Han Zaisheng^1,2 Wang Hao²

1China Geological Survey 2China University of Geosciences

Abstract: Groundwater resources play an important role in the development in Asia. The hydrogeological conditions are various. Groundwater resources assessments in Asia countries have been taken during last 30 years. The available groundwater resources of Asian countries are presented. The main problems causes by nature issues are the groundwater quality in the arid and semi-arid areas especially in the central part of Asia. Global climate change caused the hydrogological condition diversified in both inland and coastal area of Asia. Problems cause by human action is groundwater overexploitation and related Seawater intrusion to inland, land subsidence and groundwater contaminated occurred in many regions. Transboundary aquifers in Asia are important for building a society where all civilizations coexist harmoniously and accommodate each other. Those problems challenge the hydrogeologists for solution. The main tasks are groundwater assuring for the livelihoods and food security of millions of people, groundwater sustainable usage for the social and economic sustainable development, groundwater monitoring and dynamic assessment for resources management effectively and groundwater dependent ecosystems conservation.

Key words: groundwater resources, Asia, hydrogeological

1 Geography

Asia is located in the east hemisphere. Fig.1 The east, north, south and west of Asia border on the Pacific Ocean, Arctic Ocean, Indian Ocean and Mediterranean Sea respectively. The area is 44 million square kilometer. The population of Asia is 3.5 billion. It is the largest continent both in area and population in the world. There are 48 countries and regions in Asia. It could be divided into East Asia, East-south Asia, South Asia, West Asia, Central Asia and North Asia in geography. The countries with population more than 100 million are China, India, Indonesia, Japan, Bengal and Pakistan. The length of coastal line of Asia is 69900 km. There are many island and peninsulas. Arabia is the largest peninsula in the world. Kalimantan is the third largest island in the world. The characteristics of topography Asia are the big gurgitation of earth's surface, high in the central and low around, alternate with apophysis and depressed. The mountains, highland and hill are situated three fourth of the total area. Another one fourth is plain which area is 10 million square kilometer. Pamirs as the epicenter, series of mountains eradiate extend to the fringe of continent. The Qinghai-Tibet altiplano which average altitude is 4500 m is names as fastigium of the world. Everest the highest mountain in the world is altitude 8844.43 m.

The plains are situated in the outboard of mountains and tableland. These are North China plain, Northeast China plain, Middle and lower reaches of Yangtze River plain, Hindustan river plain, Ganges river plain, Mesopotamia plain and west Siberian Plain, etc. The Dead Sea is the lowest depression in the world with altitude 400 m under sea level. There are many rivers in Asia. Most of those are source from central mountains and radial flow to every direction. The major rivers flows into Pacific Ocean are Heilongjiang-Amur River, Yellow River, Yangtze River, Pearl River and Mekong River etc. The major rivers flows into Indian Ocean are Indian River, Ganges River, Sarwen River, Yilowadi River, Tigris River and Euphrates River etc. The major rivers flows into Arctic Ocean are Ebi River, Yenisei River, and Lena River etc. The inland Rivers are situated in central and west arid area of Asia. The majors are Seer River, Am River, Ili River, Talimu River and Jordan River etc. The lakes in Asia are not many compared with other continent. They could be posteriori to 5 groups, North Asia, Central Asia, West Asia, Qinghai-Tibet tableland and Middle-lowest Yangtze River. Some lakes are famous for their feature. The Caspian is the biggest salt lake in the world. Lake Baikal is the deepest lake in the world and biggest fresh lake in Asia. The Dead Lake is the lowest depression. Lake Balkhash is an inland lake with both fresh water and salt water. The three climate zones are Frigid Zone, temperate zone and Torrid Zone which across the continent of Asia. The climatic types are various and complex. The Southeast Asia, South Asia and southeast part of East Asia are in the humid monsoon torrid zone. Central Asia, West Asia and the inland part of East Asia are in the arid zone. The area between the both zones and the most part of north Asia are in the semi humid semiarid zone. Precipitation are various in difference area in Asia. The main direction of rainfall is descending from the humid southeast to the northwest part. There are abound rain fall near the equator zone. The annual rainfall is more than 2000 mm. There are rainless all over the year in the southwest and central Asia. The precipitation is littler than 150 mm in a large area.

Fig. 1 Satellite Image of Asia

2 Characters of Aquifers and Groundwater Resources

Groundwater resources in Asia are various. Some regions are underlined by aquifers extending over large areas, while the floodplain alluvial deposits usually accompanying the largest rivers. The sedimentary rocks, especially Quaternary loose sediments are very thick with good storage space. The deep fissure water is relatively abundant in confined aquifers. In mountainous regions, groundwater generally occurs in complexes of jointed hard rocks. There is a little rainfall and strong evaporation in inland arid area of central Asia. However the thawing of glaciers and snow from high mountains is favorable to recharge groundwater. The loess plateau in the central Asia has specific topography. Continuously aquifers are only distributed in loss tableland. The carbonate rocks are widely distributed in Southeast Asia. In south China and Indochina peninsula, there are stratified limestone of late Paleozoic and Mesozoic in which karst is considerable developed. The reef karst could find in the coastal island. A lot of Quaternary volcanic rock is extensive on the circum-Pacific islands, which forming asymmetrical rings aquifers. The piedmonts of volcanoes mostly occurs spring water with good water quality. Groundwater resources assessments have been taken in most countries of Asia.

Evaluation and mapping of Groundwater recharge and runoff of individual basins and regions are in progress. The hydrogeological survey on a medium scale has performed regional quantitative assessment of natural groundwater resources in most countries of Asia. Groundwater runoff is an important component of the hydrological cycle. Local hydrogeological conditions of difference regions are effect on the distribution of groundwater runoff/precipitation ratios. Those ratios are less than 10% in the arid area in central Asia, and more than 40% in the karstic area in Southeast Asia. Groundwater monitoring networks have operated at national, regional and local levels in some part of Asia.

Groundwater levels constitute the most observed parameter, continuous water quality and natural groundwater discharge and abstraction networks are operational in urban area. However groundwater assessment, monitoring, and data management activities are operated regular in China, India, Japan, Korea, and Thailand etc. But there are a few in other Asian developing Countries.

UNESCO has presented an overview of the available water resources and population of Asian countries as Table 1. The total Groundwater recharge in Asia internally is 1462 km³/year.

The development of groundwater has been increased in last 30 years. The degree of groundwater development is shown in Fig.2. The ratio of groundwater abstraction with mean recharge is upon the country. There are more areas where groundwater is over-abstraction upon the province in a country. In some arid region of Asian countries, where sufficient renewable groundwater resources are not available, non-renewable groundwater is being exploited to support development, such as Yemen and Saudi Arabia, as well as the coastal area of north China plain.

Groundwater is crucial for human drinking and food security, especially in the developing countries. The impact of groundwater use is positive and included such benefits as increased productivity, food security, job creation, and livelihood diversification and general economic and social improvement. In the long run, the impact of groundwater extraction might be negative especially in over-exploitation situation, such as permanent lowing of the water table, deterioration of water quality, saline intrusion in coastal area, etc. The social and economic dimensions of groundwater use are its benefits are important for the development in Asia. Some of these benefits are linked to the inherent character of groundwater as resources, such as most aquifers provide large natural storage space and help stabilize water supply during peak drought seasons. The sluggish flow of groundwater through small void helps in purifying water to use as drinking water. Almost ubiquitous availability of groundwater makes it resources easy to access. In areas with extensive aquifers endowed with good permeability and storage properties, groundwater exploitation could increase recharge and also decrease flood intensity. Groundwater irrigation has also ensured security and helps alleviate poverty. For example, in India, the population increased quickly in last 20 years, and it has a burgeoning grain reserve of over 60 million tons and annual grain production touched a record high 0f 210 million tons in 2002-2003. Similarly, Bangladesh, dependent on foreign aid for a long time, emerged as food sufficient in 1999-2000, all related to groundwater irrigation. That groundwater irrigation, especially in water abundant area such as eastern part of India, Bangladesh and Nepal can be powerful way to alleviate poverty.

Since the 1970s, groundwater extraction has increased greatly in China, India, Korea and some counties in South Asia. For example, In India, groundwater greatly irrigate areas witnessed a spectacular increase from around 11.9 million hectare in 1970-1971 to 33.1 million hectare in 1998-1999, an increase of over 178%. The number of groundwater extraction mechanism rose from less than 1million in 1960 to almost 26-28 million in 2002. In Pakistan Punjab, the number of mechanized wells and tube wells increased from barely a few Thousand in 1960 to 500 thousands in 2000. Bangladesh saw an increase in the number of tube wells, from 93000 m³ in 1982-83 to almost 800000 m³ in 1999-2000. The groundwater extraction in China is 111 km³ in the end of last century. Those are 57 km³ in 1970s and 75km³ in 1980s. It is double in last 30years. There are estimate 3500 thousands tube wells for agricultures, withdrawing 68 km³ of water in 1999. It is 61% of the total groundwater withdrawing. But it has decreased since 1980s when the groundwater for agriculture usage is 88% of the total. In North china plain, groundwater irrigation has supported the development of agriculture in last 30 years.

Sources: UNESCO: Water for People Water for Life0 Ranking in the world

1 Total internal renewable water Resources (km3/year)

2 Groundwater produced internally (km3/year)

3 Surface water produced internally (km3/year)

4 Overlap: Surface and groundwater renewable (km3/year)

5 Water resources: total renewable (km3/year)

6 Water resources: total renewable per capita (m3/capita year)

7 Populations in 2000 (1000 Inh)

8 Population densities in 2000 (inh//km2)

2+3-4* Aggregation of data can only be done for internal renewable water resources and not the total renewable water resources, as that would result in double counting of shared water resources.

(-) No data available

3 Problems of Groundwater

in Asia

Problems of groundwater could cause by nature issues or human action. The main problems causes by nature issues are the groundwater quality in the arid and semi-arid areas especially in the central part of Asia. Global climate change caused the hydrogological condition diversified in both inland and coastal area of Asia. Problems cause by human action is groundwater overexploitation and related Seawater intrusion to inland, land subsidence and groundwater contaminated occurred in many regions. Those problems have increased rapidly during last 30 year.

3.1 Groundwater quality

Most renewable groundwater is of high quality for domestic use and does not require treatment. But there are the resort groundwater is naturally unacceptable for drinking lead serious problems. In the arid and semi-arid areas, the salt content in shallow groundwater is high. High content of arsenic and fluorine of groundwater are in many region of Asia. In Bangladesh and the neighboring Indian state of

west Bengal, the high level of arsenic in the groundwater used for drinking water is a public health time bomb. Groundwater sources of 61 out of Bangladesh's 64 districts were found with arsenic. An estimated 35 million people are risk of being exposed to arsenic poisoning though drinking water. In China the groundwater with high content of arsenic were found in Inner Mongolia and other area. (Fig.3) However, with proper management these problems could be solved by substitute water sources or renders it unviable for mitigating arsenic poisoning. Fluoride is a common constituent of groundwater. Natural sources are connected to various types of rocks and to volcanic activity. Agricultural (use of phosphate fertilizers) and industrial activities (clays used in ceramic industries or burning of coals) also contribute to high fluoride concentrations in groundwater. High Fluoride of groundwater has emerged as an important environmental problem in India, Pakistan, Viet Nam and Indonesia. The high Fluoride content of groundwater has caused endemic in some area of north part of China. The drinking water supply must be treated with advisable methods. (Fig 4)

3.2 Overexploitation of groundwater

Groundwater overexploitation occurred in many areas of Asia, such as Gujarat, India, North China plain and some area of Pakistan. They related to declination of ground-water levels, reduction of well outputs, and seawater intrusion in coastal aquifers, land surface subsidence and movement of mineralized or polluted waters into the aquifer. Generally, the declination of groundwater levels results in the increased cost of ground water owing to the expenditure involved in deepening the wells and pumping up water from the correspondingly increased depths. In some cases, overexploitation could lower the water table to such depths that the existing wells have to be abandoned. Countries which are facing problems related to excessive withdrawal of ground water in certain locations include China, India, Japan, Maldives, Republic of Korea, Sri Lanka ，Thailand ,and so on. For example, in Thailand, increasingly heavy pumpage of ground water in Bangkok during 1955-1982 caused a decline of 45 to 50 meters in the ground-water levels. The lowering of water levels by these depths had resulted in the abandonment of old wells, increased pumping costs and encroachment of seawater. In order to prevent the situation from getting worse, to reduce the pumping rates which resulted in the cessation of declination of water levels, particularly in the central areas of Bangkok. It was reported that by May 1985, the piezometric level in central Bangkok had risen by about 2.5 meters.

3.3 Groundwater pollution and contamination

Groundwater contaminated is as a result of industry and subsistence pollution. Those are as a result of increased economic activities. Drainage waters from irrigated lands, for example, usually contain high concentrations of objectionable minerals. These contaminated waters, which flow off the land through ditches, may seep into the soil and pollute the ground water that is pumped from wells. Countries facing this kind of problem include the Republic of Korea, Thailand and Viet Nam. In the Republic of Korea, the expansion of industry during the last decade and the modernization of agriculture, that has exposed its vulnerable (shallow and permeable) alluvium aquifers to various sources of contamination. In Thailand, until quite recently, shallow ground water was generally free from pollution. However, at present it is observed that groundwater has become contaminated in some places where aquifers are directly recharged by polluted rivers or directly reached by irrigating water. Similarly, in Viet Nam, it is observed that in agricultural areas underlain by karstic limestone, fertilizers have reached the karstic water circulation, thus contaminating the ground water.

3.4. Problems related to coastal areas

Seawater intrusion to inland, encroachment of salt water is also a serious ground-water problem, particularly in coastal areas. Since a large portion of the region's population is located along the coasts of oceans and salty seas, there are many problems of this kind in the region. Some of the countries which have problems of this nature include Fiji，Guam, Japan, Thailand and Viet Nam. Basically, encroachment occurs when the water levels in a fresh-water aquifer are lowered to a point where salt water can invade beds bearing fresh water. Although the encroachment tends to be a slow process, in an area where pumping is continuous, encroachment tends to be an irreversible process. As ground water is extracted from the wells, the salt water slowly moves through the water- bearing beds in the direction of the wells and, unless corrective measures are taken, the salt water will ultimately begin to contaminate the water in the wells. Such contamination manifests itself in a gradual increase in the salt content of the water being pumped. For example, in Fiji, the majority of boreholes for water supply are situated near the coast owing to the concentration of population along the coast. This has led to saline intrusion problems at Tagitagi, Singatoka and Korotongo. In Guam, the problem of increased salinity in certain wells is due to the wells located very close to the coastline rather than due to over draught. In Kiribati, salt-water intrusion into the fresh-water lenses is observed to be the result of overexploitation, which is becoming a major problem, particularly on the low atoll islands. In Thailand, the rapid lowering of the water table due to over draught has caused the shallow aquifers in Bangkok to become contaminated with salt water. In Viet Nam, seawater intrusion into coastal aquifers is a major problem. For example, in the lower part of its major river basins, as well as in the coastal plains, the average salinity of ground water is approximately 3,000 to 4,000 ppm, while the maximum salinity sometimes reaches as high as 10,000 ppm, thus rendering the ground water unsuitable for drinking.

3.5 Land subsidence

In some countries of the region, the withdrawal of large amounts of ground water has caused serious problems of the subsidence of the land surface. Some of the counties facing such problems include China, Japan, and Thailand. Land subsidence occurred especially in coastal cities, such as Bangkok and Tianjin. In Japan, from 1961 to the present time, the occurrence of land subsidence and/or seawater intrusion was the result of over-exploitation of ground water brought about by the remarkable growth of industries and the expansion of agricultural production. Land subsidence has occurred in the low-lying land of the plains and basins where the principal cities, Tokyo, Nagoya, Osaka, Yamagata, Kofu etc., are located. In Thailand, overexploitation of ground water exists in many locations, particularly around Bangkok area. In Bangkok, the field evidence of land subsidence has been observed in the form of protrusion of well casings above the ground surface. Estimates based on the protrusion of well casings that were installed about 30 years ago indicate that the average subsidence rate in the city is approximately 1.8 to 1.9 centimeters per year. A detailed survey of ground levels carried out in Bangkok during the period 1979-1981 indicated that the existing benchmarks are 30 to 80 centimeters below their original elevations recorded 3O to 40 years ago. At present, about half of the city is less than 0.5 meters above the mean sea level. As in Bangkok, Shanghai, China experienced a severe subsidence problem between 1921-1965, particularly from 1949 to 1957, during which an increase in groundwater pumpage resulted in a corresponding increase in the rate of subsidence as well as the area affected. The measures taken in China to solve the subsidence problem included: Broadening the area from which ground water is extracted; reducing the amount of ground-water extraction; recharging the aquifers artificially wherever possible; selecting appropriate aquifers for groundwater extraction. These measures were said to be effective and to have achieved positive results. In this connection, it should be noted that where subsidence has occurred, it is not possible to reverse the process by any means whatsoever. In other words, even a complete cessation of pumping mid the injection of new water into the ground will not restore the land surface to its original elevation. Hence, it is very important to establish and implement effective groundwater management program to forestall land subsidence due to over pumping.

4 Transboundary Aquifers in Asia

Transboundary aquifers, as part of groundwater resource systems, are important for related Asian countries. They are dealing with the relationship between the countries or regions, as the international rivers. There are several transboundary aquifers, which concern two or more countries in Asia. There are concomitances with rivers pass through several countries, such as Mekong River, Ganges Rivers and Heilongjiang-Amur River.

Transboundary aquifers in Asia have been summarized. They are basis on groundwater systems analysis. For the countries such as China, Russia and India inhabit large areas. The number of international transboundary aquifers in Asia is less than those of other continent. Seventeen transboundary aquifers, which are very significant, are demarcated as table 2. That is the production of the UNESCO-IHP programme. Those aquifers in Asia are important for building a society where all civilizations coexist harmoniously and accommodate each other. According to the groundwater resource data collected, the groundwater systems in central, east, and south Asia are analyzed. The aquifers of the Heilongjiang-Amur River plain and the Ili River basin on the national boundary of China are evaluated in detail. The information about the groundwater flow should be exchanged among China with Russia or Kazakhstan, which share the transboundary aquifer system. They are the basic requirement for the joint management of water resources.

Research on transboundary aquifers is significant for the management of shared groundwater resources of neighboring countries or regions.

5 Challenges for Hydrogeologists

Groundwater demands and Dependent Ecosystems problems are driving force for Asian hydrogeologists. There are so many issues for solution. The main tasks are groundwater assuring for the livelihoods and food security of millions of people, groundwater sustainable usage for the socio - economic sustainable development, groundwater management effectively. The groundwater monitoring, dynamic assessment and groundwater dependent ecosystems conservation are the majors. Greater knowledge and improving basic data through research are prerequisites for better management of groundwater system. We should realize just using last century's schemes no longer solves challenges that today's groundwater related. For understanding the characteristics and behaviour of groundwater resources is the basis. The characteristics and behaviour of resources user communities and the institutional framework under which the resource is appropriated and use are also important for us. There is an urgent need for expansion in the knowledge of user and institutional perspectives in the groundwater knowledge base.

In general, there are two basic approaches to dealing with the problems related to over-exploitation of aquifers: the preventive approach and the remedial approach. The main objective of the preventive approach is to forestall over-exploitation by enacting and enforcing appropriate ground-water legislation. The remedial approach is useful for cases where the problem of over-exploitation has already taken place and usually requires recharge of the aquifers by artificial means. It should be noted that artificial recharge of aquifers is not always possible, and even if it is, it tends to be a costly process. Another possible measure to solve over-exploitation of ground water is to limit or reduce the supply of ground water and increase that of surface water. In this regard it is necessary to have integrated management of both surface and groundwater resources.

Groundwater benefits thereof deeply impacetd Asia. Groundwater use has indeed involved drinking, food production and created livelihood opportunity for million people. The prime aim in governing groundwater is to ensure the negative is to devise ways and means of reducing the negative impact of groundwater usage without signigicantly reducing benefit flows. In this context, hydrogeologists in Asia have an important role to play providing timely data and analyses that will help to decision makers in formulating implementable and socially acceptable policy respinses.