U.S. Water News Online
LA JOLLA, Calif. -- This year's La Niña spring could bring increased streamflows to the Pacific Northwest and Appalachia, but lower streamflows in the Southwest and in parts of the Northeast and center of the nation, according to a new report by the U.S. Geological Survey and its partners.
The new report, by the USGS, the Scripps Institution of Oceanography in La Jolla, Ca., and the Western Regional Climate Center in Reno, Nev., shows areas of the country where it is more likely that streamflows will be high -- including flooding -- and areas where streamflows will be low -- which could spell drought. The new maps are actually a statistical survey that identifies areas where during past La Niña years very high flows, floods, and very low flows have occurred.
The new maps complement other long-range predictions for this winter and spring from other agencies and institutions that forecast temperature and precipitation based on global conditions, said USGS hydrologist Michael D. Dettinger, one of the report's authors.
"Because streamflow has its own unique variations apart from those of precipitation and temperatures," he said, "We went back 50 to 100 years and looked at historic streamflow data to make these predictions. Increases in precipitation do not always produce flooding, so we've focused directly on the streamflow connections to La Niña. We've looked at La Niña years and determined where there's a higher chance of having unusually high flows and where there's a higher chance of having low flows.
"Because the earth's water system is more complicated and has a longer 'memory' than simply precipitation, because of additional features such as hydrogeology, soil moisture and snow pack, streamflows respond to climate variations for a longer period of time," Dettinger said. "This allows flow predictions that are useful for several months longer than we can expect than when simply predicting precipitation."
He said the report is aimed at assisting emergency managers and water-use managers in their planning for this year's La Niña, a subject of intense interest to water managers, who want to extend the lead time for important allocation decisions (especially in the West).
"We can't control precipitation. Either it comes or it doesn't. But we can manage water," he said. "We can decide now to intervene and make changes to reservoirs or divert water long before an emergency happens if we know the likelihood of having a problem is increased. So the streamflow forecasts are of special interest."
The USGS operates a network of more than 7,000 streamflow gages across the United States. Data from the active stations, as well as from discontinued stations, are stored in a computer database that currently holds mean daily-discharge data for about 18,500 locations and more than 400,000 station-years of record. Near real-time streamflow information is available online at http://water.usgs.gov
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