Early Rivers
DB: This is Earth and Sky. Scientific studies have shown that many rivers and streams in New England are flowing earlier each spring.
JB: The U.S. Geological Survey is measuring stream flow across the U.S. with over 7,000 gauges. The data have been collected for more than 100 years at many sites. Glenn Hodgkins is a hydrologist with the U.S.G.S. in Maine. He and colleagues studied 27 rural and unregulated rivers and streams across New England.
DB: More than a third of the rivers studied now flow 1-2 weeks earlier than 30 years ago. None of the rivers in this study showed changes toward later spring flow. Most of the rivers flowing earlier in spring were in the mountainous and snowy regions of New England. Early snowmelt would lead to earlier river flow. Hodgkins says it’s difficult to attribute a cause and effect in this study. But he did find a strong correlation between warmer spring air temperatures and earlier stream flow.
JB: He adds that in New England, lilacs are blooming earlier. The date of last frost is earlier. Air temperatures are increasing. And ponds and lakes are also melting earlier. He says these changes are consistent with predictions of global climate change.
DB: Rivers in the western U. S. – tomorrow. Thanks today to the National Fish and Wildlife Foundation. We’re Block and Byrd for Earth and Sky.
Articles:
G.A. Hodgkins, R.W. Dudley, and T.G. Huntington. 2003. Changes in the timing of high river flows in New England over the 20th century. Journal of Hydrology 278: 244-252.
G.A. Hodgkins, I.C. James, and T.G. Huntington. 2002. Historical changes in lake ice-out dates as indicators of climate change in New England, 1850-2000. International Journal of Climatology 22: 1819-1827Author’s Notes:
For each river, Hodgkins pinpointed the date that one-half of that river’s flow had gone past the gauge, for each year, for the last 50 to 100 years.
Rivers and streams as good indicators:
Because rivers encompass a large area and drainage, measuring river flow measurements integrate many variables including precipitation, temperature, and many others. So river flow measurements can be more reliable than simple point source measurements. So river basins with stable land use make for good overall indicators of landscape-wide changes or shifts. Also, rural streams and rivers make good indicators in all regions.
Impacts of shifting flows and snow packs:
If timing of peak flow shifts, it could affect a range of organisms. Insects, fish, and shellfish often time important life history traits with specific times of river flow. For example, if the highly endangered Atlantic salmon travel upriver at a particular flow, they may have trouble timing their migration if peak flow timing shifts.
According to Bob Hirsch, this is already happening in the Sierra Nevada of California. Flow is occurring 2-3 weeks early each spring, and so when people need water the most-summer and fall-the water isn’t always present in the reservoirs. That’s because the snow melted early, led to early runoff, and early filling of reservoirs. This, again, means an early depletion of reservoirs.
Hirsch also notes that warming temperatures often mean less snow in the snow pack. This can mean more rain, instead of snow. Precipitation may not change, but less snow means less water for use later in reservoirs. It may also mean higher risks of flooding since rain may fall more frequently in winter. It may fall on top of snow, which can lead to some of the most serious flooding hazards.
Climate and stream flow shifts: This research can’t say for sure that changes in climate are causing shifts in stream flow. But the shifts of streams to earlier runoff, and early snowmelt, all correlate very highly with the warmer temperatures in these areas. Furthermore, all the other measured variables predicted to change with a warming climate are also shifting. These include ice out dates for lakes, blooming dates for plants, migration patterns for birds and insects, glacial melting, and many others. Changes to stream flow patterns are one of many indicators that something about climate is changing.
Consequences of climate change in regards to water management:
The possibility of climate change and global warming makes water management all the more urgent. Hirsch says Americans (industry, agriculture, and homes) have become far more efficient at managing water use but as population continues to increase, and if the climate continues to warm, we face some significant issues in water conservation and management.
The following people were interviewed for today’s program. Our thanks to:
Glenn Hodgkins
Hydrologist
U.S. Geological Survey
Augusta, ME
Robert M. Hirsch
Chief Hydrologist and Associate Director for Water
U.S. Geological Survey
Reston, VA
