Water resource synergy management in response to climate change in China: From the perspective of urban metabolism

Highlights

• Climate change exacerbate water crisis from supply and demand-based perspectives.

• Low-carbon technologies increase water usage from an indirect demand perspective.

• Agricultural water-saving could compensate industrial water in the short terms.

• BECCS will strengthen the nexus between agricultural and industrial water usage.

• Climate change requires water synergy management of urban metabolic systems.

Abstract

Climate change exacerbates the vulnerability of water resources, and water-energy-carbon nexus makes water management more complicated. This paper attempts to explore the water resource synergy management paths within urban metabolic system against the background of human actively respond to climate change. We hold that: (1) Climate change would aggravate water scarcity risk from a supply-based perspective. Meanwhile, the normal metabolism of water consumers and energy consumption and mitigation options against climate change would directly and indirectly respectively, affect the water usage from a demand-based perspective. (2) Agriculture has great water-saving potential resulting from drip irrigation and drought-resistant technologies, but the potentials would be gradually endangered by biomass crop popularization. Industrial water saving mainly lies in energy efficiency, renewable energy, and CO₂-enhanced water recovery (CO₂-EWR). Domestic water-saving depends on sewage source treatment and awareness of water and energy conservation. Ecological water-saving should focus on the circulation of natural ecosystems and hydraulic systems. (3) Synergy management emphasizes the dynamic complementarity among water consumers in the urban metabolic system. Particularly, it is possible to compensate industrial water usage through agricultural water-saving due to fossil energy-based carbon capture and storage (CCS) in the medium to long term, while it is probably reversed due to the biomass crops expansion and bioenergy-based CCS (BECCS) deployment in the future. Additionally, seasonal changes and regional disparities should be fully taken into consideration. Overall, water resource policies should contribute towards effective water allocation within the urban metabolic system and low-carbon technologies deployment against climate change.

Introduction

Climate change has serious impacts on the frequency and intensity of extreme events such as sea level rise, increased evaporation, unpredictable precipitation and persistent drought, leading to an intensification of water cycle (Zhang et al., 2019). Particularly, the arid and semiarid regions are projected to increase by 23% compared with that of 1961–1990 and account for more than 50% of the global land surface by the end of the 21st century, largely due to the water resource vulnerability caused by climate change (Cunningham et al., 2017; Huang et al., 2016; Rajsekhar and Gorelick, 2017). Changes in water quantity and spatial distribution will affect the supply of surface water and groundwater for agriculture, industry, hydropower, river ecosystems, and domestic living (Xu and Zeng, 2012), which will further weaken the water availability.

Undoubtedly, water are basic conditions for the survival of human beings and are irreplaceable resources for supporting social and economic systems (Jia et al., 2018; Kosolapova et al., 2017). China's total water resources were 2746.3 billion m³ in 2018, which was close to the international warning level of 1700 m³ per capita (UN-Water, 2016). The State Council has established "three red lines"¹ for controlling the water usage in view of the water shortage crisis (GOSC, 2012). Meanwhile, the increasingly severe water pollution problem has imposed higher requirements on urban sewage treatment facilities (WRI, 2014). In addition, the uneven distribution of water exacerbates the water shortage crisis to some extent. Overall, the parts of the North, Southwest and Northeast and Northwest areas have been regarded as the severe drought zones in China (see Fig. 1).

The relationship between human beings and water resource is mainly reflected by urban metabolism which is a metaphor for conceptualizing the flow of resources in the urban system with several sectors, including agriculture, industry, households and commerce (Chen et al., 2020a; Serrao-Neumann et al., 2019; Yang et al., 2018), revealing the connection between human beings and the natural system (Dodder et al., 2016; Farooqui et al., 2016; Pincetl et al., 2012). Water metabolism refers to a series of processes such as evaporation, precipitation and runoff in the water cycle and their functions of maintaining water balance and natural purification to ecological metabolism (Jeong and Park, 2020; Renouf et al., 2017). Climate change accelerated the urbanization and increased water demand, resulting in an additional burden on urban water supplies (WHO, 2017). Meanwhile, water shortages caused by climate change lead to the contradiction between agriculture and industry for water conflicts in relation to urban metabolism (Bahri, 2012).

Industry is the second largest water consumer behind agriculture and is also the largest source of CO₂ emissions affecting climate change (IEA, 2016). Especially, energy sectors, such as coal mining and power generation, consume large amounts of water resource (Cai et al., 2014; Yang et al., 2020a). In 2014, primary energy production and generation accounted for approximately 10% of the global water usage (IEA, 2016). In addition, limiting warming to 1.5℃ would require a 70–95% reduction in emissions by 2050 compared with 2010 levels (IPCC, 2014; Jiang et al., 2019). Water is essential for energy-related activities, including the extraction, transportation and processing of fossil fuels and the irrigation of biofuel feedstocks (IEA, 2018). Meanwhile, energy usage is also critical for a range of water treatment processes, including water distribution, wastewater treatment and desalination (IEA, 2016). Water conservation measures can reduce energy consumption and mitigate greenhouse gas emissions (Engström et al., 2017; Xu et al., 2016; Yang et al., 2019), and similarly, improving energy efficiency will help reduce water usage and carbon emissions (Jin et al., 2017; Shang et al., 2018; Yang et al., 2020a). Accordingly, the interdependence of water and energy has become a key global issue and is the focus of the sustainable development goals (IEA, 2018; Meng et al., 2019; WEF, 2016). The proposal of a water-energy-carbon nexus plays a significant role in alleviating the crisis of water and energy as well as in reducing CO₂ emissions.

At present, climate change and water utilization are hot research topics under the global sustainable development goals. Mujere and Eslamian (2014) analyzed the potential effects of climate change on the hydrology and water resources in the Nyanyadzi River catchment in eastern Zimbabwe with focusing on climate change–water resource management nexus. Kusangaya et al. (2014) summarized the water availability and utilization in different regions of Africa against climate change. Kundzewicz et al. (2018) studied the uncertainty of climate change on hydrology and water resources and proposed two possible management strategies. Other studies have focused on sustainable water management in sectors in response to climate change, including agricultural sectors (Falloon and Betts, 2010; Liu et al., 2020; Seung-Hwan et al., 2013), energy sectors (Khan et al., 2016; Zohrabian and Sanders, 2018), construction sectors (Bertone et al., 2016) and domestic households (Haque et al., 2015; Nauges and Wheeler, 2017); however, there is a lack of research that considers the water system. In the agricultural sector, Mo et al. (2017) analyzed the stable and sustainable impact of water shortages caused by climate change on agricultural water usage in the North China Plain and further evaluated possible mitigation and adaptation measures. To achieve sustainable and stable crop production, Seung-Hwan et al. (2013) analyzed the impact of climate change on water usage in crop growing systems and water demand in agricultural reservoirs and proposed corresponding strategies. With regard to the impact of climate change on water usage in the sector, Kyle et al. (2013) explored the net impact of climate change mitigation policies on water demand in the power sector and proposed a series of global climate policies and technical strategies for the power sector, namely, a comprehensive evaluation model for energy, agriculture and climate change. Some studies also assessed the optimal allocation of regional water resources (Ahmad et al., 2018; Fu et al., 2018; Yao et al., 2019). Pingale et al. (2014) proposed an integrated urban water management model considering climate change, and the model is applicable to the optimal water allocation to meet the demand of different water consumers under change scenarios.

The water-energy-carbon nexus has been considered as a major challenge of sustainable development due to the interdependence of the energy sector on water resources and of the water supply sector on energy inputs. Fan et al. (2019) discussed the industrial water-energy relationship from the two aspects of resource management and demand management and proposed appropriate measures to provide insights for the overall sustainable planning of an urban agglomeration. Lee et al. (2017) introduced the water-energy nexus into the urban water supply system to improve urban water shortages and energy efficiency and proposed comprehensive management measures for the impact of water risk on the urban water system. Currently, the pressure of reducing emissions is increasing as a result of fossil fuel-dominated enery structure. Meanwhile, water vulnerability is aggravated, leading to a serious contradiction between water supply and demand. Therefore, the water-energy-carbon nexus is a significant force driving urban metabolism and is constrained by sustainable water usage.

There is always the risk of uncertainty about water resource and climate change, which requires supply and demand strategies for urban water management to address future water crises. Hence, it is essential to measure the availability, demand and structure of water resources through urban metabolic systems. Nevertheless, the existing literatures have some limitations. First, most studies mainly focused on water resources from the perspective of the watershed water cycle or hydrology, ignoring the impact of climate change on urban water supply and demand. Second, the water-saving and emission reduction measures are confined to a single sector, and the systematic management of water resources is limited, which is not conducive to coordination among departments. Moreover, few studies explored the impact of emission reduction on water-saving pressure in the context of climate change, and thus the water-energy-carbon nexus effects are not fully considered. Third, the water resource management is relatively simple and lack coordinated allocation in urban metabolic system. To fill the research gaps, this paper first reviews related studies to propose direct measures targeting water conservation-saving potential and indirect water distribution paths considering the influence of climate change on carbon abatement related water demands in terms of several major water consumers, including agriculture, industry, domesticity and ecology. Second, some key issues are discussed to explore the synergy management paths from the perspective of water metabolism. The results are expected to provide suggestions for sustainable water usage within urban metabolism in response to climate change. To be specific, this study aims to answer three questions: (i) what is the impact of climate change on water resource; (ii) how can water-saving potential be improved from the perspective of urban metabolism; and (iii) how can we synergistically manage urban water systems (see Fig. 2). The main contributions of this research are as follows:

• This research enriches the evidences for the impacts of climate change on urban water metabolic system from both a supply-based perspective and a demand-based perspectives. Moreover, the demand side includes not only the direct water demand from maintaining the normal metabolism of various urban water consumers, but also the indirect water demand resulting from increasing energy consumption and mitigation options in response to climate change.

• This research takes into account multiple factors including climate factors, technological factors and social factors that affect the urban water system. In particular, the effects of some emerging low-carbon technologies on urban water resource are first analyzed, which further complement and perfect the theory about water-energy-carbon coupling in urban metabolic system.

• This research refines the concept of synergy management of urban water resources and discusses the probability of dynamic complementarity among several water consumers in urban metabolic system against the context of climate change. Moreover, some suggestions are proposed considering the fluctuation of water resources caused by a variety of factors.

The rest of this paper is structured as follows: Section 2 introduces the structure of water system from the perspective of urban metabolism. Section 3 systematically summarizes the recycling and sustainable utilization of water resources in urban metabolic system in response to climate change. Section 4 provides a theoretical framework of water resource synergy management in urban metabolic system. The conclusions and policy implications are drawn in Section 5.