U.S. Geological Survey
U.S. Department of the Interior

News Release

Date:                October 29, 2007

___________________________________________________________________________­_

Building a Water Census for the Nation.
Wetter Climate and Earlier Snowmelt Runoff Noted in Great Lakes Basin Study

Editors:  The report, Historical Changes in Precipitation and Streamflow in
the U.S. Great Lakes Basin, 1915-2004, is available on: http://pubs.usgs.gov/sir/2007/5118/  
This report and others on the Great Lakes are also available on our new
website:  National Water Availability and Use Program - Great Lakes Basin
Pilot  http://mi.water.usgs.gov/projects/GreatLakesWaterAvailability/
 

More precipitation has been falling recently in the Great Lakes Basin than
in the more distant past.  During the past 90 years, total annual
precipitation increased by 4.5 inches and much of that increase occurred
during the most recent third of that time span.  These are among the
findings in a report from the U.S. Geological Survey (USGS) that describes
streamflow and precipitation changes in the U.S. Great Lakes Basin.

"We saw, as probably anyone living in the Great Lakes Basin has, substantial
variability in precipitation from year to year and season to season," said
USGS scientist Glenn Hodgkins, who led the study. "But clearly, the basin
has been receiving more precipitation than it did in the early 1900s."

Despite the increase in precipitation, the scientists determined that
streamflow in the basin increased more modestly.  During the past 50 years,
an average annual precipitation increase of 4.2 inches resulted in an
average runoff increase of 2.6 inches as measured at 43 USGS
streamflow-gaging stations.  The difference may be partly caused by
increased evapotranspiration - water lost to the atmosphere through
evaporation from water bodies and soil and transpiration from plants.

"This study is a key component in assessing water availability and use and
in building a water census for the nation," said Robert Hirsch, USGS
Associate Director for Water.  "We now have a much clearer picture of the
volume of water being added to the largest fresh-water system in the U.S.
and how those volumes have been changing over the last few decades."

The Great Lakes Basin, which encompasses Lakes Superior, Michigan, Huron,
Erie, and Ontario, contains 95 percent of the fresh surface water in North
America and 18 percent of the fresh surface water in the world. Ground water
underlying the basin constitutes another large volume of freshwater.  It has
been estimated that streams contribute 46 percent of the water that goes
into the Great Lakes.  Direct precipitation into the lakes makes up about 53
percent.  The remaining 1 percent of water comes to the Great Lakes by
diverting water from outside of the basin.

Among the findings in this report:

*       Precipitation over the land part of the U.S. Great Lakes Basin was
lower than at present for several decades-the average precipitation for
1915-1934 was 10 percent lower than for 1984-2003.
*       Precipitation did not consistently increase for all months over the
last 90, 70, or 50 years.  February and March precipitation declined
slightly for all three periods. The largest increases occurred from July
through October.
*       In February and March, precipitation declined but streamflow
increased; in contrast, April precipitation increased, but streamflow
decreased, illustrating an earlier snowmelt runoff in recent years.
*       Annual low streamflows increased more during the last 50 years in
some of the few regulated and urban basins analyzed than in all of the
relatively natural basins.

This study is part of the USGS Water Availability and Use Initiative, which
began in 2005 at the request of the Congress with a pilot study of the Great
Lakes.  The focus of the Great Lakes Basin study is on improving fundamental
knowledge of the water balance of the basin, including the flow, storage,
and withdrawal of water by humans.  A report released earlier this year
described historic lake level changes and their ecological impacts. Reports
on ground-water flow and storage, and water use in the region have also been
published and several other reports are planned. These reports are intended
to inform citizens, communities, and natural-resource managers of how much
water we have, how water availability has changed in recent decades, and how
much we will have for the future.

The Initiative will add other major water-resources regions in the future as
funding permits. At full implementation, the program would include national
synthesis component to provide an overview of the status and trends of the
nation's water resources in forms useful to policy makers, public officials,
and the general public.