Aarhus University Seal / Aarhus Universitets segl

Agriculture’s irrigation requirements are greater than we thought

New figures indicate that farmers need more water for irrigation than was previously supposed. The figures also show that annual requirements can vary by more than 300 percent.

2018.01.15 | Janne Hansen

According to Professor Mathias Neumann Andersen from the Department of Agroecology at Aarhus University, it is important to have as precise and recent figures as possible as a basis for issuing water abstraction permits. Photo: Janne Hansen

Danish agriculture needs more water. Yes, you read correctly! In recent months, so much rain has poured down on Danish fields that any talk of water shortage seems somewhat irrelevant. Nonetheless, water requirements during Danish summers can be greater than was previously supposed, according to new figures from the Department of Agroecology at Aarhus University. 

The results of the studies are described in a new report from DCA – Danish Centre for Food and Agriculture.

If crops are not irrigated during dry periods, then the quality and quantity of the harvest will suffer. Many farmers with sandy soils therefore make sure that their fields are irrigated when there is not enough rain. The amounts are extensive; in Denmark more than 450,000 hectares can be irrigated and in years of drought in West Denmark water consumption for irrigation exceeds all other kinds of water consumption.

Farmers need official permission to use groundwater for irrigation. The issuing of permits is administered according to the Danish water supply law. When evaluating whether permits should be granted, the following are taken into consideration in order of priority: 

  1. Public drinking water supply
  2. Maintenance of good conditions in waterways, lakes and natural habitats that are dependent on water
  3. Other water demands, including irrigation and industrial needs

- It is important to have as precise and recent figures as possible as a basis for issuing water abstraction permits, says Professor Mathias Neumann Andersen, who has estimated irrigation requirements for a range of crops and farm systems at 10 locations across Denmark for the years 1990-2015. Climate changes and improved methods for calculating evaporation are some of the things that can contribute to the fact that the updated figures show higher requirements than previous figures.

- In general, we found higher values for irrigation requirements than in previous studies carried out 40 years ago, says Mathias Neumann Andersen. The researchers’ updated figures also show that the annual irrigation requirements depend on year in particular but also soil type and type of farm system – for example if it is a dairy, potato or pig farm – and that the requirements can vary by more than 300 percent.

- Our figures show that it is not particularly suitable to issue permits based on average values because this may restrict farmers’ production in one out of two years. On the other hand, one should keep in mind that that the irrigation capacity on many farms is limited to about 3 mm per day. It would therefore be more appropriate to issue permits that cover requirements in eight out of ten years in areas with sufficient water resources, Mathias Neumann Andersen suggests.


You can read the DCA report ”The gross and net irrigation requirements of crops”, DCA-rapport no. 112, January 2018 here


For more information please contact: Professor Mathias Neumann Andersen, Department of Agroecology, email: mathiasn.andersen@agro.au.dk, telephone: +45 8715 7739, mobile: +45 2240 0742

Agro, Plantekongres, DCA