[Jack Stow]

Jack Stow  asked the Naked Scientists:
   
Global warming: if sea levels rise will the water levels in lakes, rivers and canals also rise?

Jack Stow
Lincs, UK


What do you think?

[dentstudent]

Climate change is likely to have an effect on water levels at most parts of the hydrological cycle. The amount of change will vary on the region in which you are assessing. The forecast changes to precipitation within Europe show a high degree of spatial variability, between the northern part (increase of up to 40%) and the southern part (decrease of up to 20%). As far as sea levels are concerned, global sea levels rose by about 1.7 mm per year during the 20th Century, with European rates ranging from 1.7 to 2.8 mm per year. Observations from the last 15 years indicate that this has increased to 3.1 mm per year. Projections for the end of the 21st century indicate that sea level rise (SLR) may be have up to an additional 0.59 m on top of the 1980-2000 level. So sea levels are very much likely to rise. These will in turn affect the tidal zones of the rivers and estuaries - the areas at the mouth of the river that are affected by the rising and falling tide. Thus, where the rivers are not tidally affected, the changes to sea level will not directly affect the level of the water upstream. One indirect change may be the fact that because there is more water at the end of the river, the flow rates may reduce, meaning that the speed that the water in the river can empty out into the sea may reduce. This would mean that the flood plains of the river are likely to grow to accommodate for the water backlog.

Where the rivers are not tidally affected, the flow rates will be affected by the local precipitation levels, catchment areas, the land-use and the amount of water being used for human requirements such as irrigation. So, though there will be changes to the water levels at these upper stages of the river, they are not going to be affected by SLR. This is also the case for lakes - their water levels will be affected by local precipitation and land-use management, but not as a direct result of SLR.

Canals are closed system waterways, which means that the amount of water that goes into and out of them is independent of SLR, and so will not be affected in this way by climate change. However, alterations to precipitation patterns may affect the amount of water available that can be put into the canals - there were instances in 2003 of some canals having reduce flow rates due to this drought.

So in short, SLR will affect the water level of rivers at their lower stages, but not at upper and middle stages, nor will it affect canals or lakes.


Additional: For information and interest, have a look at the IPCC report on Climate Change and Water and the European Environmental Agency's "Impacts of Europe's changing climate - 2008 indicator-based assessment"

[Titanscape]

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