So we have been growing the vines at Arrow Lakes Vineyard with the very least amount of water we can. We tried zero irrigation and wanted to rely on rain fall alone and while that seemed like not a bad idea given our very short growing season, we could not make it through the super hot summers without severe vine stress especially when some days are seeing the temperatures getting above 35c.
The alternative was to have very low crop loads to the level that would not be economical. So we widened the space between rows a bit from 6-7 feet to 8 feet and installed drip irrigation that is active only during the hottest periods when the vines could get damaged by water stress. The wider rows gives the vines a bit more area from which to draw water from the soil and we turn the minimal irrigation on for a short period generally between July 1st and August 31st - so just to get the vines through the hot periods.
The most important factor we have found to limiting the irrigation we need to apply is through eliminating the weeds and growth between rows. The fact is the monashee area actually gets some decent rain fall throughout the summer months - significantly more than the Okanagan gets. However, the rain that does fall has little chance of being utilized by the vines if it is intercepted by weeds or grass between the rows.
So with the weeds in check the rain that does fall doesn't require much in the way of suppliment from the irrigation.