The pressure on global freshwater resources is increasing due to consumptive water use and pollution. The water footprint is a measure of human’s appropriation of freshwater resources, looking at both direct and indirect water use. Freshwater appropriation is measured in terms of water volumes consumed (evaporated or incorporated into a product) or polluted per unit of time. A water footprint has three components: green, blue, and gray. The green water footprint is the volume of green water (rainwater) consumed, which is particularly relevant in crop production. The blue water footprint refers to consumption of blue water resources (surface and ground water). Consumptive water use is generally smaller than water withdrawal, because water withdrawals partly return to the catchment. The gray water footprint is an indicator of the degree of freshwater pollution and is defined as the volume of freshwater that is required to assimilate the load of pollutants based on existing ambient water quality standards. To assess the water footprint of e.g. a business, one starts by clarifying the purpose and scope of the assessment (phase 1 of the water footprint assessment). Phase 2 is the accounting phase. The water footprint of the whole business will be quantified through inspection of the amount of water use, the type of water use and its timing and location. In phase 3 one will then look at the sustainability of water management by assessing the environmental, social and economic impacts of the water footprint, both at local and global level. Finally, in the fourth phase of the water footprint assessment, recommendations regarding options to reduce the different components of the water footprint are formulated (Hoekstra et al., 2011).
" For countries such as the U.S., the water footprint per person is large due to a generally high consumption lifestyle there, and also high consumption of meat. "
Freshwater – a geopolitical resource
The water footprint is a multidimensional, geographically and temporally explicit indicator, showing not only volumes of water consumption and pollution, but also where and when the water has been used (Hoekstra et al., 2011). It illuminates the link between consumption in one area and its impact on water systems in other regions and raises awareness about the potential for adverse environmental impacts and for potential global water savings. In light of this, Hoekstra and Mekonnen (2012a) quantified and mapped the water footprint of nations, both from a production and consumption perspective and illustrated the global dimension of water consumption and pollution. They showed that several countries rely heavily on water resources elsewhere (for example Mexico depending on virtual water imports from the U.S.) and that many countries have significant impacts on water consumption and pollution elsewhere (for example Japan and many European countries due to their large external water footprints). This global analysis includes a breakdown of water footprints, virtual water flows and water savings into their green, blue and gray components. The global water footprint in the period 1996-2005 was 9,087 Gm3/yr (74 percent green, 11 percent blue, 15 percent gray). Agricultural production contributes 92 percent to this total footprint. The combined share of China, India and the U.S. of the water footprint of global production is about 38 percent (see Figure 1). Hoekstra and Mekonnen furthermore showed that about one fifth of the global water footprint relates to production for export.
Figure 1. Total water footprint of national production in the time period 1996-2005, shown in mm/yr on a 5 by 5 arc minute grid (Hoekstra and Mekonnen, 2012a).
The water footprint of the global average consumer in the period 1996-2005 was 1,385 m3/yr. Food consumption is the largest part of a person’s water footprint. It is disproportionally larger than direct water uses such as drinking, bathing, washing or lawn maintenance. About 92 percent of the water footprint is related to the consumption of agricultural products, 4.4 percent to the consumption of industrial goods, and 3.6 percent to domestic water use. The average consumer in the U.S. has a water footprint of 2,842 m3/yr, while the average citizens in China and India have water footprints of 1,071 m3/yr and 1,089 m3/yr, respectively (see Figure 2).
Figure 2. Per capita water footprint of consumption [m3/yr] (Hoekstra and Mekonnen, 2012a).
The water footprint of a nation is influenced by the lifestyle and consumption habits of its residents, but also by agricultural practices that affect water productivity. For countries such as the U.S., the water footprint per person is large due to a generally high consumption lifestyle there, and also high consumption of meat. This must be mentioned specifically, since the water footprint of any animal product is larger than the water footprint of a wisely chosen crop product with equivalent nutritional value. For other countries, water footprints can be large for different reasons. Niger for example does not have a high consumption lifestyle and the proportion of meat in the average diet is low. However, the grain crops grown in Niger have a relatively large water footprint. Crops can have a large water footprint because of climate conditions, inappropriate agricultural practices and low water productivity.
Considering the water footprint of livestock in more detail, it is worthwhile to note that global meat production has almost doubled in the period 1980-2004 (FAO, 2005) and this upward trend will continue, given the projected doubling of meat production in the period 2000-2050 (Steinfeld et al., 2006). It is also worth noting that global livestock production currently constitutes 29 percent of the water footprint of total agricultural production and with the rising global meat consumption this share will significantly increase (Mekonnen and Hoekstra, 2012). Mekonnen and Hoekstra (2012) show, that from a freshwater perspective, animal products from grazing systems have a smaller blue and grey water footprint than products from industrial systems, and that it is more water-efficient to obtain calories, protein and fat through crop products than animal products.
Local production and consumption – global impact
It is important to consider that water availability or stress are manifested at a local level (specific geographic regions) but the actors that are either improving or worsening the conditions are we as individuals, or companies, or governing entities. Hence knowing the temporal and spatial dimension of the water footprint of e.g. a business provides distinct information to evaluate the sustainability of its activities. It aids in formulating the most appropriate response strategies. If the region of unsustainable production is known, then a company can act accordingly. Therefore the magnitude of the water footprint of a company, together with its temporal and spatial dimension, is highly valuable information for both sustainable water stewardship and risk management (physical, reputational, regulatory and financial risk). When two similar goods have the same water footprint, it means that from a global perspective, they make a similar claim on global freshwater resources. However, when the water footprint of one good is in a water-scarce catchment area, while that of the other good is in a water-rich catchment, their local impact can differ significantly.
" Detailed information regarding the water footprint can form an important basis for further assessment of how products and consumers contribute to the global problem... "
As Hoekstra and Mekonnen (2012b) point out, reduction targets regarding water footprints within catchments should be formulated on the basis of relative water scarcity per catchment, because local environmental impact of water use is generally larger when scarcity is higher. In many river basins, the blue water footprint exceeds blue freshwater availability, causing substantial environmental impact. With the world population growing at rapid pace and related changes in lifestyle as well as consumption patterns, competition for water resources between sectors such as agriculture, industry and energy, sustaining ecosystem health, are merely a few among several pressing issues that are inseparably connected with water scarcity. The rise in demand for water to grow food, supply industries and sustain urban and rural populations has led to a growing scarcity of freshwater in many parts of the world (Postel, 2000). An increasing number of rivers now run dry before reaching the sea for substantial periods of the year,. In many areas, groundwater is being pumped at rates that exceed replenishment, depleting aquifers and the base flows of rivers.
The rising water demands require governance based on accurate and reliable indicators. Hoekstra et al. (2012) developed an innovative water scarcity indicator, that combines three improvements compared to previous indicators: (i) use of water consumption of ground- and surface water flows (i.e. the blue water footprint) instead of water withdrawal, (ii) accounting for environmental flow requirements to sustain critical ecological functions and (iii) a monthly rather than an annual time-step. Blue water scarcity is defined as the ratio of blue water footprint to blue water availability, whereby the latter is determined by subtracting the presumed environmental flow requirement from the natural runoff. Water scarcity has been analyzed for the time period 1996-2005 and categorized from low to severe for 405 river basins that account for 69 percent of global runoff, 75 percent of the world’s irrigated area, and 65 percent of world population. Improving upon previous assessments, the current monthly approach reflects the dynamic character of the hydrologic cycle and the variability of human water use over the course of a year. It must be stressed that for the assessment of social, economic and environmental impacts of water scarcity both severity and duration of water scarcity are crucial (as shown in Figure 3).
Figure 3. The number of months in which water scarcity exceeds 100% in the 405 river basins studied (Hoekstra et al., 2012).
One result of the study was that in 223 river basins (55 percent of the basins studied) the blue water footprint exceeds blue water availability during at least one month of the year, impacting 2.72 billion people, i.e. 69 percent of the population considered. For 201 of these basins, with in total 2.67 billion inhabitants, there was severe water scarcity during at least one month of the year, highlighting the fact that when water scarcity exists it is usually of a severe nature. This innovative water scarcity indicator may prove useful for governments, businesses, farmers, investors and others to evaluate water-related risks. The data on blue water scarcity are available from the WaterStat database of the Water Footprint Network.
Several strands of important applications
It must be stressed that local environmental impact is only one of a range of factors to be considered when prioritizing options for water footprint reduction. Other relevant factors are global sustainability, social equity, and economic efficiency. The key issue concerning humanity’s water footprint is that the world’s available freshwater resources are limited, so that it is important to quantify how available water volumes are appropriated (Hoekstra and Mekonnen, 2012b).
Detailed information regarding the water footprint can form an important basis for further assessment of how products and consumers contribute to the global problem of increasing freshwater appropriation against the background of limited supplies and to local problems of overexploitation and deterioration of freshwater bodies or conflict over water. Once one starts overlaying localized water footprints of products or consumers with maps that show environmental or social water conflict, a link has been established between final products and consumers on the one hand and local water problems on the other hand. Establishing such links can help to foster the dialogue between consumers, producers, intermediates (like food processors and retailers) and governments about how to share responsibility for reducing water footprints where most necessary. The Water Footprint Assessment Tool, version 1.0 to be released in December 2012, will aid in carrying out such analyses.
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