HuLin Pan

Division of Hydrology Water-Land Resources in Cold and Arid Regions,Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences,Lanzhou,Gansu 730000,China

Vulnerability of an inland river basin water resource system under the background of future accelerated glacier melt: A case of Yarkent River Basin in arid Northwest China

HuLin Pan*

Division of Hydrology Water-Land Resources in Cold and Arid Regions,Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences,Lanzhou,Gansu 730000,China

Water resources of inland river basins of arid Northwest China will be profoundly affected by future accelerated glacier melt.Based on scenarios of climate warming,accelerated glacier melt and socioeconomic development in the future,vulnerability of the Yarkent River Basin water resources for 2010–2030 is evaluated quantitatively using the indicator of water deficiency ratio.Results show that the quantity of the basin’s water resources will continuously increase over the next 20 years,mainly due to the effect of climate warming and accelerated glacier melt.But,in the next 10 years,the basin will have a deficient water status,and the water resource system will be quite vulnerable.This is due to an increased water demand from rapidly increasing socioeconomic development and a lack of low water-use efficiency in the near future.After about 2020,water supply will outstrip demand,greatly relieving the basin’s water deficient due to increased water resources and the advancement of water-saving technology.Contrast to the hypothetical situation of unchanged glacier melt,climate warming and resulting accelerated glacier melt may play a role in relieving the supply-demand strain to some extent.

climate warming;accelerated glacier melt;human activity;vulnerability of water resources;Yarkent River Basin;Northwest China

1.Introduction

Glacial melt water is an important source of inland river basin runoff in arid Northwest China,and it plays a key role in maintaining ecological functions,permitting human activities and promoting economic development.With global warming,water resources in inland river basins of Northwest China are profoundly impacted by accelerated glacier melt.The available water resources in inland river basins of Northwest China increased disproportionally within the past five decades or so and will continue to increase then decrease due to accelerated glacier melt and consequent glacial shrinkage driven by global warming (Shi,2001;Shen and Wang,2002;Liuet al.,2006;Sunet al.,2006;Gaoet al.,2008;Wanget al.,2008).As known,water resource systems have both natural and social-economic attributes (Lin,2003),and the water resources are effected by both of these factors.However,the research on inland river basin runoff variation are mostly based on the climate warming background with less consideration to effects of human activities (Sunet al.,2006;Gaoet al.,2008;Wanget al.,2008).

The Yarkent River Basin in arid Northwest China is fed primarily by glacial melt water (Shi,2001),and is presently underdeveloped.The future water resource conditions in this basin will be profoundly impacted by glacier melt and economic development.Here,we intend to evaluate the vulnerability of the Yarkent River Basin water resource system in terms of supply and demand of water resource based oncomprehensive examination of climate warming,accelerated glacier melt and future socioeconomic development,aiming to provide theoretical support for the government constructing rational water resources use policies.

2.General situation of research area

The Yarkent River Basin lies in the southwest brim of the Tarim Basin in the south of Xinjiang,China.Its administrative divisions include Kashgar,Hotan,Akesu,and KezilesuKirgiz Autonomous Prefecture,with a total area of 98,900 km2and a total population of 1,897,000.The Uyghur population accounts for 85.8% of the total.In 2005,the per capita GNP of this basin was only 3,943 yuan RMB equaling to one third of the national per capita GNP.Agriculture is the leading industry,with its production accounting for 54% of GNP.

The Yartent River system is mainly composed of the Kelechin,Tashikuergan,and Tzinafu rivers.Water resources in the Yarkent River Basin are abundant,adding up to 77.6×108m3,with surface water of 76.79×108m3and net ground water of 0.81×108m3(Qin,2009).The Yarkent River Basin is situated in the center of Eurasia,although with an arid climate,the plentiful glacial melt water from its upper mountain area accounts for 57.9% of the total average runoff since the 1950s (Mansur and Ajinisa,2005).Thus,glacial melt water is very important to the inhabitants and socioeconomic development in this basin.With climate warming in recent decades,however,the upper glaciers have been melting rapidly and their areas have been shrinking greatly.Since the 1960s,the glacier area has decreased by 183.33 km2,that is,by an average decrease of 7.8 km2per year.The trend of glacier melt and rapid glacier shrinkage will result in remarkable change in regional water resources regime (Shen and Wang,2002;Gaoet al.,2010).Simultaneously,with population growth and economic development,the water demand in this basin increased greatly within the past few decades,accounting for over 80% of the total runoff of this river (Jiang,2002).Thus,the future water resource condition of the Yarkent River Basin seems not to be optimistic.

In this paper,Yecheng,Zepu,Shache,Makit,and Bachu counties,which belong to the Kashgar District in the lower portion of the basin,are chosen as the basic research units to identify the water resources situation in terms of future accelerated glacier melt and socioeconomic development.

3.Method and data

3.1.Research scenario

The vulnerability of water resources means changes in quantity,composition,supply and demand under the combined action of natural and human factors (Tanget al.,2000).So,the assessment of water resource vulnerability is necessarily comprehensive,including evaluating water resources supply and demand and the need to consider multi-factors.Therefore,a systematic analysis method is often applied when evaluating the vulnerability of water resources,comprehensively analyzing the impact of external environmental factors on the equilibrium of water resource supply and demand (Tanget al.,2000).It should be noted that the demand of water resources has to be evaluated based on the assessment of population growth and production scales,with such a demand resulting mainly from human activity.

The scenarios of runoff changes driven by climate warming,accelerated glacier melt,and those of population and socioeconomic changes in the research areas in the next 20 years are constructed firstly in this research.Then,the supply and demand of the water resources in the next 20 years are evaluated respectively.Based on this evaluation,the equilibrium of the supply and demand of water resources,namely the vulnerability of these resources in the research area,is evaluated.For convenience,water deficient ratio is used to reflect the vulnerability of the water resources.Figure 1 indicates the special research scenario of this paper.

Figure 1 Flow chart for evaluating the vulnerability of water resources under background of climate warming and future accelerated glacier melt

3.2.Computing method

3.2.1 Available water resources

Because the inland river basins in arid Northwest China are nearly hydrologically closed,and glacial melt water and rainfall in the upper mountain area are mostly the sole source of runoff of these basins,runoff in the mountain area is the maximum available water quantity of the whole basin.In order to predict the runoff in the mountain area of the Yarkent River Basin,the hydrological integrated model Hydrologiska Byråns Vattenbalansavdelning (HBV) adapted by Kanget al.(2002) from China is used.This model has the advantage of considering not only the impact of climate change and accelerated glacier melt on runoff,but also the different responses of runoff of the permafrost zone and the alpine vegetation area in the upper of basin to climate change.Thus,it is more suitable to predict runoff change of the inland river basins in arid Northwest China (Kang,2002).In terms of the available water resources for the research units,the water allocation scheme provided by Jiang (2002)for the Yarkent River Basin is adopted in this research.

3.2.2 Demand of water resources

The demand of water resources of the basin is the function of population size,economic scale and water-use efficiency generally.The IPAT equation,which means that the impact (Im) of human activity on the environment is the product of population size (P),affluence (A,i.e.,per capita consumption or production) and technology (T,i.e.,the effect of the consumption per unit on the environment),is used to identify the demand of water resources in this research(Xu,1999).The IPAT equation means that the impact of human activity on the environment is the result of an interaction between three key forces,namely population size,per capita consumption or production and the level of technology.In this research,the IPAT equation means that the demand of water resources of the research area (D) is the product of population size (P),per capita GDP (A) and water consumption per unit of GDP (T),which is presented by the following model:

The population size of the research area in the next 20 years is predicted by using the logistic model of population growth developed by Verhulst (1838).Because the impact of both external environmental factors and population size on population growth are taken into account,the logistic model more rationally reflects future population growth patterns (Feng,2008).The model is presented as follows:

where the model parameterx0is the population in the benchmark year,xmis the maximum population capacity of the research area,ris the natural growth rate of population when the population is small in the research area,tis the modeling-time span,and sox(t) is the predicted population of a particular year in the future by the model.The model parameters are identified firstly by using the population data of the research area from 1978 to 2005,and then the model is established to predict the population of the research area in the next 20 years.The predicted values fit well with actual population growth from 2006 to 2010.

The per capita GDP in the next 20 years is predicted using the regressive model based on data from 1978 to 2005,and production data is adjusted to be equal in value every year in order to eliminate the effect of price fluctuation on GDP.It should be noted that data since 1978 used in this research for population and economic policies in the research area are relatively stable and these may be consistent with those for many years in the future.Thus,the established models may quite well predict future per capita GDP.

Future water consumption of GDP per unit depends on many uncertain factors such as economic benefit,water-saving technology,thus it is very difficult to identify this consumption.As a matter of fact,for convenience the empirical value of the average declining rate of water consumption per GDP in the past 20 years is used to predict future water consumption of GDP per unit based on 2005 data.The value is −7.96% as shown in Table 1.

3.3.Data sources

Mountain runoff in the research area is modeled using the integrated hydrological model HBV,and the inputted climate data is provided by the National Climate Center of China for 2008.This data set is for climate change in Chinese regions for the next 100 years,predicated under different scenarios of human development and carbon emission.Population and economic data used in the prediction of future water demand come from the statistic yearbook of Kashgar District from 1978 to 2006.

Table 1 The average declining rate of water consumption per GDP in Yarkent River Basin

4.Results and analysis

4.1.Scenarios of water supply

As presented in Figure 2,total runoff (Q) and the increment of glacial melt runoff (I) of the Yarkent River may increase rapidly in the next 20 years.Compared to 2005 values,they will increase by 9.77×108m3and 8.16×108m3respectively in the next 20 years,namely increasing by 0.39×108m3and 0.33×108m3per year.These results are similar to those obtained by Shi (2000) and Ding and Pan (2005).

Glacial melt water accounts for more than 80% of the increment of total Yarkent River Basin runoff,which manifests that future change of water resources will depend on climate change and resulting accelerated glacier melt.In order to further identify the impact of climate change and accelerated glacier melt on the basin’s water situation,total basin runoff without the increment of glacial melt water over the next 20 years is calculated (Q′).As presented in Figure 2,river basin runoff may increase slowly and finitely,assuming that climate and glacier melt does not change in the future.

In accordance with the change of total runoff of the whole basin,the available water resources for every county as a research unit will increase greatly as presented in Figure 3.For example,according to the water allocation scheme of the Yarkent River Basin,the available water for Shache County will increase by 3.6×108m3in the next 20 years due to an increase of total runoff of the basin.

Figure 2 Mountain area runoff with (Q) or without (Q′) the increment of glacial melt runoff (I) in the Yarkent River Basin for the next 20 years

Figure 3 Quantities of available water resources of main counties in the Yarkent River Basin over the next 20 years

4.2.Scenarios of water demand

The water resource demands for the whole basin and each county will decrease in general over the next few decades (Table 2).For example,the water demand of Shache County may decrease to 12.07×108m3in 2020,and will have decreased by 2.71×108m3in contrast to that in 2010.The demand of the whole basin may decrease by 17.63×108m3in the next 20 years.This decrease of water demand may be due to rapid improvement of water-saving technology and increase of economic efficiency.However,the water demand of each county will remain quite large in the next 20 years,because the present low economic efficiency and the irrational structure of water use may not be improved in the near future.Agriculture is still the predominant industry of the basin,and its water consumption accounts for over 90% of the total consumption.According to the statistic data,the agriculture’s input-output efficiency is still quite low and the average water consumption per ten thousand yuan is also large in this region presently.

Table 2 Water resource demands of the Yarkent River Basin and its main counties in the next 20 years

4.3.Vulnerability of the water resources system

The vulnerability of water resources in the Yarkent River Basin is assessed based on scenarios of water resource supply and demand over the next 20 years.Taken into consideration of the increment of glacial melt water (Figure 4a),the water supplies of Yecheng,Zepu,Shache,and Makit counties for 2010–2015 still cannot meet the demand,and the water deficient ratio for each county is above 10%,so the water resource system of these counties are vulnerable.By 2015,the water supply may roughly equal to the water demand;the water supply after 2015 will be more than the demand,so the vulnerability of water resources will be low at that time.

In contrast to the situation in the above four counties,the water supply in Bachu County cannot meet the demand all the time until 2020,with a water deficient ratio of about 4%–35%.In the next 10 years the water resource system in Bachu County will be quite vulnerable.The water supply after 2020 will gradually be more than the demand,so the water resources system will be less vulnerable at that time.

In terms of the whole Yarkent River Basin,the water supply cannot meet the demand until 2025,with a water deficient ratio of about 4%–7%,so the water resource system will be quite vulnerable over the next more 10 years.From 2020 through 2025,the contradiction between the supply and requirement of water resources will gradually be alleviated,and the water resources system will be less vulnerable after 2025.

If the increment of glacial melt water is not included(Figure 4b),the time when the water resources supply meet the demand in the Yarkent River Basin will be inevitably longer and the water deficient ratio will be increased.This from another point of view indicates that climate warming and accelerated glacier melt are useful in decreasing the vulnerability of water resource system,and relieving the pressure on water resources demand of the Yarkent River Basin in the next 20 years.

5.Discussion

Although almost all the inland rivers in arid Northwest China are fed partly by glacial melt water,the impact of climate warming and resulting accelerated glacier melt on the water resources in inland river basins are widely divergent due to different glacier resources in the upper portion of each basin.In the Yarkent River Basin,there are numerous large and thick glaciers in the upper mountainous area,and glacial melt water is the main source of water replenishment.

In contrast to water quality problem,water shortage is much more critical under the background of climate warming and accelerated glacier melt in the arid regions of China.In the evaluation of the vulnerability of water resource system in arid area,the water deficient ratio that indicates the conflict between water supply and water demand is chosen as the evaluation indicator,whereas the water quality indicator is not involved.

The predicted water supply is the maximum available water resources of the basin,in which the runoff loss of channels is not taken off.The predicted water demand is the minimum water demand of the whole basin,in which the domestic and ecological water demands are not included.Thus,the future actual vulnerability of the research area for every period may be even more severe than predicted.

Figure 4 Equilibrium of water resources supply and demand in research areas over the next 20 years

6.Conclusions

The available water resources of the Yarkent River Basin will constantly increase over the next 20 years driven by climate warming and accelerated glacier melt,and the increment of glacial melt water becomes the most important contributor to this increase.Driven mainly by the improvement of water-saving technology,future water demand of the basin will constantly decrease,but the water demand of each county will remain quite large in the next 10 years with the present low efficiency of water use.Under the combined act of natural and human factors,the water resource system of the whole basin may be quite vulnerable in the next 10 years,and then afterwards will become less vulnerable.Further analysis shows that climate warming and resulting accelerated glacier melt may relieve the strain between supply and demand of water and diminish the vulnerability of water resource system of the Yarkent River Basin through increased glacial melt water in the next 20 years.

Acknowledgments:

This research is supported by the Western Project Program of the Chinese Academy of Sciences (Nos.KZCX-XB2-04-04,KZCX2-XB2-09-6).The author is very thankful to the research team of glacial water resources led by Professor Liu SY from National Key Laboratory of Cryosphere Sciences,Cold and Arid Regions Environmental Engineering Research Institute,Chinese Academy of Sciences for providing climate change data of the research area.

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January 10,2012 Accepted: April 23,2012

*Correspondence to: HuLin Pan,Doctoral Candidate of Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences.No.320,West Donggang Road,Lanzhou,Gansu 730000,China.Email: panhulin979@126.com