Exploring consumption-based planetary boundary indicators: An absolute water footprinting assessment of Chinese provinces and cities

Highlights

• We develop two novel quantitative footprints to measure absolute water withdrawal sustainability.

• Water exceedance footprints reveal regions’ transgression of local planetary boundaries elsewhere.

• Water surplus footprints assess whether regions can sustainably supply and consume water.

• 47% of the Chinese territorial water exceedance is embedded in interprovincial trade.

• Consumption-based PB water footprint indicators inform water resources management.

Abstract

The water planetary boundary (PB) has attracted wide academic attention, but empirical water footprint research that accommodates local biophysical boundaries remains scarce. Here we develop two novel quantitative footprint indicators, the water exceedance footprint and the surplus water footprint. The first measures the amount of excessive water withdrawal (exceeded amount of water withdrawn against local water PBs) and the latter evaluates the potential of surplus water that can be sustainably utilised (amount of surplus water available within local water PBs). We quantify the extent to which demand for goods and services in Chinese provinces and cities are driving excessive withdrawal of local and global water resources. We investigate both territorial and consumption-based water withdrawal deficit and surplus against local water withdrawal PBs. We also trace how PB-exceeded water and surplus water are appropriated for producing certain commodities. In 2015, China’s domestic water exceedance reaches 101 km³ while the total water exceedance footprint is 92 km³. We find that 47% of domestic excessive water withdrawal is associated with interprovincial trade. Exceeded water transfers were dominated by agricultural trade from the drier North to the wetter South. A revised virtual water trade network informed by exceedance and surplus water footprint metrics could help address sustainability concerns that arise from the trade of water-intensive commodities. Our findings highlight that policy targets need to accommodate PB exceedance of both direct and virtual water use.

Introduction

Absolute sustainability assumes that natural capital stocks are not substitutable and that human activities must always remain within the carrying capacity of natural capital (Meadows et al., 1972). The idea of revisiting carrying capacity of natural capital has gained momentum in the scientific community. The planetary boundaries (PBs) framework, formulated by Rockström et al. (2009) and recently updated by Steffen et al. (2015b) proposes absolute biophysical limits that delineate a safe operating space for human prosperity at the global level by quantifying collective human modifications of the Earth system in the Anthropocene (Steffen et al., 2015a). While the global freshwater use PB has not been exceeded, many regional boundaries have been exceeded or are increasingly under threat (Lade et al., 2019). Current unsustainable patterns of freshwater use exert pressure on a number of highly stressed watersheds and basins (Mekonnen and Hoekstra, 2016; Motoshita et al., 2020). Since 2009, absolute water PB thresholds have been proposed by the academic community (Bogardi et al., 2013; Falkenmark et al., 2019; Gerten et al., 2013, 2020; Gleeson et al., 2020b; Jaramillo and Destouni, 2015).

The wide uptake of water footprint studies in recent years highlights their increasingly recognised policy relevance (Hoekstra and Mekonnen, 2012; Hoekstra and Wiedmann, 2014). Environmental footprints in general are becoming an indispensable dimension in analysing PB-related research questions as they link global production and consumption patterns to biophysical limits (Häyhä et al., 2016; Laurent and Owsianiak, 2017). The key strengths of footprint studies are their ability, in a world of trade, to encompass all upstream environmental implications of the consumptive use of natural resources, as well as to examine the inequalities and interdependencies across borders (Wiedmann and Lenzen, 2018). Virtual water trade (i.e. water scarce regions import water-intensive products to conserve local water resources) is seen as a measure to alleviate pressure on scarce water resources, to improve overall water use efficiency and to future-proof domestic water and food security (Hogeboom, 2020).

We argue that in order to enable absolute water footprinting assessment, a logical and necessary step is to incorporate local water PBs into water footprint accounting. It is the additional water extracted above a threshold that must be avoided from an absolute sustainability perspective, as this would give rise to exceedance which significantly increases the probability of local ecological impacts (Gerten et al., 2015, 2020; Gleeson et al., 2020b). Understanding which economic sectors or commodities create water exceedance indirectly along a given supply chain is essential (Li et al., 2019). The embodied part of the water footprint may often lead to exceedance of local water PBs somewhere far away from the point of consumption. This absolute sustainability perspective conveys environmental risk in a much more explicit manner compared to conventional water footprint assessments which typically encompass water thresholds in one of two ways. They either account for local water thresholds by multiplying water use with water scarcity characterisation factors in order to calculate a stress-normalised measure of water use (Chenoweth et al., 2014; ISO, 2014). This method is useful for seeking relatively more sustainable options based on overall scarcity contributions, as determined through universally applied thresholds, but does not fully encompass absolute sustainability thresholds because the degree of biophysical exceedance is not explicitly quantified (Liu et al., 2017; Ridoutt et al., 2018; Wang and Zimmerman, 2016). Alternatively, recent approaches also directly compare footprint results with local water thresholds in absolute terms (often on a per capita basis) (Dao et al., 2018; Lucas and Wilting, 2018; Nykvist et al., 2013; O’Neill et al., 2018). This latter approach tends to be more suited to globally relevant (e.g. carbon footprint) indicators that do not require a locally-specific threshold, and will only provide aggregated consumption-based impacts thus missing location-specific impacts allocation along the supply chain and effective intervention points.

Empirical consumption-based water footprint research that measures the extent of transgression and regional allocation of the locally-specific water PB control variable remains underexplored. The purpose of this paper is to introduce two novel quantitative footprint indicators to evaluate the territorial withdrawal of water in relation to its local water PBs. The water exceedance footprint measures the exceeded amount of water withdrawn in relation to local water PBs sensitive to the specific demand in a province or city. The surplus water footprint measures the amount of surplus water available within local water PBs that can be sustainably utilised to meet the demand of a province or city. The merits of using both metrics as a complementary tool to the conventional water footprint support the reconciliation of sustainable appropriation of water resources within biophysical boundaries. These novel indicators offer a new lens to explore how PB-exceeded and surplus water are appropriated, and allow comparisons across key commodities and geographical areas.

We use China as a case study as its sub-national level water availability is highly uneven, seasonal and vulnerable to climate change (Feng et al., 2019; Li et al., 2015; Piao et al., 2010). Within a nation, production in resource scarce regions can be redistributed to avoid the transgression of local PBs (Huang et al., 2020), while ensuring social equity and economic efficiency at the national level. A localised evaluation of the extent of transgression at a much greater spatial resolution is necessary. Northern China is highly water stressed (with only 18% of the nation’s freshwater resources) whereas the South, by contrast, is relatively water abundant, with most runoff wasted through flooding and some significant water quality issues (Guan et al., 2014; Liu and Yang, 2012). China has a per-capita water availability of 2100 m³/cap, only 28% of the global average (Cai et al., 2020). The North China Plain, a major food basket region and home to 200 million people, only has a per capita water availability of less than 150 m³/year (Liu et al., 2013). Outsourcing of increasing food, water and energy demand from major centers of consumption appears to exacerbate water stress elsewhere, for instance, the Jing-Jin-Ji area (Zhao et al., 2017; Zheng et al., 2019), the Greater Bay Area (Chen et al., 2019) and the Yangtze River Delta (Zhao et al., 2016). Continuing development of provinces and mega-cities may be hampered by water stress risks in their supplying hinterlands and overconsumption by a growing middle-class may further exacerbate their vulnerabilities (Liao et al., 2020; Qu et al., 2017; Zhang et al., 2020a).

The role of virtual water trade in redistributing scarce water resources within China is not always effective, in particular due to the consumption disparities between East China and West China, as well as a mismatch of arable land and water between arid North China and temperate South China (Feng et al., 2014; Guan and Hubacek, 2007; Zhao et al., 2015). Most interprovincial water footprint studies find that affluent eastern provinces and coastal cities, in addition to their significant local domestic water use, are typically net virtual water-importers from other, often water scarce northern and western provinces (Liu et al., 2020). Meanwhile, irrigation-intensive provinces in the drier North tend to export agricultural products to relatively wetter South regions where crop production is predominantly rainfed (Dalin et al., 2014). Internationally, China is a net virtual water importer for agricultural products (−25 km³) but net virtual water exporter if both agricultural and industrial products are considered (47 km³) (Hoekstra and Mekonnen, 2012; Wang and Zimmerman, 2016).

In this paper we demonstrate how novel PB-integrated water footprint indicators can be used to address ongoing challenges for water conservation policy in China. These quantitative footprint indicators link PBs at various scales to final consumption and quantify the magnitude and spatial extent required for water exceedance mitigation. Using the newly developed indicators we further explore how PB-informed virtual water trade can effectively redistribute resources within biophysical boundaries, therefore achieving absolute water sustainability.