Streaming toward a wetter United States.
"The nation is getting wetter but less extreme" in terms of stream flow, says Harry F. Lins, a USGS hydrologist in Reston, Va., who coauthored a report appearing in the Jan. 15 GEOPHYSICAL RESEARCH LETTERS. "The water resources of the nation seem to be improving, but we're not paying a price."
Lins and James R. Slack, also of the USGS in Reston, analyzed records from 395 stations that gauge water flow in streams in the conterminous United States. They chose remote streams that had not been altered by dam construction or crop irrigation.
Their analysis indicates that 30 percent of these streams are now carrying more water than they did 50 years ago. Days when streams had low to normal amounts of water showed almost all the increase. Few stations showed an increasing trend in water flow during times of peak flow. The net result is that the driest times of year grew moister, but the nation did not experience an increase during the wettest periods.
These findings run counter to climate researchers' expectations. Simulations by some computerized climate models of global greenhouse warming suggest that precipitation should be getting more extreme, possibly with more frequent flooding. "We find no substantiation of that hypothesis," says Lins.
Measurements of actual precipitation, however, tell a different story than the stream data do. Last year, meteorologists at the National Climatic Data Center in Asheville, N.C., reported that the heaviest precipitation is more frequent and has become more intense since 1910. "The wettest side of the spectrum is definitely increasing," says the center's Richard W. Knight.