Idaho water supply outlook improving

By Ag Weekly
Thursday, January 10, 2008 3:24 PM CST

BOISE, Idaho — Late December and early January storms brought above average precipitation to Idaho, but southern Idaho basins currently remain below normal snowpack levels due to previous drought conditions, according to a press release from USDA Natural Resources Conservation Serv. The Idaho Water Supply Outlook Report released today by the NRCS shows streamflow, snowpack, precipitation and reservoir storage information throughout Idaho as of Jan. 1. However, heavy storms within the past week have improved snowpack amounts statewide.

“As of January 10, some of our snowpacks have increased nearly 20 percentage points since January 1. Snowpacks range from near normal to slightly above normal except in southern Idaho. There, the snowpacks show approximately 85 percent of average,” said Julie Koeberle, NRCS hydrologist. “Our above-average fall precipitation will help prime the soils to allow for efficient spring runoff delivery to our streams and reservoirs, but we still need more snow.”

The beginning of the 2008 water year, starting Oct. 1, initially brought above average precipitation to all of Idaho’s basins. Then, the precipitation subsided in November and resumed in mid-December, lowering and then bringing most basins back to near normal levels. Since January is a critical snow accumulation month, the amount of snow received will be crucial for adequate summer water supplies.

Snowpack conditions vary statewide. Snowpacks range from above normal in the northern and central parts of the state to below average south of the Snake River. Snowpacks are the highest in the Weiser and Payette basins with 126 and 114 percent of average respectively and lowest in the Bear River basin with 83 percent of average.

Record high heat and below average precipitation in 2007 created a high irrigation demand that taxed reservoirs, resulting in below normal carryover storage for 2008. With the exception of a few northern Idaho basins, reservoir storage across Idaho is significantly lower than one year ago.

“It is just too early in the season and there is not enough information to be certain about our summer’s water supply,” Koeberle said. “However, we are on our way to a good start if this storm track continues as predicted in the long range climate forecast.” Forecast provided by the National Oceanic and Atmospheric Administration’s Climate Prediction Center.

Here is a look at the Water Supply Outlook by region:

- Northern Idaho (Panhandle, Clearwater and Salmon Basins): As of Jan. 10, the water year-to-date precipitation is above normal in northern Idaho. Snowpacks are at 98 percent in the Panhandle, 100 percent in the Clearwater and 112 percent in the Salmon. The soils are primed for efficient spring runoff and the weather shows no signs of stopping due to La Nina conditions in the Pacific Northwest. If this storm track continues, expect northern rivers to flow near average.

- Central Idaho (Boise, Weiser, Payette, Wood and Lost River Basins): Near average to above average snowpacks reside in the hills of central Idaho. This past summer was one of the driest on record, leaving the snowpack for this winter critical for summer 2008 water supplies. The La Nina conditions are forecast to keep the winter storms rolling into Idaho and building up the snowpacks, which should yield adequate water supplies.

- Southern Idaho (Bear River, Southside Snake basins including Owyhee and Bruneau): Overall, these basins are the driest in the state. The snowpacks range from 83 percent of normal in the Bear River basin to 94 percent of normal in the Oakley basin. The Southside Snake basins’ reservoirs are storing 15 percent of capacity; last year’s storage was 76 percent of capacity. The good news is that all southern Idaho basins have above average water year-to-date precipitation. This fall precipitation will help the soils deliver spring runoff to the streams and lakes more efficiently.

- Eastern Idaho (Upper Snake Basins): The Henry’s Fork drainage has the best snowpack in this region at 101 percent of average, while the upper Snake above Palisades only has 88 percent of normal snow. Fall precipitation was above average, which will allow efficient spring runoff. Right now, the upper Snake reservoirs are only at 37 percent of capacity; last year’s was at 66 percent. If the current storm track continues, the streams will flow near normal this summer.

For the complete Idaho Water Supply Outlook Report, visit www.id.nrcs.usda.gov/snow and click on the “Water Supply” link. Please contact Phil Morrisey, (208) 685-6983 or Julie Koeberle, (208) 685-6921 for additional information.

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