Water Supply-Demand Situation Analysis Based on a Hierarchical Index System


 In this study, a hierarchical index system is proposed for analysis of water supply-demand situation, which can overcome the shortcomings of complicated analysis and ambiguous decision, associated with the use of a single index like water shortage or water shortage ratio. Five indices responsible for water supply-demand imbalance are considered on both water resources supply and demand sides, and corresponding regulation strategies are proposed to restore water supply-demand balance by improving the water supply capacity of conventional and non-conventional water resources, improving water-use efficiency, and controlling the social and economic development scale. The proposed hierarchical index system has been successfully applied to the analysis of the water supply-demand situation in Qingdao. The results reveal that in order to improve the severe water supply-demand situation in Qingdao, it is necessary to divert water from other regions and improve agricultural water-use efficiency. This study may provide insights into the design and preparation of inter-basin or cross-regional water diversion projects and the formulation of annual water diversion plans.


Introduction
The gap between the uneven spatial and temporal distribution of water resources and the water demand from different sectors makes water supply a challenging task, and it is estimated that over one billion people in the world have no or limited access to safe drinking water (WHO, 2017). Worse still, climate change is exacerbating the severity of water supply-demand imbalance (Distefano and Kelly, 2017). A notable example is the so-called "Day Zero" experienced by the city of Cape Town in South Africa in June 2018, in which the city almost ran out of water due to a severe multi-year drought. In July 2019, Chennai, the capital city of Tamil Nadu in southern India, also faced an unprecedented water crisis due to monsoon failure (Ahmadi et al. 2020). Water resources allocation is expected to be a promising strategy to ensure water supply security, and the analysis of water supply-demand situation is the basic support of water resources macro-allocation. It should also be noted that the water supply-demand situation is likely to change with the advent of new policies and technologies (Schütze et al. 2019). In China, the actual water consumption described in China Water Resources Bulletin (Ministry of Water Resources of the People's Republic of China, 2010-2020) is more than 10%lower than the forecasted water demand described in National Integrated Water Resources Plan (Ministry of Water Resources of the People's Republic of China, 2010) in most basins and regions, and ecological water demand is also not taken into consideration in previous plans.
A common way for analysis of water supply-demand situation is to predict water demand and supply separately and then take the difference between them as the index of water shortage or water shortage ratio. Note that the prediction of water supply is often based on the available water supply for the basin or region of interest under the constraints of water diversion projects (Lv et al. 2016;McDonald et al. 2014); while that of water demand is mainly based on the quotas that are o cially released such as social and economic development indices, standards and speci cations. Because of this, there are several issues that need to be addressed: (1) the general neglect of ecological issues may lead to less or even no availability of water to be supplied for ecological purposes in the prediction of water supply (Paul and Elango, 2018); (2) the prediction of water demand based on various social and economic indices is highly subjective in nature that is mostly determined by basin or regional planning rather than by actual situation (Saleem et al. 2021); (3) the use of water quotas from current standards or speci cations does not take into account the improvement of water-use e ciency in the future (Ray and Shaw, 2016); (4) the prediction of water demand is often complicated considering the complex classi cation of water users, quality and quantity of data required, and choice of appropriate analysis method (Qin et al. 2018); (5) the use of a single index like water shortage or water shortage ratio makes it di cult to answer some questions that are more interesting to the authorities, such as the main causes of water shortage, satisfaction degree of rigid water demand, and exploration degree of water supply potential (Distefano and Kelly, 2017;Höllermann et al. 2010). In short, it remains di cult to match the scale, layout, structure and speed of social and economic development and water-use e ciency to the availability of water resources, and as a consequence the water demand that is closely associated with population, industrial layout, land and other resources in a given region is very likely to exceed or fall short of the supply capacity of water sources.
In this study, a hierarchical index system is proposed for analysis of water supply-demand situation considering the determinant factors on both supply (e.g., water sources and water supply potential) and demand (e.g., water users and water-use e ciency) sides from a macro perspective, based on which the causes of water shortage and corresponding regulation strategies could be determined. Thus, the results of this study may provide some insights into the design and preparation of inter-basin or cross-regional water diversion projects and the formulation of annual water diversion plans.

Methodology
In this study, the term water supply potential refers to the available water supply of conventional or nonconventional water sources on the premise that the basic ecological water demand is satis ed (You et al. 2020); and the term rigid water demand refers to the quantity of water required to ensure human survival, social stability and attainment of national strategic goals on the premise that the water-use e ciency can satisfy the water-saving requirement (Wang et al. 2020).

Development of the hierarchical index system
The water supply-demand situation is the result of numerous factors on both supply (e.g., water sources and water supply potential) and demand (e.g., water users and water-use e ciency) sides. A hierarchical index system is proposed in order to identify the determinant factors affecting water supply-demand imbalance and subsequently to develop regulation strategies that can restore water supply-demand balance. In order to achieve this objective, all possible factors on both supply and demand sides should be taken into consideration. Finally, four possible regulation strategies are proposed: improving the water supply capacity of conventional water sources, improving the water supply capacity of non-conventional water sources, improving the water-use e ciency (Hurlimann and Wilson, 2018), and controlling the social and economic development scale (Veerbeek, 2017). The hierarchical index system and representative indices are shown in Fig. 1.

Indices on the level of regulation direction
The indices on the level of regulation direction are used to determine from which side, the supply side or the demand side, the determinant factors responsible for water supply-demand imbalance might originate. Here, the water supply capacity of water sources (index A) is taken as the index on the supply side; while the proportion of rigid water demand (index B) is taken as the index on the demand side: where AWS c and AWS uc are the available water supply of conventional and non-conventional water sources, 10 4 m 3 , respectively, both of which are dependent on the design capacity of the water diversion project. However, it should be noted that the water supply capacity may decline over time because of infrastructure aging or disrepair; P c is the potential for conventional water development, 10 4 m 3 ; P uc is the potential for unconventional water development, 10 4 m 3 ; WD r is the rigid water demand, 10 4 m 3 ; and WD t is the total water demand for domestic, industrial and ecological uses, 10 4 m 3 .

Indices on the level of regulation strategy
The indices on the level of regulation strategy are used to determine the constraints of water shortage on the supply and demand sides in order to provide more appropriate regulation strategies to restore water supply-demand balance. The strategies on the supply side are intended to improve the water supply capacity of conventional (index A1) or non-conventional (index A2) water sources: A2= AWS uc / P uc (4) The strategies on the demand side are intended to improve the water-use e ciency in different sectors and control the social and economic development scale. Whether the industrial and agricultural water-use e ciency should be improved is determined by the decreasing rate of water consumption for industrial value added per ten thousand RMB (index B1) and that for irrigation per hectare (index B2), respectively: where WC i−p and WC i−f are the water consumption for industrial value added per ten thousand RMB in the present and planning year, m 3 /10 4 RMB, respectively; WC a−p and WC a−f are the water consumption for irrigation per hectare in the present and planning year, m 3 /ha, respectively.
In addition, whether there is a need to control the social and economic development scale and whether the condition is mature can be determined depending on the circumstances.  Table 1.

Evaluation of indices on the level of regulation strategy
According to the indices evaluation partition results, the regulation strategies on both supply and demand sides are calculated and evaluated in four scenarios.

Scenario 1
If the values of indices A and B fall in region I in Fig. 2, there is a need to improve the water supply capacity on the supply side and improve the water-use e ciency on the demand side according to the regulation direction described in Table 1. In this case, the indices A1 and A2 on the supply side are calculated and compared to determine the water supply potential of conventional and non-conventional water sources. The indices evaluation results are divided into three regions as shown in Fig. 3, and the regulation strategies represented by the speci c evaluation results are shown in Table 2. Also, the indices B1 and B2 on the demand side are calculated and compared to determine the industrial and agricultural water-use e ciency. The regulation strategies represented by the speci c evaluation results side are shown in Table 3.

Scenario 2
If the values of indices A and B fall in region in Fig. 2, there is a need to improve the water supply capacity on the supply side and control the social and economic development scale on the demand side. In this case, the evaluation results and the regulation strategies on the supply side can refer to Fig. 3 and Table 2, respectively. On the demand side, some regulation strategies should be taken to reduce water consumption, such as reducing the population, optimizing the scale of economic development and adjusting the industrial structure.

Scenario 3
If the values of indices A and B fall in region in Fig. 2, there is a need to control the social and economic development scale on the demand side. In this case, the evaluation results and the regulation strategies can refer to Scenario 2. Fig. 2, there is a need to develop the water transfer project on the supply side and improve the water-use e ciency on the demand side. In this case, the evaluation results and the regulation strategies on the demand side can refer to Table 3. On the supply side, the potential sources of water transfer project should be actively sought to enhance water supply capacity.

Study Area
Qingdao is located in the southeastern of Shandong Peninsula and borders the Yellow Sea (E 119°30′ 121°00′, N 35°35′ 37°09′). The geographic location is shown in Fig. 4. Now Qingdao has a total population of over 10 million and a total area of 11282 km 2 . Qingdao is an economically important city and it is well known as an important coastal open city in North China, one of the ve cities that are speci cally designated in the state plan, the leading city of the Blue Economic Zone of Shandong Peninsula. Thus, there is an increasing demand for water resources in order to maintain the rapid social and economic development of Qingdao.
However, the spatial and temporal distribution of precipitation in Qingdao is rather uneven with signi cant intra-and inter-annual variability, and it is also prone to drought and ooding. The rivers in Qingdao generally have short courses with no tributaries and ow rapidly and directly into the sea. The average annual precipitation is 679.43 mm, the average annual amount of water resources is 2.148 billion m 3 , and the amount per capita is 231 m 3 , accounting for only 11% of the national average and 73 of the provincial average of Shandong Province. As a city with limited water resources, Qingdao is facing increasing pressure on water supply security. It is necessary to develop new techniques for analysis of water supply-demand situation based on new ideas and situations, which can improve the utilization of water resources and the high-quality social and economic development of Qingdao. Hence, the water supply-demand situations of Qingdao in 2020 (current year), 2025 (short-term), and 2035 (long-term) are analyzed.

Data
The social and economic data in 2020 are obtained from the Statistical Yearbook of Qingdao 2021, the Statistical Bulletin of the Economic and Social Development of Qingdao 2020 and the data of water resources are obtained from the Statistical Bulletin of the Water Resources of Qingdao 2020.
Given the large inter-annual variation of water resources in Qingdao, the in ow and water demand in extremely dry years are analyzed in order to ensure high water supply security. The basic indices include AWS c , AWS uc , P c , P uc on the supply side, and WD r , WD t on the demand side. The calculation results are shown in Table 4.  The inter-annual variation trends of indices A and B are shown in Fig. 6. The increasing trend of index A implies that the water supply of conventional and non-conventional water sources is approaching the maximum capacity, and this will lead to an increase in the utilization rate but a decrease in the supply potential of local water sources. Once the utilization rate reaches the upper limit in the future, there would be no way to further increase the water supply if no new water diversion projects are built. However, the index B shows a decreasing trend, indicating a decrease in the percentage of rigid water demand. Although both rigid and total water demand have been increasing rapidly in recent years, there should be an upper limit for rigid water demand, and thus its percentage would decrease with the increase of water demand in the future.
In conclusion, this study emphasizes the importance of diverting water from other regions and improving the water-use e ciency in the future in Qingdao.

Water demand-supply balance
The indices B1 and B2 are calculated, as shown in Fig. 7. It is seen that the values of B2 are larger than the values of B1 in 2020, 2025 and 2035, indicating that the agricultural water-use e ciency is always lower than the industrial water-use e ciency in Qingdao. This makes it necessary to implement more effective water-saving strategies in the future, such as optimizing plantation structure, implementing water-saving irrigation, and improving the effective utilization coe cients of irrigation water, in order to maximize the agricultural water-use e ciency and avoid unnecessary waste of agricultural water. On the supply side, it is necessary not only to take full advantage of local water sources, but also to divert more water from other regions.
Increase in water demand inevitably leads to con icts among water users which usually have con icting preferences and priorities, and priority should always be given to water supply for urban domestic use. In case of water shortage in the future, the guarantee rate of urban domestic water supply should also be the highest. The industrial water demand can be adequately met because of the unique advantage of Qingdao in seawater desalinization. As long as the irrigation area remains constant, the agricultural water demand can also be met in years with normal in ow or in which in ow is slightly reduced. However, there would be a low guarantee rate for non-rigid agricultural water demand. On the whole, the future water supply-demand situation is severe in Qingdao and the current water supply system could not maintain water demand-supply balance, resulting in low guarantee rate of water supply and consequently limitation of economic and social development. In order to ensure the steady and sustainable development of Qingdao and the ecological restoration of rivers and wetlands, it is necessary to diver more water from other regions and improve the agricultural water-use e ciency.

Conclusions
In this study, a hierarchical index system is proposed for analysis of water supply-demand situation in a given basin or region, which can overcome the problems associated with the use of a single index like water shortage or water shortage ratio, such as inability to distinguish regulation direction and strategies and complex computation. Five determinant factors responsible for water supply-demand imbalance are considered on both water supply and demand sides, and corresponding regulation strategies are proposed to restore water supply-demand balance by improving the water supply capacity of conventional and non-conventional water sources, improving the water-use e ciency, and controlling the social and economic development scale. The proposed index system has been successfully applied to the analysis of water supply-demand situation in Qingdao. The results reveal that the future water supplydemand situation is severe in Qingdao and it is necessary to divert more water from other regions and improve the agricultural water-use e ciency.
However, some limitations of this study should also be acknowledged. For instance, national development strategies and regional industrial layout should be taken into consideration in the analysis of rigid water demand. However, as it is di cult to obtain the data about regional industrial layout, it is necessary to simplify the analysis of rigid water demand. In addition, the effects of water price and water supply cost on the water supply-demand situation should also be considered in the future.  The geographic location of Qingdao Page 16/17

Figure 5
The evaluation partition results of indices A and B in Qingdao The inter-annual variation trend of indices A and B in Qingdao