By the rare earth elements (REE) tracer method, four REE (Ce, Sm, Nd, Dy) were used to study the changeable process of rill erosion on loess sloping surface in runoff scouring experiments. During different stages, the erosion pattern and characteristics are different. Generally, in the process of the rill development, the soil erosion amount in the bottom section was larger, and it decreased with the increase of the flow discharge, but the situation is on the contrary to the top section, which indicated that the influence of flow discharge outweighed the gradient on the rill erosion; the rill relative erosion amount in the bottom section obviously decreased from 92% to 37%, but the other three sections gradually increased from 4.7%, 0.25%, 2.14% to 29 %, 17% and 23% respectively because of the headcut erosion. Results from the experiments have also shown that the REE tracer method can be used not only quantitatively to determine rill erosion amounts in different slope sections, but also to reveal the changeable trend of rill relative erosion amounts. It provides a reliable and effective method for the research on rill erosion process.

A set of data on the grain-size of suspended sediments and river basin characteristics has been collected from the first order tributaries of the Middle Yellow River. A systematic study on quantitative relationships between grain-size of suspended sediments and the characteristics of these basins have been made for those river basins by using statistical methods. The following conclusions can be drawn: Precipitation, surface material, drainage density, vegetation coverage and hyperconcentrated flows act as an important controlling factor on the grain-size of suspended sediments in the Middle Yellow River. The grain-size of suspended sediments increases with an increase in drainage density, the maximum suspended sediment concentration and unevenness of precipitation, and decreases with an increase in the percentage of loess and vegetation coverage. Multiple regression analysis has shown that surface material is the most important factor influencing the grain-size of suspended sediments, followed by vegetation, hyperconcentration and precipitation. The drainage density exerts minor influence on the grain-size of suspended sediments.

Based on the results of the remote sensing investigations of the land-use and land-cover of 1995 and 2000, the national distribution of sandy desertified land and its interaction with other landscapes are classified, and five zonal types are distinguished. In arid and semi-arid areas of China, the intensity of wind field is one of the key factors that control the development of landscape especially in desert and its adjacent area. To better understand the spatial distribution of wind erosion landscapes as well as their dynamic changes, essential work is needed to expose the spatialy distribution of wind field and its changes. In the paper, the data of nationally distributed 400 meteorological stations of 1999 are processed. With the GIS method, the data are spatially interpolated, and the national database of wind field concerned with wind erosion is established. Wind speed and its duration are one of the most important factors that control wind erosion of soil. When the friction speed is satisfied, wind erosion occurs. Different indexes are set up to describe the intensity of wind field, such as the number of days that their daily average wind speed exceeds the value of threshold speed and the number of records that their speed surpass the threshold speed. The method suggested by the wind erosion prediction models of RWEQ is also adopted to express the intensity of wind. The results are compared, and the distribution of wind field in China is discussed. The relation of the distribution of landscape and wind field is then discussed indicating the strong wind field in Northwest China as a most important factor that causes serious landscape change especially to the diminishing of the grassland and contrarily the expansion of the sandy desertified land.

The impact of interbasin water transfer on environment is very significant. The affected area of the west route scheme of South to North Water Transfer Project in China (SNWT) is located in the southeasten part of the Tibetan Plateau, where the altitude is high with fragil eco-environment. Therefore, it is necesary for SNWT to analyze the natural eco-environment. In the article, we apply the remote sensing and GIS to analyze the natural environment of the study area which lies in the range of 31o27'～33o58'N and 96o57'～102o30'E, covering an area of 91 200 km^{2. The materials we used include 8 images of TM, 1:1 000 000 basic geographic data of China, the meteorologic data from 631 stations in China (1958~1998), statistic data and natural resources maps of Qinghai and Sichuan provinces. We obtained natural environmental factors such as land cover, vegetation cover, NPP(Net Primary Productivity), temperature, precipitation and topographic terrain by remote sensing and GIS method. We use the natural environment index which contains natural factor index and the total number of natural factor analyzed to express the natural conditions of the study area. The natural factor index of land cover, vegetation cover, NPP, temperature, precipitation and altitude are calculated and the natural environment index is divided into four grades or four level sub-areas. According to the calculation result, we analyze the features of each grade of the natural environment index or the natural eco-environment of the four sub-areas, so as to provide new trajectories and new methods that can be used for reference in environmental impact assessment of the affected area of the west route of South-to-North Water Transfer Project in China.}

According to inquisitional result based on remote sensing technology, this paper narrates the regulations of Yutian oasis land cover dynamic change. Considering macroscopic research, 4 main land cover types are chosen, which are desert, oasis, ecotone and water body and they represent distinct characteristics of the local place. On the basis of field survey and statistical data, the paper uses PCI software to preprocess these data and the 2 satellite images (see Fig. 1). To improve overall post-classification precision, this study uses spatial structure information of satellite images to reclassify the result by using fuzzy optimum clustering firstly and gains a rather high classification precision which guarantees the need of analysis fully. Through analyzing these images resulting from post-classification comparation, the paper sums up the concrete quantificational dynamic distributed data of 4 main land types covering a span of 9 years and regulation of the local ecological environmental system. It finally points out that the trend of Yutian regional oasis desertification expansion are related to two important reasons, i.e., impact of natural environment and impact of human activities. In order to improve the local ecological environment, people in Yutian county should take measures suitable to local conditions to protect oases environment through shelterbelt construction, development of socio-economy and sustainable development.

Taking the region around the Qinghai Lake as the study area and using the Landsat Thematic Mapper data and the measured grass yield data, the monadic linear regression models and the non-linear regression models were established, respectively, to express the relations between grassland biomass and the vegetation indices. There are two types of sampling site, i.e., the larger one is 30 m×30 m and the smaller one is 1 m×1 m. Each larger sampling site includes one smaller one which was randomly selected. The major conclusions from this study are: 1) the fitting accuracies of the non-linear regression models are much higher than those of the non-linear regression models, namely, the results obtained from the non-linear regression models are more accordant with the measured grassland biomass data in comparison with those from the monadic linear regression models; 2) the comparison of different forms of the non-linear regression analysis on the relations between the vegetation indices and the measured grassland biomass data indicates that the cubic equation is the best one in terms of the suitability of use in the study area; 3) the results from the non-linear regression analysis show that the order is RVI, NDVI, SAVI, MSAVI and DVI in terms of the fitting accuracy between these vegetation indices and grassland biomass data; and 4) the non-linear model Y = -18.626RVI3+220.317RVI2-648.271RVI+691.093 is the best model which can be used in monitoring grassland biomass based on the vegetation indices in the region around the Qinghai Lake.

This paper studies the effects of grassland improvement on distributions and circulations of nutrients in terrestrial ecosystems, taking Jian'ou Niukenglong Grassland Ecosystem Experimental Station as a case. During two years experiment, the land cover types had been transformed from desert slope-land to grasslands. The experimental results indicate that with the increase in vegetation coverage, the soil total concentrations of nitrogen, phosphorus, and potassium grow rapidly, but that of aluminum decreases obviously. The increases in the total concentrations of nitrogen, phosphorus, and potassium are mainly the consequences of changes of the factors affecting soil evolution, e.g., soil moisture, and changes of soil evolution processes, e.g., weathering rate and decrease of soil erosion. The changes are caused by land coverage growth during the processes of land cover change from desert slope-land to grassland. Conversely, with the change of the land cover types, the increase of land coverage, the activity of aluminum accelerated as well, the down-penetration and lateral penetration of aluminum have been strengthened. Therefore, the loss of aluminum within the experimental terrestrial ecosystem was inevitable, and the total concentration and content of aluminum in the soil have become smaller and smaller, though the growth of grass has been absorbing some amounts of aluminum. Land cover change also affects the circulations of nutrients in terrestrial ecosystem, for the purpose of study on nutrient circulations, we choose plant's absorption, litter and reservation of nutrients to establish the index to indicate the situations of nutrient circulations within terrestrial ecosystems. The results made it clear that in the two land cover types, i.e., two grassland ecosystems, the sequence of nutrient circulation indices are N＞K＞P＞Al in Chamaecrista rotundifolia (pers) green ＋ Pasalum thunbergii and P＞N＞K＞Al in Glycine max var. ＋ Pasalum thunbergii. On the basis of the study, we can conclude that land cover change affects both distributions and circulations in terrestrial ecosystems, different changes have distinct influences on distributions and circulations, and different nutrients are affected to varying degrees in some contents.

The Mapped Atmosphere-Plant-Soil System (MAPSS) model has been improved for simulating the potential vegetation distribution over China. Unlike North America, the environment in East China is largely controlled by the monsoon system, which affects the vegetation distribution differently than in North America. Furthermore, in MAPSS, the boreal forest is evergreen conifer, whereas in China it is largely deciduous conifer. To make the MAPSS results more suitable over China, we modified the lowest monthly temperature, which determines the northward boundary of temperate deciduous forest from -16o to -28oC. In addition, the minimum monthly rainfall during the growing season, which is used to judge broad-leaved-deciduous from evergreen need-leleaved forest, was changed from 40mm to 20mm. Other parameters related to rainfall patterns were also changed. The results were greatly improved, when compared to the map of Chinese vegetation zonation and more than 12 years of satellite data (NDVI). Using output from the General Circulation Model, HadCM2, for simulating possible future climate changes induced by enriched greenhouse gases (GHG) and sulfate aerosols (SUL), we simulated the possible future (2020s, 2050s) potential vegetation distribution modeled by MAPSS with and without consideration of CO2-induced water-use-efficiency (WUE) changes. The results show that in East China, forest boundaries could shift northward, especially the boreal deciduous conifer forest, which may disappear from China. In the North China, and Liaohe river drainage area, forests and savannas could be replaced by grasslands.

The interannual changes of precipitation and land cover in East Asia during May-September have been studied using geographical information system technology based on the time series precipitation data and AVHRR 8 km NDVI data. Simultaneously, the variance regularities of precipitation and land cover in research period have been revealed separately. Furthermore, the paper studied the relationship of interannual changes between land cover and monsoon climate that is represented by changes of precipitation using Singular Value Decomposition (SVD) method. The results are as follows: 1. The precipitation dynamics: (1) The interannual changes of precipitation are apparently divided into three regions, i.e., east monsoon climate region, northwest inland arid region and northern part of East Asia. (2) The interannual changes of precipitation of monsoon region in summer have shown a zonal extension from northeast to southwest, and in that range the precipitation have obvious differences from south to north. (3) The interannual changes of precipitation of northern part of East Asia in summer season present a regularity of east to west zonal distribution, and that zone has character of annual swings of north to south. In the same year, although there exists an east to west change in the same zone, the change range of precipitation is basically unanimous within the whole strip. (4) In the northwest inland arid region except Tianshan and Altay mountains, the precipitation has obvious annual fluctuation in summer, but the range is insignificant in other regions. (5) The positive anomaly percentage of precipitation tends to expand westwards in the late 1980s, i.e., summer precipitation in western China increased gradually in the late 1980s compared with that of the earlier 1980s. 2. The land cover dynamics: (1) Land cover dynamics of summer (May-September) in East Asia are apparently differentiated into three regions such as the northwest inland region, eastern monsoon region and northern part of east Asia. (2) In the monsoon region, land cover dynamics have shown southeast to northwest and south to north differentiations. As regards the whole, the interannual changes of land cover of Northeast China Plain, North China Plain, Southwest China and Huaihe basin are relatively great. (3) In the marginal monsoon area, there exists an obvious dynamic zone expanding from northeast to southwest. This is consistent with eco-environmental fragile area of northern part of China.(4) In the northern part of East Asia, the interannual dynamics of land cover have zonal distribution features. In the same zone, there exist differences from east to west, but the interannual changes are very simple. (5) From the interannual changes of land cover, an increasing trend is seen, especially in the northern part of East Asia and midwest Qinghai-Tibet Plateau except northwest inland arid region. 3. The precipitation and land cover's relations: Based on the SVD models, we have found out that the relation of precipitation dynamics and land cover dynamics are apparently divided into three regions i.e., eastern part of monsoon region, northern part of East Asia and central part of arid region.

Spatial interpolation of climate data is frequently required to provide input for regional plant growth models. As no single method among so many available ones to spatial interpolation of climate variables is optimal for all regions and all variables, it is very important to compare the results obtained using alternative methods applied to each set of data. For estimating 30-year of 10-day mean air temperature and monthly photosynthetic active radiation (PAR) fluxes at specific sites in China, we examined ordinary Kriging (OK) and other two relatively simple methods, one is inverse distance squared (IDS) technique and the other is gradient plus inverse-distance-squared (GIDS) technique. Based on the mean absolute errors from cross-validation tests, the methods were ranked as GIDS>OK>IDS for interpolating 10-day mean temperature, and IDS>GIDS>OK for interpolating monthly mean PAR fluxes. GIDS gives the lowest errors which averaged 1.3 oC for 10-day mean temperature. IDS gives the lowest errors averaged 0.46 MJ/(m²·d) for monthly PAR fluxes. Although OK errors were more consistent for temperatures of different seasons, yet GIDS had lower errors during crop growth seasons. Compared with OK, GIDS was simple to apply for interpolating 10-day mean temperature. Since PAR was affected by so many factors, the performance of GIDS and OK were not as good as we expected. It also implied that the complex methods could not ensure the best results. The multiple linear regressions carried out for GIDS revealed strong gradients in temperature and PAR fluxes varied by month in a fairly consistent way. For all 10-days, r was above 0.94 for temperature, and temperatures decreased with increasing latitude, longitude and elevation. The elevation coefficient for temperature during the year ranged from -0.0033~-0.0048 oC/m. For PAR, r was lower than that for temperature. The coefficients of PAR for latitude, longitude and elevation ranged from positive values to negative values during the year. Using a 1 km Digital Elevation Model (DEM) for China, the first 10-day mean temperature and monthly mean PAR flux of July were estimated for each pixel to assess the performance of the three interpolation techniques. From temperature maps, we can see that GIDS gives more reasonable estimates in valleys and mountainous area than the other two techniques. The temperature map generated by GIDS shows the elevation effects of temperature in West China especially in valleys and Tibet Plateau. The strong temperature trends towards the northeast in East China and PAR trends towards the northwest were also shown in the maps.

Subglacially-formed debris-rich chemical deposits were found both on bedrock surface and in bedrock crevice at the edge of Qiangyong Glacier, one of the continental glaciers in Tibet. Grain size distribution, internal structures and chemical components of the chemical deposits were analyzed. It can be inferred that the temperature of some parts of the ice-bedrock interface is close to melting point and there exists pressure melting water under Qiangyong Glacier. Debris, especially those from continental aerosols, can release Ca⁺⁺ in the water. At the lee-side of obstacles on glacier bed the CO² in the melted water might escape from the water and the melted water might refreeze due to the dramatically reduced pressure, making the enrichment and precipitation of CaCO³. The existence of subglacial melting water and the process of regelation under Qiangyong Glacier indicates that sliding could contribute some proportion to the total movement of Qiangyong glacier and it belongs to multiplex cold-temperate glaciers.

The models for landscape connectivity are distinguished into model for line connectivity, one for vertex connectivity, another for network connectivity and still another for patch connectivity. Because the models for line connectivity, for vertex connectivity, and for network connectivity have been long studied and have become ripened, the model for patch connectivity is paid special attention in this paper. The patch connectivity is defined as the average movement efficiency (minimizing movement distance) of animal migrants or plant propagules in patches of a region under consideration. According to this definition, a model for landscape connectivity is mathematically deduced, which applies to GIS data. The application of model for patch connectivity in the new-born wetland of the Yellow River Delta shows that patch connectivity has a negative interrelation with human impact intensity and landscape diversity.

The morphological and ecological response of tidal flat and coastal wetlands to sea level rise is one of the basic aspects of the impacts of global warming on coastal zones. Jiangsu coastal plain, located in the middle of China's coastal area, is the vastest area with most diversiform ecological types of mud flat in China, even all over the world. Therefore, research on the morphological response of mud flat to sea level change in this area undoubtedly is typical and of global significance. Based on the 112 times of field elevation measurements to 19 typical sections since 1980, using statistic methods, the morphological response of typical accretion and erosion section of mud flat to sea level rise was discussed in this paper. The estimated results show that, there are good correlations between accretion rate (both the horizontal and the vertical) of mud flat and sea level change in the study area, just the correlation is diverse in different sections or different parts of the same section due to the various distributions of current velocity and silt flux. The general tendency of the response of mud flat to sea level rise is that the accretion will tend to slow down and erosion will tend to be intensified. To typical accretion section, when sea level rises, the parts of mud flat above mean tidal line will still accrete, but the accretion rate will decrease except the part around mean high tidal line, the speediest rate of accretion occurs in the part between mean high tidal line and that one of the neaps. Whereas, the parts below mean tidal line will experience more intense erosion. The convex profile of mud flat will become more and more steeper and curving due to the upper side accreting and the down side eroding. To typical erosion section, the response of mud flat profile to sea level rise will present a opposite trend. The parts above mean tidal line will be eroded intensively, but the parts below mean tidal line will accrete. The concave profile will become more and more straight.

The model of dual-nuclei spatial structure is a kind of phenomena of spatial structure that is composed of a regional central city, a port city and their relations at a certain region.It is generally founded in the coastal belt, the region along the Yangtze River in China and other countries and regions in the world. From the view of the mechanism, the phenomena of dual-nuclei spatial structure comes from spatial compag of a regional central city and a port city. Because giving attention to centered nature of a regional central city and fringe nature of a port city, it can carry out complements in station and function. From the view of type of formation, the dual-nuclei spatial structure can be classified into two types, namely, endogenic pattern and ectogenetic pattern. China and America are their typical deputies. From the latter, it derives the special phenomena of dual-nuclei spatial structure that is made up of the new capital and the old.The formation of dual-nuclei spatial structure has something to do with the drainage basin. According to it, we can build up an ideal model about the formation of dual-nuclei spatial structure that is based upon the drainage area. The integrated action which includes the natural condition character of drainage area, the change of transport structure and the direction of mostly transport route can make the forming area of dual-nuclei spatial structure spread from the drainage area to other common area.

This paper uses the first-hand data of 1987 and 1999 to analyze the spatial evolvement of Guilin's domestic tourist origins of the years concerned. It is revealed that the number of tourists increased steadily after 1980, while the 1980s were the golden era of Guilin's domestic tourism development. The spatial concentration index (SCI) of tourist origins indicates a drop of 12% from 1987's 43.50 to 1999's 38.27, which means that after 12 years, Guilin's tourist origins have expanded and have become more stable, while the spatial distribution has become less concentrated. Taking into account the increment percentage of tourists from each tourist origin, the paper develops a formula to calculate the attraction radius (AR) of tourist destination (TD) revised from the formula of standard distance given by Stephen Smith (1989). Using the railway distance between Guilin and the capital city of each province as the mean of the traveling distance from each region, the paper shows that Guilin's AR raised by 40.84% from 1987's 568.12 km to 1999's 800.14 km. From the view of macroeconomics, we consider the following as the possible reasons for the drop of Guilin's SCI and the rise of its AR: firstly, as a long-established tourist destination, Guilin's word-of-mouth reputation played a very important role in attracting tourists. Secondly, the rapid increase of living standard and the practice of long weekends/vacations has brought China to a golden era of domestic tourism where more people travel more frequently than before. Thirdly, the social and economic development in areas such as Beijing, Shanghai, Jiangsu, Shandong, has made it possible for Guilin to attract more tourists from them. As a result, the spatial distribution of Guilin's domestic tourists origins has developed a pattern that is different from the law of distance decay. Fourthly, the degree of increment in a tourist origin is mainly due to two factors--spatial distance and the level of economic development. A place near a tourist destination may have a low increment of market share because of its low level of economic development. A place far from a tourist destination may have a high increment of market share because of its high level of economic development. The intervening opportunity is probably the fundamental factor to analyze this phenomenon. According to the conclusion, the paper proposes some guidelines for Guilin's tourism marketing. Finally, the paper discusses briefly the difference of evolvement in the domestic tourist markets between Guilin and Huangshan.

The contingent valuation method (CVM) is a direct interview approach that can be used to provide acceptable measures of the economic value of preservation of natural resources. While the estimates from CVM may not be perfect, neither are estimates from any other economic or physical science model. The need for an assessment of the nonmarket benefits of restoring Ejina Banner's ecosystem is clear. In this paper, we take it as a case to analyze the WTP of restoring ecosystem service. Obtaining accurate benefit estimates using CVM requires detailed descriptions of the resource being valued. In our survey, we use a 12-page paper with maps depicting the reason why Ejina Banner ecosystem deteriorated, the means by which ecosystem services could be restoring from their current level. The actual valuation portion of the survey has three elements: (1) portrayal of the resources to be valued, (2) description of the particular mechanism to be used to pay for the resource; and (3) the question format used to elicit the respondent's money amount of willingness to pay. Due to concern over the influence of institutional and culture setting, the method of payment we adopted is payment cards in the survey. We employed a parametric model to estimate the welfare of restoring Ejina ecosystem. Their functional relationships between WTP values and the characteristics of responses are built respectively. Results from 700 in-person interviews indicate that per household would pay an average of RMB 37.96 yuan per year, US$ 40.15 for the main river household, 32.10 yuan for the rest of the Heihe basin. The aggregate benefit to residents of the Heihe basin is 15.98 million yuan annually for 20 years. Taking into account the ecosystem discount rate, the aggregated benefit of restoring Ejina Banner ecosystem is 1637 million yuan. These estimates suggest that the general public in Heihe valley would be willing to pay for restoring the Ejina banner ecosystem. Finally, we put forward some suggestions on how to apply the contingent valuation method in developing countries, and believe future efforts may apply CVM efficiently accompanying with benefit-cost analysis.

Study on change of weather and climate extremes has become an important aspect in modern climate change research. Based on the daily surface air temperature data from 200 stations and daily precipitation data from 739 stations during the second half of the 20th century, schemes for analyzing climate extremes were designed mainly according to percentiles of a non-parametric distribution and the gross errors in the daily data were removed based on a newly designed quality control procedure. The spatial and temporal characteristics of change of climate extremes over northern China were studied. The main conclusions are summarized as follows: 1) The number of days with maximum temperatures over 35^oC decreased slightly. The decreasing trends are obvious in the North China Plain and the Hexi Corridor. However, since the 1990s, the extreme hot days increased greatly. Meanwhile, the frost days decreased significantly in northern China, especially in the eastern part of northern China and Xinjiang Uygur Autonomous Region. Increase trends were found for the 95th percentiles of daily maximum temperatures except in the southern part of North China, while obvious decrease trends were found for the 5th percentiles of daily minimum temperatures. 2) The extreme intense precipitation events obviously increased in much of northwestern China but decreased in the eastern part of northeastern China and most parts of North China. The number of heavy rain days increased in eastern Inner Mongolia and eastern Northeast China, but obviously decreased in the Northeast China Plain and North China.

Based on daily mean surface temperature of 110 stations over China from 1951 to 2000, trends of days and intensity of extreme temperature over arid and semi-arid area of China have been analyzed, and the trend of annual extreme temperature and differences among regions were shown; also temporal and spatial characteristics of extreme temperature and its relationship to regional warming have been discussed finally. The results show that there is a remarkable decreasing trend of days of minimum temperature over arid and semi-arid areas during the period, and the beginning date of trend is different in different regions. Compared with the trend of minimum temperature, there is no obvious trend of maximum temperature days before the 1990s, but there is a remarkable increasing trend in maximum temperature days since 1990. Except days of extreme temperature, there is decrease trend of annual minimum temperature. The results have also shown the trend of zero temperature(under 0^oC), i.e., there is reduction trend of zero temperature days, and its beginning date delays, and ending date is earlier. In addition, we found that the regional warming in northern China is closely related to reduction of minimum temperature days, and increase of maximum temperature days has intensified regional warming since 1990.

Using monthly precipitation and monthly mean temperature, a surface humid index was suggested. According to the index, the distribution characteristics of extreme dryness has been deeply analyzed. The results indicated that there is an obvious increasing trend of extreme dryness in the central part of North China and Northeast China in the last 10 years, which is a high frequent period of extreme dryness; and a low frequent period in the regions during the last 100 years. To compare with variation trend of the temperature in these regions, the high frequent extreme dryness region is consistent with the warming trend in the same region.

The station data, including precipitation, air temperature and soil humidity are employed to investigate the arid climate trend for the past 50 years over northeastern China. "Atmospheric drought index" is proposed based on monthly mean temperature and precipitation anomalies as well as mean variance. The variations in the index and soil humidity show that the arid situation gets deteriorated throughout the northeastern China, this arid trend is more significant since the mid-1990s, especially in semi-arid area located in northeastern Inner Mongolia. Air temperature increase plays a more important role than precipitation decrease does in terms of the formation of drought. Although rainfall has slightly increased over the southern part of northeastern China in recent 50 years, arid trend remains to be developing, which is obviously associated with global warming. The responses of aridity developing over northeastern China to the global warming are explored using linear regression analyses. The results show that under circumstance of global temperature increase by 1^oC the aridity extent will rise 5-20%, its maximum will reach 22%.

Regional characteristics of soil moisture evolution in northern China are analyzed based on the monthly retrieved soil moisture data of 139 stations from 1951 to 1999. The results show that evolution of soil moisture at different levels coincides with each other very well. North China experienced a wet period during the late 1960s to late 1970s. An abrupt change occurred at the end of the 1970s and the soil moisture began to decrease. The descending trend of soil moisture in North China is especially evident in the late 1990s. For Northeast China, the 1970s is a distinct dry period. In terms of seasonal trend, however, no apparent decrease of soil moisture has been found since 1980 in North China. In addition, a notable phenomenon is the general decrease of soil moisture in autumn over wide regions of northern China, especially in Northeast China.

Drought during the period 1999-2000 in North China is studied by using monthly mean temperature and precipitation data from 160 stations covering January 1951 to October 2000. The revised Palmer drought severity index (PDSI) of the 160 stations covering the same period was also calculated. It is found that the protracted drought was a manifestation of an abnormal form of general circulation. The PDSI can characterize the temporal and spatial distributions of remarkable droughts and floods in China. During 1999-2000 there was a persistent negative PDSI in North China, the PDSI also shows that there is a marked interannual and interdecadal variation of drought in North China. From 1950-1970 there is a wet summer climate, while since 1970 there have been more drought years in North China.

The monthly PDSI, surface moisture index and percentage of precipitation anomaly are calculated for the past 49 years with data from 160 stations in China. The result shows that PDSI and surface moisture index can grasp rainfall, a decisive factor of drought. Moreover, they reflect the process of drought on a greater space and time scale. In the region with more actual evaporation, PDSI describes the severity of drought more precisely than percentage of precipitation anomaly. In North China, before the 1980s, the rainfall was more sufficient, the temperature was higher and the potential evaporation was lower. It was a relatively moist period. Since the 1980s, the rainfall has been less sufficient together with higher temperature, the drought in North China has become more and more severe.

The present paper consists of three parts: 1. Chapter One solves mainly two problems: (A) "Yo Gu Tsung Lieh Ch'(river)”as the principal source of the Yellow River investigated in 1952 was first discovered in 1717. The source of the Yellow River which was drawn in "The Complete Atlas of the Imperial Territory" and described in Ch'i Shao Nan's "The Outlines of the Water Canals" was no other than the same mentioned above and that known by Mongolian terms as Soloma, or Altar Gol, was also the same as the one Albert Tafel inves-tigated in 1707.

我仔细阅读了苏联地理学家Д.Л阿雨孟特的“自然地理区划的几个原则”(其中有些我还不够了解),并看了地理学报第20卷第4期所刊载的“中国自然地理分区草案”和“中国自然地理分区讨论总结”等文章,主观地感觉到对 中国自然区域的划分是有些问题的，尤共是在分区原则的运用上，更有提出商榷的必要，希望同志们给以指正。

在划分中国自然区域的工作上,我们最近又得到了兰璋先生提示意见。这里,首先让我向丁先生致谢！他对“中国自然地理分区草案”一文作了详细的分析,所提出的意见,很能促进今後的区划工作。他的意见对我很有启发,下面附带说几句话。