(Wines&Vines) - With all the talk about the current drought, Garrett Buckland of Premiere Viticultural Services introduced some interesting perspective about water at a seminar on groundwater during the Napa Valley Grapegrowers’ sustainable vineyard series.

He pointed out that California doesn’t really have a normal rainfall pattern. The amount of precipitation varies dramatically from year to year; few years are “average.”

Two indices are used to monitor droughts: the Palmer drought severity index (PDSI) and the drought monitor.

The Palmer drought severity index uses temperature, precipitation, soil moisture, water supply and water demand. “It is most effective in determining drought status for non-irrigated crop land,” Buckland said. “It is much better than the ‘drought monitor’ we see often used in the media.” The reason is that the drought monitor incorporates human “fudge factors” and incorporates “snow-pack” figures.

The Palmer model is based on numbers and accounts for local evapotranspiration, temperature, soil recharge and other factors. Buckland added, “It does not do well with ‘snow-pack,’ which is irrelevant to Napa County agricultural water supplies.” The same is true of some other areas.

Napa is doing fine

Buckland went on to describe the present situation in Napa County: “The rainfall totals are strong: above average to date in Carneros and Napa, below average to date up-valley. There was no measurable rainfall in January, four days of rain in February and one day of rain in March. We can expect 2-5 inches of rain ‘average’ for the remainder of April and May.”

He said that groundwater levels are holding steady and improving in some areas. Rainfall from July 1, 2014, to April 7, 2015, ranged from 21 inches in Carneros to 31 inches on Atlas Peak. Other areas got mostly in the upper 20s.

The same is likely true in Sonoma and Mendocino counties, but clearly conditions in other areas are different. Paso Robles has been suffering from shrinking groundwater, and growers in much of the Central Valley are almost completely dependent on imported irrigation water.

Some background

For more than two years, the state’s experts have been managing water resources to ensure that California survives this drought and is better prepared for the next one.

Last year, the governor proclaimed a drought state of emergency. The state has taken steps to make sure water is available for human health and safety, growing food, fighting fires and protecting fish and wildlife.

Overall in California, irrigated agriculture used about 40% of water, cities 10%, and half went to streams, wetlands and rivers in 2010.