Irrigation needs for arable land and grassland under current climatic conditions

The demand for irrigation is increasing and a further increase is expected with future climate changes. To support the planning of technical and political measures, data for current and future irrigation water requirements are necessary. Here, a hydrological simulation model was used to determine the need for irrigation water across Switzerland for the period 1980-2006 at a 500 x 500 m resolution. The resulting maps depict the risk for drought-related yield losses of arable crops and grasslands based on a threshold for relative evapotranspiration, together with the trend in the occurrence of periods with insufficient soil water availability. Most affected regions are located in the western part of the country, in the lower Rhone valley, and in small alpine valleys. Overall, 41 % of the arable crop area appears to have a significant irrigation need, and 26 % of the total agricultural land area. An increasing trend towards longer drought periods was found for central and eastern Switzerland.