HEAVY WINTER STORMS IN February 2004 have piled Sierra snow to above-normal depths, with a month remaining to build the snow pack on which California, US relies for much of its water and hydroelectricity.

Snow depth in the northern Sierra Nevada range, from Mount Shasta to the Feather river, was at 141% of normal, the equivalent of about 1m of liquid awaiting the spring thaw. Monthly snow surveys are conducted to gauge how much water will be available for California farms, cities and hydroelectricity the following summer.

The central Sierra, from the Yuba river and Lake Tahoe basin to the Merced river, was at 112% of normal; and from the San Joaquin river south, the snow pack was at 108% of the depth in a typical year. Across the entire range, the depth was 127% of average.

More than a third of California’s drinking and irrigation water comes from Sierra snow, while snow-fed hydroelectric plants produce about a quarter of California’s power. The amount of water that will actually be delivered to farmers and communities depends not only on the snow accumulation, but also on water stored in reservoirs and how much water managers think they need to hold in the event the string of dry winters continues.