OMINOUS WATER CRISIS
Mismanagement of water resources, population growth and changing weather patterns are at great concern
Dr. S. M. Alam
May 30 - June 05, 2005
Water is an essential factor for life and nothing can stay alive without it. Plants can not grow without water. When plenty of water was available, more and more barren lands were brought under cultivation. The uses of water are numerous and life without water is impossible. A constant supply of clean and healthy water is most essential for all citizens of the country. Water is of the human body's primary and basic need. As water quality degrades or quantity diminishes, it can affect people's health and destroy livelihoods that depend on water. Our earth is composed of 28.88 percent of land and 71.11 percent of water. However, a shortage of fresh water is probably going to be most serious resource problem, and the burgeoning population of the world will face in 2020. As with food, this problem is not one of global shortage, but one of uneven distribution. Three-quarters of the fresh water on the planet is held in the polar icecaps and glaciers and on so is unavailable for use. This scenario leaves only a small percentage of readily manageable fresh water as a source of the water supply, where water is plentiful, people are frequently a few, and vice-versa. The most water-rich country in terms of the run-off from rainfall to population is Iceland with more than 500,000 cubic meters per person per year; but the most water- poor country is Egypt, with just only 0.02 cubic meters per person.
Some 70 per cent of the water used by people goes to irrigation. Since 1950, the amount of irrigated land has tripled and one-third of the world's food is grown on it. Without that increase the world might now be starving. But the price has been environmental damage, which in some areas is now starting to reverse the rise in foods production which has taken place. The most serious long-term problem is salinization. When irrigation water soaks down into the soil, it absorbs mineral salts from the earth, flushing them to the surface. As the water evaporates, these salts dry out on the fields, gradually destroying their fertility. Some 25 percent of Pakistan's cultivated land has been damaged in this way. Recovering poisoned fields is vastly expensive. The environmental damage done by ill-managed irrigation schemes is a time bomb which threatens to reverse the progress in food production made by past schemes.
Four countries in particular face serious problems — India and China, which between them account for one-third of the world's irrigated land; Pakistan 80 percent of whose fields are irrigated and Egypt with a similar percentage of irrigated land and particular problems from its dependence on one source of water, the Nile. All have suffered to a greater or lesser extent from salination. For them, maintaining their irrigated land will be a constant struggle, even with regular flushing and the use of salt-resistant varieties of plant, ultimately the salt will win. Already, several countries are using most of the water available to them. India, for example uses 97 percent of its water for irrigation. The country is currently using half its available run-off, that is the water that falls on a country and is collected in rivers and lakes and drawing half as much again from underground springs. China, also facing severe water shortages. Feeding China will require gigantic schemes to be successful or it will require farmers to use water more efficiently. At present, one-third of the water used for irrigation worldwide actually goes into making plants grow, the rest is wasted..
Providing water for irrigation and for cities require damming more rivers, flooding more valleys, carrying out more giant water-engineering schemes. Such projects are often hugely expensive and not only in economic terms. Large dams frequently involve massive changes in the use of land. That means not only the displacement of people from their homes but the loss of farm land, disturbance to water tables. Build-up of silt and other environmental costs. Of course, dams also produce water for irrigation and for hydroelectricity, but serious attempts to measure the benefits from dams suggest that the gains are often smaller than the costs.
The world is facing looming crisis of water shortage due to mismanagement of water resources, population growth and changing weather patterns. By the year 2005, according to UN Report, more than 2.7 billion people will face severe water shortage if the world's water consumption rate continues to be the same. Water situation has worsened to the extent where the whole world has arisen to tackle the challenge. The world is losing about 4 cm per km of storage capacity per year. The world's thirst for water is likely to become one of the most pressing resource issues of the 21st century. Global water consumption rose six-folds between 1900 and 1995 more than double the rate of population growth and continues to grow rapidly as agricultural, industrial, and domestic demand increases. Globally, water supplies are abundant, but they are unevenly distributed among and within countries. In some areas, water withdrawals are so high, relative to supply, that surface water supplies are literally shrinking and groundwater reserves are being depleted faster than they can be replenished by precipitation. This situation has already caused serious water shortages to develop in some regions, short changing human water needs and damaging aquatic ecosystems.
A 1997, United Nations assessment of fresh water resources found that one-third of the world's population lives in countries experiencing moderate to high water stress. To arrive at its estimate, the United Nations determined each country's ratio of water consumption to water availability — its use-to-resource index — which is a good gauge of overall pressure on water resources. Moderate to high stress translates to consumption levels that exceed 20 percent of available supply. The UN assessment makes clear that the global water situation will get considerably worse over the next 30 years without major improvements in the way water is allocated and used. In fact, the United Nations projects that the share of the world's population in countries undergoing moderate or high water stress could rise to two-thirds by 2025. Population growth and socioeconomic development are currently driving a rapid increase in water demand, especially from the industrial and household sectors. Industrial water use, for example, is predicted to double by 2025 if current growth trends persist. Water use in agriculture is slated to increase as world food demand rises. Agriculture already accounts for about 70 percent of water consumption worldwide, and the United Nations projects a 50 to 100 percent increase in irrigation water by 2025. Much of the projected increase in water demand will occur in developing countries, where population growth and industrial and agricultural expansion will be greatest. However, per capita consumption continues to rise in the industrialized world as well.
As clean water supplies have diminished, competition for them has been growing, usually between expanding urban areas and rural users. Where systems of water law and allocation exist, water markets can operate to transfer supplies between buyers and sellers for an agreed price. Such systems are operating with some success in an increasing number of countries, including the western United States and Australia. However, effective water pricing, which sets water prices high enough to discourage waste, remains a highly sensitive issue in low-income countries, where most people depend on irrigated agriculture for their living. Even so, socioeconomic development in water-scarce countries may depend critically on more rational distribution of scarce supplies. Planners in China have estimated that a given amount of water used in industry generates more than 60 times the value of the same water used in agriculture. Better management of water resources is the key to mitigating water scarcities in the future and avoiding further damage to aquatic ecosystems. In the short term, more efficient use of water could dramatically expand available resources. In developing countries, for example, 60 to 75 percent of irrigation water never reaches the crop and is lost to evaporation or runoff. In the longer-term, however, the UN water assessment makes clear that looming water crises in many regions must be addressed through hard policy decisions that reallocate water to the most economically and socially beneficial uses. Far greater emphasis on water-efficient technologies and pollution control is also essential. However, even with measures to contain the growth of demand and use water more efficiently, new supplies will be needed. The World Bank has estimated that the financial and environmental costs of tapping new supplies will be, on average, two or three times those of existing investments, because most of the low-cost, accessible water reserves have already been exploited. The UN study also highlights the potentially desperate situation of developing countries that combine high water stress with low per capita income. The majority of these countries are found in the arid or semiarid regions of Africa and Asia. Many use most of their available water supplies for farm irrigation and suffer from a lack of pollution controls. Future development in these countries appears severely constrained because they have neither the extra water nor the financial resources to shift development away from intensive irrigation and into other sectors that would create employment and generate income to import food.
The challenge for future water management is enormous. In 1995, 29 countries with populations totaling 436 million experienced water stress or scarcity. By 2025 about 48 countries will do so and the number of people adversely affected will exceed 1.4 billion, the majority in the least developed countries. An estimated 3 billion people will be living in water-stressed countries in 2035. In addition, many countries with limited water availability also depend on shared water, which increases the risk of friction and social tensions — as is already the case along the rivers Euphrates, Jordan, and the Nile. Improved water management has brought enormous benefits to people in developing countries. Between 1950 and the mid-1980s global per capita grain production increased by 38 percent and grain prices dropped by about 50 percent. The driving force behind this has been an increase in irrigated area (from 100 to 250 million hectares) and an increase in productivity. Over the past 20 years more than 2.4 billion people have gained access to water supply and 600 million to sanitation, and about 20 percent of the world's electricity comes from hydro-electric dams.
Since the mid-1980s there has been a pronounced slowing down in food production from irrigated agriculture, both as a result of little expansion in irrigated area, and reductions in productivity growth. There are still about 1 billion people without an adequate supply of drinking water, and about 2 billion people without adequate sanitation services. Groundwater aquifers are being pumped unsustainably in many developing and some developed countries. Ten percent of food is grown with water pumped from overexploited aquifers. And much aquatic biodiversity is being lost in overstressed rivers — the rate of extinction of freshwater fish species is five times that of saltwater species. Spreading water shortages threaten to reduce the global food supply by more than 10 percent. Left unaddressed, these shortages could lead to hunger, civil unrest, and even wars over water, reports a new book from the World Watch Institute. Irrigation accounts for two thirds of global water use, but less than half that water reaches the roots of plants. Without increasing water productivity in irrigation, major food-producing regions will not have enough water to sustain crop production. Some 40 percent of the world's food comes from irrigated cropland. But the productivity of irrigation is in jeopardy from the over pumping of groundwater, the growing diversion of irrigation water to cities, and the buildup of salts in the soil. Our civilization is not the first to be faced with the challenge of sustaining its irrigation base. A key lesson from history is that most irrigation-based civilizations fail.
Today, irrigation problems are widespread in the grain-growing regions of central and northern China, northwest and southern India, parts of Pakistan, much of the western United States, North Africa, the Middle East, and the Arabian Peninsula. Water tables are dropping steadily in several major food-producing regions as groundwater is pumped faster than nature replenishes it. The world's farmers are racking up an annual water deficit of some 160 billion cubic meters-the amount used to produce nearly 10 percent of the world's grain. The over pumping of groundwater cannot continue indefinitely. Eventually the wells run dry, or it becomes too expensive to pump from greater depths. Meanwhile, the amount of irrigated land per person is shrinking. It has dropped 5 percent since its peak in 1978, and will continue to fall. At the same time, one in five hectares of irrigated land is damaged by salt-the silent scourge that played a role in the decline of ancient Mesopotamian societies and other ancient civilizations.
So much water is being diverted for irrigation and other human uses that many major rivers now run dry for large portions of the year-including the Yellow in China, the Indus in Pakistan, the Ganges in South Asia, and the Colorado in the American Southwest. The Yellow River, the cradle of Chinese civilization, ran dry for a record period in 1997, failing to reach the sea for 226 days. With population growing rapidly in many of the most water-short regions, water problems are bound to worsen. The number of people living in water-stressed countries is projected to climb from 470 million to 3 billion by 2025, the study notes. Already many countries do not have enough water to meet domestic demands for food, creating a source of potential political instability. Water-short countries are increasingly turning to the world grain market. In the swathe of countries from Morocco across North Africa and the Middle East to Iran, virtually every nation is facing water shortages as rising populations draw against a limited supply and as irrigation water is diverted to satisfy growing urban demand. To meet their food needs, these countries are importing grain.
Last year, the water required to produce the grain and other farm products imported into the region was equal to the annual flow of the Nile River. And this deficit is growing year after year. Jordan is importing some 91 percent of its grain, Israel 87 percent, Libya 85 percent, Saudi Arabia 50 percent, and Egypt 40 percent. As water shortages continue to mount, it is dangerous to presume, as many officials do, that there will be enough exportable grain to meet the import needs of all water-short countries at a price they can afford. Most of the growth in water-stressed populations will be in South Asia and sub-Saharan Africa, where the majority of the world's poor and malnourished are today. In five of the world's hot spots of water dispute-the Aral Sea region, the Ganges, the Jordan, the Nile, and the Tigris-Euphrates-the population of the nations within each basin is projected to climb between 44 and 75 percent by 2025. Some 260 rivers flow through two or more countries, but in most cases there is no treaty among all the parties that sets out how that river water should be shared. In the absence of water-sharing agreements, tensions are bound to rise.
Irrigation's heavy water demands are also damaging the health of the aquatic environment-shrinking wetlands, reducing fish populations, and pushing species toward extinction. Using water as inefficiently as we do today, meeting the food demands of the projected 8 billion people in 2030 would result in costly losses of ecological services that the economy depends upon. To meet the challenges of a water-short world, there is a need to obtain a Blue Revolution to dramatically boost water productivity. Most farmers today irrigate the way their predecessors did hundreds of years ago. Just as raising land productivity helped meet food needs during the last half of this century, boosting water productivity will be the agricultural frontier during the next century. The challenge today is to substitute technology and better management for water. A possible idea to diverse and creative mix of "Blue Revolution" strategies are: Farmers in Pakistan, India, Israel, Jordan, Spain and the United States have shown that drip irrigation systems that deliver water directly to crop roots can cut water use by 30 to 70 percent and raise crop yields by 20 to 90 percent.
Irrigation means artificially watering the soil to initiate or increase the growth of crops. Irrigation water has the advantages over rain water of being under control with respect to time and amount of application. The scarcity of good quality irrigation water is becoming more acute day by day. Crop water used is expressed in acre-inches, when an acre inch is the amount of water required to cover one acre of land with one inch of water. Irrigation accounts for most of the water used throughout the world. Egypt is irrigated, about half in China, Japan and Pakistan, about 33 million acres in the United States and large parts of Europe. No country, in fact, is without its irrigation projects. Yet only one small percentage of the agricultural land is irrigated, about 400 million acres — often using only a small proportion of the available water. One reason for this is that irrigation requires enormous quantities of water. For instance, one ton of sugar beets need 1000 tons of water during period of its growth; wheat 1500 tons and rice 4000 tons. Furthermore, most of the water used for irrigation cannot be re-used. At least half of its is lost by evapo-transpiration. The rest is incorporated into the plants themselves (which are over 60 per cent water) and drains down into the subsoil.
By far the greatest area of irrigated land exists in hot, humid climates. Here the commonest crop is rice, which provides the main caloric intake for about one-third of the world's population. Most rice is grown in paddy fields that are flooded with about six inches of water during the growing season. There is usually no shortage of water in humid climates, either because the annual rainfall is very high, or because there are large rivers with a reliable water flow. In arid lands, on the other hand, the main problem of irrigating large area is a shortage of water. Agriculture in arid lands is also beset by problems that do not occur in humid regions. Where, there is bad drainage in flat plains, irrigation may eventually raise the water table so that the land becomes waterlogged. Good drainage is just as important as irrigation. In the past, many peoples have neglected this principle, and many millions of acre now lie unused. Water logging prevents oxygen from reaching plant roots, which then suffocate, because of oxygen deficiency and build up of salt in soil profile. Also, waterlogged soil does not encourage crops to develop deep roots, so that during drought they are unable to tap the deeper moist soil.
The Indus Basin has a flat topography, poor natural drainage and a semiarid climate with high evaporation. In such an environment, irrigation without adequate drainage has inevitably resulted in the twin problem of water logging and salinity. Increases in diversion of river flows and seepage from canals, watercourses and irrigated areas have led to a gradual rise in groundwater levels. Within 100 years, the water-table has risen from 40 to 3 meters on about 42 percent of Indus Basin. The situation is worst in Sindh province where water table is within 3 meters on 60% of irrigated area. Water is a unique natural resource. In Pakistan, conservation and management of water supplies is crucial as the need for water continues to rise because of burgeoning population, while its supply is limited. With this scenario, a time is approaching fast, when the only additional natural water supplies available in the country would be those salvaged from losses through consumptive waste, inefficient application and conveyance practices and run off. To overcome this crucial situation, it is imperative to save water, make its use more effective and obtain optimum results through reduction in its losses. This method will alone have a chance to guarantee adequate supplies of water for the next time to come.
The ongoing water shortage has jolted the very foundations of the national economy on the one hand and has eroded faith in the decision-making capacity of our institutions on the other. Pakistan's economy being an agricultural area has sustained an irremediable damage as a ramification of the water shortage. Our negligence in making proper policies has created drought-like situation in the country. As result of global warming, intensity of precipitation from sky is decreasing every year. The majority of cropland areas of the country is irrigated through canals and rightly called "Irrigated Agriculture". In fact, it is reliable area which supports and fulfils the needs for food, fiber and industrial raw materials in Pakistan. Other areas are at the mercy of rains and called as "Rain-fed Agriculture". The contribution of this area is minor or negligible compared to the irrigated area. Our irrigated area is also facing drought-like situation for the last 10 years due to less availability of water in canals and through precipitation.
The shortage of irrigation water may develop through a high degree of water losses, which are observed due to seepage in canals, watercourses and field channels and further aggravated by field application losses. The poorly managed farm irrigation application is one of the root cause of water losses. In this way a colossal amount of more than 40 percent of total available water is lost, and for our existing irrigation system this is a huge loss. Unlined or poorly lined water conveyance channels cause inadequate water supply to the crops thus reducing the crop yield. Water scarcity also reduces the cultivable area thus limiting the quantum of agricultural produce. Pakistan is a land rich area (79.61 million hectares), water-short and population burdened rich country, where the population is increasing (birth of 10 children per minute) at a rapid rate and where per capita availability of water has been constantly decreasing for the last fifty three years. The present level of water shortages in the country hampers the growth and well being of its people and severe constraints may be caused to human life if such situations continue in the country. Pakistan is basically an agricultural country and irrigation is the lifeblood of its agriculture. Of course, the land, water vegetation and human beings are important for agriculture but the development of water resources is more complex and cost intensive as compared to land and vegetation sources. For agriculture, water seems to be the major source of development. Whatever may be the nature of technology, crop production cannot be increased without recourse to adequate water resources so essential for crop growth. The recent development in agriculture land reforms, green revolution etc. was limited in scope and ineffective as regards overall development. If due emphasis is placed an irrigation development (mainly conservation of rainfall water and proper application of irrigation water, rural development could be brought about speedily than under any other measure.
God has gifted Pakistan with abundant water resources, with water flowing down the Himalayas and Karakoram heights from the world's largest glaciers, a free and unique bounty of nature for this land of alluvial plains. As a result of this natural resource, today we have the world's marvelous and the largest contiguous irrigation system that currently irrigates over 36 million hectares of land, out of 34 million hectares of cultivable lands available. Irrigation plays a central role in Pakistan's economy. Irrigated land supplies more than 90 percent of agricultural production and most of the country food, which accounts for 23.6 percent of GDP and 50% of the employed labour force. It is also the source of raw materials for major domestic industries, particularly the cotton products, which accounts for 85 percent of the value of exports. Agriculture sector is the major uses of water and its consumption will continue to dominate water requirements.
At the time of independence, we had about 67 million acre feet (MAF) water available for diversion, this amount increased to about 85 MAF by 1960. The recent statistical data shows that the river Indus and its tributaries provide about 147 MAF during flood season, out of which nearly 106 MAF is diverted into canals and is available for irrigating 14.6 million hectares of land.. This is a huge unrecoverable national loss and reflects on poor water resource development policy of the concerned quarters. Presently, Pakistan's irrigation system encompasses only three dams Mangla,. Tarbela and Chashma dams. Whose storage capacity would be lost by 34 percent due to excessive sediment inflows in river water, which virtually means loss of one mega storage project, The present storage capacity is only 11 percent of the total surface water and there is potential for development of 65 MAF of storages, whereas about 38 MAF of water escapes annually into sea. Due to the sedimentation, it may further decline by nearly 6 MAF by the year 2010, which is nearly equal to the original storage capacity of the Mangla dam, when it was constructed in 1967. At present, the storage capacity of our major reservoirs has already declined to 12.6 MAF, which is hardy 20 percent of our potential storage capacity of 64.4 MAF. The sub-soil water availability in Pakistan has dropped from 5,300 cubic meter per person per annum from 50 years to 1,100 cubic meter per person per annum at present. Though, the per capita per year water available in Pakistan is also much less than the international standards, the situation would be much more worrisome after 20 years when the availability of water would go down to 600 cubic meter water per person per annum much less than the per capita subsistence level. According to experts, as per the international standards an individual need 1700 cubic meter water per year. Pakistan if facing severe shortage of water. If the over-exploitation of the water resource is not controlled by avoiding misuse of the same, the decreasing sub-soil water level is, apparently going to aggravate the current conflict on water shortage among the provinces.
Irrigation in the country, depends on both surface and underground water resources. The quantum of water entering the rivers aggregates to about 145 million acres feet per year. Of this about 110 million acre feet is transferred to canals for irrigation annually (80 percent) and remaining 35 million acre feet flows down into the sea because of lack of storing facilities. The quantum of water entering irrigation water courses from the canals amounts to 98 million acre feet per annum. Water obtained from 605,000 public and private tube wells for irrigation purposes has been estimated at 45 million acre feet annually. Thus, the total quantum of water entering the water courses both from canals and tube wells aggregates to 122 million acre annually. Of the 145 million acre feet water entering the canals each year, about 28 million acre feet is lost in transit due to a number of factors. Thus, only 73 million acre feet water reaches the field. Taking into account all the losses as indicated above, only 55 MAF water is normally left for the irrigation of crops. The farmers normally need 3.5 MAF water per acre for cultivation, our crops get only 1.5 MAF water per acre.
To keep up the pace of agricultural growth comparable to population growth, we must bring additional lands under cultivation. In order to achieve the required growth targets in agriculture in future, we needed an estimated amount of about 155 MAF by 2006 and will need 215 MAF by the year 2015 and about 277 MAF by the year 2025. Since no additional water is available, it is better to improve the existing water system and land capabilities, other wise, Pakistan will be facing acute shortages of food, fiber and edible oils in near future. We must keep an eye on the issues such as inadequate management and inefficient operation of irrigation system, poor water application and unequal water distribution, depletion of ground water resources, reduction in storage capacities of existing system, and wastage of summer river surpluses and slow agricultural growth. Water in the Indus is coming from melting of different glaciers.
The irrigation system in the Indus Valley River System had been practiced through centuries and it is the prime source of Pakistan's water resources. Later on in 19th century barrages and head works were constructed for supply of water to the agricultural lands. Now the irrigation system is comprised of three reservoirs (Tarbela, Mangla and Chashma), 19 barrages or head works, 14 link canals, 48 number of command canals covering about 90,000 villages/chaks, more than 12,000 distributaries and about 107,000 water courses. The length of the canals is about 62,000 km with communal watercourses, farm channels and field ditches covering another, 1,600,000 km. The canal system up to distributary level is being maintained by the government through the irrigation department, whereas the operation and maintenance of watercourse is the responsibility of farmers. In the Indus Basin irrigation System, river water is directed by barrages and head works into main canals and subsequently into branch canals, distributaries and minors. The flow to the farm is delivered by the watercourses, which are supplied through outlets from the distributaries ad minors. Farmers receive water proportional to their land holdings.
Pakistan with population of about 150 million is the largest single irrigated region in the world. The total geographical area of Pakistan is 79.61 mha. Out of 39 million acres of fertile soil, 23 million acres are irrigated by an extensive system of feeder canals. Yet, the population lives in hunger and poverty, because event he vast, fertile Indus plain cannot provide enough food, due to inefficient irrigation and farming practices. Pakistan has very poor saturate drainage and irrigation has produced 11 million acres of waterlogged land, which is not good for country. The main cause of this is that a large quantity of water is irrigated canals has seeped through their beds and has raised the water table to large extent. Pakistan has significant water resources but these are inadequate for crop production on the available land. Improved water control is important to the achievement of the full yield potential of latest recommended varieties of crops and is by far the most promising means of increasing food production. The design of irrigation systems for long-term stability must include not only engineering considerations of water storage, conveyance and delivery, but also agricultural economic considerations.
The construction of new dams and water reservoirs is of vital importance to meet our growing demand of energy and water supply for our land irrigation system. There is an urgent need to construct many small dams on river Indus, Jhelum, Chenab etc. The potential sites for these small reservoirs/dams need to be surveyed. However, some of these sites are located at Sehwan-Manchar lake, Hamal lake, Skardu, Bhasha, Yugo, Kalabagh. Bunji, Kohala, Kunhar, Rohtas, Neelam valley, Thal reservoirs etc. and these may be utilized. The significance of small dams and reservoirs can not be denied. Practically, it takes about 10-15 years to build a dam. In order to properly manage the impending water and energy crisis, construction of dams should be started with immediate effect. Currently, the biggest dams. Mangla and Terbala can not meet the demand of water. Dams have specific life and addition of silt gradually decrease their water storage capacity. The levels of these two dams can also be raised to increase their storage capacity. Another option is to manage the existing irrigation system in a better way and undertake new schemes wherever possible. A consideration amount of water is lost during its conveyance due to seepage in lengthy canals, lining of the system channels could reduce these losses. As reported by WAPDA, more than 5 MAF of irrigation water could be saved by lining the minor canals only and additional amount of about 3.6 MAF could be saved by water course improvement.
A study of international climate changes indicates that the frequency of droughts is likely to increase by 50 per cent in the coming years. Pakistan can be a major victim of the lurking drought syndrome because for economic and political reasons it has not expanded its already inadequate and constantly declining per capita availability of surface water resources. During the last 25 years, China and India built 45 and 25 dams, respectively. Pakistan is a water-short land-rich and demographically burdened country, where the population is increasing at a rapid rate. At present, the population growth of the country is flourishing at the rate of 10 births per minute, 600 births per hour, 14,400 per day and 4,966,000 per year and so on. According to the internationally recognized water scarcity indicators, the present level of water shortage in Pakistan hampers the growth and well-being of its people, and severe constraints may be caused to human life, if this downward trend continues. It is tragic that downward trend is continuing. Tarbela and Mangla dams have lost 25 percent and 20 percent storage capacity because of siltation.
Cropping schedules are generally controlled by soils, rainfall distinction and the availability of irrigation water. The potential to improve water management is tremendous, considering the low water use efficiencies of present systems. At farm level, seepage and percolation losses are small, but surface losses resulting from insufficient attention to water management and distribution are large. Surface drainage often exceeds 50 per cent of the total supply during period of high rainfall. Therefore, reducing surface drainage loss offers the greatest opportunity for increasing efficiency of water use. In Pakistan, failure of electricity at peak water requirement of standing crops or when growing period sets in brings reduction in yield. This results in delay in cultural operations like preparation of seedbed, sowing, harvesting etc. Delay in operations not only upsets production plans but marketing conditions as well, bringing reduction in price and income to the farmers. The network of rivers in Pakistan carries more than twice the flow of the Nile. Half of this water is diverted into a highly developed system of irrigation canal and is used to irrigate more than 21 million hectares, which by far is the largest single irrigated mean on earth.
Scarcity of water is world wide problem, the gravity of which can be assessed from the fact that the next world war may be fought between nations on distribution of water. This is situation of the planet earth, which is 71 percent water, but it should also be kept in mind that less than 3 percent of this water if fresh. Most of this water is either in the form of rice and snow or in deep ground water aquifers. Less than 1 percent of this water, which comes to about 0.01 percent of the earth water, is considered available for human needs and much of it is far from large population. More than 1 billion of this earth's people do not have access to safe drinking water, about 2.4 billion people lack adequate sanitation and some 3.4 million die each year from water related diseases. In spite of these facts, proper attention has still not been paid to conserving and using the available water judiciously for domestic and agricultural purposes and the situation is specially bade in countries which are already in the water-short region.
In Pakistan, like in many other countries, precipitation exceeds rainfall and availability of water from the mountain tops and the reservoirs is depleting day by day. The situation, however, is not as bleak as it seems as with proper management of the available water, we can still manage to cope with the water shortage. This has been manifested in the past couple of years when in spite of sizeable reduction in availability of irrigation water, the yield of the crops did not reduce proportionally, we rather had surplus of wheat last year. This paper discusses the current situation of the availability of water with reference to Pakistan and the options to meet the challenge of the scarcity effectively. In many parts of the world, enormous quantities of water are needed for irrigation. Other areas of low rainfall, such as the valleys of the Nile, Tigris and Indus, at least have the benefit of river water. Many parts of the world are now short of food because their populations have grown too large to be fed by locally grown crops. Expanding populations require more water. It has been reported that for the last 60 years, the demand for water by the population has been increased manifolds. Thus in 1940, the total water use was about 1000 km3 a year. It doubled by 1960, and double of again by 1990, when it reached 4130 km3 a year. Global water use is expected to increase by a further 20 per cent to 6,150 km3 by the year 2005. Heavily polluted water can lead directly to water scarcity because very dirty water is of little use unless it can be cleaned. The world's available supplies of water are becoming increasingly polluted. Today, many rivers are polluted from source to estuary the natural cleansing action just cannot cope.