Simulation of population size and economic scale supportable by the Yellow River's available freshwater in 2030 under multiple scenarios

Water is fundamental to human and ecological well-being and is central to multiple UN Sustainable Development Goals. The Yellow River Basin (YRB) is economically vital yet water-scarce, with declining runoff and intense development pressures. Traditional assessments of water resources carrying capacity (WRCC) use dimensionless indices, which lack intuitive, quantitative meaning for planning. This study reframes WRCC in terms of population size and economic scale supportable by the YRB’s limited freshwater in 2030 under multiple development scenarios. It addresses two research questions: (1) Can approximately 39.5 billion m³ of available freshwater meet the needs of a projected 0.13094 billion people by 2030? (2) What population size and economic scale can be supported by that freshwater volume? The context includes basin-wide allocation plans and anticipated changes from projects such as the South-to-North Water Diversion, alongside national strategies emphasizing ecological protection and high-quality development.

The paper situates its contribution within WRCC research, noting that many studies use composite, dimensionless indices (e.g., values from 0 to 1) to assess carrying capacity or suitability, which provide relative measures but lack direct interpretability for policy and planning (Li et al., 2023; Peng et al., 2023; Wang et al., 2023; Chen et al., 2023). Foundational definitions of WRCC in China link available freshwater to supportable population, urbanization, and welfare levels, including per capita domestic water use and per capita GDP (Shi and Qu, 1992; Xia and Zhu, 2002; Jia et al., 2004; Wang et al., 2017). The YRB faces runoff declines, water scarcity, and competing demands for ecological protection and development (Wang, 2015; Wang et al., 2019; Dai et al., 2023; Niu et al., 2023). Prior work by Guo et al. (2022) developed a WRCC model for historical periods, highlighting sensitivity of WRCC to per capita GDP growth and water use per GDP. The present study advances the literature by quantifying WRCC in absolute terms (population, GDP) under scenarios reflecting historical trends, thereby improving interpretability and planning relevance.

Study area and data: The YRB spans nine provinces (Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan, Shandong). The analysis adopts provincial units and the 2030 water allocation from the Yellow River Basin Comprehensive Planning (2012–2030), assuming the western route of the South-to-North Water Diversion is operational. Table 1 provides province-level water allocations summing to 39.845 billion m³. Urbanization rates for 2030 were taken from provincial planning. Per capita domestic water use in urban (QU) and rural (QR) areas for 2030 was derived from 2013–2020 time series: trends detected by Mann–Kendall; if rising, predicted using ANN backpropagation autoregression; otherwise, mean values were used. Upper limits were capped by WHO-informed standards: 330 L/d (urban), 165 L/d (rural). Production water use efficiency QGDP was computed as (industrial + agricultural water use)/GDP, excluding domestic and ecological use. Annual growth rate of per capita GDP (gr) and decrease ratio of QGDP (dr) were estimated from historical trends with 2020 as the base year. Assumptions: Ecological water use WE2030 for each province was assumed to be near zero by 2030 due to environmental improvements, based on past basin averages (about 1.5 billion m³ total historically) and recent declines; thus, simulations yield maximum supportable population and GDP under allocated freshwater. Model structure: A WRCC prediction model determines supportable population P2030 and economic scale TWGDP2030 subject to water availability constraints. Total water use equals domestic (WD), production (WP), and ecological (WE) uses, constrained by allocated freshwater TW2030. Domestic use: WD2030 = P2030 × uR2030 × QU2030 + P2030 × (1 − uR2030) × QR2030, where uR is urbanization. Production water: WP2030 = P2030 × Ya2030 × QGDP2030, with Ya per capita GDP and QGDP water per 10,000 CNY GDP. Dynamics: Ya2030 = Ya2020 × (1 + gr)^10; QGDP2030 = QGDP2020 × (1 − dr)^10; QGDP2020 = (WI2020 + WA2020)/GDP2020. Solving for population under constraints gives P2030 approximately equal to TW2030 divided by the sum of per-capita domestic water terms and Ya2030 × QGDP2030. Economic scale is TWGDP2030 = P2030 × Ya2030. Scenario design: Two sets of scenarios were analyzed. (1) Steady-reform, no-major-shock grid: gr from 1% to 8% (step 1%) and dr from 40% to 70% (step 5%), reflecting policy baselines and historical improvements (e.g., ~28% reduction in 2016–2020). Basin totals were obtained by summing provincial results. (2) Most-likely scenarios (high, moderate, low) set by province-specific upper bounds informed by recent averages (NBS 2019–2021) and observed deceleration of growth (World Bank and DRCSC, 2013), and by province-specific upper bounds for dr based on 2011–2020 averages with a 40% lower bound; moderate equals mean of upper and lower bounds. These yield province-level gr and dr settings (Table 2) used to compute maximum supportable population (Table 3) and GDP (Table 4) for each scenario.

- Under the most-likely scenarios, the 2030 allocated freshwater can support maximum populations of 0.16 billion (high), 0.152 billion (moderate), and 0.147 billion (low), all exceeding the planning projection of 0.13094 billion for 2030. - Corresponding maximum economic scales supported are CNY17.5 trillion ($2.52T), CNY15.01 trillion ($2.18T), and CNY13.2 trillion ($1.91T). This represents about 6.9–8.0% of China's total economic scale and 22.4–24.6% of the nine provinces’ total economic scale. - In the broader scenario grid (steady reforms, no major shocks), at gr = 1% and dr = 40%, 39.845 billion m³ can support about 0.18 billion people and an economic scale exceeding CNY12 trillion. - Spatial distributions: Middle and upper reaches (Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia) together can carry about 42.39, 39.14, and 36.98 million people under high, moderate, and low scenarios respectively, while middle and lower reaches (Shanxi, Shaanxi, Henan, Shandong) can carry about 117.17, 112.43, and 109.60 million—about three times as many people with about four times the economic scale (CNY13.67T, 11.89T, 10.50T vs. CNY3.69T, 3.13T, 2.71T for upper/middle) despite only 1.18× more water allocation (21.345 vs. 18.14 billion m³). - Drivers of disparity: Significant interprovincial differences in per capita GDP and water use efficiency (water per 10,000 CNY GDP). For example, in 2030 under high/moderate/low scenarios, average water use per 10,000 CNY GDP for upper/middle reaches is 37.74/45.74/54.19 m³ versus 12.50/14.27/16.09 m³ for middle/lower reaches, a roughly threefold gap. Ningxia’s water use per 10,000 CNY GDP is about seven times Shandong’s under the same scenario. - The YRB can support 8.76–11% of China’s total population by 2030, consistent with national population peaking near 1.45 billion.

The study’s core question—whether approximately 39.5 billion m³ of freshwater can support the projected 2030 YRB population—is answered affirmatively across multiple scenarios. By quantifying WRCC in absolute terms (maximum supportable population and GDP), the analysis offers actionable insights beyond relative indices. Findings underscore the importance of improvements in water use efficiency (reducing water per unit GDP) for expanding both population carrying capacity and economic output, especially under limited water supplies. The strong spatial heterogeneity highlights that middle and lower reaches, with higher water use efficiency and higher per capita GDP, leverage available water to support substantially larger populations and economic activity than upper/middle reaches. These results are relevant for basin management, allocation policies, industrial structure optimization, and targeted technological investment to enhance water productivity, in line with the Yellow River Protection Law and high-quality development goals.

By applying a WRCC prediction model and scenario analysis, the study shows that the YRB’s 2030 freshwater allocation can support populations of 0.16, 0.152, and 0.147 billion and economic scales of CNY17.5T, 15.01T, and 13.2T under high, moderate, and low development scenarios, respectively—exceeding planning population projections. The study advances WRCC assessment by using population and economic scale rather than dimensionless indices, quantifying carrying capacity under multiple trajectories, and providing narratives relevant to water security and socioeconomic planning. Future work should incorporate population density distributions and finer spatial units (municipal/county) to better reflect intra-provincial variability and to align with water-diversion constraints; integrating dynamic ecological water requirements would further refine estimates.

- Ecological water use in 2030 was assumed near zero for provinces, reflecting recent declines; this yields maximum, idealized supportable population and GDP and may slightly overestimate carrying capacity compared to actual future ecological requirements. - Water use efficiency (QGDP decrease ratios) was set using historical trends and expert judgment; unforeseen technological or industrial structure changes could lead to higher or lower efficiencies, introducing uncertainty and potential bias in 2030 projections. - The model does not incorporate population density or spatial distribution within provinces, assuming even distribution. Using provincial units may mask finer-scale constraints; municipal or county-level analyses would improve spatial accuracy and planning relevance.