Safety analysis of precipitation water supply in China

I. Distribution of Annual Per Capita Precipitation in China

Water consumption refers to the total water consumption allocated to users, including the loss of water, according to the statistics of agricultural, industrial and domestic water consumption. Agricultural water includes farmland irrigation water and forest, animal husbandry and fishery water; Domestic water includes urban residents' domestic water, public water, rural residents' domestic water and livestock water; Industrial water is newly used water, not including the reuse within the enterprise.

Affected by monsoon climate, the temporal and spatial distribution of rainfall in China is extremely uneven. The average annual rainfall in China decreases from southeast to northwest, from 1600mm in the southeast to less than 200mm in the northwest (attached figure 1). China's population distribution is more in the southeast than in the northwest, so we can draw a line from Heihe City, Heilongjiang Province to Tengchong County, Yunnan Province. The southeast of this line is densely populated, accounting for only 43% of the country's total area, but the population accounts for 94% of the country's total population; Northwest China is vast and sparsely populated, accounting for 57% of the country's total area and only 6% of the country's population.

According to the climatic precipitation in China and the population distribution in China, the per capita precipitation distribution map of China for many years is divided into five regions (Attached Figure 2), and the zoning situation is as follows:

Ⅰ. Areas where precipitation is fully utilized. Including most of Xinjiang, northwestern Gansu, western Inner Mongolia and northwestern Qinghai. The area is vast, located in the frontier and inland, with many mountains, plateaus and deserts. Belonging to a resource-scarce area, water resources are "congenital" insufficient, with extremely uneven distribution, and "acquired" water resources utilization efficiency is low. The area is dominated by desert, lacking of flat land, harsh natural environment, extreme climate and insufficient rainfall. The average annual precipitation is less than 200 mm, which brings difficulties to the development of agriculture. The production and domestic water in this area is mainly stored in puddles. The area is remote, with inconvenient transportation, short development history, weak economic foundation and small population, so the per capita water consumption in this area is mainly rainfall.

Ⅱ. Areas with sufficient precipitation utilization. Including Tibet, central Qinghai, central Gansu and Inner Mongolia. The plateau in northern Tibet is 4700 ~ 5500 m above sea level, with a monsoon dry climate in the cold region of the plateau, the average temperature in the warmest month is lower than 6℃, and the annual precipitation is100 ~150 mm. It is a vast natural pasture. From June 10 to April of the following year, the sky above the Tibetan Plateau is westerly jet, and the ground is controlled by cold and high pressure, with drought and strong wind, low temperature and little rain and snow, and the precipitation only accounts for 10% ~ 20% of the annual precipitation. For example, the precipitation from June 10 in Lhasa to April of the following year only accounts for 3% of the annual precipitation, so it is called dry (dry) season or windy season. The whole territory of Inner Mongolia is dominated by plateaus, and the elevation of most areas is above 1000 meters. The main mountain ranges are Daxinganling, Helan, Wula and Daqingshan. The eastern grassland is vast and the western desert is widely distributed. This area belongs to temperate continental monsoon climate. Due to the vast territory, there are great differences among regions. There are four distinct seasons in most areas, with short summer and long winter, which are relatively dry and cold. The annual average temperature is-1℃ ~10℃; The annual precipitation is about 50 ~ 450 mm, which is reduced from 500 mm to about 50 mm from east to west due to the influence of topography, distance and ocean distance. On the contrary, the evaporation decreases from 3000mm to1000mm from west to east. The surface water in this area is richer than that in areas where precipitation is fully utilized.

ⅲ. moderate precipitation utilization area. Including the southwest and most areas north of the middle and lower reaches of the Yangtze River. Sichuan is located in the subtropical zone, which is affected by complex topography and different monsoon circulation alternately, and its climate is complex and diverse. The eastern basin has a subtropical humid climate with an annual precipitation of 900 ~ 1200mm. Most of the climate in the middle and lower reaches of the Yangtze River belongs to the north subtropical zone, and a small part belongs to the northern edge of the middle subtropical zone. Annual precipitation 1000 ~ 1400 mm, concentrated in spring and summer. The area has developed water system, rich groundwater resources and dense population.

Ⅳ. Areas with insufficient rainwater utilization. Including northwest Sichuan, Loess Plateau, North China and Northeast China. Northeast China is located in the humid and semi-humid monsoon climate zone in China. Winter is cold and dry, and summer is warm and rainy. Northeast China spans three temperature zones (warm temperate zone, middle temperate zone and cold temperate zone) and two dry temperate zones (humid and semi-humid zones). North China belongs to warm temperate semi-humid continental monsoon climate: dry and windy in spring; Summer is hot and rainy; It is cool and rainy in autumn; It is cold and snowy in winter. The area is rich in groundwater and surface water, and its population is less than that in the middle and lower reaches of the Yangtze River.

ⅴ. Areas with insufficient utilization of precipitation. Including south China and the south of the middle and lower reaches of the Yangtze River. The annual precipitation in most parts of South China is 1400 ~ 2000 mm, which belongs to tropical-south subtropical region with high temperature and rainy. There are many zonal vegetation, such as tropical rain forest, monsoon forest and subtropical monsoon evergreen broad-leaved forest. Vegetation is mostly tropical shrubs, subtropical grass slopes and small secondary forests. Tropical forest animals are rich and diverse, and there are many typical species of oriental animals. The population of South China is 654.38+69 billion. If Hong Kong, Macao and Taiwan are added, it will reach 200 million. The area south of the middle and lower reaches of the Yangtze River is flat, rich in water and heat resources, with a long history of development, developed industry and agriculture, convenient transportation and many cities, so the population density is high. The surface water system is developed, the groundwater resources are abundant, and the rainfall utilization in this area is insufficient.

Two. Regional distribution map of acid rain in China

Acid rain refers to rain, freezing rain, snow, hail, dew and other atmospheric precipitation with pH less than 5.6. A large number of environmental monitoring data show that the cloud water over most parts of the earth is becoming sour due to the increase of acidic substances in the atmosphere. If it is not controlled, the area of acid rain area will continue to expand and the harm to human beings will increase day by day.

The formation of acid rain has three reasons:

(1) acidic pollutants. The combustion of petroleum, coal and other minerals, chemical plants, power plants, automobiles and so on will discharge a large number of nitrogen oxides, sulfides, ammonia and so on. After these gases reach a certain concentration in the air, they will combine with water vapor in the atmosphere to form acidic substances such as sulfuric acid and nitric acid, and then land on the ground in the form of rain, snow and fog.

(2) Soil that is extremely sensitive to acidic substances. For example, in the southwest of China, the soil is mostly acidic red soil, and many acidic substances are usually suspended in the air here, so these areas are prone to acid rain.

(3) closed terrain. In areas with poor ventilation conditions, the wind speed is low, the air fluidity is poor, and air pollutants are not easy to spread, which leads to frequent acid rain.

In 2006, the regional distribution of acid rain in China was basically stable. Cities with annual precipitation pH less than 5.6 (acid rain) were mainly distributed in the south of the Yangtze River, including Jiangsu, Shanghai, Zhejiang, Fujian, Jiangxi, Hubei, Hunan, Guangdong, Guangxi, Hainan, Guizhou, Sichuan, Chongqing, Yunnan and other provinces (autonomous regions and municipalities). Jiaodong Peninsula and Tumen River are two local areas. The latter two "acid rain" islands are formed because there are big cities (Changchun and Jilin) nearby and there are strong sources of acidic substances. On the other hand, they are close to the ocean (Qingdao), and the humid climate of the ocean provides a hotbed for acid rain.

The acid rain area in China can be divided into four areas (Attached Figure 3). The zoning situation is as follows:

Ⅰ. Acid rain-free areas. The pH value in precipitation is greater than 5.6, and its range is mainly in most parts of the north. There are four main reasons why there is no acid rain in northern China:

(1) soil. The content of alkali metal ions and pH value in soil are one of the important factors affecting the formation of acid rain. The main alkaline ionized calcium (Ca2+), magnesium (Mg2+) and ammonium (NH4+) in precipitation in China mainly come from soil. The soil in northern China is alkaline, with a pH of 7-8. The south is slightly acidic, with a pH value of 5 ~ 6. The contents of alkali metal sodium (Na) and calcium (Ca) in soil gradually increased from south to north, especially in Huaihe River basin and Qinling Mountain area. Because about half of the particulate matter in the air comes from soil, ammonia volatilization in alkaline soil is greater than that in acidic soil, so the alkaline substances in the atmosphere in northern China are much higher than those in the south, which leads to acid rain mainly occurring in the south with low alkaline substances content and low pH value.

(2) ammonia. Ammonia (NH3) is a common gaseous alkali in the atmosphere, which is easily soluble in water and can neutralize acidic substances in the atmosphere or rainwater, thus reducing the acidity of rainwater. For example, NH3 can react with sulfur dioxide (SO2) in the presence of water to generate ammonium sulfate and ammonium sulfite, thus neutralizing acidic substances. Generally, the NH3 content in acid rain area is one order of magnitude lower than that in non-acid rain area, indicating that ammonia plays an important role in the formation of acid rain. Ammonia in the atmosphere mainly comes from the decomposition of organic matter and the volatilization of nitrogen fertilizer applied in farmland. The volatilization of ammonia in soil increases with the increase of soil pH value. The soil in northern China is alkaline and acidic, and the ammonia content is high in the north and low in the south, which is an important reason why acid rain is mainly distributed in the south and less in the north.

(3) Atmospheric particulate matter. Alkali metals and alkaline earth metals in precipitation mainly come from particulate matter in the atmosphere, and particulate matter mainly comes from dust flying on land. Compared with foreign countries, the concentration of atmospheric particulate matter in China is large, especially coarse particulate matter, with significant differences between north and south. The northern region is dry, the soil is bare and the concentration of atmospheric particles is high. The average content of total suspended particulate matter (TSP) in the atmosphere is 426 μ g/m3, which is about twice that in the south. By harnessing the environment, the concentration of atmospheric particulate matter has been continuously reduced, but the relative level of atmospheric particulate matter concentration in the north and south has remained unchanged. Not only is the concentration of particulate matter in the north higher than that in the south, but the ratio of alkaline substances to acidic substances in atmospheric particulate matter in the north is also higher than that in the south. For the same precipitation, the buffering capacity of atmospheric particles in the north is much greater than that in the south. This is because atmospheric particulate matter mainly comes from land dust, and its composition is basically the same as that of soil, and the acidity and alkalinity of particulate matter mainly depends on soil properties. Due to the high content of alkaline substances in the soil in the north, the concentration of alkaline substances in the atmospheric particles in the north is also higher than that of acidic substances, and these atmospheric particles have great neutralization and buffering ability for acidic precipitation in rainfall; On the contrary, the concentration of alkaline substances in atmospheric particles in the south is low, and its buffering capacity is lower than that in the north (for example, the neutralization capacity of atmospheric particles in Beijing in spring is three times that of particles in Liuzhou). Therefore, the competition between the acidification of rainwater and the neutralization of alkaline substances leads to no acid rain in most parts of the north, while there is a large area of acid rain in the south.

(4) The solar intensity in northern China decreases with the increase of latitude, and the atmospheric humidity in China also decreases from south to north. Therefore, other things being equal, SO2 in southern China can be transformed into sulfuric acid faster than that in northern China, acidifying the local atmospheric environment and forming acid rain through precipitation erosion. Therefore, the acid rain areas in China are mainly distributed in the south, and the north is relatively light.

Ⅱ. Weak acid rain area. The pH is 5.0 ~ 5.6, and the main scope includes Sichuan, Guizhou, Fujian, Guangdong, Guangxi, Hainan and other provinces (regions). In 2 1 cities in Sichuan Province, except Deyang, Dujiangyan and Marcand, acid rain occurred in other cities. Among them, there are 6 cities with acid rain frequency greater than 40%. The five-year average frequency of acid rain in this 2 1 city is 28.5%, and the amount of acid rain accounts for 37.7% of the total rainfall. The main reason for frequent acid rain is SO2 in coal-fired power plants.

During the Ninth Five-Year Plan period, the precipitation in the acid rain control area of Fujian Province was acidified to some extent. The annual average pH of precipitation is 5.20 ~ 5.35, lower than 5.6, and the frequency of acid rain is 29. 1% ~ 55.6%. All cities in the acid rain control area of Fujian Province, except Sanming City and Longyan City, have low concentration of particulate matter in the air and weak acid buffering capacity. In addition, the soil in Fujian province is mainly red soil with strong acidity, and the pH value is 5.0 ~ 5.5. Soil dust cannot provide an effective acidification buffer and neutralization mechanism for precipitation. In addition, the subtropical humid climate, strong solar radiation, high temperature and high air humidity in this province have a strong air oxidation atmosphere, which is conducive to the transformation of acid precursors SO2 and nitrogen oxides (nitrogen oxides). Therefore, although the content of acid-causing substances in the air of this province is small, the buffering and neutralizing effect of precipitation on the acid-causing process is weak, showing an acidification trend.

The most striking feature of southwest China is the steep mountains (especially in Guizhou), and the city is surrounded by these middle and low mountains, which leads to the occlusion of the terrain and the difficulty of gas diffusion and convection. Therefore, no matter SO2 produced by coal burning or nitrogen oxides discharged with the increase of the number of motor vehicles, except a few directly return to the ground, most of them gather over the city, and then return to the ground under the scouring of rain, forming acid precipitation; Because the soil in this area is mostly acidic, the particulate matter in the atmosphere mainly comes from the dust flying on the land, and the particulate matter in the atmosphere is also slightly acidic, so the buffering capacity of sandstorm dust is low and the acidity of precipitation naturally increases; The widely distributed forest vegetation in this area covers a large area, which also makes it difficult for pollutants to spread and become a strong acid rainfall area; Climate conditions have a very important relationship with the serious pollution of SO2. First, the climate in this area is warm and humid, which is favorable for the transformation of SO2 and nitrogen oxides into acids. Second, the mountain wind is obvious, and the mountain wind and valley wind alternate during the day and night, which makes the air pollutants fluctuate in the region and difficult to spread, which aggravates the acid rain pollution in the region; Thirdly, this area is also a lightning-prone area (Liuzhou, Guangxi is an example). Lightning can increase the concentration of nitrogen oxides and accelerate the oxidation of SO2 and nitrogen oxides.

Iii. Acid rain area: the pH value is 4.5 ~ 5.0, mainly including Chongqing, Hunan, most of Jiangxi, southern Zhejiang, Taiwan Province and other areas. See Table 4- 1 for the monitoring results of 36 precipitation monitoring points in Chongqing during 1998. Statistics show that the average pH value of precipitation in Chongqing is 4.88, the average pH value of acid rain is 4.59, the frequency of acid rain is 45.6%, and the amount of acid rain accounts for 49.8% of the total precipitation. The changing trend of acid rain intensity and frequency is outer suburbs > urban areas > suburbs, showing the spatial mobility of acid rain.

According to the monitoring data of precipitation pH value from1993 to 2007 in the main city of Chongqing, the changing trend of acid rain in Chongqing since 15 was analyzed. The results show that: ① the pH value of precipitation in the main urban area of Chongqing is low, and the average pH value from 2002 to 2007 is between 3.8 and 4.5. In the monthly variation of 6 years, the precipitation acidity is high in summer and low in winter, and the acid rain frequency is low in summer and high in winter. The change of acid rain intensity is mainly affected by factors such as pollution source discharge. (2) The pH value of annual precipitation in Chongqing basically shows an upward trend. In each season, the interannual variation of pH in autumn showed an obvious fluctuation trend, while the other three seasons showed a weak fluctuation state, with no obvious fluctuation trend. ③ The frequency of acid rain (pH < 5.6) in Chongqing is relatively high, and the frequency of acid rain in each season is basically above 80%, and that in most years is above 90%. Frequency of annual precipitation pH < 5. There are six in Chongqing, with ups and downs. The frequency of acid rain in Chongqing shows an obvious upward trend in spring, with a weak fluctuation in summer and winter, and a large fluctuation in autumn, with no obvious upward and downward trend. ④ Acid rain frequency (pH < 4. 5) The intensity of Chongqing varies greatly from 30% to 80% over the years. Frequency of annual precipitation pH < 4. Chongqing 5 fluctuates violently, and the changing trend is not obvious.

Table 4- 1 1998 Monitoring Results of Precipitation in Chongqing

Acid rain is a comprehensive function of atmospheric chemical process and atmospheric physical process, in which the emission of acid-causing precursors and the diffusion conditions of atmospheric pollutants are the main reasons for acid rain pollution. The discharge of acidic precursors is the fundamental cause of acid rain in Chongqing. For a long time, Chongqing's energy consumption has been dominated by raw coal. In 2004, the city * * * consumed 290×108kg standard coal, of which180×108kg standard coal accounted for 62.4% of the total energy consumption. In particular, Chongqing is the main producing area of high-sulfur coal in China. In 2004, the annual output of coal was 300× 108kg, of which more than 9 1% was high-sulfur coal with sulfur content exceeding 3%. The extensive use of high-sulfur coal leads to a large number of SO2-based sulfide emissions. In 2005, the industrial waste gas emission in Chongqing was 3650× 108m3, of which SO2 emission was 6.8× 108kg.

In the main urban area of Chongqing and its surrounding areas, there are heavily polluting enterprises such as Chongqing Power Plant, Jiulong Power Plant, Huaneng Road Sulfur Power Plant and Chongqing Iron and Steel Co., Ltd., which produce a large number of nitrogen oxides, but they have not taken effective measures to control the emission of nitrogen oxides. At the same time, with the rapid development of social economy, the number of motor vehicles in Chongqing has increased rapidly in recent years. The rapid increase in the number of motor vehicles leads to an increase in the total emission of nitrogen oxides. In addition, the use of inferior oil, diesel construction machinery mainly serving construction sites, traffic congestion, and the difficulty in effectively solving the problem of CNG vehicle gas supply have all aggravated the pollution of nitrogen oxides in urban areas, especially in urban areas.

In atmospheric particles containing elements such as iron, copper, magnesium and vanadium, a large number of SO2 and nitrogen oxides react as acidic catalysts. Or under the oxidation of lightning, etc. Sulfuric acid, sulfurous acid, nitric acid and their salts are generated by gas phase or liquid phase oxidation reaction, which become the main anionic components in the precipitation.

The special terrain of Chongqing is an important reason for the serious acid rain pollution in the main city. Chongqing is located in the east of Sichuan Basin, bordering Daba Mountain in the east and northeast, and Guizhou Plateau in the south and southeast. This special topographical condition leads to high annual static wind frequency and low annual average wind speed in Chongqing, with the annual average wind speed below 1m/s in low-lying valley areas and behind prevailing winds. The atmospheric stability is mainly neutral, with high inversion frequency, long duration, high inversion intensity and thick mixed layer in urban areas. Fog is easy to form under the inversion layer, which makes it difficult for pollutants near the ground to spread outward. The above harsh atmospheric diffusion conditions are not conducive to the translational diffusion and vertical diffusion of pollutants. Especially for the main urban area, the Yangtze River and Jialing River cross it, with hills and valleys accounting for 76%. The peaks and valleys are staggered, and the basin and hills are staggered. The mountain wind and valley wind are obvious, and the mountain wind and valley wind alternate during the day and night. The benefits of urban heat island are remarkable, which makes the air pollutants in the area fluctuate and difficult to spread out, which aggravates the acid rain pollution in Chongqing.

In 2004, four cities in Hunan Province/KLOC-0 reported the monitoring data of precipitation pH value. Among them, acid rain samples with pH≤5.6 account for 76.4%. The pH value of a single precipitation sample is 3.05 ~ 8.24.

Ⅳ. Strong acid rain area: The pH value of precipitation is less than 4.5, and the main range of acid rain includes Shanghai and northeastern Zhejiang. From 2002 to 2005, the statistical results of annual average precipitation pH value and acid rain frequency at 22 monitoring points in Shanghai are shown in Table 4-2 and Table 4-3 respectively.

Table 4-2 Statistical Results of Annual Average Precipitation pH at 22 Monitoring Points in Shanghai from 2002 to 2005

Table 4-3 Statistical Results of Acid Rain Frequency at 22 Monitoring Points in Shanghai from 2002 to 2005

The monitoring results show that from 2002 to 2005, the proportion of points with pH less than 5.6 in Shanghai increased year by year, and the phenomena of strong acid rain (pH less than 5.0) and strong acid rain (pH less than 4.5) increased year by year. The frequency of acid rain is increasing year by year. In 2004 and 2005, the frequency of acid rain in two monitoring points and four monitoring points was above 75% respectively.

As a megacity with population and economic development in China, Shanghai's coal consumption per unit GDP has been declining, but the absolute amount of coal consumption is still very large. In recent years, Shanghai's coal consumption has been rising, and sulfur dioxide emissions have also risen rapidly. At the same time, due to the shortage of energy supply, the quality of coal is declining, and the sulfur content of coal is increasing, which leads to the increase of SO2 concentration in the ambient air in Shanghai, which leads to the increasingly serious acid rain pollution. The environmental air pollution in Shanghai belongs to the compound pollution of paying equal attention to soot and oil, but the dust pollution is the main pollution, which is acidic and has little buffering capacity to acid rain. The annual increase of dust in the ambient air in Shanghai has aggravated the degree of acid rain pollution. At the same time, the soil in Shanghai belongs to acidic soil in the south, and acidic soil particles enter the air through secondary dust, which slows down the buffering capacity of acid rain and intensifies the pollution degree of acid rain. Shanghai belongs to the northern subtropical monsoon climate, with abundant sunshine, abundant rainfall and distinct four seasons. The dominant wind direction in Shanghai is east-southeast wind, southeast wind in spring and summer, northeast wind in autumn and northwest west wind in winter. From 2002 to 2004, the maximum frequency of acid rain in Shanghai appeared in winter and the minimum frequency appeared in summer. The seasonal variation of acid rain is closely related to the pollution situation and meteorological conditions in each quarter. Usually, in winter, the atmospheric stratification is stable, and the frequency of inversion increases obviously, which inhibits the diffusion of pollutants and is prone to high-concentration air pollution; The high wind speed and weak atmospheric stability in summer are conducive to the diffusion of pollutants, and the pollution level is relatively low.

According to the monitoring data of acid rain in Zhejiang Province in 2002 by Zhejiang Environmental Monitoring Station, in 2002, the frequency of acid rain in Hangzhou was 73.6%, and the average pH value of precipitation was 4.68. The frequency of acid rain in Lin 'an was 97.5%, and the average pH value of precipitation was 4.04. The pH values of precipitation in other counties (cities) were all less than 5.60. See Table 4-4 for the pollution degree of acid rain.

Table 4-4 Acid Rain Pollution Grade

According to Table 4-4 and the analysis of precipitation monitoring results, Hangzhou was covered by acid rain in 2002. The area of heavy acid rain area is 13625km2, accounting for 82. 1% of the total area of the city. These areas are Hangzhou, Tonglu, Chun 'an, Yuhang, Lin 'an and jiande city. The acid rain area (Xiaoshan) is 1 163km2, accounting for 7% of the city's total area; Fuyang is a moderate acid rain area, accounting for 10.9% of the city's total area. From 1998 to 2002, the mass concentration ratio of sulfate so42- to nitrate NO3- in precipitation in Hangzhou and Yuhang showed a downward trend, and the contribution of so42- to precipitation acidity gradually decreased. The main reason is that the number of motor vehicles in Hangzhou is increasing year by year (the five-year growth rate is 392.8%), which leads to the increase of nitrogen oxide emissions and the gradual increase of NO-3 mass concentration in precipitation. The mass concentration ratio of SO2-4 to NO-3 in jiande city is slowly increasing. Coal and petroleum are the main industrial energy sources in Hangzhou, accounting for 3 1% ~ 37% of the city's total energy consumption. SO2 produced by the combustion of coal and petroleum is the main factor leading to the acidity of precipitation during the Ninth Five-Year Plan period, which is called "acid rain precursor". SO2 discharged into the atmosphere in Shanghai will continuously spread to the surrounding areas, which is called "long-distance transportation of acid rain precursors". In winter and spring, the dominant wind direction is downwind from north to northeast, which has a superposition effect on the formation of acid rain in northern Zhejiang, such as Hangzhou. Exotic acid rain precursors may be a factor that cannot be ignored. Compared with the north, the concentration of total suspended particles in the air in Hangzhou is low, and its soil is mainly paddy soil, and the pH value of the top soil is about 5.74, so soil dust can not effectively buffer the acidification process of precipitation.

Three, the national atmospheric precipitation safety analysis map

According to the national multi-year per capita precipitation distribution map and the national acid rain regional distribution map, China's atmospheric precipitation safety is divided into four regions (Attached Figure 4), and the zoning situation is as follows:

Ⅰ. Relatively safe area for atmospheric precipitation water supply. Per capita rainfall is sufficient, and there is no acid rain. The main areas are Xinjiang, western Tibet, northwest Gansu, northwest Qinghai and Inner Mongolia.

Ⅱ. Safe area for atmospheric precipitation water supply. Average rainfall per capita is moderate, with acid rain in some areas, mainly covering southeastern Tibet, Sichuan, Yunnan, western Guangxi, Guizhou, Hunan, Hubei, Chongqing, Henan, northern Anhui, northern Jiangsu, Shaanxi, southeastern Gansu, Shanxi, Hebei, Shandong, Tianjin, Beijing, Liaoning, Jilin and Heilongjiang.

Ⅲ. The atmospheric precipitation and water supply in the whole area are relatively unsafe. The per capita rainfall is insufficient, and the pH of acid rain area is 4.5 ~ 5.0, mainly covering eastern Guangxi, Guangdong, Fujian, Jiangxi, southern Anhui, southern Jiangsu, southern Zhejiang, Hainan and Taiwan Province Province.

Ⅳ. Atmospheric precipitation and water supply are unsafe areas. The per capita rainfall is insufficient, and the pH value in strong acid rain areas is less than 4.5, mainly concentrated in Shanghai and northeastern Zhejiang.