Impacts of human activity on river runoff in the northern area of China

Global environment has changed very much with human activity. There is no exception to hydrological regimes (Conway, 2001; Garcia, et al., 1998). In fact, due to agricultural, industrial, urban development, such as irrigation and drainage, hydraulic structure across a river, the elements of hydrological cycle have changed in terms of quantity and quality, both in time and in space. In this section, an attempt is made to analyze quantitatively the effect of human activity on river runoff in different spatiotemporal scales including daily, monthly, annual, inter-decade, inter-century variations, according to long-term observation data (Ren et al., 2005). The driving force of annual runoff change in a river will be analyzed also. In this section, natural flow means runoff generated without the impacts of the human activity. It is derived from the summation of measured runoff plus water amount both stored in the reservoirs and taken directly from river course for various kinds of utilization during the computed period.

The following basins are taken as case study areas: the Yellow River, the Haihe River, the Luanhe River, the Songhuajiang River, and the Liaohe River in the northern area of China, covering Bejing, Tianjin, Ningxia, Shanxi, Hebei, Liaoning, Jilin, Hailongjiang Provinces, and partial area of Shaanxi, Gansu, Qinghai Provinces and Inner Mongolia Autonomous Region, as shown in Table 5.1 and in Fig. 5.21. The total area is almost 2 million km2.

On one hand, the total amount of water use has been increasing within the study area since 1949. Capitation amount of water use came up to 450 m3 at the beginning of the 1980's, and has been kept as this value in China to the end of the 20th century. Although annual growth rate of water use decreases from 7.1% in 1959 to 1.8% in 1997, the total amount of water use increases because of economic development especially along the coast in China.

On the other hand, water-use structure has been changing. The percentage of industrial and municipal use in total amount of water use grows at a great rate. The percentage of agricultural use in total amount of water use decreases with time. The ratios of agricultural, industrial, and municipal use in total amount were 88.2%, 10.3%, and 1.5% in 1980; 69.2%, 20.7%, and 10.1% all over the country in 1999, respectively. The annual growth rate of agricultural, industrial, and municipal use was -0.058%, 8.1%, and 38.5% respectively in China from 1980 to 1999. The water-use structure has changed as well with the development of industry, agriculture and urbanization from the 1980's to the 1990's. The ratios of agricultural, industrial, and municipal use in total amount were 77.3%, 16.8%, and 5.9% in Beijing; 90.6%, 7.2%, and 2.2% in Hailongjiang Province; 90.5%, 8.4%, and 1.1% in Shanxi Province in 1988, respectively. However, they were 44.2%, 25.3%, and 30.5% in Beijing; 65.2%, 28.9%, and 5.9% in Hailongjiang Province; 62.6%, 23.5%, and 13.9% in Shanxi Province in 1999, respectively. As remarked above, water use outside of river increases rapidly. And river discharge decreases. Such case has become more and more serious. Some evidences are given as follows. Analyses will be made on the change of daily, monthly, annual, inter-decade, inter-century runoff due to human activity.

Fig. 5.21 Location of study area in China map (Ren et al., 2005)

Table 5.1 Outline of rivers in the study area

Name of River Total length(km) Total Area (km2) Annual runoff (109 m3)

Yellow River Luanhe River Haihe River Liaohe River Songhuajiang River

5,464

1,090

1,390

2,308

752,444

263,631

44,100

228,960

557,180

• Effect on order of daily discharge

Since the 1990's, the number of days in which daily discharge is more than 3,000 m3/s, is no more than 4 days on the average at Huayuan-

kou Station controlling the area of 730,037 km2 in the lower reach of the

Yellow River. Fig. 5.22 shows statistical characteristics of daily discharge data series measured at Huayuankou Station from 1946 to 1998.

Fig. 5.22 Statistical characteristics of daily discharge series observed at Huayuankou Station from the 1940's to the 1990's (After Zhu, et al., 1999)

The number of days in which daily discharge was more than 2000 m3 /s, decreased from 86 days in the 1950's to 17 days in the 1990's. However the number of days in which daily discharge at Huayuankou Station was less than 3000 m3/s, increased from 300 days in the 1940's to 361 days in the 1990's, and the occupying percentage in total number of days during the whole year increased from 82% in the 1940's to 99% in the 1990's correspondingly. That's to say, minor daily discharge, measured at a specific downstream site, occurs more often than before. The reason is that upstream runoff is retained and stored in reservoirs, perhaps flowing lately in the coming year, or that upstream runoff is taken from river course for agricultural irrigation (consumed by plant transpiration), industrial and municipal consumptions. Daily discharge at downstream is becoming less and less. More serious situation has occurred, i.e. river flow cutoff in the lower reaches of the Yellow River Basin. In 1972, river flow was cut for 19 days, beginning on April 23rd; and the length of flow cutoff was about 310 km. In 1998, flow was cut for 142 days, beginning on January 1st; and the length of flow cutoff expanded for about 515 km. The decrease of discharge, even flow cutoff, could cause four serious results: (1) to deteriorate aquatic ecological environment in the lower reaches of the Yellow River Basin; (2) to aggravate deposition of sediment, so as to raise the risk of floods; (3) to make water supply difficult for domestic, agricultural, and industrial use in the Yellow River Delta; (4) to aggravate intrusion of sea water in the outlet.

• Effect on monthly runoff

The human activity such as the construction of reservoirs across a river would make the distribution of monthly runoff in one year changed. For instance, the proportion of runoff during rainy season in the annual runoff decreases, while the proportion of runoff during dry season in the annual runoff increases. And the ratio of the maximum to the minimum of monthly runoff decreases further. For example, the differences between natural and observed monthly runoff data at Fuyu Station controlling 71,783 km2 in the Songhuajiang River and at Wangben Station controlling 10,418 km2 in the east upper area of the Liaohe River in 1994 are almost the same as above. Owing to irrigation in the growth period of crops, observed monthly runoff decreased by 83.8% at Wangben Station, 67.2% at Fuyu Station, respectively with respect to natural runoff in June of 1994.

• Effect on annual runoff

Fig. 5.23 represents the variation of annual precipitation, observed runoff, and runoff coefficient series in the upstream of Xiaoheyan Station, controlling the area of 18,599 km2 over the Laohahe River Catchment, from 1955 to 1998. The Laohahe River lies in the west upper reach of the Liaohe River Basin. It could be seen from Fig. 5.18 that there is no a trend towards decrease in the series of annual precipitation from 1955 through 1998. However, there is a tendency towards decrease in the series of annual runoff observed as well as in the series of annual runoff coefficient from 1955 through 1998. That's to say, the same order of precipitation produced less runoff in the Laohahe River Cachment in the 1980's than that in the 1950's.

The differences between natural and observed runoff within the area of 72,875 km2 in the upper reach of the Songhuajiang River Basin, and within the area of 10228 km2 in the east upper reach of the Liaohe River Basin are larger in 1990 and in 1994 than the other. Anyhow, there exists the same phenomenon that observed runoff is less than natural runoff.

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 Year

Fig. 5.23 Variation of annual precipitation, observed runoff, and runoff coefficient series at Xiaoheyan Station controlling the area of 18, 599 km2 in the Laohahe River Catchment from 1955 to 1998 (Ren et al., 2005)

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 Year

Fig. 5.23 Variation of annual precipitation, observed runoff, and runoff coefficient series at Xiaoheyan Station controlling the area of 18, 599 km2 in the Laohahe River Catchment from 1955 to 1998 (Ren et al., 2005)

• Driving force analysis

In general, there are three aspects of reasons in the reduction of river runoff. Firstly, the amount of precipitation becomes less. Secondly, water is artificially drawn out from river channel. It contains the inter-basin transfer of water quantity as well, which could show up in the flow regime in the coming days. And groundwater is overexploited. That makes underground water table decrease. Finally, climate variability or climate change induced by human activity has influence over water resources.

The decrease in natural precipitation is the principal, main and direct cause of runoff reduction. But more or less of natural precipitation varies in space. Precipitation does not decrease in all the northern area of China. The main reason of runoff reduction is the growth of population, the enlargement of the scales of agricultural and industrial production, as well as urban development within Jilin Province, which consume a large amount of river flow and groundwater.

The annual growth rate of population was 1.59%, and the amount of water use increased by 12.5% in the whole basin of the Yellow River in 1999 than that in 1980. 3380 reservoirs, with the total storage capacity of 27.37 billions m3, had been built before 1985. Also effective irrigation area had reached 43.8 thousands km2 before 1985. Those are the main rea son why measured runoff decreases. As regards the influence of climate variability/change on water resources, it does not look very obvious. The same situation appeared in the Chaobaihe River (Li, et al., 2000) having 19,354 km2 of area, the tributary of the Haihe River, nearby Beijing. According to statistics, total storage capacity of reservoirs reaches 4.8 billions meters, and real irrigation area is more than 2,500 km2. With socioeconomic development, the utilization ratio of water resources becomes larger and larger, so that river flow cutoff began to occur in the Chaobaihe River in 1972. Moreover, stream flow had cut off for 276 days from February through December within the year of 1984. The utilization ratio of water resources, which has been increasing continuously beyond the limited ratio of 40%, makes it tend to be a seasonal river. The general hydrological regime is changed fundamentally. The local ecological landscape is difficult to be rehabilitated. The decrease of annual runoff is mainly caused by human activity rather than under the impact of climate change, though the climatic condition serves as the background of runoff change.

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