15.10.2009

Water management could boost crop yield, but not enough, study suggests

Source: Cordis

This research was partly funded under the 'Sustainable Development, Global Change and Ecosystems' Theme of the Sixth Framework Programme (FP6) through the ENSEMBLES ('ENSEMBLE-based predictions of climate changes and their impacts') project.

'Use of water in agriculture is a key problem for the 21st century: without improvements neither the consequences of climate change will be manageable nor [will] the demand of 2 or 3 billion additional people for food be met,' says co-author Professor Wolfgang Lucht of the Potsdam Institute for Climate Impact Research (PIK) in Germany. 'In this study we therefore investigated whether there are realistic opportunities to close the emerging gap in water supply for agriculture at least partially for many world regions. The results are quite encouraging.'

Using a vegetation-water model, the researchers identified two key strategies: the reduction of soil evaporation and the harvesting of rainwater. Through mulching and different tillage systems, water evaporation from the soil could be cut by 50%, at the same time turning the unproductive evaporation into productive plant transpiration. According to the researchers, such measures alone could increase global crop yield by 2% to 25%. The most promising regions for this strategy are the semi-arid regions of the midwestern United States, the Sahel, southern Africa and central Asia.

In addition, the researchers suggest that rainwater should be harvested in ponds or with the help of dikes and subsurface dams to compensate for dry periods. In this way, global crop yields have the potential to be augmented by between 4% and 31%. 'However, the detrimental effects of climate change could reduce global crop production by almost 10% by 2050,' explained PIK's Stefanie Rost.

In order to meet the food needs of a world population of 10 billion in 2050 - an estimate of the Intergovernmental Panel on Climate Change (IPCC) - the portion of land used for crops would have to be expanded by 10 million square kilometres (km2) to 25 million km2 worldwide. This would also result in a substantial increase of freshwater consumption by 4,500 cubic kilometres (km3) to 13,300 km3.

'However, in many regions of the world that already face limits of water availability, that is not an option,' pointed out Dr Dieter Gerten, hydrologist at PIK. 'Instead, we need to think of better ways to use the water that is there.'

The researchers conclude that even large-scale water management efforts on current cropland will not be sufficient to ensure that the food needs of the growing global population are met. 'This evidence poses crucial questions about trade-offs between future land and water use for irrigated and rain-fed agriculture, natural ecosystems and bioenergy,' they write.

'It furthermore highlights the need for exploring and combining all options of more efficient irrigation and/or expansion of irrigated agriculture, of plant breeding and genetic development, and of more effective virtual water trade.'

Further information:

Environmental Research Letters:
http://www.iop.org/EJ/erl

Potsdam Institute for Climate Impact Research (PIK):
http://www.pik-potsdam.de