Chun-lei Liu, Jian-hua Zheng, Zheng-hong Li*, Ya-song Li, Qi-chen Hao, Jian-feng Li

1 Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China.

2 Key Laboratory of Groundwater Sciences and Engineering, Ministry of Natural Resources, Shijiazhuang 050061, China.

3 Xiamen Institute of Environment Science, Xiamen 361000, Fujian, China.

Abstract: The small and medium-sized river basins along southeast coast of China hold comparatively abundant water resources. However, the rapid resources urbanization in recent years has produced a series of water problems such as deterioration of river water quality, water shortage and exacerbated floods, which have constrained urban economic development. By applying the principle of triple supply-demand equilibrium, this paper focuses on the estimation of levels of water supply and demand in 2030 at different guarantee probabilities, with a case study of Xiamen city. The results show that water shortage and inefficient utilization are main problems in the city, as the future water supply looks daunting, and a water shortage may hit nearly 2 × 108 m3 in an extraordinarily dry year. Based on current water supply-demand gap and its trend, this paper proposes countermeasures and suggestions for developing and utilizing groundwater resources and improving the utilization rate of water resources, which can supply as a reference for other southeast middle-to-small-sized basin cities in terms of sustainable water resources and water environment protection.

Keywords: Xiamen City; Water resources; Triple equilibrium; Probability; Supply and demand forecast Received: 04 May 2021/ Accepted: 03 Nov 2021

Introduction

Water resources are fundamental in terms of sustainable development of the national economy and society. Sustainable water resources management is pivotal for improving human living environment and economic and social conditions. As urbanization is speeding up and people’s living standards are continuously improving, the total water consumption is expected to be 7 000-8 000 ×108m3in 2030 (Qian, 2001), making the water resources supply-demand conflict more prominent.The rapid urbanization in small and medium-sized river basins in the southeast coast has already led to rapid increase in water demand, increasing water pollution, and the disappearance of rivers and drainage systems. This has triggered a series of urban hydrology, water resources and water environment problems, which has a far-reaching impact on the sustainable use of water resources, hinders local people’s lives, and impedes the sustainable development of the urban economy.

As the development core of the Southwest Fujian Economic Cooperation Zone, Xiamen City has an ever-increasing demand for water resources,and its freshwater resources are very scarce. In the past ten years, the total water consumption in Xiamen has been fluctuating and slowly rising,with the annual average water consumption of 6.28 × 108m3and an annual average per capita water consumption of 331.9 m3. According to the reference index of water stress proposed by the United Nations in the “Comprehensive Assessment of Freshwater Resources of the World”, Xiamen City faces high water stress and the ratio of water consumption to available water is ＞40% (Shi,2002). In the past decade, Xiamen’s average utilization ratio was 26.52%, peaking 46.76% in some years, which exceeded the internationally recognized ecological alert line of 40%. Influenced by growing pressure of urbanization, insufficient water endowment and other factors, Xiamen’s water resources are highly vulnerable (Xie et al.2020). Huang et al. (2009) constructed an index system to characterize the water resources supply and demand balance (WRSDB) of each link of its water cycle system, and their results showed that the WRSDB index of Xiamen is lower than that of other regions in Fujian Province, indicating that Xiamen is under higher demand pressure. Xu(1999) measured the water resources required for the rapid development of Xiamen Special Economic Zone, and found that the city’s water shortage was 500 × 106m3in 2010. Previous studies have preliminarily evaluated the current situation of water resources in Xiamen and concluded that the acute water shortage may hinder socio-economic development. However, previous studies failed to analyze water supply sources and demand structure. Therefore, there is an urgent need to research the supply and demand balance of water resources and to analyze Xiamen’s water supply and demand in 2030 under different scenarios, so that we can identify the supply security issues, and help develop a joint resources distribution plan.

Water resources supply and demand balance analysis, as foundational preliminary work, is indispensable in mapping out the future spatial and temporal distribution of surplus and deficit, mitigating the supply and demand conflict, and formulating a long-term plan (Wang et al. 2003; Dong et al. 2008). The traditional methods of water resources supply and demand balance analysis mainly include series method and typical year method (Liu et al. 2011). In recent years, the utilization of water resources has coordinated with the social, economic and ecological factors. Also,water resources management has shifted from supply decided by demand to demand management. Many scholars have adopted new theories and methods to analyze the balance of water resources supply and demand, such as numerical modeling method (Hao et al. 2017; Diao et al. 2017;Read et al. 2014; Margaret et al. 2011) and triple equilibrium method (Kang et al. 2011; Cheng et al.2015). The latter, triple supply-demand balance analysis follows the “three first and three later”principle of “saving water first and water transfer later, pollution control first and water supply later,and ecology first and water use later”. This method is benefit for water resources development, economic development, and ecological environmental protection, and provides a scientific basis for the reasonable configuration plan of efficient water use.

1 Study area

Xiamen is an area of scarce freshwater resources(Fig.1). Firstly, water supply for the city is mainly dependent on surface water, lacking a diversified source. The city's water supply in 2018 was 6.73 ×108m3(excluding seawater supply and ecological water compensation), of which surface water,groundwater and other water supply accounted for 92.35%, 6.62% and 1.03%, respectively. Secondly,the surface water is yet insufficient, thus its water supply highly depends on transferred water (Lin et al. 2016). The ratios of local water and transferred water to the total supply in 2018 were 38.01% and 61.99%, respectively. Thirdly, the distribution of water resources quantity, the level of regional economic development and population are imbalanced. Siming, Huli, Haicang and Jimei Districts are home to 75.9% of the city's population and 80.3% of the gross regional product (GDP), but only 24.5% of water resources is available in the region; Tongan District, on the other hand, holds 55.4% of the resources, respectively accounting for 14.9% and 8.8% of population and GDP of the city(Table1).

Fig.1 Terrain and location of the study area

Table1 Population, GDP, water resource distribution of Xiamen in 2018

2 Methods and data

2.1 Methods

Water supply and demand balance analysis refers to the analysis of the relationship between the water supply and demand of each sector in a certain region and a period of time with a guarantee probability. In this study, the triple equilibrium method was applied in performing the supply-demand analysis at a full-caliber and a basin-wide level for different purposes.

The first equilibrium analysis aims to quantify the regional water resources supply and demand without supplemental water supply and water conservation, from which the gap between the supply and demand under the circumstance of population growth and economic development can be identified. Furthermore, this gap will be used as the maximum level for the local government to plan the socio-economic development goals in the target years of planning.

Based on the local water resources, the second equilibrium analysis aims to suppress the demand for water supply so as to reduce the supplydemand gap derived from the first equilibrium analysis. The resulting gap from the second equilibrium analysis is hence considered as the prevailing gap for planning to fully utilize the water supply capacity in the area of interest in the target years of planning.

Based on the second equilibrium, the third equilibrium analysis aims to balance the supply and demand at a regional level by transferring water. The subsequent gap is the unsolved shortage of water resources in the target years of planning,after supplementing the resources via transferring water.

2.2 Data

The data on water consumption are mainly obtained from the Statistical Communiqué of Xiamen’s Economic and Social Development (2009-2018),Xiamen Special Economic Zone Yearbook (2009-2018), Xiamen Water Resources Communiqué(2009-2018), The 13th Five-Year Plan for Economic and Social Development of Xiamen City, the 13th Five-Year Plan for Water Resources Development, the Xiamen Population Development Plan(2016-2030), Beautiful Xiamen Environment Master Plan (2014-2030), Xiamen Strategic Plan for Water Resources (2015-2030), and etc.

3 Results and discussion

3.1 Water supply and demand in 2030

3.1.1 The first supply and demand balance

Taking 2018 as the base year, the forecast of Xiamen's water supply and demand situation under different guarantee rates (i.e. p=50%, p=75%,p=95%) in 2030 was conducted without considering the increments in both water supply and water saving based on the changes in climate, hydrology, population, urbani zation, industrial layout,industrial, agricultural and domestic water supply conditions in the past ten years, as well as the regional development plan for the year of 2030.

3.1.2 Water supply

When the probabilities are 50%, 75% and 95% in 2030, respectively, the surface water supplies available in Xiamen will be 3.19 × 108m3/a, 2.80 ×108m3/a, and 2.28 × 108m3/a, while the quantities of water transferred from other regions are 5.32 ×108m3/a, 4.32 × 108m3/a and 2.36 × 108m3/a.Other sources such as groundwater and recycled sewage water will be 0.49 × 108m3/a and 0.07 ×108m3/a. For the probabilities of 50%, 75% and 95%, respectively, the available supplies are 9.07 ×108m3/a, 7.68 × 108m3/a and 5.20 × 108m3/a(Table2).

Table2 Available water resources in 2030 at different guarantee rates (108 m3)

3.1.3 Water demand

According to estimates of Xiamen’s residential,industrial, agricultural and ecological water uses at each district in 2030, the total water demand will be 10.11 × 108m3/a, 10.21 × 108m3/a and 10.32 ×108m3/a for the guarantee rates of 50%, 75% and 95%, respectively (Table3).

Table3 Estimated total water demand in Xiamen, 2030 (108 m3)

3.1.4 Analysis of supply and demand balance

It can be learned from the estimates of water demand and supply of Xiamen in 2030 that the regional water shortages will be 1.04 × 108m3,2.53 × 108m3and 5.12 × 108m3in normal years(p=50%), dry years (p=75%) and extraordinarily dry years (p=95%), respectively, with water deficiency ratio of 10.29%, 24.78% and 49.61% (Table4, Fig.2). Among these, Tongan District will have the surplus in normal years (p=50%) and dry years(p=75%). Besides, Jimei District will have the surplus in normal years (p=50%). Other districts will face water shortage.

Fig.2 Water resource demand and supply in 2030(First equilibrium)

Table4 Predicted water demand and supply (First equilibrium) (108 m3)

3.2 The second supply and demand balance analysis

3.2.1 Water supply

The water available in the second balance analysis is the same as in the first balance analysis, i.e. the total available water quantities are 9.07 × 108m3/a,7.68 × 108m3/a and 5.20 × 108m3/a for the guarantee probability of 50%, 75% and 95%, respectively.

3.2.2 Water demand

On the demand side, the water consumption quota for residential use will be reduced by promoting water conservation campaigns, water price adjustment and various measures; industrial water consumption will be reduced by adjusting the industrial layout, optimizing the internal structure and improving production technology; agricultural irrigation water consumption will be reduced by targeted management, water-saving irrigation technology and other measures, so as to contain the rapid increase in the total water demand.

According to Xiamen City Water Resources Report (2009-2018), based on the permanent population, the comprehensive daily water consumptions for per capita in urban and rural areas in the past decade were 157 L/(cap.d) and 153.4 L/(cap.d)respectively, which were both higher than the quota set by Fujian Province Local Standard for Industrial Water Use DB35/T772-2007 (referred to“the Standard” ) of 120-180 L/(cap.d) for urban residents and 70-150 L/(cap.d) for rural residents.Therefore, a huge potential for water conservation can be seen.

In the past decade, Xiamen’s water consumption per ¥10 000 of the industrial gross value added(GVA) has shown a significant downward trend,from 24.1 m3in 2009 to 7.7 m3in 2018. But Xiamen still has more water-saving potential compared with other developed cities in China. For example, Shenzhen’s water consumption per¥10 000 of the GVA in 2018 was 5.25 m3, 68% of that in Xiamen.

Xiamen’s average water consumption per Mu for agricultural irrigation fluctuated between 491.6 and 677.8 m3from 2009 to 2018, with no discernable drop. Compared with the quotas in “the Standard”, on average, all crops in Xiamen consumes more water per Mu, thus indicating a bigger potential for water saving in farmland irrigation.We suggest that various water conservation measures should be adopted to reduce industrial consumption quotas and water demand. In this forecast of water demand in 2030, the domestic water quota is set to be 132 L/(cap.d) for urban residents and 77 L/(cap.d) for rural residents. The industrial water quota is set as 5.12 m3for per ¥10 000 GVA in light industry and 5.66 m3for per ¥10 000 GVA in heavy industry. The agricultural quota is set according to the water quota for all crops specified in irrigation zone II of “the Standard”.

It is estimated that compared with the results of first demand and supply balance analysis, the second balance analysis can reduce the demand for residential, industrial, and agricultural water by 0.51 × 108m3/a, 11.05 × 108m3/a and 0.61×108m3/a respectively in a normal flow year (p=50%).Therefore, after the second balance, Xiamen’s total water demands in 2030 at the guarantee levels of 50%, 75% and 95% are 7.94 × 108m3/a, 8.03 × 108m3/a and 8.13 × 108m3/a, respectively (Table5).

Table5 Water demand in 2030 by the second budget analysis (108 m3)

3.2.3 Analysis of supply and demand balance

Water conservation measures further reduce water consumptions which eases the conflict between regional water supply and demand in 2030. A normal flow year (p=50%) will see a water surplus of 1.13 × 108m3(Table6, Fig.3). However, their spatial distributions are uneven. There is still water supply gap in the Huli and Xiangan Districts,where the water shortages are 0.39 × 108m3and 0.07 × 108m3, respectively, and the deficiency rates are 28.26% and 4.64%. The dry years(p=75%) and extraordinarily dry years (p=95%)will see a supply and demand conflict, with the water shortages of 0.35 × 108m3and 2.93 × 108m3,and water deficiency rates of 4.36% and 36.04%,respectively.

Fig.3 The water resource demand and supply in 2030 (Second equilibrium)

Table6 Water resource demand and supply in 2030 (Second equilibrium) (108 m3)

3.3 The third supply and demand analysis

According to the Three-Year Action Plan for Improving Urban Water Quality in Xiamen, the water supply project, Changtai Fangyang water conservancy project, was completed by the end of 2020.The project will provide the average annual water supply of 2 × 108m3to the Xiamen city, which in 2030 will further narrow the gap between the water supply and demand and meet the domestic and production demands for water supply in both normal (p=50%) and dry (p=75%) years (Table7,Fig.4). In extraordinarily dry years (p=95%), the district of the city remains a water shortage of 1.83× 108m3and a water deficiency ratio of 22.51%.The water deficiency ratios of 36.61% and 37.82% in the Siming and Huli districts, respectively, yet show a high water shortage in the extraordinarily dry year.

Fig.4 The water resource demand and supply in 2030(Third equilibrium)

Table7 Water resource demand and supply in 2030 (Third equilibrium) (108 m3)

4 Conclusions and Suggestions

4.1 Conclusions

(1) The results of the triple balance analyses show that Xiamen is an extremely water-stressed city with a large water supply gap in 2030. In the case of no effort made towards saving the water resources, the maximum water deficiency in an extraordinarily dry year is as high as 5.12 × 108m3, with the water deficiency ratio of 49.61%. In a normal year, the total water demand will drop to 7.94 ×108m3, 80% of the total demand before taking water conserving measures. The industrial water conservation will be the biggest contributor, accounting for 48.4% of the total saved water, whereas domestic water and agricultural water will take up 28.1% and 23.5%, respectively. Haicang and Xiangan districts will still have comparatively huge water conservation potential, but not for Siming districts where the saved water will be mainly from domestic usage.

(2) Transferring more water can increase the regional water supply for Xiamen in 2030, but in extraordinarily dry years, the area still has a water shortage of 1.83 × 108m3(p=95%), with a water deficiency ratio of 22.51%. In addition, domestic water use tends to gradually rise, especially in the Siming and Huli districts, where most water is used for domestic supply, leaving a small potential for water conservation. Their water deficiency ratios will be 36.61% and 37.82%, respectively.

4.2 Suggestions

The cities in the middle and small watersheds along the southeast coast are affected by factors such as geographic location and population, which are water-scarce cities. The level of water resources carrying capacity is more affected by the level of water resources development and utilization and the degree of social and economic development, and less affected by the amount of local water resources.

In order to improve the urban water resources carrying capacity in the short term, it is necessary to seek new water sources and accelerate the construction of new water diversion projects, but it is difficult to improve the water availability and water quality of small and medium-sized river basins. Compared with Shenzhen, which is also a water-scarce city, the utilization efficiency of water resources in small and medium-sized river basins in southeast coastal cities such as Xiamen is not high. The overall strategy for ensuring the water security shows that local water should be conserved, transferred water should be wisely used, desalinated water should be prepared, and recycled water should be prepared. China Institute of Water Resources and Hydropower Research.2015. Amoy Strategic Plan for Water Resources(2015-2030) (in Chinese). In addition, it is proposed to optimize the water consumption structure,accelerate industrial upgrading, and improve water resources utilization, so as to conserve more water,balance the supply and demand for the resources,and improve the carrying capacity of urban water resources.

Acknowledgement

This paper was funded by the Geological Survey Project of China Geological Survey "Comprehensive Geological Survey of Xiamen-Zhangzhou-Quanzhou City" (DD20190303).