Fei Yu-hong^1,2, Zhang Zhao-ji², Zhang Feng-e², Chen Jing-sheng², Chen Zong-yu², Wang Zhao²

(1. Hohai Univerty, Nanjing 210098; 2.Institute of Hydrogeology and Environmental Geology, CAGS ,Shijiazhuang 050061)

^* Grant Project：The Project Supported by Natural Science Foundation of Hebei Province “Hebei province south-to-north water diversion midline underground potential (SN: 403614); the broad subject matter of National Land and Resource “The foreground for sustainable exploitation and utilize of groundwater in North China” (Project SN: 20023064).

The brief introduction of author: Fei Yuhong (1960-), female, from Shanghai, Researcher, in-service doctor of Hohai University, mainly engaged in water resource research. E-mail:yuhong_fei@163.com

Abstract: The North China Plain is an important producing area of domestic foodstuff. The underground water resources are main water supply source of this district. Under influence from increasing produced quantity and climate change, water resources restrict its development. With the trends of decreasing precipitation and ascending air temperature in recent years especially, originally tiny water resources weaken the supply resources much more. With analysis of precipitation, evaporation, surface runoff, changes of underground water flow field and series changes of underground water resources, it is thought that the factors such as decreasing precipitation, ascending air temperature, human riparian work and exploitation of underground water etc are important to cause the decrease of the water resources in this district.

Key words: Water Resources; North China Plain; Climate Change; Human Activities

The water for living and plant water of industry and agriculture in the North China Plain adopt mainly underground water. The produced quantity of underground water accounts for about 70% of overall water consumption according to the statistics. Under the influence from a series of factors such as the exploitation of underground water, superterranean hydraulic engineering, precipitation, evaporation etc in recent 50 years, the short of water resources became more and more conspicuous.

1 General Description

1.1 Geographic position

     North China Plain lies between east longitude 112°~120° on westward of Bohai Sea, north latitude 35°~43° on northward of Yellow River (Figure 1), including whole of Beijing, Tianjin, Hebei province plain, and the plain in Shandong province and Henan province to the north of Yellow River.

The Haihe River valley is the main river of North China Plain. There are Luanhe River, 3 rivers in north (Including: Jiyunhe River, Chaobaihe River, Beiyunhe River), Yongdinghe River, Daqinghe River, Ziyahe River, Zhangweihe River, Tuhaimajiahe River from north to south. There are 4 water resources computing subregions according to the characteristics of valley: coastal Luanhe River to the east of Hebei Province, the north of Haihe River, the south of Haihe River and Tuhaimajiahe River. By formation cause and morphological characteristic, they can be differentiated as alluvial and flood clinoplain in piedmont, alluvial plain to the middle and east, alluvial plain and marine plain on contiguity to the sea

1.2 Hydrology characteristic

The North China Plain is dry or semiarid area, where multi-year average precipitation is 556.0mm. The distribution of precipitation in a year is very asymmetric, the 75~85% of which is concentrated between June and September. The continuous high-flow year or continuous low-flow year is the characteristic of precipitation.

The source of surface runoff mainly relies on precipitation. The distribution of high-flow and low-flow, terrain and time has analogy with precipitation code. Multi-year average annual runoff depth is 41.0mm and the runoff coefficient is 0.1.

Since impounding of mountain pass reservoir in recent years, the runoff from mountain land hardly drained into the plain riverway, majority of which became seasonal stream or perennial dry. Annual variation of runoff is bigger than that of precipitation. The coefficient of variation of annual runoff Cv is 0.42～1.10.

1.3 The distributing and recycling characteristic of underground water

The underground water of North China Plain mainly exists in the aquifer system of Quaternary System hole. They are divided into 4 water-bearing formations from top to bottom by their embedding characteristic and waterpower character. The underground water in the 1^st aquifer system is called the shallow underground water and the underground water in the 2^nd~4^th aquifer system is called deep underground water. The commingling of 1^st and 2^nd aquifer system on piedmont plain has been done. They are called by a joint name as shallow underground water. ^[1]

The buried depth of shallow underground water on piedmont plain is 120~150m, which is above salt water geologic body on plain to the middle and east. The shallow underground water takes active part in the circulation and alternation between atmospheric precipitation and surface water, the change of which keeps close connection with human activities and climate change. The underground water storage medium on piedmont plain has strong percolation capacity, which is the main infiltration accumulation area of local underground water. The 62% underground water resources are stored in piedmont plain.

2 The Variation Character of Water Resources

There were great changes on the quantity and distributing of North China Plain water resources in recent 50 years. Especially the change of underground water gravitational field and water cycle condition affected the utilization of water resources in this district. The main variation character is showed as following.

2.1 The supply, runoff and drainage condition of underground water

The supplementation of underground water changes as the variation of natural condition and artificial condition. The supply resource of shallow underground water is mainly precipitation infiltration supply. The second resource is piedmont lateral runoff supply and riverway leakage supply. By the influence from factors such as surface water irrigation and underground water irrigation etc, the recharge source of underground water adds canal system leakage supply, irrigation infiltration supply among farms and well irrigation regression supply etc.

The underground water runoff flows from piedmont to the contiguity to the sea in natural condition. By the influence from durative degression of underground water and degression of supply, the characteristic of underground water runoff changes a lot, which alter the direction of runoff in natural condition. The trend interflowing from around to center is formed in the concentration of mining area and the hydraulic slope changes a lot.

The drainage mode of underground water is influenced greatly by its model of occurrence and exploitation condition. In piedmont plain area, with degression of underground water level, increase of aeration zone thickness and the water level buried depth under phreatic evaporation limit, the drainage mode is mainly vertical drainage by man-made recovery and draining to downriver runoff. In the littoral plain, the drainage mode of underground water is mainly phreatic evaporation consumption for the higher mineralization degree of underground water, worse exploitation technique, lower utilizing of underground water exploitation, lower buried depth of underground water elevation.

2.2 The sharp drop of underground water level

In the beginning of twentieth sixties, the shallow underground water level in piedmont plain area was between 25～80 m. The underground water gravitational field keeps natural state basically. The shallow underground water level in piedmont plain area declined 5~20m generally till 1984. In 2001 it declined 5~10m.

With the decline of shallow underground water level, the uneven underground water coning appeared in the central city areas along the line of piedmont which exploited underground water concentratedly, such as Beijing funnel, the Gaoyang-Lixian-Qiangyuan funnel nearby the Baoding, Shijiazhuang funnel, Ningjin-Baixiang-Longyao funnel, Handan funnel etc. Thereinto the Beijing funnel and Shijiazhuang Funnel had great influence on city water.

The figure 2 reflects the developing process of Shijiazhuang underground water coning. The funnel began in 1965. Till to 2001, the buried depth of water level in center of funnel became 43.89m from 7.57m, with the annual average degression of 1.2m. Averagely it declined 0.76m annually between 1965~1975. The number was 1.60m between 1975~1985. Between 1985~1995 it became 1.22m. Between 1995~2001 by the influence of flood in 1996, the number became 0.07m. The acreage of funnel arrived at 348km2 in June, 2001.

2.3 The decrease of overland runoff generation

It was calculated that the average of surface water resources amount in Haihe River valley was 220×10⁸m³/a between 1956～1998 and that between 1956～1984 was 264×10⁸m³/a, which decreased 16%. It can be concluded from the relation of precipitation and runoff that the runoff volume generated by onesize precipitation decreased by comparing the afterward of twentieth eighties to the previousness (Figure 3). For example, the runoff coefficient in this district was 0.48 when there was flood in 1963, but it was 0.25 when there was flood in 1996. ^[2]

2.4 The decrease of amount of water into sea

The amount of water into sea is decreased for the reduce of direct runoff rate and increase of runoff consumption. It was calculated that the average amount of water into sea from Haihe River valley was 107×10⁸m³ between 1956～1998, thereinto the data was 241×10⁸, 161×10⁸, 116×10⁸, 26.9×10⁸, 68.5×10⁸m³ in fifties, sixties, seventies, eighties, nineties respectively. Then it can be seen that the data in eighties and in nineties was lower than the average and being decreased continuously.

2.5 The decrease of riverway leakage

The long-term dry of rivers resulted in the obvious decrease of recharging underground water quantity along riverway line in the plain terrain. For example, the multi-year average recharging quantity of underground water in piedmont plain was 66.2×10⁸m³/a between 1956～1980, thereinto the supply from riverway leakage accounting for 7.29%. The stock size that riverway leakage supplied to underground water decreased to less than 3% between 1980～2000.

3 The Physical Factor Analyses of the Change of Water Resources

3.1 Precipitation

From the comparison between the hydrology series between 1956~1998 and those between 1956~1984, the multi-year average precipitation decreased 1.6%.

The most important factor to restrict water cycle is the climatic factor, which has two kinds of influences (direct influence and indirect influence). The former is mainly from the change of precipitation spatiotemporal distribution, intensity and gross aroused by the change of general atmospheric circulation. The indirect influent is mainly from land factor. ^[3] Compare the climate characteristic (R/P and E/P) of water cycle on land in the Haihe

River valley with that of each valley: it was 0.16 and 0.84 in the Haihe River valley; 0.18 and 0.82 in the Yellow River valley; 0.49 and 0.51 in the Changjiang River valley. ^[4] In contrast the ground runoff generation in the

Haihe River valley was the least, the evaporation quantity from land was the most, and the consumption of precipitation was the most.

Since twenties fifties, the precipitation of fifties, sixties and seventies was higher than the multi-year average precipitation of decades in this district. But that of eighties and nineties was lower than average. The average was 3.2%, 7.1%, 2.0%, -7.2%, -5.3% respectively. For example the precipitation of Tianjin city decreased nearly 100mm in recent 50 years.

It can be seen from the anomaly change process of precipitation of Shijiazhuang city, the representative of submountain region, between 1956～2002 (Figure 4) that the average precipitation was 531.4mm, in fifties it was 580.6mm which was about 9.4% higher than the average; In sixties it was 581.2mm, which was about 9.4% higher than the average; it was 500.6mm in seventies which was about 5.8% lower than the average; it was 501.1mm in eighties which was about 5.7% lower than average and in nineties was 549.3mm, which was about 3.4% higher than the average.

3.2 Air temperature

According to research, there was a trend of rise in multi-year average air temperature of North China Plain. For example, the annual average air temperature of Tianjin city rose 1ºC between 1949~2001. The mean annual temperature of Shijiazhuang city in nineties was higher 1.3ºC than that in fifties．

Figure 5 shows the change process and trend of air temperature in Shijiazhuang city. The multi-year average air temperature between 1956~2002 is 13.3℃. Thereinto the temperature in fifties was 12.64℃, 12.93℃ in sixties, 12.96℃ in seventies, 13.18℃ in eighties and 14.03℃ in nineties. The average air temperature before eighties was lower than the multi-year average air temperature whereas in nineties it was higher than the average.

3.3 Evaporation

With the compare to the precipitation of corresponding year, the evapotranspiration rate on land has trend of increase in recent 40 years. Table 1 shows changes of precipitation and evapotranspiration rate in Baiyangdian Plain. In fifties the precipitation was more than evapotranspiration rate. After sixties the precipitation became less and less than evapotranspiration rate, which resulted in the increasing of water consumption in valley.

4 The Human Factor Analyses of the Underground Water Change

The influence by human activities to water cycle is mainly on following 2 aspects: One is the productive activity and socioeconomic development which change the chemical constituent of atmosphere to raise air temperature and increase evaporation, the other is that the human activity mainly acts on the underlaying surface of valley, such as exploitation of water resources etc, to change physical parameters such as albedo that the land has to the solar radiation, roughness, and the expands acreage of impermeable layer etc. Although the latter acts on local, the intensity is always very strong.

The engineering of flood defending, flood impounding and flood discharging etc to avoid flood and alleviate the flood disaster is called flood control works. After developing for 50 years, the North China Plain has built more than 1900 pieces of reservoirs for flood preventing, irrigating, water supply, electricity generating, breeding etc. The total reservoir capacity of reservoirs in mountainous area accounts account for 97% of total reservoir capacity of reservoirs (Table 2), which forms flood control works system for valley preliminarily.

The large-scale reservoir impounds large quantity of flood from mountainous area, which decreases loss against disaster in plain region. The eight large-scale reservoirs on the south of Haihe River cut more than 30% of the peak discharge, with the maximum 89% at the time of cataclysm in 1963. In 1988 there was another cataclysm with flood discharge of 41.47×10⁸m³ since 1963 in the Daqinghe River and Hutuohe River. The large-scale reservoir over the river impounded 10.83×10⁸m³ of flood which accounted for 26% of the flood volume and cut more than 60% of the peak discharge (table 3). ^[5]

4.2 Underground water exploitation

The shallow underground water is exploited easily and has good connectedness with surface drainage system and atmospheric precipitation system. The shallow underground water system is sensitive to human activities and climate change.

According to the statistics, the yield of shallow underground water in the North China Plain was 179.19×10⁸m³/a, the overall supplementation of shallow underground water was 234.89×10⁸m³/a, the overall output was 257.51×10⁸m³/a, difference between supplementation and output was -22.62×10⁸m³/a. It was at an overdraft state in whole. The exploitation degree was 14×10⁴m³/a·km².

5 The Trend Prediction

The change of underground water resources has its nature factor and human factor. Generally, the nature factor is slower and human factor is faster. However, by the analyses of nature factors such as precipitation and air temperature of Shijiazhuang city, the precipitation has saltation during the megatrends of decline and the air temperature is at trend of decline as a whole. This will mainly result in the decrease of water resources quantity, as well as cause urban heat island effect.

The change of temperature and evaporation capacity has direct or indirect influence on change of water resources. According to the research, every elevation in temperature will result in 12% decrease of Chaobaihe River valley annual runoff. ^[6] From the information in hand at present, it can be concluded that the valley evapotranspiration is influenced by climatic variation and massive human activities jointly. The influence will increase year after year to decrease water resources quantity.

Some research concludes that there is positive correlation between the decrement of underground water resources in Haihe River plain (DQ）and the decrement of annual precipitation, which can be expressed as following correlation formula:

DQ=1.16DP - 3.64 ^[7]

That is, if we take the whole North China Plain as a whole and the multi-year average underground water resources quantity and precipitation between 1956~1984 as cardinal number, when the decrement of North China Plain average precipitation is 1%, the underground water resources will decrease 4.8%, which is about 12.81×10⁸m³/a. When the precipitation keeps unchanged, by the influence from human activities, the underground water resources will decrease by 3.64%, which is about 9.72×10⁸m³/a.

6 Conclusions

Water resources in the North China Plain become the bottle-neck of economic development for their insufficient. The analyses show that the local climate change under macroscale is an inducement of the change of water resources in the North China Plain. However the human activities with certain scale that will change directly or influence human living environment at some space-time scale is also an important factor to result in changes of water resources. ^[8]