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ARTICLE OPEN Water scarcity will constrain the formation of a world-class in North China ✉ ✉ Zhuoying Zhang 1,2, Minjun Shi 3 , Kevin Z. Chen4,5 , Hong Yang6,7 and Shouyang Wang 1

The formation of world-class has been a goal of urban development agencies around the world owing to their economic advantages. On their bids of becoming a world-class megalopolis, water availability is a factor that requires consideration. China has set an ambitious goal of developing a world-class megalopolis in the water-scarce Beijing-Tianjin-Hebei (BTH) region. This study investigates the water challenge the BTH region faces and the effects of main water conservation measures in the region towards the goal. An inter-city input–output model was constructed for identifying the water gap in the region and analyzing the effectiveness of main water conservation measures under various scenarios. The results indicate a significant gap between the water required to achieve the goal of becoming a world-class megalopolis and the region’s available water resources. Although proposed water conservation measures of improving water use efficiency and reducing agricultural water use provide a modest improvement, the amount of water required for urban development still exceeds the availability. The study emphasizes the significance of agricultural water use reduction in Hebei through crop system replacement from water-intensive winter wheat to water-saving crops. The study also proposes an alternative option of adjusting the development plan through redefining the boundary of the BTH megalopolis by excluding part of cities in Hebei. The results of this study contribute to a better understanding of the effect of water scarcity on urban development and thus provide references for other water-scarce regions with ambitious

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INTRODUCTION There are six internationally acknowledged world-class megalopo- The past decades have witnessed significant through- lises, including the Atlantic Coast megalopolis, the Japan Pacific out the world. According to a report by United Nations, 55% of the Coast megalopolis, the , the Northwestern world’s population lives in urban areas in 2018 and this proportion Europe megalopolis, the Yangtze River Delta megalopolis, and the 12,13 is expected to increase to 68% by 20501. Acceleration of urban British megalopolis . expansion and transformation has boosted the formation of Not surprisingly, the formation of megalopolises has become a megalopolises, which are concentrated urbanized areas with goal of many urban development agencies around the world. A highly developed spatial form of integrated cities2. Extensive challenge is how to ensure a rapid urban expansion sustainably. empirical studies showed the positive productivity gains from the Water is indispensable in almost every production and consump- formation of megalopolises for countries engaging in international tion process. Water scarcity has been challenging sustainable competition and cooperation in an increasingly global economy3–5. urban development globally. In 2019, the United Nations World The formation of megalopolises fortified urban scale economies Water Development Report indicated that the global water use through better access to inter-industry information flows, abun- had been increasing worldwide by ~1% per year since the 1980s, dant, and diversified labor forces, specialized services, as well as driven by a combination of population growth, socio-economic general public infrastructure and facilities. World-class megalopolis development, and changing consumption patterns14. Global represents the highest level of megalopolises. The earliest water demand is expected to increase by 20–30% until 2050, prototypical conception for world-class megalopolis can be traced and much of the growth will be attributed to increase in demand back to the megalopolis of “BosWash corridor” in the northeastern of the industrial and domestic sectors15,16. Megalopolises, where United States, which included the large cities of , New York, agglomerations of population and production activities bring Providence, Hartford, New Haven, Philadelphia, Baltimore, and about the increasing demand for water resources, commonly Washington6. From this study onward, the connotation has been encounter water crisis and this, in turn, restricts their further continuously enriched by subsequent scholars7–11. However, a development17,18. Figure 119 demonstrates a high correlation consensus on a specificdefinition for world-class megalopolis has between the economic growth of the world-class megalopolises yet to be reached. It is generally agreed that the common features and the abundance of water resources, verifying the significance of the world-class megalopolis should include: densely clustered of water resources to megalopolises’ economic development. A cities and non-agricultural population, sufficiently large economic high level of economic growth requires sustained and adequate size, highly developed industries (particularly, tertiary industries), water supply, as water is the principal factor supporting the one or multiple internationally influential core cities and closely development of a region. Given the fact that the six internationally integrated economic connections among cities in the megalopolis. acknowledged world-class megalopolises are not water-scarce

1Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, China. 2Key Laboratory of Management, Decision and Information Systems, Chinese Academy of Sciences, Beijing 100190, China. 3School of Public Affairs, Zhejiang University, Hangzhou 310058, China. 4China Academy for Rural Development, Zhejiang University, Hangzhou 310058, China. 5International Food Policy Research Institute. 1201 Eye St. NW, Washington, DC 20005-3915, USA. 6Swiss Federal Institute of Aquatic Science ✉ and Technology, Duebendorf 8600, Switzerland. 7Department of Environmental Sciences, University of Basel, Basel, Switzerland. email: [email protected]; [email protected]

Published in partnership with RMIT University Z. Zhang et al. 2 4,200

The Great Lakes The Atlantic Coast The Japan Pacific Coast 3,600 megalopolis megalopolis megalopolis

3,000

2,400 The British megalopolis The Yangtze River Delta megalopolis

GDP (billion USD) 1,800 The Northwestern Europe megalopolis

1,200

The BTH region

600

0 0 300 600 900 1,200 1,500 1,800 Water use per capita (m3/cap) Fig. 1 Correlation between economic growth and water use in the BTH region and existing world-class megalopolises (year 2017). A plot of GDP versus annual per capita water use in the BTH region and the six existing world-class megalopolises. It demonstrates a high correlation between the economic growth of the world-class megalopolises and the abundance of water resources.

regions, the restrictive effect of water did not capture much economic development and water resources. Beijing is the most 1234567890():,; attention in their development. As ambitious urban development economically developed entity, with the highest GDP per capita, goals are being put forward in a number of water-scarce regions in followed by Tianjin. Hebei is the least developed area among the the world, water availability is a critical factor that requires three. Water conditions are relatively better in the cities in consideration. northern Hebei, with annual per capita water resources averaged The Chinese government is promoting the Beijing-Tianjin-Hebei over 400 m3. The cities in southern Hebei are water scarcest, with (BTH) region to become a world-class megalopolis in China in annual per capita water resources <150 m3 (Fig. 219; Supplemen- addition to the Yangtze River Delta megalopolis20. Much attention tary Table 4). A challenging question is whether water scarcity will has been focused on the BTH region since the implementation of prevent the BTH region from becoming a world-class megalopolis. “The Plan for the Coordinated Development of Beijing, Tianjin, and Given the significant spatial heterogeneity and nonnegligible Hebei” enacted by the Chinese central government in 2015. The economic connections across cities in the BTH region, it is Plan has proposed the long-term goal for the BTH region to necessary to incorporate city-level differences and inter-city become a world-class megalopolis. However, the BTH region is connections in analyses of the region’s water challenge on its severely constrained by water availability, with an annual per ambition to become a world-class megalopolis. capita water resources of <200 m3, approximately one-tenth and In recent years, the intensifying resource and environmental one-fortieth of the national and world averages, respectively21.In pressure has attracted an increasing attention from scholars and addition to water scarcity, three further shortcomings of the BTH policymakers on the sustainable challenges encountered in urban region can be identified compared with the existing world-class development22–25. As one of the most fundamental and megalopolises. Firstly, the economic size of the BTH region in indispensable natural resources, water constraint on urban terms of gross domestic product (GDP) is still small. In 2017, the development has led to concern in public and academic BTH region’s GDP was 1.19 trillion USD (The exchange rate circles26–28. Moreover, the studies that look at the water effect between USD and CNY is based on the averaged central parity of developing world-class megalopolises are rare since the rate of 2017, released by the People’s Bank of China), only existing world-class megapolises are not water-scarce regions. ~30–50% of the GDP levels of the six acknowledged world-class Existing studies mainly assessed water-carrying capacity as megalopolises (Supplementary Table 1). Second, most of the reflected in the assessment of population carrying capacity. Water world-class megalopolises are tertiary industry dominated, while carrying capacity was typically defined as the water resources the proportions of the tertiary industries in most BTH cities are needed to sustain a healthy social and economic system, the lower than 50% (Supplementary Table 2). Third, cities in the BTH maximum threshold of water resources to sustain human region are not closely connected with each other to form an activities29–32. As the connotation of water-carrying capacity still integrated megalopolis. The intra-regional trade value of the BTH remains divergent and elusive, a consensus on a specificdefinition region takes up only 29% of the total trade value, indicating the has yet to be reached33. Moreover, previous studies investigating intra-regional trade of the BTH region is not paramount in water constraint on urban development rarely considered the composition of their total trade (Supplementary Table 3). In order implications of intra-regional economic connections owing to lack to achieve the ambitious goal of becoming a world-class of data. This is particularly so between different cities within the megalopolis, it is requisite for the BTH region to put forth efforts megalopolis owing to lack of information of inter-city economic to overcome these shortcomings by promoting the economic connections34–38. Inter-city economic connections reveal how growth, adjusting industrial structure and enhancing intra- different cities depend on each other in terms of intermediate and regional economic integration, while alleviating the severe water final products and services. The pattern of inter-city economic shortage. connections is closely related to the scale and structure of water Moreover, it is worth noting that there is a significant level of use in each city and is therefore an important factor to consider in heterogeneity amongst the cities in the BTH region in terms of the analyses of urban development under water constraints. Inter-

npj Urban Sustainability (2021) 13 Published in partnership with RMIT University Z. Zhang et al. 3

Fig. 2 The administrative areas of the BTH region and its economic and water resource conditions (year 2017). This figure shows the geographical location of the BTH region in China and the significant level of heterogeneity amongst the BTH cities in terms of economic development and water resources. The size of the yellow circles represents the level of GDP per capita and the gradation of colors represents the amount of water resources per capita in the BTH cities. city input–output model is recognized as a robust assessment tool gap for the BTH region in becoming a world-class megalopolis? (ii) representing inter-city economic connections as well as capturing To what extent can the water conservation measures offset the city heterogeneities. Although the importance of city-level water shortages? The Yangtze River Delta megalopolis and the input–output model has been well acknowledged in the Great Lakes megalopolis, which are representative of world-class literatures, the model compilation and application are generally megalopolises of relatively smaller economic size and larger limited due to the unavailable data such as city-level input–output economic size, are set as the two benchmarks for the BTH region. tables39. The existing studies mostly remain at the stage of The results of this study contribute to a better understanding of proposing conceptual and methodological framework for model the BTH region’s challenge of reaching economic development compilation40,41. goals under water resources constraints, and also provide This study makes contribution to existing literatures in the references for other water-scarce regions attempting to develop following aspects: (i) conduct a comprehensive investigation of to the world-class megalopolises. the restrictive effect of water resources relevant to world-class megalopolises, which were rarely studied in previous literatures. This study is of practical meanings for providing references for RESULTS other water-scarce regions attempting to develop to the world- Minimum water requirement for world-class megalopolis class megalopolises. (ii) Investigate the function of water in The minimum water requirement for the BTH region to achieve ensuring urban development from the perspective of water gap, the goal of becoming a world-class megalopolis is simulated by which further enriches the connotation of water-carrying capacity. applying an inter-city input–output optimization model. The (iii) Perform an investigation on urban development under full requirements for the BTH to become a world-class megalopolis consideration of the interaction between economic interconnec- are set as constraints in the optimization model. These constraints tions and water constraints based on an inter-city input–output are concretized by indicators including economic size, industrial optimization. We are fortunate to obtain the city-level structure, and inter-city connection. The selection of these input–output tables of Beijing, Tianjin, and 11 prefecture level indicators was based on the aforementioned shortcomings cities in Hebei and then link them into the inter-city input–output identified by the comparison of the BTH region to the acknowl- model using multi-regional input–output modeling techniques42. edged world-class megalopolises, whereas the values of the The stability and reliability of the inter-city input–output table of indicators were established by referring to the benchmarking the BTH region were verified through its rudimentary application world-class megalopolises (Supplementary Table 5). in the analysis on industrial adjustment43. This approach is capable The simulation results show that to achieve the benchmarks of of fully reflecting the impacts of economic connections across the Yangtze River Delta megalopolis and the Great Lakes cities on water requirements in the BTH region. megalopolis, the minimum annual water requirement for the The study aims to take the BTH region as an example to BTH region would be 37.58 billion m3 and 53.26 billion m3. investigate the effect of water scarcity on urban development by respectively. Given that the annual average water resources of answering the following two questions: (i) how large is the water the BTH region is 20.40 billion m344, an extra amount of 17.18

Published in partnership with RMIT University npj Urban Sustainability (2021) 13 Z. Zhang et al. 4

Fig. 3 Water gaps for the BTH region to achieve the two benchmarking goals (unit: billion m3). The bars show the minimum annual water requirement for the BTH region to achieve the benchmarking goals of the Yangtze River Delta megalopolis and the Great Lakes megalopolis. The blue line is the level of the annual average water resources in the BTH region. The red areas above the blue line represent the water gaps for the BTH region to achieve the benchmarking goals.

billion m3 and 32.86 billion m3 water would be needed. Even for The simulation results indicate that by improving water use the most achievable goal of the Yangtze River Delta megalopolis, efficiency, the minimum amount of water required for the BTH the water gap is almost equivalent to the current amount of water region to achieve the goal of benchmark I (the Yangtze River Delta resources in the BTH region. The modeling results indicate that the megalopolis) will fall to 30.84 billion m3, 6.74 billion m3 lower than gap between the local water resources and the water required for the aforementioned minimum water requirement without any becoming a world-class megalopolis is high (Fig. 319). additional conservation measures. However, subsequent to conservation efforts there is still a remaining water gap of 10.44 3 The BTH region’s maximum GDP without conservation measures billion m between the water required for development and local water resources. The results show that reducing agricultural water This section investigates the maximum GDP that the BTH region use is a more significant water conservation measure, leading to a can achieve under the current conditions without the application water use reduction of 14.86 billion m3. However, a water gap of of any additional water conservation measures, based on the 2.32 billion m3 still remains. If the two measures are jointly simulation of the inter-city input–output optimization model. In adopted, the minimum water requirement would be decreased to the model, it sets maximize GDP of the BTH region as the 15.58 billion m3. The local water resources of the BTH region objective function and predicted water use not exceeding the would be sufficient to meet its demand to achieve the goal of local water available as the constraint. benchmark I. The results indicate the importance of adopting The results indicate that in the absence of additional water different water conservation approaches simultaneously when conservation measures, the maximum GDP that is achievable in addressing water scarcity. Under the goal of benchmark II (the the BTH region would be 1.34 trillion USD, only 12% higher than Great Lakes megalopolis), the water conservation effects of the current level of 1.19 trillion USD. The maximum GDP of the improving water use efficiency and reducing agricultural water BTH region is well below that of the six acknowledged world-class use are 7.39 billion m3 and 16.4 billion m3, respectively. However, megalopolises. This is significantly smaller than the existing world- the joint effect of the two measures is 24.71 billion m3, which is class megalopolises. Even compared with the British megalopolis, incapable of offsetting the water gap for benchmark II (Fig. 519). which has the smallest GDP, the maximum achievable GDP for the BTH region is still ~35% lower (Fig. 419). DISCUSSION Effects of water c