Globalization of water: The connection between water consumption and production in a globalizing world. Water footprints

Source: Arjen Hoekstra & Winnie Gerbens-Leenes, University of Twente, the Netherlands, p.w.gerbens-leenes@utwente.nl

Introduction Fresh water of adequate quality is a critical natural resource indispensable for life on earth. At present, about 86% of all fresh water use is applied in agriculture to grow crops for food and feed purposes, for materials, such as cotton, and increasingly for the growth of energy crops. More and more, water is used to produce commodities for export that are traded all over the world. This means that consumers can have a so termed water footprint (WF) outside their national borders. Trade can enhance global water-use efficiency when crops are grown at other locations with the use of less water, but trade can also shift the environmental burden to distant locations.

Matching water demand and supply is no longer a river basin issue, but a global issue Many goods consumed in a country are produced abroad. Consumption in a country impacts water systems elsewhere in the world at the various locations where the production processes take place. This makes most countries in Europe, North Africa and the Middle East dependent on water resources in other parts of the world.

Water footprint The WF is an indicator of both direct and indirect water use of a consumer or producer. Both the operational and supply-chain WF split up into three types of water: blue, green and gray. The blue WF is the volume of freshwater that evaporated from blue water resources which are surface water and ground water; the green WF is the volume of freshwater evaporated from the green water resources, in practise rainwater stored in the soil as soil moisture; the gray WF is the volume of polluted water, calculated as the volume of water that is required to dilute pollutants to such an extent that the quality of the water remains above agreed water quality standards. Consumption volume and pattern, and production circumstances are major determinants of the WF. Production is mainly determined by climate and agricultural practice. The WF of a crop is the water use (m³/ha) / crop yield (ton/ha). The WF of an animal is the sum of water used for feed, drinking and production. To calculate the WF of a crop or livestock product we distribute the WF of the root product over its derived products.

Table: The WF of some products (global averages)

Economy National policy makers are not interested in global water savings but in the status of national water resources. An example is Egypt importing wheat which saves 3.6 Gm3/yr of the national water resources. Water use for producing export commodities can be beneficial, as for instance in Brazil, where the use of green water resources for the production of crops for export has a positive impact on the national economy. However, export of 28 Gm3/yr of national water from Thailand related to rice export is at the cost of additional pressure on its blue water resources. Virtual water flows not only across national borders but also within a country. Current water use in China is 550 billion cubic metre per year. The proposed water transfers from South to North China are 40 to 50 billion cubic metre per year.

Bio-energy The WF of energy from biomass is 70 to 400 times larger than the WF of other primary energy carriers, excluding hydropower. It is more efficient to generate electricity than to produce biofuel or ethanol. The weighted average WF of energy is a factor two to four smaller for bio-electricity made of the whole crop than for bio-ethanol or biodiesel which is made from only sugar, starch or oil. In general, when considering biofuels for transportation, the WF of bio-ethanol is smaller than the WF of biodiesel.

Conclusion The link between national consumption of food, materials and energy from agriculture on the one hand and the use of water resources across the globe on the other can be assessed with the WF methodology.

More information at: www.waterfootprint.org