Green Water Blue Water

New water terminologies: Green water and blue water


New jargon is replacing old water and groundwater terms, and these new terms are now widely accepted, with all scientific journals accepting and propagating the terminology.

To my understanding the first use of the term "Green water" was in an article by Falkenmark of the Stockholm International Water Institute, Sweden in his 1995 paper at the Conference of SADC Ministers in Pretoria, South Africa (Coping with water scarcity under rapid population growth. Conference of SADC Ministers, Pretoria 23-24 November 1995). He and Rockstrom in their 2006 paper on "The New Blue and Green Water Paradigm: Breaking New Ground for Water Resources Planning and Management" in the Journal of Water Resources Planning and Management, v 132, no. 3, pp. 129-132. May-June 2006. reiterate these ideas of water. A draft of this paper is available at the University of Texas website http://www.ce.utexas.edu/prof/mckinney/ce385d/Papers/Falkenmark.pdf

In that paper the authors argued that "The production of biomass for direct human use-e.g., as food and timber-is by far the largest freshwater-consuming human activity on Earth. However, water policy and development concentrate on a fraction of the water for food challenge, namely, irrigated agriculture, which uses an estimated 25% of the global water used in agriculture, and on the industrial and domestic water supply, which corresponds to less than 10% of direct human water requirements (considering only water for food, domestic use, and industry).

The reason that biomass production so strongly outclasses other water-dependent processes is that water is one key element involved in plant growth. Simultaneous with the photosynthesis process, when stomata in the foliage open to take in carbon dioxide, large amounts of water are being consumed as transpiration flow and released as vapor from the plant canopy. Furthermore, this productive flow of vapor is accompanied by nonproductive evaporative losses of water (from soil, ponded water, and intercepted water from foliage surfaces).

Together, vapor fluxes as evaporation and transpiration, here defined as green-water flow, constitute the total consumptive water use in biomass production. "

The latest Nature editorial also uses this terminology (see Nature 452, 253 (20 March 2008) | doi:10.1038/452253a; Published online 19 March 2008) while talking about "A fresh approach to water".

Excerpts from that editorial ... " blue water in rivers, lakes, reservoirs and underground aquifers. ... blue water accounts for only 40% of the world's freshwater balance, and for much less in dry regions. The key to tackling the crisis in the most food-insecure parts of the world is managing 'green water': the less spectacular, but more abundant moisture that infiltrates the soil from rainfall, and that can be taken up by the roots of plants."

So transpiration losses could be losses of greenwater plus some part of blue water. Blue water is the water that is predominantly being used by all of us as drinking water and water for almost all other purposes, drawing directly from rivers, lakes and other reservoirs like aquifers. When we talk about rain-water harvesting or about check dams, or underground dams we are talking about tapping the green water. Its all just in the terminology, but surely it helps in consolidating concepts. Green water need to be exploited effectively so that blue water resources may be conserved.

The rainbow of water also consists of brown water, yellow water, grey water, black water, and virtual water. See Prof Ottopohl's (of Hamburg University of Technology, Institute of Municipal and Industrial Wastewater Management) presentation to get an idea of these waters http://www.les2004.iwa-conferences.org/uploads/LET%202005%20Sapporo/08_3.pdf

Prof J. Anthony Allan of the SOAS, University of London coined the term virtual water in 1994. See one of his papers on the topic http://www.ciaonet.org/wps/aln02/

See also http://books.google.co.in/books?id=lRec8rs6g_IC&printsec=frontcover&dq=Bekithemba+Gumbo&sig=CvijputWwSOhFlPiApCWbA91-wI