Unraveling the effect of inter-basin water transfer on reducing water scarcity and its inequality in China

Highlights

• Inter-basin water transfer impacts water supply of 43 out of 76 sub-basins.

• More than a half of the national population benefit from water transfer in China.

• Some water scarce sub-basins along Yellow River act as a water transfer source.

• The high inequality of water scarcity is reduced by up to 7.8% by water transfer.

• China still faces high population weighted water scarcity with water transfer.

Abstract

Securing water supply in the face of increasing water scarcity is one important challenge faced by humanity in sustainable development. Inter-basin water transfer is widely applied to provide water supply security in regions where water demand exceeds water availability. However, the effect of inter-basin water transfer on alleviating water scarcity and its inequality is poorly understood especially at the national scale. Based on a newly compiled database of inter-basin water transfer projects in China, here we report a first national assessment of their effect on securing water supply in different basins. We developed a number of indices to facilitate quantifying the effect of water transfer on water scarcity and its inequality. The capacity of inter-basin transfer projects has been steadily increased, which achieved ~48.5 billion m³ yr⁻¹ by 2016 (equivalent to ~8% of the national water use). The results indicate that water transfer has impacted water supply of 43 sub-basins out of a total of 76 sub-basins, but it hardly changes a basin's water scarcity level (e.g., from water scarcity to low water scarcity). Approximately three quarters of people in China are affected by water transfer. More than a half of the national population (705 million) benefit from alleviated water scarcity, leading to the inequality coefficient reduced from 0.64 under natural water availability condition to 0.59 considering water transfer in 2016. However, 357 million people in water transfer source basins are subject to increased water scarcity, in which ~21% are from water stressed sub-basins. This study reveals for the first time water transfer induced water scarcity and inequality change across sub-basins in China, and highlights the challenges to secure water supply across basins.

Introduction

Securing sufficient water supply to meet the increasing demand from growing population and developing economy is a great challenge facing humanity in this century (Haddeland et al., 2014; Brauman et al., 2016). In China, where per capita water resources availability is only one fourth of the world average and the spatial water resources mismatch population distribution (Yuan et al., 2008; Guan et al., 2014; Sun et al., 2017), an increasing number of river basins are reaching the limit at which water supply can be sustainably delivered to irrigation, industrial and domestic uses. Insufficient water supply may cause portable water supply interruptions, reduced agricultural production and decelerated industrial development. Furthermore, the depletion of local water resources threatens in-stream environmental flows and groundwater, often leading to degraded ecosystem services and adverse environmental impacts. Therefore, securing water supply for human needs while preserving environmental flows is a high priority on the policy agenda of national and local governments of China (Jiang, 2015; Zhao et al., 2015; Wang et al., 2017).

Among many interventions for providing water supply security, inter-basin water transfer is a commonly used engineering approach that directly supplements water to reduce water deficit in water stressed areas (Yevjevich, 2001; Gupta & van der Zaag, 2008; Zhang et al., 2015; Shumilova et al., 2018). This intervention, which often involves large-scale constructions of reservoirs, tunnels and pumping schemes, is a supply-oriented measure to societal challenges (Gupta & van der Zaag, 2008). Though inter-basin water transfer has been criticized for its associated negative societal and environmental impacts (Gohari et al., 2013; Barnett et al., 2015; Berbel et al., 2016; Li et al. 2016; Ding et al. 2020), many applications have been found worldwide (Erskine et al., 1999; Liu & Zheng, 2002; Rey et al., 2016; Nong et al. 2020), because of its effectiveness in reducing regional water pressure and improving water supply security. A recent study analyzed the economic, environmental and social impacts of mega water diversion projects in China, but did not analyze their impact on national water scarcity (Yu e al. 2018).

In many river basins in China, especially in semi-arid and arid regions, water scarcity often occurs when the demand for freshwater exceeds available supply (Jiang, 2009; Liu et al., 2017; Sun et al., 2019), imposing a threat to human water supply security and environmental sustainability. Understanding water scarcity underpins water resources management and water security (Liu et al., 2017). Previous studies assessed water scarcity at different spatial scales (Schlosser et al., 2014; Zhao et al., 2016; Mekonnen & Hoekstra, 2016; Ma et al., 2020), revealing widespread water stress and an exacerbated trend of water shortage in many parts of the world. Most studies have focused on evaluating how human water demand matches/mismatches natural water availability. In particular, the effect of water transfer on provincial water stress alleviation in China was analysed (Zhao et al., 2015), however, it was based on rather coarse provincial water transfer statistics without considering detailed water transfer project data. Yet, there is lack of good understanding of the degree to which water scarcity at the basin scale can be alleviated through a large number of inter-basin water transfer projects.

Water scarcity shows high spatial inequality across regions in China (Sun et al. 2017; Ma et al. 2020). For instance, North China supports more than half of the total population with around 20% of the total water resources in China (Guan and Hubacek, 2007). Water inequality undermines productivity and economic growth, and is likely to reinforce socio-economic inequalities (UNDP, 2006). Previous studies have assessed inequality of water use or scarcity by quantifying regional differences of corresponding spatial variables (Sun et al. 2017; D'odorico et al. 2010; Ma et al. 2020), which advanced our understanding of spatially varied water use stress exerted on natural water systems. Inter-basin water transfer can effectively reduce inequality of water scarcity by relocating water resources across regions. However, the effect of inter-basin water transfer on regional water inequality at a national scale is poorly understood.

The goal of this study is to assess the effect of inter-basin water transfers on securing water supply of China given large spatial disparity between water availability and demand across basins. Here we compile a comprehensive database of inter-basin water transfer projects in China. In combination with sub-basin natural water availability and water use data, we report a first analysis of water scarcity in China considering the effect of inter-basin water transfer. Inter-basin water transfer enables one region's water supply to be strengthened by access to water resources from another region. The results provide a better understanding of the role of inter-basin water transfer in securing water supply and reducing the inequality of spatial water scarcity, which are critical to inform policies towards integrated water resources management across basins.