The water footprint of humanity

April 16th, 2012

Dr. Mesfin M. Mekonnen, University of Twente, The Netherlands

Many countries have significantly externalized their water footprint (WF) without looking at whether the imported products are related to water depletion or pollution in the producing countries. Conventional national water use accounts are restricted to statistics on water withdrawals within their own territory1,2.

National WF accounts extend these statistics by including data on rainwater use and volumes of water use for waste assimilation and by adding data on water use in other countries for producing imported products as well as data on water use within the country for making export products3.

The WF is a measure of human’s appropriation of freshwater resources and has three components: blue, green and grey3,4. The blue water footprint refers to consumption of surface and ground water resources. The green water footprint is the volume of rainwater consumed. The grey 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 estimate WFs and virtual water flows, we followed the Global Water Footprint Standard developed by the Water Footprint Network3. WF of national production is calculated by summing all the freshwater consumed or polluted within the territory of the nation as a result of activities within the different sectors (agricultural, industrial and domestic water supply) of the economy. International virtual-water flows are calculated by multiplying, per trade commodity, the volume of trade by the respective average WF per ton of product as in the exporting nation. WFs of national consumption, for agricultural commodities, is calculated by multiplying all agricultural products consumed by the inhabitants of the nation by their respective product WF. For industrial commodities, WFs of national consumption is calculated as the WF of industrial processes taking place within the nation plus the virtual-water import related to import of industrial commodities minus the virtual-water export.

The WF of National Production

The global annual average WF related to agricultural and industrial production and domestic water supply for the period 1996-2005 was 9087 Gm3/yr (74% green, 11% blue, 15% grey). Agricultural production takes the largest share, accounting for 92% of the global WF. Industrial production contributes 4.4% to the total WF and domestic water supply 3.6%. Figure 1 shows the global WF at a high spatial resolution. China, India and the USA are the countries with the largest total WFs within their territory, with total WFs of 1207, 1182 and 1053 Gm3/yr, respectively. India is the country with the largest blue WF within its territory: 243 Gm3/yr, which is 24% of the global blue WF.

International Virtual-Water Flows

The global sum of international virtual-water flows related to trade in agricultural and industrial products in the period 1996-2005 was 2320 Gm3/yr on average (68% green, 13% blue and 19% grey). About 76% of the virtual-water flows is related to international trade in crops and derived crop products. Trade in animal products and industrial products contributed 12% each to the global virtual-water flows. Global virtual-water flows related to domestically produced products was 1762 Gm3/yr, which is 19% of the global WF.

Figure 2 shows the virtual-water balance per country and the largest international gross virtual-water flows. Countries shown in green colour have net virtual-water export. Countries shown in yellow to red have net virtual-water import. The biggest net virtual-water exporters are found in North and South America (the USA, Canada, Brazil and Argentina), Southern Asia (India, Pakistan, Indonesia, Thailand) and Australia. The biggest net virtual-water importers are North Africa, Middle East, Mexico, Europe, Japan and South Korea.

The WF of National Consumption

The global annual average WF related to consumption was 1385 m3/yr per capita over the period 1996-2005. Consumption of agricultural products largely determines the global WF related to consumption, contributing 92% to the total WF. Consumption of industrial products and domestic water use contribute 4.7% and 3.8% respectively. At the level of product categories, cereals consumption contribute the largest share to the global WF (27%), followed by meat (22%) and milk products (7%).

The WF of consumption in a country depends on two factors: (a) the volume and pattern of consumption; and (b) the WF per ton of consumed products. The latter, in the case of agricultural products, depends on climate, irrigation and fertilization practice and crop yield.

The average consumer in the USA has a WF of 2842 m3/yr, while the average citizens in China and India have WFs of 1071 m3/yr and 1089 m3/yr, respectively. A general trend is that industrialized countries have a larger WF related to consumption of industrial products than developing countries. In the range of relatively large WFs per capita we find both industrialised and developing countries. The latter are in that range generally not because of their large consumption but because of their low water productivities, i.e. large WFs per ton of product consumed.

Countries with large external WF apparently depend upon freshwater resources in other countries. Highly water-scarce countries that have large external water dependency are for example: Malta (dependency 92%), Kuwait (90%), Jordan (86%), Israel (82%) and United Arab Emirates (76%). Not all countries that have a large external WF, however, are water scarce. In this category are many Northern European countries like the Netherlands and the UK.

In conclusion, the study shows that about one fifth of the global WF in the period 1996-2005 was not meant for domestic consumption but for export. The relatively large volume of international virtual-water flows and the associated external water dependencies strengthen the argument to put the issue of water scarcity in a global context4. For governments in water-scarce countries such as in North Africa and the Middle East, it is crucial to recognize the dependency on external water resources and to develop foreign and trade policies such that they ensure a sustainable and secure import of water-intensive commodities that cannot be grown domestically. Detailed WF data will help national governments understand to which extent the WF of national consumption relates to inefficient water use in production and to which extent it is inherent to the existing national consumption pattern. Thus it helps governments that strive towards more sustainable water use to prioritize production policies (aimed to increase water use efficiency) versus consumption policies (aimed to influence consumption patterns so that inherently water-intensive commodities are replaced by commodities that require less water).

References:

1. Van der Leeden F, Troise FL, Todd DK (1990) The water encyclopedia, Second edition (CRC, Boca Raton, FL).

2. Gleick PH (ed.) (1993) Water in crisis: A guide to the world’s fresh water resources (Oxford Univ Press, Oxford).

3. Hoekstra AY, Chapagain AK, Aldaya MM, Mekonnen MM (2011) The water footprint assessment manual: Setting the global standard (Earthscan, London).

4. Hoekstra AY, Chapagain AK (2008) Globalization of water: Sharing the planet’s freshwater resources (Blackwell, Oxford).

5. Hoekstra AY, Mekonnen MM (2012) The water footprint of humanity, PNAS, vol. 109 no. 9 3232-3237.

Dr. Mesfin Mekonnen is a postdoc researcher at the Department of Water Engineering and Management, University of Twente, the Netherlands. His research focuses on the analysis of virtual water trade, the spatial and temporal dimension of global water footprint and water scarcity. The article is based on an original piece of research published in the Proceedings of the National Academy of Science (PNAS) titled,’The water footprint of humanity’ by Arien Y. Hoekstra and Mesfin M. Mekonnen.

The views expressed in this article belong to the individual authors and do not represent the views of the Global Water Forum, the UNESCO Chair in Water Economics and Transboundary Water Governance, UNESCO, the Australian National University, or any of the institutions to which the authors are associated. Please see the Global Water Forum terms and conditions here.