TDR tubes are used to insert a probe into the soil and to be able to measure soil moisture. Limitations of current water management strategies call for a stronger emphasis on soil water or so-called green water. Photo: R. Kautsky/Azote

A paler shade of blue

- Improving productivity of green and blue water can help curb global water crisis, say researchers.

It´s a tall order: if the world is to achieve its Millennium Development Goal of eradicating hunger, a doubling of food production over the coming 20-30 years is required. But for the agricultural sector to produce more food, more water is needed and this is getting more and more scarce in many parts of the world, partly because of the unproductive use of blue and green water.

Centre researchers have already called for a paradigm shift in Integrated Water Resource Management (IWRM), a water management philosophy that currently focuses too much on blue water (water in rivers, lakes and groundwater) and which is considered increasingly unsustainable. Green water (soil water), which plays a dominant role in global food production also needs to be managed better.

A concerted effort for change
In a special issue on green and blue water modeling which has recently been published in the Journal of Hydrology, centre researchers Malin Falkenmark, Line Gordon, Louise Karlberg and Johan Rockström along with researchers from SEI and Potsdam Institute for Climate Impact Research present a concerted effort to quantify at global scale the full green and blue water resource.

The special issue synthesizes results from a set of eight leading global models, ranging from hydrological, crop and vegetation models all the way to partial and general economic equilibrium models.

- We are developing new assessments of green and blue water in food production and trade, co-author Line Gordon says.

The invisible alternative
The current limitations of IWRM call for a stronger emphasis on green water, which supplies the plant cover of agricultural and other ecosystems. Through improved land management, this invisible water resource can enhance crop production and indirectly also benefit livestock production.

Now new research and technology can improve things.

- With new and advanced models at hand, we identify considerable potential to complement conventional blue water irrigation with measures such as improved rainwater harvesting and vapour shift as well as soil and nutrient management, says Gordon.

The models presented in the special issue provide a better picture of how a wide range of integrated blue-green water interventions can increase food security and future sustainability.

Despite differences in model design, all models came up with the same message: green water dominates food production, there is a critical overexploitation of water in many regions of the world and there is large potential for integrating green and blue water management.

Africa: increasing scarcity but enormous potential
Africa is highlighted as a critical region of increasing water scarcity and low productivity, but also of enormous potential for the development and improved management of the total water resource.

But, the researchers warn, the full green-to-blue spectrum of water management options needs to be integrated beyond agriculture, addressing the full range of water-dependent ecosystem services.

- The world is facing a water crisis, but improved water management in particular in rainfed agriculture can build resilience to cope with future water related risks and uncertainties, say Gordon, Karlberg and Rockström.

Source: Hoff, H., et al. Greening the global water system. J. Hydrol. (2009), doi:10.1016/j.jhydrol.2009.06.026



Hoff, H., et al. Greening the global water system. J. Hydrol. (2009), doi:10.1016/j.jhydrol.2009.06.026


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