HYDROLOGICAL CYCLE AND SURFACE WATER
Nanjing Hydraulic Research Institute, Ministry of Water Resources, Nanjing 210029, China
The researches on water science in China have continued to make new advances since 1998, promoted by the two major causes: (1) Participating in the international cooperative scientific research programmes, such as the International Geosphere and Biosphere Programme (IGBP), World Climate Research Program (WCRP), International Hydrological Program (IHP), Global Energy and Water Balance Experiment (GEWEX) etc. These scientific programmes face the common challenges of the human, such as climate warming, sea-leval rising, aggravating hydrological and meteorological disasters and deteriorating ecological habitat etc., aiming at protection of living environment and sustainable development of the human. To develop international cooperation researches, China actively participates in those research activities organized by such international scientific organizations, as IHP, IAHS etc. Many aspects of current international scientific cooperation are involved in these research fields, to which China makes own contributions. (2) Conducting research activities to solve the important challenges encountered in sustainable development of the country, for instance, flood and drought, water resources scarcity and water environmental deterioration etc. This article will describe the progress made in these aspects respectively. The reference materials of the article are mainly from 30 open-publishing domestic and oversea scientific journals involved with the water field, e.g. “Journal of Geographical Sciences”, “Acta Meteorolgica Sinica”, “Journal of Hydraulic Engineering”, “Advances in Water Science”, “Journal of Glaciology and Geocryology”, “Journal of Lake Sciences”, “Journal of Natural Resources”, “Advance in Earth Science” etc. The papers published in these journals in the past five years are reviewed. Simultaneously, the important national projects and project research reports of the National Natural Science Foundation of China in the recent five years, such as “Study on ecological environmental change in the West China”, one of national key scientific and technological projects during the Ninth National Five-Year Plan, also are referred to. However, we are very regret that some excellent results cannot be introduced into this article due to limitation of the length as well as obtained materials.184.108.40.206 Study on precipitation
Some remarkable progresses in the study on precipitation are made in following several aspects in the last five years:
（1）Strengthening the study on macroscopic background of precipitation, i.e., exploring the physical climatic causes of generation and evolution of extensive precipitation in the country, with regard to the global climatic background. Our meteorologists with great scientific interesting work on studying the effect of El Nino and South Oscillation (ENSO) phenomena on the space-time distribution of precipitation in the country. They open out the fluctuation of high and low precipitation during the four seasons over the various regions in the country with regard to different ENSO phases (Jin et al., 1999; Gong, 1998). These meteorologists and oceanographers find out many significant scientific facts that influence the ocean-atmosphere relationship on the space-time distribution of precipitation in the country, through analyzing the changes of atmospheric physical field due to the unconventionality of oceanic temperature. For instance, studying the impacts of the strong and weak characteristics of the East Asia tropical and subtropical monsoon in the summer in the rainfall of the East China in summer by Zhang et al. They point out that the rainfall in the downstream of Yangtze River and Huaihe River Basins concerns with the tropical monsoon trough and the intensity of subtropical bai-u front very nearly, and is on the rich side when the tropical monsoon trough is on the weak side and bai-u front is on the strough side (Zhang et al., 1998). With regard to the effects of the unconventionality of oceanic temperature in the northern Pacific on the precipitation of the country, findings of the numerical experiment by Zhu et al. show that the reduction of extensive oceanic temperature in the northern Pacific with the middle latitude would lead to the aptness at excess rainfall in the summer in the northeast region and that the rainfall would be less than the normal years in the extensive regions to the south of 40o N (Zhu et al., 2000). The study of Guo et al. shows that the unconventionality of convection activities in the West Pacific in the country is closely related to the rainfall in the Yangtze and Huaihe River Basins in the summer (Guo et al., 1998). Wei et al. analyzed the changes of the temperature in the Pacific, Atlantic and Indian Oceans, which have a significant statistical correlation with the rainfall during the summer in the Northwest China under the special ordonnance (Wei et al., 1998). These studies in the field, however, are still preliminary because of the complexities of relationship between the ocean, atmosphere and waters.
（2）In the last five years, a significant progress in the aspect of describing space-time distribution characteristics of precipitation is that the concepts and methods of entropy are introduced so as to open out the spatial structural characteristics of space-time distribution of precipitation, and some conclusions according to facts are drawn. This shows that application of entropy to analyses of uncertainties in hydrology and water resources is an effective technique (Zhang, 2000). Under the promotion of the national strategies of the western development, some important progresses have been obtained with regard to the study on secular variation of space-time distribution of precipitation in the Northwest China and the variation rule of precipitation in this region is opened out. The rule shows that it was more water year in the 1960s, less water in 1970s and more water again in the 1980s as well as less water in the 1990s (Ding et al., 1999; Wei et al., 2000). Another study indicates that the serious drought and flood disasters in the Yangtze River Basin are not only related to the precipitation amount, but also to the relations of space-time distribution of precipitation very nearly. One also arrived at a similar conclusion in the middle Yellow River Basin. All these are new progresses in the study on drought and flood causes in the Yangtze and Yellow Rivers (Li, 1999; Kang et al., 1999).
（3）With regard to the aspects of design storm, the studies on urban design storm patterns are developed and new formula of urban storm patterns are produced in order to respond to the impacts of urban effects on storm (Cen et al., 1998). A monograph of “China Storms” written by Wang summarizes those findings of design storm research in the country in the late 50 years.
220.127.116.11 Study on runoff
In the aspect of study on the runoff, the great attention was given to the study on the transit curves in the 1960s to 1970s (such as study on Nash's hydrograph etc.) and to the study on hydrological models in the 1980s to middle 1990s. Since the next half of 1990s, studying response of river runoff to climate change, the effect of human activities on runoff and further on water resources, the runoff-generating mechanism in the Northwest China, and the application of modern technology to the runoff computation etc. is the emphasis during the period. In terms of study on response of river runoff to climate change, the study on possible change of runoff amount under various climate scenarios is mainly developed so as to expatiate the possible effect of climate changes on water resources. Thereinto, the study on response of variation trend of outflow runoff from the mountains in the northwest arid inland river basins to the climatic change (Kang et al., 1999) and the study on the glacial change in the northwest arid region and its runoff effect (Liu et al., 1999) are of representative.
In terms of studying the influence of human activities on runoff generation, those investigation in infiltration and runoff-producing rules are mainly conducted. For example, Liu et al. opened out the retarding effect of the slope rainfall infiltration process in the loess region (Liu et al., 2001). Gu opened out the retarding effect of rainfall in the Chuzhou runoff experiment station of Anhui, using the isotopic tracer technique (Gu Weizu, “Advances in Water Science”, 1999). And Chen et al. conduct the numerical modeling of slope rainfall infiltration and runoff-producing rules (Chen et al., 2001) are original results during the recent years. Many new techniques are applied to runoff computation and forecasting, which promote greatly improving of runoff analysis and computation of China. The study on applying technique of artificial neural network to runoff forecasting (Zhang et al., 2001), the study on storm runoff-producing models aided by remote sensing and GIS techniques (Zheng et al., 1999) and application of genetic arithmetic to the runoff computation (Jin et al., 1999) are all representative results. The northwest arid region of China is mostly selected as the work platform of these studies mentioned above, which promote developing study on runoff in the northwest region, benefited by the national western developing strategies.
18.104.22.168 Study on evaporation
The desertification of land has become a serious ecological environmental problem in the West China and its influence has covered Beijing and Tianjin cities, the North China and Northeast China regions. The national authorities have been taking effective measures to prevent and control the desertification of land. Some very great progresses in study on evaporation in the arid and semi-arid regions in the West China have been achieved in order to satisfy needs of preventing and improving desertification of land. One of significant progresses is that some evaporation experiment stations located in the arid and semi-arid regions in the West China have been set up and some experimental researches have been conducting. For example, a water surface evaporation experiment station with a 20 m2 evaporator in the Changji region located in the plain of the northern part of the Tianshan Mountain, Xinjiang has been founded. The water evaporation coefficients of E601 and 20 m2 evaporator in the northern Xinjiang have been obtained using observed data in the current years, and experiential formulas for assessing water evaporation have been created (Zhou et al., 1999). In the Mu Us desert region of the Inner Mongolia, an evapotranspiration experimental observation of sand and sand plants was conducted, which open out the moisture evaporation mechanism of sand hill and its computation models. The observation results synchronously show that the daily evapotranspiration of land-plant (in the summer) is five times larger than that one of sand land in the same period and the average daily evaporation is up to 5.0 mm. These experimental observation results provide bases for controlling and improving desertification of land in the Northwest China (Zhou et al., 1999; Li et al., 2000).
In order to monitor the countrywide drought regime, the computation study on area evaporation capacity is conducted using real-time collecting meteorological data. And the daily countrywide drought level distribution maps are drawn utilizing these study results, which play a greater role in the real-time monitoring of drought regime (Zhou et al., 1998). The study on water surface evaporation and soil evaporation is strengthened to satisfy the needs of planning and utilization of water resources. The study on water surface evaporation of plateau salt-water lakes, from the observation experiment to analyzing and estimating the regularities, has obtained some important achievements. For example, the normal annual evaporation of 925.1 mm, the maximum evaporation of 1111.5 mm (1975) and the minimum of 791.9 mm (1987) are firstly obtained in the Zigetangcuo site of the Tibetan Plateau. And the study shows that there exist a long-term variation and an increasing trend of the evaporation population (Li et al., 2001). In the field of study on soil evaporation, Lei et al study the modeling of the phreatic evaporative rule in the soil-frozen process and present a concept of reduction coefficients of the phreatic evaporation during the frozen period, which provided bases for water conservation measures in the farmlands (Lei et al., 1999).
Concerning the study on large-scale hydrological cycle process, Zhang addresses the complicated process of moisture cycle at a mainland scale with regard to climatic change such as El Nino and global warming. Simultaneously, he expatiates on the relation between water resources situation and terrestrial process of hydrological cycle, and points out that human may coordinate the relation of human-self and the nature to ensure the normal moisture cycle, thereby various flood and drought disasters and problems of inhomogenous space-time distribution of water resources are mitigated. Zhang's opinions break a new thoughtful path for the study on hydrological cycle (Zhang, 1999). The effects of large-scale ocean-atmosphere interaction on hydrological cycle described by Xing is one of representative results in the field in the country in the recent years (Xing 1999)
In the side of study on regional scale hydrological cycle and water balance, Zhang et al. make a study of hydrological cycle and moisture balance of the land-atmosphere system in the Brahmaputra River Basin, which locates in the middle and upper reaches of Yangtze River. They develop the hydrological inner cycle model based on regional gridding and estimate each grid's hydrological inner cycle coefficient as well as obtain these estimating values of regional inner hydrological cycle and moisture balance components. Following the monograph “Atmospheric process of hydrological cycle” written by Liu in 1997, this is a new representative progress in the field (Zhang et al., 2000).
Zhang et al. apply the concept and method of entropy to studying hydrological cycle evolution and try to find out the criterion (shreshold value) of hydrological cycle structure when the normal state shifted to the break or catastrophic change (Zhang, 2000). It provides new thinking for predicting the trend of hydrological cycle evolution.
In the last five years, the following three aspects in the study on potamology are worthy of introduction: (1) the book “Fluvial Hydrology of China” edited by Tang et al. and published in 1998. This book addresses the fluvial zoning in China based on analyzing the geographical conditions of fluvial generation in China. And it describes the fluvial hydrological characteristics in different climatic zonings on the basis of summarizing the studies on potamology in China in the past 30 years. Especially it discusses the fluvial hydrology in the Tibetan Plateau, and promotes the knowledge about fluvial hydrology in this region (Tang et al., 1998).
To predict the channel evolution in the downstream of Yellow River after Xiaolangdi Reservoir is built and in the middle and downstream of Yangtze River after Three-Gorge Reservoir is built, the study on channel evolution is promoted. The study on channel evolution in the downstream of Yellow River further opens out the basic characteristics of channel in the downstream of the Yellow River, i.e., the sections are very wide and shallow, the longitudinal slope is not steady and the channel sedimentation is serious. These characteristics are the elementary causes of the channel evolution in the downstream of Yellow River, combined with various instances of incoming flow and sediment (Ying, 1998). With regard of understanding of these characteristics, these syudies on modeling fluvial plan features and predicting river bed evolution obtained some applicable progresses (Huang, 1999).
Under different applied conditions in the Three-Gorge Reservoir of the Yangtze River, though those studies on evolution of riverbed in the downstream of Yangtze River have obtained some progresses, the explicit conclusions still have not drawn. In addition, many rivers in the North China are in a state of water interception due to severe shortage of water resources in the North China, which results in many adverse influences on fluvial development and ecological environment in these basins, whereas the systematic and mature studies in the field is still not so much.22.214.171.124 Study on lakes
Before 1990s, the research on limnology in China was mainly involved in the fields of making investigations of countrywide lakes, lake-hydrology, lake-physics and lake-chemistry as well as lake-basin structures. These monographs, such as “Records of Chinese Lakes”, “Survey of Chinese Lakes” and “Dongting Lake” etc., have been successively published since 1998. These books comprehensively and systematically summarize these research results of Chinese lakes before 1990s (Wang et al., 1998; Dou et al., 2000).
The study on lake and climatic change is actively carried through in the country in the recent years under the promotion of the International Geosphere and Biosphere Programme (IGBP). This study project discusses the effect of climatic change on lakes and reconstructs the palaeoclimate through lake-sediment study etc., further, provides bases for the study on the modern climatic change. These representative research results in the field are “The Comparative Analysis of Spore Sollen with Climate to Reconstruct the Climate in the Western Shanghai Region since 85 kaB. P.” (Cai, 1999) and “The Lake Gyration and Its Palaeoclimatic Significance in the East Reach of the Hexi Corridor” (Wang et al., 1999) etc.
The water environment has been tending to deterioration since 1990s, which promotes the study on lake water environment. Thereinto, these studies in the aspects of lake eutrophication, lake water chemistry, lake water movement and diffusion of pollutants etc. have obtained better scientific results (Chen et al., 1998; Chen et al., 1999; Wang et al., 2001). The studies on lake pollution, prediction and prevention as well as improvement will be sequentially taken as one of important topics in the field of lakes in China.
126.96.36.199 Study on marsh
The highly effective studies have been made in the aspects of ecological diversity in marsh and protection of marshes in China in the last five years and a significant exploration is also conducted in the study aspects of palaeoclimate and disposal of contaminative water in marches, using these marshes.
Mu et al. study the floral diversity in the interlaced zones of forest and marsh in the forest region of the Changbai Mountain. Their study results indicate that the floral diversity in the interlaced zones possesses such a gradual heightening trend along the surroundings gradient of the zones and the mature communities in the zones have the highest floral diversity as well as the number of some preponderant species communities in the zones is 5 times more than that one in the forest zone. Accordingly, it outstandingly shows the important role of the ecological environment of interlaced zones of forest and marsh in protecting the structural diversity (Mu et al., 1998; 2001). Yang et al. work on the study on the marsh degeneration and its causes in the Zoige Plateau. They analyze these relations between the marsh ecological environmental deterioration and marsh degeneration and the interference of human activity and the effect of natural factors. And they point out that the interference of human activity is the main cause of the marsh ecological environmental deterioration and marsh degeneration, and give the countermeasure and suggestions (Yang et al., 1999).
More studies are also involved in the disposal functions of contaminative water in marshes in the recent years and some valuable results are obtained. For example, the study of Liu Zhenqian et al. that the capacity of the ecological system of the Three-River Plain arsh for decontaminating N and P in the contaminative water would decrease at an exponential rule as the time extended. The study also indicates that the floral species and its number in the marsh and the thickness of peat layer have different impact on the decontaminating effects. Thereinto, the decontaminating effect of comospore sedge system is higher than the others, moreover, the decontaminating efficiency varies with different parts of the comospore sedge. For instance, the sequencing efficiencies of decontaminating N are: haulm > peat > root system > floral defoliate materials and that the sequencing efficiencies of decontaminating P are: root system > peat > haulm > floral defoliate materials.
These studies provide scientific foundation for protecting and utilizing marshes.
China is one of the countries where the mountainous glaciers are developed very much. In the recent years, the study on glacial snow cover and permafrost has made new progresses, driven by the climatic change and the western development.
In the aspect of glacial observation, the Glacial Catalogue of China has completed in 2000. According to the statistic amount in the sub-volume 21, volume 11 of the catalogue, there are 46298 glaciers with total area of 5490 km2 and glacial storage of 5590 km3 in the domain of China. This is of a great significance for the development and utilization of water resources, prevention and control of ice and snow disasters in the western mountain regions (Liu et al., 2000).
Concerning aspects of studying glacier and climatic change, the representative research results are as follows:
（1）Kang et al. study the recent 200 years climatic records in the Far East Rongbuk ice cores in the northern part of the Mountain Everest, Himalayas. They rebulit the climatic series of the late 200 years in the northern part of the Mountain Everest using the analyzing results of a 41m long ice core, and recognized five cold periods and five warm periods during this era and the general trend to warming, which is accordant with the climatic warming trend in the Northern Hemisphere in this century (Kang et al., 2000).
（2）Su and Shi study the responses of temperate glaciers of China monsoon to the global climatic warming since the Little Ice Age. The southeast part of Tibetan Plateau is the main distribution zone of the monsoon temperate glaciers and these studies show that this type of glacier is very susceptible to the response of climatic change. The studies indicate that the mean temperature of the temperate glacial region has raise 0.8˚C and the glacial area has reduced 30% since the Little Ice Age. It predicts that the temperature along the glacier region will increase 2.1˚C and the glacial area will reduce 75% and reach about 9900 km2 in that time. And the glacial shrinkage proportion will be not greater than 80%, which will bring important impacts on the resources environment in this region (Su and Shi, 2000).
（3）He et al analyze the climatic fluctuant characteristics in this region, using these climatic environmental records of the 10m long shallow ice core and the 78m long ice core in the Yulong Mountain Glacier (He et al., 2000). Ding et al analyze the climatic change and its effect on runoff in the late 40 a in the middle region of the Qilian Mountain and also obtain some results with scientific significance and actual applicable value (Ding et al., 2000).
In the fields of hydrology of ice and snow as well as water resources, Yang et al. write the book “The Hydrology of Cold Zone”, which summarizes research results in the field in the late 40 years in China.
Implementing the western development strategy will need to construct many works, such as roads, bridges and culverts etc., in the high cold permafrost region of the western China. Many permafrost problems have been raised in foundation treatment of these works and safety operations after completed. Accordingly, these studies on engineering problems of permafrost are promoted, e.g. the freeze-thaw analysis of the tunnel adjoining rocks of the Daban Mountain (Lai et al., 2000) is a current representative result.
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