Almost half of irrigated agriculture uses groundwater. “That’s why groundwater is so important to global food security,” says research associate Inge de Graaf. But pumping up water on a large scale can have an impact on groundwater levels. That’s a problem, because natural habitats are drying out where this is happening. “There’s a big gap between how much food the world wants to produce and how much we can produce sustainably, meaning without causing groundwater levels to drop.”
De Graaf is working on this problem by developing a global model for water and crop production. It’s a combination of existing models, rather than an entirely new one. In previous research, De Graaf had actually already shown that pumping up too much groundwater has an effect on river outflows. “It’s not just that groundwater levels fall, but also that streams and rivers have less water to carry. The effect is noticeable when you study it on a large scale. This link is currently often overlooked. Even in the Netherlands, we’re only slowly starting to realise this now that we’re more often experiencing drought and its negative impacts.”
Large agricultural areas in countries such as China, India and the US are all experiencing serious problems related to falling groundwater levels. The decline in those levels can be as much as a metre per year. Particularly in the dry season, the outflow of water through rivers, streams, ditches and lakes is almost completely dependent on groundwater. “This is a major threat to the freshwater ecosystems found in these rivers and streams,” warns De Graaf. “Water levels are dropping too far and water temperatures are increasing too much for organisms that live underwater, such as fish, plankton and aquatic plants.”
A global model for groundwater, river water and crop production would show where problems can be expected to arise. “We’re using the IPCC’s different climate scenarios, which are all the various projections of how quickly the earth is heating up and how our water usage is expected to change as a result,” says De Graaf. “This reveals where problem hotspots can be expected, as well as the places where there is plenty of room for sustainable water use. This knowledge is important for the development of adaptation strategies that can helps us achieve a more sustainable world.” In areas not currently experiencing problems, models tend not to be available. But a global model would include those areas too.
“The challenge is to close the gap between what we want to produce and what we can sustainably produce. This calls for targeted measures, such as smarter irrigation,” she adds. Existing global models tend to assume that different regions water their crops in the same way, using drip irrigation, for example. But that’s an expensive way of doing it, and that alone means it’s not the best option everywhere. De Graaf is therefore trying to select the most suitable method for each region. Her model will then work out how sustainable that method is, and what that means for crop production. She will then look at whether those same methods would be an appropriate solution in other areas.
“I want to make the approach more realistic for farmers. Even if we’re still not talking about individual fields, but about large regions, such as a river basin.” The outcomes will give regional water managers something to start working with. That includes regions where, according to De Graaf, there are currently few problems, such as some parts of Africa. “If we don’t act now, falling groundwater levels will cause major problems there.”