If one considers the depth of the rootzone, and then steps day by day through the year, the irrigation water requirement can be calculated as part of the daily soil water balance.
I downloaded data for Sapporo for the past few years. Since the ground is covered in snow during the winter, I'll just show the daily water balance from 1 April to 31 October. This is for a simulated 10 cm rootzone with a field capacity of 23% and irrigation applied to keep the soil from dropping below 10%. That will be something like a golf course putting green. The blue line shows the soil water content. The black circles show the irrigation events. Interesting stuff.