How much water is there on the earth?

How much water on the earth is different from other resources is very important to life. The ancestors of human beings originated from water, and the fetus still grows in the amniotic fluid of the mother. The human body is 60% liquid, mainly water. Water is very important to human health. Once the water in the body is lost 10%, the physiological function will be seriously disordered. If you lose 20% water, people will die soon. The same is true for life outside human beings. It is the source of all life. When people look for life on other planets, the first thing they need is water. Water is indispensable to the economy. Without water, crops will die, and without aquaculture, they cannot produce. Water is the source of all human civilizations.

There is a lot of water on the earth. It is estimated that the total volume of water is about 65.438+0.38 billion cubic kilometers. If these layers are distributed on the earth's surface, it is equivalent to that the whole earth's surface is covered with a layer of water with an average depth of 2650 meters. Unfortunately, 98% of this water is salt water, which is mainly distributed in the ocean. Fresh water accounts for only 2% of the total water volume of the earth, about 30 million cubic kilometers, and this 2% fresh water cannot be fully utilized by human beings, because 88% of it is frozen in polar ice sheets and glaciers, and the remaining 12%, that is, rivers, lakes and exploitable shallow groundwater, can be utilized by human beings, most of which are groundwater, and the water of rivers and lakes can be directly utilized without exploitation. The water on the earth is always changing. Water in the ocean and land evaporates into the atmosphere, and then rain or snow falls back to the earth, nourishing everything, replenishing rivers and lakes or injecting into the sea. Water will also seep into the ground and flow into the aquifer. The extremely deep groundwater can neither be replenished nor exploited, which is called primary water, so it can't be regenerated. It is precisely because of this fluidity of water resources that land floods or droughts occur, resulting in uneven distribution of water resources. Every year, about 65% of the world's water resources are concentrated in 10 countries, while 80 countries (including 9 countries in the Middle and Near East) with 40% of the world's population are seriously short of water, and 26 countries (* * * 230 million). We call these countries water-deficient countries. The international standard of water-deficient countries is based on the definition given by Swedish hydrologists Marin and Falkenmark: If the supply of renewable fresh water in a country is less than 65,438+0,700 tons per person per year, then the country will be in a state of water shortage regularly or frequently; If the annual per capita water supply is below 1000 tons, you will feel water shortage. At present, there are 15 countries with per capita annual water supply below 1000 cubic meters. Among these countries, Malta's annual per capita is only 82 cubic meters, and its water shortage ranks first among water-deficient countries. Apart from Malta, the countries with the most water shortage are Qatar (9 1 m3 per year), Kuwait (95 m3), Libya (1 1 m3), Bahrain (162 m3), Singapore (180m3) and Singapore. Jordan (3 18 m3), Yemen (346 m3), Algeria (527 m3), Burundi (594 m3), Cape Verde (777 m3), Oman (874 m3), United Arab Emirates (902 m3) and Egypt (936 m3). It is predicted that by the middle of 2 1 century, water in these countries will be more expensive than oil. For example, the annual per capita in Malta will be 68 cubic meters.

Due to the different living standards and production methods, the water consumption is also very different. The average daily water consumption per person in the world is: 600 liters in the United States, 200 liters in Europe, 260 liters in Israel, 70 liters in Palestine and only 30 liters in Africa. Americans use 20 times as much water as Africans. In developed countries, as long as you turn on the tap, you have used up a lot of water before you realize it; In hot developing countries, especially those shanty towns on the edge of cities, dozens or even hundreds of households only have one faucet, so it is a luxury to use 2 liters of water every day. Mahmoud Abu-Abuzeid, President of the World Hydrological Council, said: "In the 1950s, only a few countries were short of water, but by the end of 1990s, 300 million people in 26 countries were short of water. It is estimated that by 2050, 66 countries, which account for two-thirds of the world's population, will develop from widespread water shortage to serious water shortage. " At present, 2.9 billion people in the world have no access to clean drinking water. Water pollution makes the already scarce water resources worse. The resulting waterborne diseases cause150,000 deaths worldwide every year, most of which are children. Diarrhea alone kills 40,000 to 50,000 babies and almost the same number of adults every year. Some famous scientists in the world have been studying the prospect of world water for decades, and their conclusion is that the situation is very serious. They remind people that if water resources are exhausted, human health, economic development and ecosystem will be threatened.

Based on the information from all over the world, the actions taken by human beings to avoid water crisis at present mainly include the following aspects:

The first is to control population growth. Since the beginning of this century, with the continuous increase of population, the speed of human water consumption has increased rapidly. The world population was 2.5 billion in the 1950s,16 billion in 1999, and increased by 1.2 times in the past 50 years. At the same time, agricultural water consumption increased by 5 times, industrial water consumption increased by 26 times, and municipal water consumption (urban and rural domestic water consumption) increased by 18 times. At present, the world population is growing at the rate of 8 1 10,000 per year, and it is expected to reach 9.4 billion in 2050, and the demand for water will also increase exponentially, making the situation even more tense. However, some authoritative population experts believe that with the improvement of people's culture and living standards and the development of family planning work, the population situation may change. They are seriously considering the possibility that in our lifetime, the world population growth will peak and then begin to decline irregularly.

The second is to change the concept and manage water as a scarce resource. This change in concept may save a lot of money. For example, in some cities of some third world countries, 60% of drinking water is lost due to rust of water pipes or illegal overlapping of pipes. The displacement of the main water pipe in Manila has reached 58% of the total water supply, while the average leakage of the water pipe in Singapore, which is relatively well managed, is only 8%. According to a survey report of the United Nations, the proportion of water wasted in Britain and the United States is about 12%, and the waste caused by leakage in industrialized countries is about 10%. Some areas can even save more water by taking measures to save water and recycle water. At present, there is no water war, but due to the increase of population and the improvement of people's living standards, the demand for water resources increases, and the control of upstream areas to downstream areas (the control of river flow by upstream) and other factors may ignite long-standing conflicts. At present, there are 2 15 international rivers and 300 groundwater basins and aquifers shared by several countries. These places are in great need of establishing good cooperative relations.

Third, replace or improve the traditional way of industrial and agricultural water use with high technology. The way humans use water resources is also an important reason to aggravate the shortage of water resources. Among the water resources consumed, municipal water accounts for 8%, industrial water accounts for 22%, agricultural irrigation water accounts for 70%, and the latter two accounts for 92%. The water consumption per hectare of irrigated farmland in developing countries is twice that of industrialized countries, but the output is only 1/3 of the latter. The reason is that there are different ways, one is flooding irrigation, the other is sprinkler irrigation or underground pipe irrigation. Because of the hot climate, half of the water in the former evaporates in the water storage area or when it flows through the open-air irrigation canal (generally, the evaporation amount is 1/8). The flooding method will also lead to soil degradation (salinization). In the first half of the 20th century,100000 hectares of land in the Indus plain of Pakistan were fully irrigated. However, waterlogging and high evaporation rate cause soil salinization and a large area of farmland is barren. FAO pointed out that adopting more effective irrigation methods can save 10%-30% of agricultural water. Underground canals have been used in oases such as Iran, Chile and Egypt in North Africa since ancient times, and water can be taken from wells several kilometers away. Israel adopts a more scientific method-modern underground drip irrigation technology. Israel is the country with the most water shortage, where "water is more expensive than milk". A bottle of mineral water costs 1.25 USD, and this 1.25 USD can buy four bottles of milk. In order to solve the problem of water shortage, Israel has been committed to developing new technologies for a long time. There, as long as there are green fields, there will be drip irrigation, which is a high-tech technology. The thin tube will spray water drops from small eyes every once in a while and accurately pour them to the roots of plants, only watering the plants without watering the land, and not wasting a drop. In Israel, buried drip irrigation, spray drip irrigation and decentralized drip irrigation were also invented.

Modern industry is not as greedy as agriculture, but it still uses a lot of water. Turning wastewater into pure water and then using it for irrigation or industrial circulating water is the only way to reduce industrial wastewater pollution, which has been adopted by more industrial enterprises. In developed countries, this technology is fully mature. As early as a few years or even more than a decade ago, all polluted rivers have been cleaned up. Israel will improve about 230 million cubic meters of wastewater into agricultural water every year, and this number is still expanding. The "polluter pays" principle will promote the rapid implementation of this method.

Fourth, build water conservancy to intercept flood and store water, and plant trees to protect vegetation and store water. Building water conservancy projects and turning harm into benefit are two internationally recognized examples. One is Valencia, Spain. This is a world-famous agricultural area. They have kept the ancient Arab irrigation system for thousands of years, and rational water use and distribution have always been the "iron law" they consciously abide by. The other is the Mississippi River in the United States, which is an outstanding example of river management with modern system engineering. The Mississippi River is 6262 kilometers long, with an average annual runoff of 580 billion cubic meters and a drainage area of 3.22 million square kilometers. It is the fourth largest river in the world, and about half of the population in the United States lives in this basin, with 34,000 square kilometers in the upper reaches of Canada. From May 65438 to May 0928, the United States Congress passed the Mississippi River Flood Control Act. Now this river has become a place to prevent disasters; River water resources development and utilization (power generation, irrigation, shipping, aquatic products, water supply, tourism, etc.). ); Examples of water conservancy projects with complete functions such as soil and water conservation, greening, vegetation protection, water source protection and ecological environment protection. It can prevent the flood with a return period of 100- 150 years, the annual navigation time is 325 days, and the freight volume has increased from1380,000 tons in 1980 to 585 million tons in1980. The irrigation area of the basin is 710.3 million hectares, of which the sprinkler irrigation area is10.57 million hectares. There are 27 large and small hydropower stations11in this basin, with a total installed capacity of 28.44 million kilowatts and an average power generation of 98.3 billion kilowatts, accounting for 18.6% of the United States. More than 50 reservoirs/kloc-0 have been built in its tributaries, and the effective storage capacity of 6 reservoirs with a storage capacity of more than 4.5 billion cubic meters exceeds 70 billion cubic meters. An important cause of natural disasters such as waterlogging and high temperature is the destruction of vegetation. According to scientists' experiments, a 25-year-old natural tree can absorb 150 mm of precipitation per hour, and a 22-year-old artificial water source forest can absorb 300 mm of water per hour. The bare ground only absorbs 5 mm per hour. 60% of precipitation in woodland is intercepted or evaporated by canopy, and 30% becomes groundwater. On the bare ground, about 55% of the precipitation becomes surface water loss, 40% is temporarily retained or evaporated, and only 5% seeps into the soil. The water conservation capacity of forest land is 7 times higher than that of bare land. A forest with an area of 6,543,800 mu is equivalent to a reservoir of 2 million cubic meters. The annual water conservation capacity of forests in China is 347.3 billion tons, which is equivalent to 75% of the total storage capacity of existing reservoirs in China. However, it is a great pity that the world lost 1.980 and 1.995 hectares of forest. In the past 200 years, more than 1/3 of the forests on the earth have been cut down or destroyed. At present, although the trend of forest area reduction in the world has not stopped, it has indeed attracted great attention. The slogans of "environmental protection" and "sustainable development" have spread all over the world, and various countries have introduced a series of powerful measures and achieved fruitful results in some countries.

Fifth, establish an aquatic fresh water industry to turn seawater into fresh water. As mentioned above, seawater accounts for 98% of the total water volume of the earth, which can be said to be inexhaustible. It is an ideal way for human beings to obtain fresh water from seawater. But so far, seawater desalination technologies are generally distillation and electrodialysis, which have been gradually abandoned because of high energy consumption and low water purity. With the increasing shortage of fresh water resources and the development of science and technology, the Millennium dream of seawater desalination will come true, and a new type of big industry-future aquaculture may appear in 2 1 century. At present, there are 1. 1 10,000 desalination plants in the world, and the daily output of desalinated seawater is about 5.36 billion gallons, of which Saudi Arabia accounts for 25.9%, ranking first in the world. The United States accounts for 15.2% of the total output, ranking second. The treated seawater in Gulf countries can meet nearly two-thirds of the drinking water demand in these countries. Thirty years ago, the total production capacity of the world was less than 200 million gallons/day, which proved that the output of seawater desalination increased geometrically. However, the investment in seawater desalination is quite large, with the Gulf countries alone investing more than 654.38 billion dollars, including billions of dollars for the operation and maintenance of seawater desalination facilities. Not long ago, another "reverse osmosis method" appeared. This method consists of multilayer wound films or hollow fiber bundles. When seawater or water to be treated is pressed in from one end, drinkable fresh water or pure water flows out from the other end. NAJIA VAL, a company on the banks of the Seine in France, has successfully developed a hand-pumped seawater desalination device, which can turn 1 liter of seawater into one kilogram of fresh water within 10 minute. At present, this device can only benefit the needs of islands, fishing villages and fishing boats, and its next development may form a large-scale seawater desalination technology. According to the data of the International Atomic Energy Agency, the use of nuclear energy to desalinate seawater is attracting people's interest in water-deficient countries. The aquatic fresh water industry also includes writing articles on poles and ice. Australia plans to cover domestic icebergs with plastic sheets to reduce evaporation. The six Gulf countries plan to drag icebergs from the Arctic Ocean to the Gulf by boat and then melt them into fresh water.