Today In Energy: Friday, February 22, 2013
Republished February 22, 11:15 a.m.: Text was modified to correct errors.
A number of dry years have left California dealing with low water supply, but increased precipitation in December 2012 contributed to near-normal snowpack levels in the Sierra mountains this winter. Snowpack and its snow water equivalent affect California's hydroelectric availability and reliance on sources of various electric generation and imports.
What is snow water equivalent?
Snow water equivalent is a common snowpack measurement referring to the amount of water contained within the snowpack. It can be thought of as the depth of water that would theoretically result if you melted the entire snowpack instantaneously.
According to the California Department of Water Resources's February 1, 2013 report, snowpack in the northern Sierra Nevada range is 94% of normal, year-to-date from October 1. (Seasonal precipitation accumulation is often described in water years, which run from October 1 to September 30, rather than calendar years). Precipitation in this mountainous region during December was twice the average, a significant departure from the prior year, which was significantly below normal. This latest snowpack measure is somewhat reduced from the prior month's, as January precipitation was significantly below normal.
A previous Today in Energy article on this year's water supply forecast for the Pacific Northwest described the importance of such snowpack and water supply forecasts to the electric power sector, as they provide critical data on the outlook for hydroelectric power in the region. California hydroelectric generators are found along different river basins, and the weather patterns can be significantly different between the two regions, resulting in different water supplies. Therefore, the regions have separate water supply forecasts. California's recent history includes many drought years, bringing additional attention to California precipitation this winter.
Hydroelectricity in California. Almost 14% of the nation's hydroelectric generating capacity is concentrated in California. Since 1989, hydro has accounted for varying portions of electricity generated within the state of California, from 11% in 1992 (reflecting a low water year) to a high of 28% in 1995 (a high water year). The chart below also shows the seasonal variation in California hydro output over the past several years. Hydro output peaks in the spring and early summer as melting snow flows through the river basins. Overall demand for electricity, however, peaks slightly later, at the height of summer, when air conditioners are running most often.
The chart below shows power generated within California only; to meet total power demand, California also imports power from neighboring regions, including more hydropower from the Pacific Northwest.