In dry years the amount of rain is too low to provide all greenhouse holdings in the west of the Netherlands with sufficient irrigation water. This problem is larger than the expected effects of climate change, says Wim Voogt, researcher at Wageningen UR Greenhouse Horticulture. He is concluding this on the basis of a study conducted upon commission by the Province South-Holland. “In the years ahead policy will need to keep an eye on an adequate availability of good quality irrigation water for horticulture.”
Local authorities have commissioned a number of regional studies to acquire a view of possible water shortage problems in the Netherlands in the years ahead. Greenhouse horticulture in South-Holland is considered as a sector with its own water problems. Wageningen UR Greenhouse Horticulture has therefore, upon commission by the province and the water board authorities, conducted an exploratory study into the effects of climate change on water demand and water supply of greenhouse holdings in West-Netherlands. This exploration is part of the large national Drought Study. The calculations have been conducted with the ‘Waterflow’ model developed by Wim Voogt of Wageningen UR Greenhouse Horticulture.
The study shows that in an average year, with the current climate, most greenhouse holdings in West-Netherlands have sufficient rain water at their disposal. This, however, does not apply for soil-bound cultivations where surface water is still being used.
Two climate change scenarios have been computed with the Waterflow model, a warm and wet scenario, and a warm and dry scenario. The degree of self-sufficiency of greenhouse horticulture will improve if the coming years will be warmer and wetter. The situation becomes less favourable under the dry scenario. The effects of a year with dry weather, such as 1976 and 2003, however, are much larger than the effects expected due to climate change.
The possibilities of using surface water and osmosis water as an addition to precipitation under the different scenarios have been investigated as well. The differences are not large but the use of surface water will sooner result in problems because more discharging will be required. The brine problem needs to be solved in all cases.
“Sufficient good quality irrigation water is a focal point for the coming years,” says Wim Voogt. He continues: “We are identifying a number of bottlenecks. Precipitation is now already insufficient for some cultivations, such as when lighting is applied in rose and tomato. It is not inconceivable that water demand will increase in the future as result of intensified cultivation. Making use of the basin of a neighbour with a different cultivation may then be a solution. This does of course require the right infrastructure.” The scientist points out that there are on the other hand developments such as the semi-closed greenhouse and ecocultivation that may result in a decreasing water demand.
A solution for the brine problem must be found if osmosis water is going to be used. This certainly is the case if this water is increasingly used in dry years. Voogt: “When in dry years more surface water is used, discharge water is a bottleneck. In theory, increasing the size of the rain water basin is a solution but this is often impossible due to insufficient room. A poorer surface water quality due to the future salinisation problem must be reckoned with as well.”
Voogt says: “This means that the availability of sufficient water for greenhouse horticulture is surrounded by a number of tension areas for which policy needs to be developed in the years ahead. This study offers a number of handles on which such a policy can be based.”