Late summer streamflows decreasing, says study

A University of Montana study published this week in the international journal Climate Change discovered that late-summer streamflows have decreased in the western United States over the past half century because of higher air temperatures and earlier spring runoff. Scientists examined 50 years of U.S. Geological Survey streamflow data on 153 streams in Montana, Idaho and Wyoming. They found that 89 percent of the streams experienced substantial declines in streamflow by August, likely as a result of longer and warmer summer temperatures. If this trend continues into the next half century, small streams in the central Rocky Mountains could start to run dry by late summer, the study said. That can affect aquatic animal populations, said Steve Running, UM regents professor of ecology and co-author of the study. Even when water temperatures increase in streams in the late summer months, there’s less oxygen in the stream for trout populations to live. Already, state fish and game departments have had to limit fishing on some streams because of warm water temperatures, he said...more