The EU has recognised the impact of climate change on water and the subsequent effects on agriculture in its white paper on adaptation1. The Intergovernmental Panel on Climate Change predicts in its A2r scenario that if the global population increases to 10 billion by 2050, then an additional 5000 km3 of water per year will be required to produce enough food.
The study numerically examined the current level of crop production and the potential influence of several water management strategies that could be conducted at a farm-level. It was supported by the EU ENSEMBLES project2.
Under present irrigation the model calculated a global crop production figure of 13.3 gigatons (Gt) of crops measured as dry matter for the period 1971-2000. It was estimated that a reduction in evaporation of water by 25 per cent could have increased this figure by about 0.80 Gt. The greatest potential for an increase was in semi-arid regions, such as the mid-west USA and Southern Africa.
It was estimated that global crop production could have been increased by 1.52 Gt if 25 per cent of run-off was collected. This was best achieved in tropical and wet regions, such as Central America and parts of Brazil. If both management strategies were combined (reducing evaporation by 25 per cent and harvesting 25 per cent of run-off) the global crop production could have been increased by 2.50 Gt, or about 20 per cent.
The study examined the possible impact of future climate change (for the period 2041-2070) and increasing levels of CO2. Climate change alone reduces crop production by 9 per cent, largely through decreased rainfall and higher temperatures. This could be buffered by reducing evaporation by 50 per cent or harvesting 25 per cent of run-off. Rising CO2 levels alone increase global crop production by 28 per cent by the 2050s, which more than offsets the drop caused by climate change. However, the researchers believe this is unlikely in reality as increases in CO2 will cause complex interactions that have not been considered in the model, such as limiting crop growth through crop degradation and increased weeds.
Lastly, the study estimated the number of people who would be water-stressed by 2050 under a water management strategy that combined a 25 per cent reduction in evaporation with the harvesting of 25 per cent of run-off. Under these conditions water availability would be sufficient to fulfill food demand in most developed countries but not for countries in North Africa, the Middle East and South Africa. The number of those living without enough water to produce a healthy diet is estimated to increase from the current 2.3 billion to 6 billion in 2050. This highlights the need to explore other options, such as more efficient irrigation and plant breeding for these future conditions in addition to water management.
- See http://ec.europa.eu/agriculture/climate_change/index_en.htm
- ENSEMBLES was supported by the European Commission under the Sixth Framework Programme. See http://ensembles-eu.metoffice.com/index.html
Source: Rost, S., Gerten. D., Hoff., H. et al. (2009). Global potential to increase crop production through water management in rainfed agriculture. Environmental Research Letters. Doi: 10/1088/1748-9326/4/4/044002. This article is free to download from: http://www.iop.org/EJ/abstract/1748-9326/4/4/044002