Main question

Food security to sustain the growing world population is one of the key challenges for mankind. According to a recent FAO study about 800 million people in the developing world do not have enough to eat. Although food production is still on the rise, increases are more profound in the developed world than in the developing world where population growth will mainly take place.

To produce our food an enormous amount of water is required. The question whether water resources will be sufficient to feed the world’s people includes many aspects with many uncertainties and subjectivity and it is therefore no surprise that many different estimates have been presented on whether sufficient food can be produced and what the consequences on water resources are. On top of this will be the impact of climate change on food production. It has been discussed that the impact of climate change in comparison to changes in population and socio-economic issues will be minor. One important issue ignored in these considerations is that changes in population and socio-economic issues are gradually and therefore easier to cope with. However, climate change will include such a gradual change, but more importantly it is expected that extremes will increase substantially. Especially these extremes are very difficult to cope with in the context of food production.

A recent study by FAO claims that in the next three decades, climate change is not expected to depress global food availability, but it may increase the dependence of developing countries on food imports and accentuate food insecurity for vulnerable groups and countries. In terms of water requirements the projections for developing countries indicate that a 14% increase in water withdrawals for irrigation by 2030 is expected. In contrast to these figures, results presented by the International Food Policy Research Institute show that the increase in irrigation water will be only 4%, mainly as a result of water shortages. The International Institute for Applied Systems Analysis presented a study based on their GAEZ approach (Global Agro-Ecological Zonering) indicating that the impacts of climate change on crop production are geographically unevenly distributed. Developed countries experience an increase in productivity. In contrast, developing regions suffer a loss in cereal productivity. It was concluded that climate change will most likely increase the number of people at risk of hunger, and that the importance and significance of the climate-change impact on the level of undernourishment depends entirely on the level of economic development assumed in the scenarios. In response to these issues this research project was carried out which develops and evaluates adaptation strategies for river basins to alleviate negative impacts of climate change and variability emphasizing water for food, nature and industry. Seven contrasting basins were selected ranging from dry to wet as well as from “rich” to “poor.


This study has applied the Soil-Water-Atmosphere–Plant (SWAP) model for the seven selected basins to simulate all the terms of the water and salt balances and to estimate yields. For each basin two crops were selected to analyze. Three time slices were used, 1961-1990, 2010-2039, 2070-2099, and for each basin-crop-time slice a business as usual (base line) and two adaptation strategies have been explored. Climate data for the three periods of 30 years considered have been subtracted from two General Circulation Models (HADCM3 and ECHAM4) and for each of them two emission scenarios (A2 and B2) were used.

Result and conclusions

Overall, the general picture is that crop yields will be higher in the future, but that variation in yields between years will increase as well. This indicates that concerns are not so directly over total food production as well as over food security, and, related to this, farmers income.

One of the most striking conclusions of this study is that the overall picture of the impact of climate change on crop yields is positive. In the business as usual option expected yields are higher for all except one basin-crop combination (Figure 1). One of the dominant factors is the impact of elevated CO2 levels on crop production. The impact of this, and especially the long-term impacts and feed-back and secondary factors, is still under debate. However, using results of numerous experimental data indicates clearly that a doubling in CO2 levels can indeed induce higher yields up to 50%.

Figure 1. Changes in yield (top) and variation (bottom) for the periods 2010-2039 and 2070-2099 as compared to the baseline 1961-1990. Displayed are values for HADCM3 A2 climate change projections and business as usual scenario.

Also variation in crop yields, expressed as the coefficient of variation, is going down for more than half of the basin-crop combinations despite the increase in variation climate change according to the HADCM3 projections. One of the most important reasons for this is the way irrigation scheduling was included in the simulations. It was assumed that irrigation timing is always optimal, i.e. if crop experienced stress beyond a defined threshold value irrigation was considered to take place. This ensured that results are not affected by this timing but only by the total water applied.

The consequence of this is that during dry years, either by low rainfall or by high temperatures, more irrigation would be applied than during wet years. This is only a realistic assumption when sufficient storage capacity exists in a basin. However, there is a price to pay for these positive impacts and that is that more water is consumed, and especially for the end of this century this increase is expected to be substantially.

Finally it should be stressed that results presented here relates to field scale processes and ignoring basin scale water resources. The ultimate objective of the results presented is therefore to provide the required field-scale information in a consistent manner to be used in basin-scale analysis.

Please feel free to contact the Project Leader of this project for more information.