Water Resources in China—2004.08.02
I. PHYSICAL BACKGROUND
China is situated at the southeastern part of Eurasia on the Northern Hemisphere, closed to the Pacific Ocean on the southeastern side, stretching into the hinterlands of Asia, bordered by the subcontinent of southern Asia. The total land area is 9.60 million km2, or equivalent to about 1/5 of the world total, ranking third among all countries in the world. China borders more than ten countries with the total length of land boundaries being more than 2000 km. China has a sea area of about 3 million km2, and more than 5400 islands of various sizes, in which Taiwan is the largest. The total length of coastal lines of the mainland and islands is 32000 km, in which the coastal line of the mainland occupies 18000 km.
The topography of China is characterized by high west part and low east part, gradually descending in elevation from the west towards the east to form three steps. The highest step is the Qinghai-Tibentan Plateau with the elevation being generally more than 4000 m above sea level, hence known as "the roof of the world". To the east of the Qinghai-Tibetan Plateau is the second step with much lower elevations, ranging between 1000 m and 2000 m and alternating with huge basins. The third step stretches from the line in the west composed of Mounts Daxing'an, Taihang, Wu and the eastern rim of the Yunnan-Guizhou Plateau to the coast in the east, and embraces alternating hills and plains, and there are large areas of low mountains and hills at elevations of less than 500 m above sea level with only a few peaks being at 2000 m, and the elevation of plains is all less than 200 m. The plains are distributed in the north to south direction, including Northeast Plain, North China Plain, Middle to Lower Yangtze Plain and Pearl River Delta Plain, being important industrial and agricultural bases and economic centers of China.
Classified according to types of topography, mountains account for 33.3% of the national land area, plateaus 26.0%, basins 18.8%, hills 9.9% and plains 12.0%. Mountains, hills and rugged plateaus, which are customarily called mountainous areas, totally account for 2/3 of the national land area.
As affected by the vast area and complex topography, China's climate is endowed with a feature of complex types. China is subject to strong monsoon climate and most of the areas
are under the impacts of the southeastern and southwestern monsoons, thus making the southeastern China wet and the northwestern China dry. The precipitation varies greatly from year to year and from season to season. As affected by monsoon and topography, China becomes one of the countries with most frequent drought, flood and waterlogging hazards in the world.
The average annual precipitation in China is 648 mm, or 19% less than the world average 800 mm on land, and the volume of average annual precipitation is 6190 billion m3. The regional distribution of precipitation is very uneven, showing a general trend of gradually descending in magnitude from the southeastern coastline to the northwestern hinterlands. The annual precipitation in the southeastern coastal areas and parts of the southwestern areas is more than 2000 mm, but that in the northwestern China is usually less than 200 mm, and 50 mm in the Tarim and Turpan basins in Xinjiang and Chaidamu Basin in Qinghai, etc, even less than 25 mm at centers of those basins.
As affected by the monsoon climate, the precipitation shows not only a big inter-year variation, but also wet spans and dry spans, and inter-year variation is bigger in areas or for seasons with less precipitation. The ratio of maximum annual precipitation to minimum at observation station has the biggest value in the northwestern China, possibly exceeding 8, but only has values ranging 2-3 or less than 2 in the southern and southwestern China. Except in a few small special areas, precipitation is usually concentrated in summer and mainly occurs in rainstorms. In most of the areas, the ratio of average maximum precipitation of four consecutive months to average annual total ranges 60-80% from the south to the north. The average annual evaporation from water surface also varies greatly over regions, with the lowest value being only 400 mm, and the highest up to 2600 mm. The low values mainly occur in mountainous areas and the high ones on plains and plateaus. The average annual land evaporation also shows a trend similar to precipitation, descending in magnitude from the southeast to the northwest. It has a value of 700-800 mm in the eastern areas and usually less than 300 mm in the western areas.
3. Rivers and River Basins
China has a large number of rivers with a total length of 420000 km. There are more than 50000 rivers each with a drainage area of more than 100 km2 and more than 1500 each with a drainage area of more than 1000 km2. As affected by the topography and climate, the rivers are distributed very unevenly over regions. Most of the rivers are situated in the wet eastern monsoon climatic zone, directly flowing into the sea, with the major ones including the Yangtze, Yellow, Heilong, Pearl, Liaohe, Huaihe, Haihe, etc. The northwestern China is dry
with slight precipitation, and has only a small number of rivers, most of which are inland ones without connection to sea, and there are also large none-runoff areas.
The whole country may be divided into nine major river basins, including Yangtze, Yellow, Haihe, Huaihe, Songhua-Liaohe, Pearl, Southeast Rivers, Southwest Rivers and Inland Rivers, by combining a large river with nearby smaller rivers flowing directly to the sea or out of the region or by combining a number of neighboring rivers in a region. The Songhua-Liaohe, Haihe, Yellow, Huaihe and Inland Rivers are practically situated in the northern areas of China and the Yangtze, Pearl, Southeast Rivers, Southwest Rivers in the southern areas (see attached figure in Annex).
II. WATER RESOURCES
Water Resources are referred to the fresh waters that are renewable, closely related with uses by human societies and ecosystems, including both surface water and groundwater with precipitation being the main source of recharge.
1. Surface Water Resources
The volume of surface water resources is referred to the dynamic volume of water in rivers, lakes, glaciers, etc and generally expressed in volume of natural river runoff. The volume of annual river runoff in the country is 2711.5 billion m3, equivalent to a depth of 284 mm over the whole land area. The direct recharge by precipitation accounts for about 71% of this volume, and indirect recharge by precipitation via aquifer 27% and recharge by glacier and snow melt 2%.
The depth of natural river runoff, which depends on precipitation and conditions of watersheds, gradually descends in magnitude from the southeast towards the northwest, having values of more than 1000 mm in some southeastern areas and values of less than 10 mm in some western areas. The total volume of river runoff in the five northern river basins account for less than 20% of the national total, but the four southern river basins account for more than 80% of the national total.
The river runoff shows inter-year variation similar to precipitation, but to a bigger extent with the impacts of watershed. The ratio of maximum annual runoff to minimum usually has a value of less than 5 in the southern areas, but may exceed 10 in the northern areas. The intra-year variation of river runoff is also big as affected by the size of river basin as well as intra-year variation of precipitation. The rivers in the northern areas show a bigger intra-year runoff variation with the maximum runoff of consecutive four months accounting for more
than 80% of the annual total in some areas, and this ratio has a value of about 60% for rivers in the southern areas.
Table 1 Average annual river runoff by river basin
2. Groundwater Resources
The volume of groundwater resources is referred to the dynamic volume of water in aquifer that is directly related with precipitation and surface water via recharge and/or discharge. Most of runoff formed by precipitation flows into rivers, but there is a part of runoff that percolates into underground to form groundwater. The volume of groundwater resources is usually expressed in terms of volume of groundwater recharge. As activities of human beings affect groundwater recharge to some extent, the volume of groundwater resources is defined under specific conditions of development and utilization of water resources. The annual volume of groundwater resources in China is 828.8 billion m3, in which groundwater in mountainous areas occupies 676.2 billion m3 and that in plain areas 187.4 billion m3 with 34.8 billion m3 of overlapping volume between them. Most of groundwater in mountainous areas flows out as base flow of rivers, thus overlapping with surface water resources and being mainly exploited as surface water. The groundwater resources in plain areas are mainly in the northern areas and the five northern river basins occupy 78.8% of national groundwater resources in plain areas. Table 2 shows groundwater resources by river basin.
3. Total Water Resources
Total water resources in a region are referred to the total yield of surface water and groundwater formed by local precipitation. Surface water interacts with groundwater with the river base flow formed by groundwater and part of groundwater recharge coming from percolation of surface water. In calculating total water resources the overlapping volume between them should be deducted.
With 2711.5 billion m3 of annual river runoff, 828.8 billion m3 of annual groundwater resources and 727.9 billion m3 of overlapping volume between them, the volume of total water resources in China is 2812.4 billion m3. The five northern river basins totally have 535.8 billion m3 of annual total water resources, accounting for 19% of the national total, and the four southern river basins 2276.6 billion m3, 81% of the national total. Table 3 shows the annual total water resources by river basin.
4. Characteristics of Water Resources in China
？1？Small per capita volume
The total volume of water resources in China ranks sixth among all the countries in the world, but, because of the huge population, the per capita volume of water resources is small, about 2200 m3, only equivalent to 1/4 of the world average. Particularly, in the Haihe, Huaihe and Yellow river basins the per capita volumes of water resources are only 290 m3, 478 m3 and 633 m3, respectively. The small per capita volume of water resources decides that stress on water will be long lasting in some areas.
？2？Great inter- and intra-year variation of river runoff
As mentioned above, the river runoff varies greatly from year to year with the ratio of maximum annual runoff to minimum exceeding more than 10 in some areas. In addition, some major rivers have seen consecutive dry years and wet years. For example, the Yellow River once saw a low flow span of 11 years from 1922 to 1932 with an average annual flow 24% less than the normal one, and also saw a wet span of nine years from 1943 to 1951 with an average annual flow 19% more than the normal one. The river runoff is also unevenly distributed within the year. Those features of spatial distribution are among the important causes for the frequent occurrence of drought, flood and waterlogging hazards, hence unstable
agricultural production and serious imbalance between water supply and demand.
？3？Inconsistency between distributions of water resources and productivity over regions The water resources in China are distributed unevenly in space, rich in the southern areas and poor in the northern areas, which is inconsistent with the distribution of population, farmland and economy. The four northern river basins account for 46% of the national population, 45% of the national GDP, 65% of the national farmland, 59% of the national irrigated farmland, but less than 20% of the national water resources and the per capita volume of water resources is only 1/3 of that in the southern river basins. The plain areas in the lower reaches of the Yellow, Huaihe and Haihe rivers account for 1/3 of the national GDP and industrial output, but only 7.7% of the national water resources, while the Southwestern Rivers accounts for 21.3% of the national water resources, but only 0.7% of the national GDP and industrial output.
III. CURRENT STATUS OF DEVELOPMENT AND UTILIZATION OF WATER
1. Water Resources Engineering
China is among the countries with the longest history of building water resources projects in the world. Among the splendid historical achievements are the legendary flood harnessing lead by Great Yu, construction of flood prevention embankments along the Yellow during the Spring and Autumn Period, Grand Canal, Dujiang Weir irrigation system, etc, all showing the importance of water resources engineering in the development of the Chinese nation. But the history of water resources shows alternating rises and downfalls, in particularly in modern history, China frequently suffered invasion by foreign countries, which, plus a corruptive government and extensive poverty, made development of water resources engineering stagnated. After the founding of P. R. China, construction of water resources engineering on an unprecedented scale was carried out. Up to 2000, 85000 dams had been constructed with a total storage capacity of 518 billion m3, in which 397 are large-sized with a total storage capacity of 326.7 billion m3，2634 medium-sized with a total storage capacity of 72.9 billion m3. The engineering achievements also include 270000 km of embankments and 7900 km of sea embankments, either constructed or consolidated, including 65700 km of major embankments; 31742 sluices, including 340 large-sized and 2836 medium-sized; 98 flood storage or detention zones for the Yangtze, Yellow and Huai rivers, etc, with a total area of 34500 km2 and a total storage capacity of 100 billion m3.
2. Current Status of Development and Utilization of Water Resources
The general degree of exploitation of water resources in China is at present not very high, but, because of the inconsistent distributions of water resources and productivity, the status of development of water resources varies greatly with river basins, in some of which water resources are under great stress. According to statistics 2002, the total water use in China was 549.7billion m3，in which surface water occupied 440.4 billion m3 or 80.1% of the total，
groundwater 107.2billion m3 or 19.5% of the total，and other water sources 2.1 billion m3.
The water use in some river basins includes water transferred from other river basins. For example, 4.6 billion m3 of water was transferred from the Yellow to the Haihe, and 6.09 billion m3 and 2.03 billion m3 from the Yangtze and Yellow to the Huai, respectively. Besides, the water used in a year also depends on available water storage at end of last year, precipitation and river flow in the current year, etc. Nevertheless, the ratio of water use in 2000 to volume of water resources still may be used to roughly indicate the current degree of exploitation of water resources in a river basin。By using this ratio, it is shown that the degree
of exploitation of water resources in China is about 19.5%, and the Haihe, Huaihe and Yellow river basins all have a very high or high degree of exploitation of water resources.
In the national water use of 549.7billion m3 in 2000, 373.6 billion m3 was for agriculture, accounting for 68% of the total, and 90.3% of agricultural water use was for irrigation; 114.2
billion m3 was used for industries, accounting for 20.8%, 61.9 billion m3 for domestic uses, accounting for 11.2%. Agricultural irrigation is the biggest water user, but according to trend of development, water use by agricultural irrigation has more or less declined since the 1980s, while industrial and domestic water uses have increased rapidly.
During the process of water conveyance and uses, some volume of water is consumed via evaporation and transpiration, soil absorption, product absorption, uses by residents and livestock, etc and hence cannot return to surface water or groundwater, thus called "water consumption". The national water consumption in 2000 was 298.5 billion m3, accounting for 54% of the national water use. Among the various kinds of water uses, the rate of water consumption was 68% for agricultural irrigation, 24% for industries, 24% for urban domestic uses, and 88% for rural domestic uses.
IV. ACHIEVEMENTS AND PROBLEMS IN DEVELOPMENT AND UTILIZAITON OF
Great achievements have been made in China in the development and utilization of water resources and control of water related hazards, which plays an important role in providing guarantee for the economic and social development, protecting the life and property of the people and maintaining stable operation of economy. In the last more than 50 years, the capacity of water supply in China has increased by about 5 times to enable the industrial and agricultural development and improvement of people's livelihoods. China is a large country in
terms of population and agriculture, and provision of grain is concerned with the national economy and the people's livelihoods. In the more than 50 years the area of irrigated farmland has increased by 2.5 times and the grain yield by 3.8 times, and the needs by a population accounting for 21% of the world total for grain and other agricultural products have been satisfied with farmlands accounting for 9% of the world total. A flood control system capable of preventing ordinary floods has been formed by constructing water resources complexes, heightening and consolidating embankments, training river channels, opening up flood diversion and retention zones in lower river reaches, etc, thus greatly enhancing the capacity against floods. At present, the water resources projects in China provide protection for 465 million people, 39.3 million hm2 of farmland, more than 600 cities and a lot of infrastructure such as railways, roads and oil fields. Safety against flood has also been achieved for the Yellow, which frequently caused flooding disasters in history, in more than 50 years. China has the biggest potential of hydropower in the world, with an exploitable quantity of 378 GW. Up to now, about 80 GW has been developed, accounting for 25% of the national installed capacity of power generation, and corresponding to an annual power output of 2200 TWh, which can replace 140 million t of coal and is equivalent to reduction of 80 million t of CO2
emission, thus achieving significant environmental benefits.
But problems still exist in the development and utilization of water resources in China,
1！ A Big Gap between Water Supply and Demand
Because the per capita volume of water resources is small and there is a great variation of water resources in time and space, and the demand for water continuously increases with the growth of population, development of urbanization and industrialization, the gap between water supply and demand in China has become increasingly wide. At present, the annual agricultural water shortage in the whole country is about 30 billion m3, and the annual average areas of farmland affected by drought is 20 million hm2, resulting in an grain yield reduction of 10 billion kg to 25 billion kg，or even up to 50 billion kg in a year of serious
drought. The annual shortage of urban and industrial water is about 6 billion m3， resulting in
an industrial output reduction of 230 billion yuan. Among the 660 cities in the country there are more than 400 suffering water shortage, affecting 160 million people. In addition, there are more than 24 million rural people without access to adequate drinking water supply. In particular, in the plain areas in the lower reaches of the Yellow, Huaihe and Haihe rivers, the average per capita water use is only 332 m3 and the annual water shortage is up to 18 billion m3，ranking the areas among those with the most serious water shortage in the whole country.