The study reveals that the proportion of the world’s population living in regions subject to water scarcity has gone up more than 10% from 1905 to 2005. But it also finds that, if modern farms were managed as they were in the early 20th century, the population living in regions subject to water scarcity would be roughly double.
The historical picture of water scarcity could help policy makers tackle the problem in some of today’s worst-affected areas, the authors of the analysis say.
"The efficiency of agriculture has increased tremendously during the 20th century, and its effect on food production potential has been far greater than that of land expansion, for example," said Miina Porkka of Aalto University in Finland.
Porkka and colleagues – who are based at Aalto University, the Potsdam Institute for Climate Impact Research in Germany and the University of Bonn, Germany – used a vegetation and hydrology model to simulate historical levels of the availability of "green water" (in soils) and "blue water" (in rivers, lakes and so on). For individual regions able to manage their water supplies, known as food production units (FPUs), the researchers then calculated the amount of water required to produce enough food for the population.
According to the Food and Agriculture Organization of the United Nations, the average calorie requirement for a person is 2300 kcal. Allowing for wastage in the food supply chain, Porkka and colleagues set their required amount of food at 3000 kcal, including 20% meat.
Based on these figures, the researchers estimated the numbers of people living in FPUs that did not have enough water to fulfil the calorie requirement. In 1905 this was 360 million, or 21% of the world’s population; in 2005 this was 2.2 billion, or 34% of the population. The results also show that water scarcity has increased in area, and become more frequent in regions where it does occur.
But Porkka and colleagues point out that the efficiency of agriculture enabled the 20th century’s spiralling population growth without even more drastic increases in water scarcity. This could be a lesson for some regions of the world today, according to Porkka.
"An example of this could be the development in sub-Saharan Africa, where the efficiency of agriculture has been improving much slower than in other regions with similar climatic conditions," she explained. "This suggests that there’s a huge potential to increase food production with policies – and obviously successful implementation of these policies – that promote better management and resource use efficiency."
Ways to improve efficiency could include better irrigation systems and the growth of more productive crop varieties, as well as more novel approaches such as consuming less meat and reducing food waste, Porkka added. "Global agricultural trade will also continue to play a key role in food security," she said. "Efforts should therefore also be put on improving global trade policies to create a more just and sustainable global food system."
The study is published in Environmental Research Letters (ERL) in the ERL Focus on Food, Trade and the Environment.
Related links
- Causes and trends of water scarcity in food production Miina Porkka et al 2016 Environ. Res. Lett. 11 015001
- ERL Focus on Food, Trade and the Environment
- Miina Porkka, Aalto University