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Runoff would be welcome in Sioux Falls, S.D., which was among countless communities that clamped down on water use last summer as rivers and lakes that supply power plants and households grew shallower.

South Dakota’s biggest city imposed its first water restrictions since 2003 as the Big Sioux River, which recharges its aquifers, dropped. Homeowners were limited to watering lawns once a week. Washing outdoor surfaces such as sidewalks, driveways and parking lots was banned.

“This is the driest year in our town’s history since the early 1950s,” Mayor Mike Huether said as 2012 drew to a close.

With just 5 inches of snow and some rain so far this winter, the conservation efforts will be back in place next year “unless we get one heck of a snowfall and bust this drought,” Mr. Huether said.

Western states rely on snow and ice that accumulate in the mountains during the winter for as much as 80 percent of their freshwater for the year, according to the Department of Agriculture’s Natural Resources Conservation Service. The melting snowpack replenishes streams, rivers and reservoirs and provides water for cities and crops.

A deep snowpack also can make the wildfire season more manageable by wetting forests and fields.

Tom O’Connor, the rural fire chief in Divide, Colo., would relish that after enduring what the governor called the state’s worst wildfire season ever in 2012.

Chief O’Connor’s volunteer department responded to more than 80 calls in June, compared with the usual 30 calls. Three-fourths of the calls were related to wildfires.

The fires came after Colorado got one of its smallest snowpacks in years — by some accounts tying 2002 as the lowest snow buildup in the 45 years that records have been kept.

Still, climatologists caution that it’s too early in the winter to give up hope.

“We could be singing a different tune this winter if a storm system cooperates,” said Dave Robinson, a Rutgers University geography professor who’s also the New Jersey state climatologist. “Sometimes you get what you wish for.”

• Associated Press writers Scott Bauer in Madison, Wis.; Matt Volz in Helena, Mont.; and Mead Gruver in Cheyenne, Wyo., contributed to this article.