Climate and Streams
DB: This is Earth and Sky. Yesterday we talked about streams and rivers in New England that are flowing earlier now every spring. Warmer temperatures seem to be a driving force.
JB: Iris Stewart-Frey is a climate researcher at the Scripps Institute of Oceanography. She and her colleagues have documented shifts in the timing of stream flow and snowmelt runoff in rivers across western North America. They’ve determined that runoff timing has shifted 10 to 30 days earlier each spring over the last 50 years.
DB: According to Stewart-Frey, warmer temperatures throughout western North America are triggering the earlier snow melts and stream flows. What’s more, Stewart-Frey used a widely accepted climate model to predict what the rivers will do for the next 100 years if greenhouse gases are not reduced. The model predicted that snow melt runoff – and stream flow – of many rivers across the western U.S. will come another 30 to 40 days earlier than now.
JB: When streams flow earlier, it is more difficult to store water. And that’s a critical issue in the drought-ridden western U.S. Earlier flow means short supplies and longer drought periods since reservoirs are more likely to run dry earlier in the summer season. For more about global warming and streams – come to today’s show at earthsky.org.
DB: Thanks today to the U. S. Geological Survey and to the National Fish and Wildlife Foundation. We’re Block and Byrd for Earth and Sky.
Articles referred to in today’s program:
Stewart, I., D. Cayan, and M.D. Dettinger. Changes in snowmelt runoff timing in Western North America under a “business as usual” climate change scenario. Climatic Change 62: 217-232, 2004.
As the West Goes Dry. By Robert F. Service. News Focus. Science 303: 1124-1127. February 20, 2004.
Changes in streamflow timing in the Western United State during recent decades. USGS fact sheet. Spring 2004.
Defusing the Global Warming Time Bomb. By James Hansen. Scientific American, March 2004. pp. 68-77. Or go here. Click on March 2004 and scroll down to find and download this article.
West Getting Burned by Global Warming (CNN.com, May 4, 2004)
Additional Information about climate change and stream flow:
Iris Stewart-Frey says there is no question that the North and Western parts of North America have warmed by 2-3 degrees Celsius over the last hundred years, while the globe itself has warmed by about .5 degrees C. Thus, with global warming there can be extreme regional warming. She adds that the rise in carbon dioxide along with temperature is unprecedented. This evidence, alone, she says is a very good basis for establishing human-induced warming changes.
She notes that changes in stream flow and snow runoff are just one of many consequences of climate change in the West. Others include earlier blooming plants, ecosystems moving to higher elevations, disappearance of glaciers, and lower snow pack.
Her research indicates that at least some of the shifts are due to human-induced warming, while some is due to natural climatic variability.
Water stress brought about shifts in stream flow and runoff timing will impact humans, as well as wildlife and ecosystems. Salmon spawn at precise water temperatures and flow regimes. The San Francisco Bay ecosystems are also being affected since river water flowing into the Bay has shifted to earlier in the season. This means that there is less fresh water in the Bay later in the season, and causes higher salinities. This impacts a variety of Bay organisms.
As climate warms over the next century, she adds, greater changes in stream flow timing could result in greater affects on water, ecosystems, and wildlife. But, she cautions these may not necessarily be linear or predictable changes. Some changes could happen very rapidly with relatively slower shifts in stream flow timing. For instance, salmon only spawn within a given range of temperatures. They may have an all or nothing response to shifts in stream flow and temperature.
She notes that it is important to recognize the problem and plan for it. She envisions adjusting water operations-the amount and use of water, operating dams in different ways, and looking for innovative strategies. She also points out that the effects could be lessened if we can curb greenhouse gas emissions. The future shifts are based on a “business as usual scenario,” which means no reduction in our current emissions of greenhouse gases.
The following people were interviewed for today’s program. Our thanks to:
Iris Stewart-Frey
Scripps Institution of Oceanography
Climate Research Division
La Jolla, CA,
Robert M. Hirsch
Associate Director for Water
U.S. Geological Survey
Reston, VA
