Quantitative Estimation of Annual Runoff Variation from the Hotan River , China

Starting from the existing analysis of runoff from the Hotan River, the varying cause of runoff in the Hotan River is analyzed using the annual runoff accumulated curves and the orderly cluster method, pointing out that the runoff from the Hotan River coming from the mountains falls into the natural runoff with the fluctuations because of being subject to climate changes. It is worth noticing that the Xiaota annual runoff flowing into Tarim River was reduced by 0.322 billion m in comparison of the postior 1989 series with the prior 1989 series and under the join action by both human being activities and climate changes.


General situation
The Hotan river basin is located at the north of the Kunlun Mountain and the southeast of Tarim Basin.The Hotan River is 1127km long whose area is 48870km 2 .It is the biggest river in the southeast of Tarim Basin and the secondly big river in the north of the Kunlun Mountain.It flows into the Tarim Basin from south to north, comes through the Takelamagan Desert and arrives to the Tarim River.It is the only river throughout the Takelamagan Desert and one of four existing source regions, too.
The Hotan river basin falls into the arid desert climate in the warm temperate zone with abundant light and heat resources.Temperature is 12.2 yearly and rainfall is 35.6 mm yearly on average.The observed values of water ℃ evaporation range from 2159mm to 3137mm.Dry degree is higher than 20, thus making for conduct the plant diseases and insect pests.Strong wind occur in spring and sand storms often break out in April and May that can bring the serious economic loss affect the life of the local persons.
There are two tributaries in the upper reach of the Hotan River.One is the Yulongkashi River; the other is the Kalakashi River.They converge at Kuoshilashi.There are three hydrological stations on the Hotan River (Fig. 1), one is Tonguziluoka station on the Yulongkashi River, second is Wuluwati station on the Kalakashi River, and the other is Xiaota station on the lower reach of the Hotan River, whose catchment area is 48870 km 2 .Surface water flowing into and out the Hotan Oasis is determined by three hydrological stations.
The Hotan Basin is one of the aridest areas in Xinjiang.Drought, sand storm and salt-alkalization are three natural disasters in the Hotan Basin; the utilization of soil and water resources is very low.The area of natural forest decreases 36% by disafforestation; the area of soil salt-alkalization accounts for 37.3% of the whole farmland; the area of soil desertification account for 52% of the whole area.The desertification area is increasing gradually because of big wind and sand storm.The lower reach of the Hotan River flows through the Takelamagan Desert where vegetation is very thin and big wind and sand storm is very so that its ecological system is very sensitive for the outer effect.Its capacity of renewing itself is very poor, thus it is the most frangible headstream.The area of vegetation cultivated by human in the middle reaches accounts for 32.4% of the oasis area.At a certain extent, the environment frangibility is improved, but the comprehensive assessment shows that the environment quality of the Hotan River falls into the moderate vulnerability (Wang, 2001).
Uyre, as a minority in China, is the main people in the Hotan River Basin.Irrigation agriculture plays an important role for the local economy.However, the limited water resources restrict the social and economic development, restoring and building on environment.The change low of runoff from the Hotan River is studied to develop the local economy, improve the life and protect the environment, etc. under the condition of global climate warming and human activities.

Existing situation of runoff
There is a great deal of glaciers whose area is 10785 km 2 where annual precipitation is up to 800mm in the high mountainous area of the Hotan River distributes, so it is the place where runoff generates; in the low mountainous area falling into the hungriness zone, the vegetation is very thin and the velocity of runoff is very high, therefore it is not benefit for the runoff generation without the regulation fluctuation for the runoff supply; in the middle-lower reaches of the Hotan River falling into the transportation area and dissipation area of runoff, the runoff is gradually decreased, even dry, because of water diversion for agricultural irrigation, strong evaporation and seepage loss.
The Hotan River is the biggest river in the southwest of the Tarim Basin.The total of runoff is 43.8×10 8 m 3 on average (from 1957 to 2003) which can be taken as the surface water resources flowing into the Hotan Oasis, in which it is 22.3×10 8 m 3 for the Yulongkashi River, and 21.5×10 8 m 3 for the Kalakashi River.At the same time, there is 10.1×10 8 m 3 on average (from 1961 to 2003), accounting for 23.3% of the total of the Hotan River runoff, which is very important to maintain the ecological balance of the Tarim River and the whole Tarim Basin, prevent the desert from erosion and protect the green corridor.
The runoff distribution in a year lies on the supply condition.According to the calculation(Yang, 1987), the runoff from glaciers is 14.8×10 8 m 3 for the Yulongkashi River, accounting for 66.4% of its total; 10.01×10 8 m 3 for the Kalakashi River, accounting for 46.6% of its total.In addition, there are 18.3% and 24.3% respectively from the groundwater which is from the glaciers in the mountain area.So it is evident that the glaciers are the main source of runoff.The flood season occurs in July and August affected by the temperature and heat in the Hotan River Basin; the runoff highly concentrates in summer, accounting for 80.7%and 72.9%, respectively for the Yulongkashi River and the Kalakashi River; that is very less than 10% in Winter.Therefore, runoff can not be used effectively in flood season when the pressure of flood control is very large; water shortage is very serious in spring and in winter for agricultural irrigation and hydroelectric power.

Runoff change
The Hotan River Basin has a long history; oasis economy is closely linked with the runoff from the Hotan River.It is observed that no water is no oasis, no agriculture, either.So the stability of the runoff from the Hotan River is the prior condition of survival and development for the Hotan Oasis.According to the previous findings, it can be known that the runoff from the Hotan River has an unremarkable degression trend and the runoff flowing into the Tarim River has a remarkable degression trend (Huang, 2000).

Accumulated curves of the annual runoff
If the runoff is not affected by human activities, it has stochastic change among high, normal and low water.The accumulated runoff is dotted in a coordinate graph, which has no systematic deviation.By contrast, if the runoff is affected, its accumulated curves take on the systematic deviation.So we can judge whether the runoff series is affected by human activities according to its accumulated curve (Zhou, 2002).
The annual runoff accumulated curves of the Hotan River are made in Fig. 2.These curves of the Kalakashi River and the Yulongkashi River take on the fluctuation, but they basically like as a straight line.Their fluctuation occurs because of the stochastic change of hydrological series with the climate change.It can be seen that the runoff from two tributaries is not affected by human activities.The curve of Xiaota station has an outstanding deviation trend.The deviation dot presents in 1989, that is, the curve basically takes on a straight line before 1989 and it deviate from the straight line after 1989.While the Hotan River flows through the Hotan Oasis, runoff is diverted out the river to be used for agricultural irrigation.It became a seasonal stream in 1962.When the temperature rises in summer and runoff increases, surplus runoff flows through the desert to the Tarim River; no runoff flows to the lower reaches in the other seasons.So runoff under the canal headwork is affected by human.From the curves of Xiaota station, the interference is larger after 1989 than before 1989.The runoff series can be taken as two series from the time angle: one is before 1989; the other is after 1989.

The orderly cluster method
The hydrological series is affected by human activities is different from the intrinsic one.From the 'cluster' angle, it can be taken as two 'cluster'.The cutting point can be found with the orderly cluster method (Liu, 1991).
The cutting point is the outstanding interference point in the hydrological series.It can make the sum of deviation square smallest for the same cluster series (in equation 1 and 2) and the sum of deviation square relatively bigger for the in the south of Xinjiang, the northwest arid regions and the whole globe affects the temperature in Kunlun Mountain to lead to an unremarkable degression trend of the runoff from the source regions of the Hotan River.In the source regions, runoff is not affected by human activities because of under population.When the Hotan River flows through the oasis, a great lot of runoff is diverted into the irrigation area to give rise to obvious runoff decrease flowing from the Xiaota station to the Tarim River.Water diversion for irrigation, evaporation, seepage and overflow are main reason to lead to runoff decrease flowing to the Tarim River, that is, the combination with human activities and climate change.
The change trend of the runoff from the Hoton River is not good to the development of the agricultural economy and ecological environment, not good to the survive and maintainment of the "green corridor" of the main river of Horton River in the Desert, and not good to the ecological protection and economic stability of the Tiam main river.So it is necessary that the scientific planning and comprehensive treatment are carried out for the Horton River.1956 1961 1966 1971 1976 1981 1986 1991 1996 1961 1965 1969 1973 1977 1981 1985 1989 1993 1997 Year Sn(τ)

Figure 2 .
Figure 2. The annual runoff accumulated curves about three gauging stations of the Hotan River Figure 3. ) (τ n S hydrograph of annual runoff from Xiaota station