Water scarcity will constrain the formation of a world-class megalopolis in North China

The study addresses whether severe water scarcity will prevent the Beijing–Tianjin–Hebei (BTH) region from achieving China’s policy goal of becoming a world-class megalopolis. Megalopolises deliver productivity gains via agglomeration, specialized services, and strong inter-city linkages, but typically rely on abundant water resources. Unlike six internationally acknowledged world-class megalopolises, the BTH region is extremely water-scarce (annual per capita water resources <200 m³, about one-tenth of China’s average and one-fortieth of the global average). Beyond scarcity, BTH also lags in economic size, tertiary-industry share, and intra-regional integration. Substantial heterogeneity exists across BTH cities in development and water endowments, especially between northern and southern Hebei. The study’s purpose is to quantify the water gap associated with attaining world-class status and to evaluate how far conservation measures could close this gap, using benchmarks from the Yangtze River Delta and the Great Lakes megalopolises.

Prior research highlights the growing global water demand driven by population, socioeconomic development, and changing consumption patterns, with megalopolises facing heightened water crises. Existing world-class megalopolises are not water-scarce, so water has received less attention in their development. Studies often evaluate water-carrying capacity (maximum water resources to sustain human activities), but definitions are divergent and may not capture inter-city dependencies. A key gap is the limited consideration of intra-regional economic connections due to data constraints, despite their strong influence on city-level water use through intermediate and final demand linkages. Inter-city input–output models are recognized for capturing these connections and city heterogeneity, but applications are limited by the scarcity of city-level IO tables. This study advances the literature by: (i) directly examining water constraints for aspiring world-class megalopolises; (ii) reframing analysis around a quantified water gap; and (iii) integrating inter-city economic linkages and water constraints via an inter-city IO optimization using newly compiled city-level IO tables for BTH.

The study develops an inter-city input–output (IO) optimization model based on the BTH region’s 2012 city-level IO tables (Beijing, Tianjin, and 11 Hebei prefectures), compiled and linked using multi-regional IO techniques. Although not up to date, 2012 reflects conditions around the 2014–2015 planning period and macroeconomic and water-use parameters remained relatively stable; the inter-city IO framework had been previously validated. Simulations use different objective–constraint combinations to estimate: (1) minimum water required to reach benchmarks of world-class megalopolises; (2) maximum GDP achievable under current water availability; and (3) effects of water conservation measures. Objectives: (O1) minimize total regional water use Σ_r Σ_i ω_ir x_ir; (O2) maximize GDP Σ_r Σ_i v_ir x_ir, where ω_ir is direct water use per monetary output for sector i in city r, and v_ir is value-added rate. Constraints include: (C1) IO balance ensuring total demand does not exceed production; (C2) minimum GDP level consistent with benchmark targets; (C3) minimum tertiary-industry share per city; (C4) minimum intra-regional inter-city trade intensity; (C5) total water use not exceeding annual average available water resources W0; (C6) city-level improvements in water-use efficiency, bounding water use per GDP to (1–p_r)ω_e^r; (C7) an upper bound on Hebei’s agricultural water use Σ_r w_agr^r x_agr^r ≤ W_agr^H. Benchmarks: Two reference megalopolises set target levels for economic size, industrial structure, and inter-city connections—Benchmark I: Yangtze River Delta; Benchmark II: Great Lakes—used to parameterize constraints (C2–C4). Conservation scenarios implement policy-planned improvements in water-use efficiency (C6) and reductions in Hebei’s agricultural water use (C7), individually and jointly. The South-to-North Water Transfer Project (SNWTP) is discussed qualitatively regarding potential contributions and utilization constraints.

- Minimum water required to reach benchmarks: • Benchmark I (Yangtze River Delta): 37.58 billion m³/year. • Benchmark II (Great Lakes): 53.26 billion m³/year. Against BTH’s annual average water resources of 20.40 billion m³, the water gaps are 17.18 and 32.86 billion m³, respectively, indicating substantial shortfalls. - Maximum GDP under current water availability without added conservation: 1.34 trillion USD, only 12% above the current 1.19 trillion USD (2017), and still ~35% below the British megalopolis (2.02 trillion USD), implying strong water-imposed economic limits. - Effects of water conservation measures (Benchmark I): • Improve water-use efficiency: reduces minimum requirement to 30.84 billion m³ (saving 6.74), leaving a 10.44 billion m³ gap. • Reduce agricultural water use (Hebei): saves 14.86 billion m³, leaving a 2.32 billion m³ gap. • Jointly applying both: lowers requirement to 15.58 billion m³, enabling achievement within local resources (no gap). - Effects under Benchmark II: • Efficiency improvement saves 7.39 billion m³; agricultural reduction saves 16.40 billion m³; joint effect 24.71 billion m³, still insufficient to close the larger gap. - External water transfer (SNWTP): designed transfer to BTH is 5.73 billion m³ (1.24 Beijing; 1.02 Tianjin; 3.47 Hebei). If fully utilized, it could reduce gaps by ~33% (Benchmark I) and 17% (Benchmark II), but high cost and reliance on subsidies lead to uncertain uptake; much is used for ecological recharge rather than industry. - Agricultural restructuring in Hebei: replacing winter wheat with lower-water crops (spring/summer maize, peanuts, cotton, cereals) can save 2,700–3,000 m³/ha; with 2.35 million ha of winter wheat (2018), potential savings are ~6.34 billion m³ (~50% of Hebei’s agricultural water use). - Redefining BTH boundary: excluding four southern/central Hebei cities (Handan, Xingtai, Hengshui, Cangzhou)—which are weakly connected economically and winter-wheat intensive—reduces water gaps to 11.15 (Benchmark I) and 19.81 (Benchmark II) billion m³, i.e., 35% and 40% lower than for the full region, making goals more attainable.

Water scarcity markedly constrains BTH’s path to world-class megalopolis status; the minimum water needs to meet benchmark economic scale, industrial structure, and inter-city integration exceed local resources by large margins. While improving water-use efficiency helps, the most impactful measure is reducing agricultural water use in Hebei—particularly by shifting from water-intensive winter wheat to less water-demanding crops—which can deliver multi-billion-cubic-meter savings and mitigate groundwater depletion. However, reliance on external transfers (SNWTP) is risky due to high costs, uncertain industrial uptake, and current emphasis on ecological uses; thus internal demand management is essential. Redefining the megalopolis boundary to exclude agriculturally intensive, weakly connected cities further lowers water requirements without undermining regional contiguity and can support an upgraded industrial mix. Collectively, these findings show that the BTH can only achieve world-class status if stringent conservation and/or administrative boundary adjustments are adopted. The study suggests that, in water-scarce contexts, criteria for world-class megalopolises should incorporate water resilience, adoption of advanced water-saving technologies, modernized agriculture, and regional water coordination.

The paper demonstrates that the BTH region’s ambition to become a world-class megalopolis is fundamentally constrained by water availability: required water to match benchmark megalopolises exceeds local resources by 17–33 billion m³. Without additional measures, economic growth potential is limited. Jointly improving water-use efficiency and substantially reducing Hebei’s agricultural water use can make the Yangtze River Delta benchmark achievable within existing water resources; the larger Great Lakes benchmark remains out of reach. An alternative policy is to redefine the megalopolis boundary by excluding four agriculturally intensive, weakly connected Hebei cities, which significantly reduces water gaps. More broadly, for water-scarce regions, the definition of world-class megalopolises should evolve to include water-related capacities and governance. Future research should integrate climate change impacts, consumption pattern shifts, and broader socioeconomic trade-offs to provide more targeted policy guidance.

- Supply overestimation: local water availability is represented by annual average water resources; some portions may be inaccessible or non-exploitable, likely underestimating the true water gap. - Optimistic modeling: optimization provides an idealized allocation that may not be fully attainable in practice. - Data vintage: the inter-city IO base year is 2012; although macro and water-use parameters were relatively stable, more recent dynamics are not captured. - External transfers: SNWTP utilization is uncertain due to high costs and dependence on subsidies, limiting its reliability as a gap-closer. - Socioeconomic trade-offs: measures such as reducing winter wheat may negatively affect farmer incomes; these distributional impacts are not fully quantified.