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Published online: 6 April 2006; | doi:10.1038/news060403-9
Arctic water flow speeding upMeasures of rain, snow and runoff in Siberia show hefty changes.Quirin Schiermeier 
| Arctic rivers are gushing more fresh water into northern seas. © Getty |
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One
of Siberia's largest rivers is dumping about 10% more fresh water into
the Arctic today than it was some 60 years ago, thanks to the complex
effects of increased snowfall, melting permafrost and changing weather.
The
result is in line with predictions of how climate change is expected to
alter the Arctic water cycle, and is a worrying sign in terms of
maintaining important ocean currents. The more fresh water that enters
the northern seas, the less dense this water becomes and the less
likely it is to sink. This sinking currently helps to drive a powerful
Atlantic current that keeps the climate temperate and steady.
Freshening
of the Arctic Ocean may already have begun to affect this so-called
thermohaline circulation, but oceanographers and climate modellers are
still puzzling about the magnitude and likely effects of the changes
(see 'Climate change: A sea change').
Jessie
Cherry of the University of Alaska in Fairbanks and her team analysed
records of precipitation, snow depth and runoff in the catchment area
of the Lena River, an area of more than a million square kilometres
east of the Ural mountains in Siberia.
The
team, including two Russian scientists, found that the average winter
snow depth there has doubled to 44 centimetres from 22 centimetres in
1940. Although summers in the region have become significantly dryer,
and also slightly cooler, total runoff from the Lena has increased by
around 10%, they reported at the European Geosciences Union annual
meeting in Vienna, Austria, on 5 April.
Other
research projects have looked at river runoff before: the annual runoff
of the six mightiest rivers draining into the Arctic Ocean, including
Russia's Ob, Lena and Yenisey, increased by about 7% between 1936 and
19991. But the study by Cherry and
colleagues looks at the full hydrological cycle, in order to unpick
exactly how and why the rivers are pouring out more water.
 Having this kind of information Arctic-wide would be incredibly valuable.  |
Michael Vellinga
UK Met office, Exeter |
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Melting land
An
increased snowmelt plays a big role during the spring, but there are
other factors too. The atmosphere is getting warmer and moister, says
Cherry. And, whereas Siberian summer days are getting cooler, night
temperatures have increased, allowing for more permafrost thawing and
more water drainage. In the winter, warming has enhanced evaporation,
precipitation and runoff.
Permafrost
thawing could be the biggest effect in the future, Cherry says.
Increased melting of frozen soils has so far only been observed in the
southern third of their study area. If it were to spread further north,
which could happen as temperatures continue to rise, this would really
boost runoff, she says.
Validation
Given
the number of factors involved in the water cycle and the difficulty of
maintaining devices that collect data, it has proven much harder to
quantify changes in water flow than, for example, global temperatures2.
Cherry's unpublished analysis, which is based on daily observations
from seven Russian meteorological stations and 40 stations recording
snow depth, is one of few studies that climate researchers can use to
validate their models of hydrological changes.
"It
is always fairly useful to know what the real world does, and the
Arctic freshwater budget is indeed very important," says Michael
Vellinga, a climate modeller at the UK Met office in Exeter. "Solid
data about one large river system are therefore very welcome; having
that kind of information Arctic-wide would be incredibly valuable."
Cherry
and others are now working on a model to help scientists calculate
details of snowfall from available measurements, such as snow depth and
air temperature. The model, known as the Pan-Arctic Snowfall
Reconstruction, should help to pin down details of the hydrological
cycle in other parts of the Arctic.
Visit our newsblog to read and post comments about this story.
References
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Peterson
B. J.,
et al. Science, 298. 2171 - 2173 (2002). | Article | PubMed | ISI | ChemPort |
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Ingram
William J.,
Allen
Myles R.,
et al. Nature, 419. 224 - 232 (2002). | Article |
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