Methodological Challenges in Volumetric and Impact‐Oriented Water Footprints

Abstract

Keywords:industrial ecology life cycle assessment (LCA) water consumption water footprint water resources water withdrawal SummaryThis work identifies shortcomings in water footprinting and discusses whether the water footprint should be a volumetric or impact-oriented index. A key challenge is the current definition of water consumption according to which evaporated water is regarded as lost for the originating watershed per se. Continental evaporation recycling rates of up to 100% within short time and length scales show that this definition is not generally valid. Also, the inclusion of land use effects on the hydrological balance is questionable, as land transformation often leads to higher water availability due to locally increased runoff. Unless potentially negative consequences, such as flooding or waterlogging, and adverse effects on the global water cycle are considered, water credits from land transformation seem unjustified. Most impact assessment methods use ratios of annual withdrawal or consumption to renewability rates to denote local water scarcity. As these ratios are influenced by two metrics-withdrawal and availability-arid regions can be regarded as uncritical if only small fractions of the limited renewable supplies are used. Besides neglecting sensitivities to additional water uses, such indicators consider neither ground nor surface water stocks, which can buffer water shortages temporally. Authors favoring volumetric indicators claim that global freshwater appropriation is more important than local impacts, easier to determine, and less error prone than putting complex ecological interaction into mathematical models. As shown in an example, volumetric water footprints can be misleading without additional interpretation because numerically smaller footprints can cause higher impacts.

Quantifying the human impact on water resources: a critical review of the water footprint concept

“…Some of these simply elaborate the WFN method whereas others critically argue for omitting or adding certain elements in order to enhance its potential as an impact indicator. Furthermore, some of these methods are proposed as stand-alone procedures (even though some use LCA software) whereas others are designed to be part of a broader and more comprehensive LCA (Berger and Finkbeiner, 2012). This section reviews several of the most important stand-alone alternatives whereas the next section examines full-blown LCA-oriented approaches.…”

“…In contrast, many authors still argue that green water resources are also limited, scarce and highly variable, and can be substituted by blue water as well as, in the case of agriculture, act as a substitute for blue water (Jefferies et al, 2012), especially in areas where blue water resources are scarce. According to Berger and Finkbeiner (2012), the actual question to be addressed is how the green water footprint affects blue water availability 4 .…”

The WULCA consensus characterization model for water scarcity footprints: assessing impacts of water consumption based on available water remaining (AWARE)

“…For example, a DTA ratio of 0.5 describes that half of the water is required by current users, but whether this amount of water is 10 or 1,000,000 m 3 for the same area is unknown. This sometimes leads to arid areas showing less scarcity than known water-abundant regions (Berger and Finkbeiner 2013) and the relevance of this for LCA application can be questionable (Boulay et al 2015a). Three proposals emerged during the workshops, as described in Boulay et al (2015a) that could overcome this limitation, called DTA A , DTAx, and 1/AMD.…”

Assessing Uncertainties of Water Footprints Using an Ensemble of Crop Growth Models on Winter Wheat

“…Since international trade in commodities creates flows of so-called "virtual water" [2][3][4], by importing and exporting goods that require water for their production, the indicator provides valuable information for a global assessment of how water resources are used, although it was controversially discussed since water scarcity of the region is not accounted explicitly [5]. In recent years, WFs and virtual water was assessed for crops, goods, services, as well as on generic regional or national levels [2,4,[6][7][8][9].…”