When a larger evapotranspiration than precipitation creates a precipitation deficit, crops suffer from lack of water. The magnitude and timing of the deficit differs spatially and temporally each year. How much water deficit that can be tolerated by a crop differs between soils, crop types and the stage of development the crop happens to be at the time. Consequently, the issue of when and in what proportions irrigation is needed is a complex matter and not one that could be answered on a general basis. Due to climate change, more and more farmers in Sweden are forced to make these decisions, decisions that most Swedish farmers and advisors lack experience of. The aim of this project is to create a software that spares farmers and advisors the effort of having to make the necessesary calculations of evapotranspiration to time the irrigation, the extensive measurements of water holding capacity and soil moisture and research on drought stress sensitivity in different crops themselves. The software would instead provide information on timing of irrigation, amounts of water, yield response and other key parameters. If succesful, such a software would make the economy of Swedish farmers more secure and the national production food and feed less exposed to risk, as well as increase the quality of Swedish agricultural advisory and contribute to efficient utilisation of those water resources that are been claimed by the agri sector for irrigation.