Shulou(Shulou.com)11/24 Report--

From small to big, we will all be taught to save water. If you don't turn off the tap casually, you will be greeted by a bloody meal. But when you grow up, someone suddenly tells you that water is infinite-because it circulates, the water we use will return to our cups in various ways, which is a renewable resource, and even fresh water is inexhaustible. Is that true? Is this another lie made up by scientists?

First of all, we need to know how water is stored. The vast majority of the earth's water is salt water, and fresh water accounts for less than 3%, of which ice sheets and glaciers account for the majority. Groundwater accounts for the majority of the parts that can be directly used by human beings, and most of the groundwater is deep groundwater, so it seems that there is very little that human beings can use directly. However, if you count the total amount, it is still a very large quantity, with an order of magnitude of 100 trillion tons.

Water body

Volume (km3 x 106)

Percentage of the total

Ocean

1370

97.25

Ice sheet and glacier

twenty-nine

2.05

Ground water

9.5

0.68

Lake

0.125

0.01

Soil water content

0.065

0.005

Atmosphere

0.013

0.001

The amount of water on the earth's surface (PhysicalGeography.net) China's annual water consumption is about 600 billion tons. In this way, the annual global water consumption is only a few trillion tons. It seems that human beings can last for more than a hundred years without saving water. However, only a small part of this water can be used by humans, which is about 1 trillion tons [2]. Even with the recycled part of these water resources, it is still not optimistic. The scientific community uses the benchmark water pressure to describe the water pressure in a region, which is calculated by the ratio of total water intake to renewable water supply. The higher the value, the greater the pressure. Most of northern China is in extremely high water pressure. It can be seen that the problem is not that the water cycle leads to an inexhaustible supply of water, but that even with the water cycle, we are under extremely high water pressure.

The reference water pressure in China (Zhong Lijin et al., 2016) the speed of water cycle is also different in different bodies of water. The residence time in the atmosphere is relatively short, with an average of 9 days, most rivers cycle once every 3 months to 6 months, and the lake time is mainly concentrated in the period of 50 to 100 years, while the shallow groundwater takes more than 100 years. These bodies of water are the main source of water for human use, but they are being threatened to varying degrees.

Groundwater: the subsidence of urban groundwater is one of the main sources of water in the city. However, the replenishment of groundwater is a slow process, and excessive absorption of groundwater will inevitably lead to the loss of surface support and subsidence. The cumulative settlement in Shanghai was 2.63m from 1921 to 1965, and the maximum cumulative settlement in Tianjin from 1959 to 1982 was 2.15m. The subsidence of the two cities has been effectively controlled after reducing the amount of groundwater exploitation. The two cities have access to water in other ways to make up for the deficit caused by reducing groundwater. However, in some cities in the northwest, groundwater has almost become the only source, and as a result, the Xi'an clock tower has sunk nearly 400 mm, and the Great Wild Goose Pagoda, which has stood for thousands of years, even tilted thousands of mm [4].

The clock tower of historical and cultural business cards in Xi'an has been facing the risk of subsidence. In addition, groundwater pollution is also a serious problem. The pollutants in the soil are carried to the aquifer with precipitation, but we do not know the specific situation in which the water is polluted. The exploration, protection and sustainable utilization of groundwater will become a core content of human water use in the future [5]. Therefore, the theme of "World Water Day" in 2022 is "cherish groundwater and cherish hidden resources". The theme of "China Water week" commemorating "World Water Day" in 2022 is "promoting the over-exploitation of groundwater to comprehensively control the ecological environment of Fu River and Lake".

Rivers and lakes: the dilemma of water intake and pollution if groundwater is too hidden to explore, there is no such problem with surface runoff. They are another major source of urban water, have a closer relationship with human beings, and, of course, are more seriously affected by the development of human society.

With the development of economy and society, rivers and lakes in China are generally polluted, none of the seven major river systems are immune, while lakes are generally eutrophicated. This situation was most serious at the end of the last century and the beginning of this century. Among the seven major river systems, the quality of Huaihe River, Yellow River and Haihe River is relatively poor, of which Huaihe River is the most. In the Huaihe River basin, Xuyi area has been inferior to five categories for 100 days in a row, and Bengbu even appeared the phenomenon of "drinking mineral water in the Huaihe River". By 2014, the poor water quality still accounted for 20% of the river length. In the lake pollution, the pollution of Dianchi Lake is the first to bear the brunt. As one of the earliest control projects in the history of pollution control in China, the water quality of Dianchi Lake still belongs to mild pollution and moderate eutrophication. Another difficult problem in the treatment of Chaohu Lake is mild pollution and mild eutrophication [7].

On the one hand, rivers and lakes are the sources of water, on the other hand, they are the main destinations of sewage discharge. Social development will promote the development of both, and the needs of the two contradict each other. At present, the more effective way to deal with this contradiction is to carry out strict sewage treatment and water source protection. In recent years, under the strict efforts of several rounds of national environmental protection supervision and inspection, some more serious water pollution problems have been dealt with and the national water quality has been improved. how to maintain such a good situation still requires a lot of efforts.

2020 overall surface water quality in China (2020 China Environmental Bulletin) atmosphere: the threat of climate change the atmosphere is the fastest and most unstable of all water bodies in the water cycle. The Asian monsoon region has a deep understanding of this unstable precipitation. The heavy precipitation in Henan in July and in Shanxi in October in 2021 is much higher than that in the same period of history. In winter, the water shortage crisis is caused by the lack of precipitation in South China. According to the United Nations Global Water Development Bulletin 2020, the seasonal variation of available water in most areas is relatively large, and atmospheric precipitation is the main influencing factor of this change.

Seasonal changes in available water use (World Water Development Bulletin 2020) to make matters worse, climate change will exacerbate this change and change the distribution of water between regions. The impact of climate change on precipitation is a topic of great concern in the scientific community, and it has basically become the consensus of the scientific community that the extreme nature of precipitation increases with the warming of the climate. In terms of details, the researchers found that precipitation variability increases with global warming on all time scales from synoptic scale to monthly, intraseasonal and interannual. In the context of global climate change, most regions are faced with an increase in precipitation variability. Drought and flood coexist, which will be the future that most people will have to face.

The variability of precipitation and the change of average precipitation, blue and green for more changes (Zhang Wenxia et al., 2020) obviously, freshwater resources seem endless, but the water resources available for human direct use are extremely tight. Over the past 100 years, global water use has increased sixfold, and global water consumption is still increasing at a rate of 1% a year [9]. In front of us is a growing water gap and a more and more serious water crisis.

Therefore, what we need to think about today is not whether to save water, but how to save water better. Even in areas with rich water resources, we should establish a sense of water conservation; in addition, for the sake of our future health, we should also protect these precious water resources from pollution. To protect water resources is to protect our future.

reference

[1] China Water Resources Bulletin 2020 [J]. Water Resources Development and Management, 2021 (08): 2.

[2] Global water resources status [EB / OL]. [2017-02-03]. Http://www.waterfoundation.cn/ news / information / 212.html.

[3] China Geological Environment Information Network. Geological hazard-land subsidence [EB / OL]. [2015-05-20]. Http://www.xian.cgs.gov.cn/ kpzs / dxzs / 201608 / t20160813_358786.html.

Zhang Xiaosong, Han Jie. Groundwater overexploitation leads to the tilt of Xi'an Millennium Big Wild Goose Pagoda [EB / OL]. [2006-10-11] https://www.cgs.gov.cn/ ddztt / ddyw / djgj / mtgz / 201603 / t20160309_290892.html

[5] UNWATER.GROUNDWATER-MAKING THE INVISIBLE VISIBLE [EB/OL] .https://www.worldwaterday.org/learn.

[6] Xinhua News Agency. The situation of water pollution in the Huaihe River Basin is still grim. The five-class water quality accounts for 20% of the total water quality in the Huaihe River [EB / OL]. [2014-10-27] http://www.gov.cn/ xinwen / 2014-10 Universe 27 / content_2770893.htm.

[7] State Environmental Protection Administration. 2020 China Environmental State Bulletin [R]. 2020.

[8] Zhang W, Furtado K, Wu P, et al. Increasing precipitation variability on daily-to-multiyear time scales in a warmer world [J]. Science advances, 2021, 7 (31): eabf8021.

[9] UNESCO.2020 UN Water Development report [R]. 2020.

This article comes from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), author: Xing Si, American Editor: Liu Yuling

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