of the observations on pan evaporation in China, with an average rate of 17.2 mm/10a in China. In the humid region, the decreasing rate was 29.7 mm/10a, presenting the most significantly decreasing trend, while the decreasing rate were 17.6 mm/10a and 5.5 mm/10a in the semi-arid/sub-humid region and arid region, respectively. Temporally, most significant decreases occur in summer with a rate of -16.2 mm/10a; then, -9.7 mm/10a in spring; the decreasing rates in autumn and winter are relatively low. On the attribution, we calculated the complete correlation coefficients of 7 climate factors with pan evaporation. And decreases in diurnal temperature range and wind speed were found to be the main influencing factors leading to the decrease of pan evaporation. The decrease in diurnal temperature range might relate to the increase of aerosol as well as the other pollutants under the circumstance of global warming, which is one of the main features in the context of climate change; and the lowering of wind speed might be associated with the weakening of the Asian winter and summer monsoon under the global climate warming.
Based on the climate and hydrological data of Dongjiang River Basin covering the period 1956-2003, the changes of actual evapotranspiration and pan evaporation and their relationship with climatic factors are analyzed to reveal the similarity and dissimilarity. The results show that there is a decreasing trend in both actual evapotranspiration and pan evaporation, with an insignificant decrease in the former while a significant decrease in the latter. Both of the minimum values of evaporation occur in the 1990s. There is an uncertain and weak negative correlation between actual evapotranspiration and pan evaporation. There is an uncertain relationship between air temperature and actual evapotranspiration and pan evaporation. Wind speed presents a positive correlation with pan evaporation, but an uncertain correlation with actual evapotranspiration. The change of rainfall results in the opposite changes with the two kinds of evapotranspiration, if one increases, the other one decreases. Sunlight radiation causes the opposite changes in trendline analysis and set pair analysis. Through climate patterns analysis, pan evaporation increases with radiation, and actual evapotranspiration increases first and then decreases. The pan evaporation is much more significant than the other climate patterns that the sunlight is more than normal, and the precipitation is less than normal. The actual evapotranspiration is much more than other climate patterns in climate patterns that the sunlight is at the medium level, and the precipitation is more than normal.
Based on the daily precipitation data of flood season in 1961-2006 from 145 stations over Sichuan Basin, we analyzed the temporal and spatial variations of extreme precipitation events. Results indicate that the extreme precipitation event frequency of flood season shows a gradual decreasing trend from west to east, which is remarkably different from the precipitation distribution. The anti-phase changes between Western Sichuan Plateau and Sichuan Basin, as well as west and east Sichuan Basin, are the main spatial models of extreme precipitation event frequency in flood season. The spatial distribution of extreme precipitation event frequency in flood season over Sichuan Basin can be identified into eight regions: central Sichuan Basin, east Sichuan Basin, south Sichuan Basin, west Sichuan Basin, west of Western Sichuan Plateau, central Western Sichuan Plateau, southwest Sichuan and east Chongqing. In terms of long-term trend, there is an apparent linear trend in extreme precipitation event frequency for all the regions, with the exception of a slight decrease and increase for west Sichuan Basin and east Chongqing. Among the eight regions, east Sichuan Basin, southwest Sichuan, western and central parts of Western Sichuan Plateau show an increasing trend, whileas central and southern Sichuan Basin show a decreasing trend. The fluctuating West Pacific Subtropical High and the varying intensities of East and South Asian monsoons have significant impact on extreme precipitation events over eastern, central and western parts of Sichuan Basin, respectively.
Using the data of daily temperature from China Meteorological Administration and the NCEP/NCAR reanalysis data, we analyze the relationships between the summertime high/low temperature events in the middle and lower Yangtze River and the related circulation anomalies in the Eastern Hemisphere from 1960 to 2005. The summer temperature shows a significantly increasing trend, which are explained by the rise of daily minimum temperature in the past 50 years. In the major regions, the opposite scenarios are observed circulation anomalies in lower and upper parts of the troposphere in the years when the temperatures are higher than normal, as compared to those in the years when the temperatures are lower than normal in the middle and lower Yangtze River. The emergence and maintenance of the anomalous circulations are found to be related to three wave train related teleconnection patterns. The anomalous circulation structure in vertical direction in both the high and lower temperature years are barotropic. Influences of the long wave surfaxe radiation on the air temperature are found to be stronger in the nighttime than in the daytime. Both the maximum and minimum temperatures have negative relationships with the sensible heat flux but positive relationships with the latent heat flux. To some extent, the anomalous dynamic heating (cooling) caused by the vertical thermal advection as well as the diabatic heating (cooling) caused by diabatic processes can explain the formation of the high (low) temperature events in the middle and lower Yangtze River in boreal summer.
More and more natural vegetation land has been transformed into crop fields in the Lhasa river valley on the Tibetan Plateau with the local population growth and economic development. However, the land cover changes would exert great impact on ecosystems energy and water balance and water use. We did experiments in crop fields at Lhasa Plateau Ecosystem Research Station and the nearby shrub grassland. Then we researched the water and energy balance and the processes of water extraction from roots using SHAW model based on experiment data and climatic data obtained at Lhasa Plateau Ecosystem Research Station. By the analysis of the simulated results, some main conclusions were drawn as follows. (1) Net radiation received by crop fields was more than shrub grassland; and the outgoing latent heat from crop fields was dominating, with the all-year Bowen ratio being 0.29. As for the shrub grassland, the all-year Bowen ratio was 0.89. The outgoing latent heat of shrub grassland was 53% of crop fields. Thus, shrub grassland limited evapotranspiration to some extent. (2) The water consumed of crop fields was nearly twice of that of shrub grassland. Irrigation resulted in much deep percolation and increased soil evaporation. (3) The deep soil water supply and root extraction indicated that shrubs could absorb deep soil water that could not be used by crops.
In this paper, the residence time of groundwater in dry season, wet season and yearly average is estimated based on daily streamflow records of 11 hydrological stations in Wudinghe River Basin. Results show that: (1) recession constant of groundwater in the Wudinghe River Basin, ranging from 0.72 to 0.89, has a larger recession rate in wet season than in dry season. (2) Spatially, the recession rate of groundwater in hilly region is the biggest, but is the smallest in the sandy region. (3) Half-residence time of groundwater varies from 1.8 to 45.5 days while the residence time of groundwater is between 34 and 105days in different catchments, showing significant spatial variation. The annual average residence time of groundwater decreases from 101 days in the upper reaches to 84 days in the lower reaches.
The statistical characteristics of individual storms are the basis for rainfall event simulation. This paper selected hourly precipitation data from May to September covering the period 1954-2001 from 62 weather stations throughout China to analyze the individual storm characteristics. The individual storms in China obey the gamma distribution by using chi-square test. Only several stations did not pass the test due to the poorly simulated effects for extreme events. Five indexes including two parameters in gamma distribution and the 90th, 95th and 99th percentiles of individual rainfall amount were used in the method of K means clustering. The results present a distribution of five zonal regions from southeast to northwest, with the decreasing ranking of the skewness, heterogeneity and dispersion for the individual rainfall amount during May to September in China. The regionalization of individual rainfall amount is the basis for estimating regional parameters in storm-based simulation models.
Three cross-sections of paleovalley depositional sequences were established with references of hundreds of bore data and documents of the No.3, No.1 and No.4 Nanjing Yangtze River bridges. Through analyzing age results of 14C from samples of four drilling cores near the No.4 Nanjing Yangtze River Bridge (to be built), we can find that the time range of paleovalley is dated LGM at a depth of -60~-90 m near Nanjing. It is also indicated that the deep incised-valley channel was narrow and the river flew swiftly. The ancient Yangtze River deep channel presented partially and deeply incised features near the No.1 Nanjing Yangtze River Bridge. According to previous publications, much research has been done on the main paleochannel of the Yangtze River, but few results have been achieved on discharge estimation. In this paper, the incipient velocity and average velocity of the LGM was calculated with Vcetc., in terms of the river shape, sedimentary grain size and sequences near the No.3 and No.1 Nanjing Yangtze River bridges. Moreover, the discharge in Nanjing reach of the Yangtze River during the LGM has been estimated to be around 12000~16000 m3/s according to the relationship of discharge, velocity of flow and cross-section.
There are numerous dry salt lakes in the hinterland of the Ulan Buh Desert and around them are lakeshore terraces at different heights. The Herom Xil spit discovered in extensive field investigation is the most typical among them. The spit falls from northwest to southeast with elevations ranging between 1052-1035 m a.s.l. and has a length of 11 km. This is an important evidence for the existence and development of the palaeolake. The spit was formed during the period 8.6-7 ka B.P. in early Holocene, based on the OSL dating on beach sediment. The period was coincident with the moist environment observed in many deserts of western China. The strong palaeowind, rich lake sediment sources and currents of Jarantai and Hetao palaeolakes led to the formation of the spit. According to the elevation of the spit, we estimated that in the Ulan Buh Desert hinterland developed a relatively large palaeolake which extended to Jarantai basin westward and to Hetao basin eastward, and thus formed Jarantai megalake in Holocene. With the intensification of dry climate, the palaeolake level declined and the area shrank. Furthermore, numerous lakes remained and evolved into salt lakes in the hinterland of the Ulan Buh Desert. The sands around the palaeolake might have resulted in the formation of the present Ulan Buh Desert.
The prominent types of Danxia landform in Fangyan include enclosed valleys, mesas, peaks, stone columns and grooves etc. Their spatial combination has regular order along the direction of northwest-southeast: typical grooves and caves are mainly located in northwestern Wufengshuyuan; abundant fresh collapsed stones can be observed in central Jimingfeng and Taohuafeng; stone drums and stone columns are in the southeastern Shiguliao particularly; enclosed valleys are encircling joints of peaks and plains from three directions of east, west, and south. The spatial combination suggests that the development of Danxia landform experienced procedures of geomorphic cycle erosion of weathering, collapse, erosion by rivers etc. under the "sculpture" of external force mainly as tectonic uplifting, picturesque Danxia landform was conceived then. They are developed mainly in the strata of Fangyan Formation (K1f) of alluvial fan-braided river phase of anterior fan in the late period of Early Cretaceous. Regular pattern of weathering of stones and features of sediments of braided river phase can be identified by analysis of experimental data obtained from three sample points. Danxia landform of Fangyan is a unique representive of the "adolescent" type of China's Danxia landform in the application of the World Natural Heritages with outstanding universal aesthetic and scientific value.
This paper firstly analyzes the geomorphological changes of the tidal deposition based on the bathymetric charts and Landsat data. Then it makes a full study of the evolution of the tidal deposition system in the past 20 years in the Liaohe River by drilling and shallow substrata data. The main tidal depositional body of modern Liaohe River delta is located in Shuangtaizihe River estuary. There are three sedimentary facies, including tidal bank facies, tidal channel facies and shallow sea facies. The sediments of tidal bank facies mainly consist of sand and silty sand. The sediment gradation is middle. The percentage of saltation load and suspension load is about 50% each in tidal bank facies. The sediment of tidal channel facies is composed of silty clay and clayey silt, which belongs to suspension load. The results reveal a net accretion trend in the Shuangtaizihe River estuary. The area of tidal bank is increasing and expanding towards south, west and north. The maximum expansion speed is 87 to 683 m/a. The mean depositional rate is 0.189 m/a. The average erosional rate is 0.122 m/a in some parts of tidal flat. It is filled with sediment in tidal channel, with a migration rate of 48-200 m/a. The geomorphological evolution is influenced by runoff, ocean power and human activity. The main source of sediment changes from river sediment to tidal current and littoral stream sediment.
Sample survey is the groundwork of the studies of natural resources, environmental problems and socio-economy. The geo-related characteristic of spatial data limits the application of classic sampling theory, which is essentially based on independent assumption. Spatial sampling theory is the foundation of sample survey of spatial related resources. Firstly, this paper introduces the history of spatial sampling theory and presents four main issues addressed by this theory. Then it reviews the theory and the applications of model-based and design-based statistics inference. Finally, this paper gives a detailed description of (1): Kriging theory application in spatial sampling; (2): forward and backward samples distribution methods, and the combination of the above two; (3): six criteria for optimization of sample selection.
