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Rain doesn’t follow the plow: climate change, agriculture and water

19 June 2014
by Patrick Love
Coming your way soon?

Coming your way soon?

It takes about 1000 cubic metres (m3) of water to produce the food that one person eats in a year, assuming a daily intake of 2800 kilocalories (kcal) per day. This doesn’t include all the food wasted, and the average hides enormous differences in diet. For example, producing 1kg of meat requires between six and twenty times more water than 1kg of cereals, depending on how much feed is converted to flesh, but the 1000m3 per person figure means that global annual needs average over 6000 cubic kilometres of water, almost all of it for crops. Non-food agriculture, notably biofuel crops, adds to the total amount of water used as well. About 85% of the water for agriculture comes from rain stored in the soil, with the rest provided through irrigation.

Water withdrawals from rivers and lakes for irrigation, household and industrial use has doubled in the last 40 years, and in some regions, such as the Middle East and North Africa, humans use 120% of renewable supplies (“mining” groundwater that is not recharged). At a global level, some 1.2 billion people live in basins where the physical scarcity of water is absolute (human water use has surpassed sustainable limits). By 2025, 1.8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world population could be under stress conditions, mostly in non-OECD countries.

Farmers have always had to react to changes in rainfall and temperature, but as a new OECD report Climate Change, Water and Agriculture argues, climate change poses challenges on a different scale from the variations that can affect crops and livestock during the course of a season or even a year or two. Future changes in the climate could have significant impacts on land use, commodity production, and where different activities are viable. We can’t forecast exactly what will happen, but history shows us numerous examples of how human actions both influence the environment and are influenced by it.

Today people forced to leave their homes because of drought or some other “natural” disaster are called “environmental refugees”. In 1930s America, they were called Okies, because so many of them were driven from their homes in Oklahoma by the “Dust Bowl” created by a combination of drought and wind that “blew away everything but your debts”. This was a natural disaster in the sense that it came after a series of severe droughts and dust storms hit the US and Canadian prairies from 1930 to 1936. But drought wasn’t unusual in these regions, nor were high winds, and the prairies had resisted similar episodes in the past.

The difference was that a few exceptional periods of higher than average rainfall had encouraged extensive and intensive farming, with no attempt to protect the soil. People believed that “rain follows the plow”. It doesn’t, and when the grasses that held the soil in place and trapped moisture had been ploughed under, the droughts turned the earth to dust that the wind then carried off, often in so-called black blizzards that blotted out the sun and caused drastic, rapid drops in temperature. Millions of acres of farmland were lost, and hundreds of thousands of people made destitute.

Starting in 1933, the US government undertook a massive programme combining investment in soil conservation, education and subsidies to adopt more sustainable practices. It took over a decade for the region to recover but most of the people who left never came back. What can we do today to stop climate change provoking similar catastrophes?

In one sense, the Dust Bowl was easy to deal with because the causes, effects and consequences were identified. Regarding the main linkages between climate change, water and agriculture, however, the OECD book warns that “an important knowledge gap is related to seasonal impacts, extremes and variability of water availability since many current studies focus on annual timescales. There are challenges in comparing regional impact assessments driven by climate (and other) data from widely differing sources, and this may lead to conflicting and potentially misleading results. Significant uncertainties in future hydrological responses to climate change across models also exist.”

That doesn’t mean we have to wait until we’re sure. Climate Change, Water and Agriculture looks at what can be done starting now. Strategies for adapting agricultural water management to climate change need to target five different levels of intervention, and the linkages among them:

  • On-farm: adaptation of water management practices and cropping and livestock systems.
  • Watershed: adaptation of water supply and demand policies in agriculture and with the other water users (urban and industrial) and uses (ecosystems).
  • Risk management: adaptation of risk management systems against droughts and floods.
  • Agricultural policies and markets: adaptation of existing agricultural policies and markets to the changing climate.
  • Interactions between mitigation and adaptation of agricultural water management.

In many areas today, there is no such thing as a “natural” landscape. Thousands of years of farming have selected and encouraged some species, marginalised or eliminated others. The land itself has been altered by ploughing, enclosure, herding and other human interventions. We may feel that we have tamed Nature. Reports like this new one from the OECD remind us of our ignorance and warn us about our arrogance.

Useful links

OECD work on water use in agriculture

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