The effect of climate on the Thames

The effect of Climate on The Thames
1 October 2008
Rising sea levels and fuller rivers are likely to increase the risk of flooding around the Thames Estuary over the next century, according to research published last week.
The findings are part of the Environment Agency’s Thames Estuary 2100 project, and mean flood management plans will have to be overhauled.
Scientists used sophisticated computer models and data from long-term monitoring projects to investigate whether extreme weather would get more or less common in future, and by how much. Their work has reduced uncertainty around the probable effects of climate change on the Thames.
Their results suggest that potentially the biggest problem, and the biggest area of uncertainty, will be sea level rise in the Thames Estuary over the next century. This rise is likely to be between 20 and 90 centimetres by the end of the century, largely due to thermal expansion of the oceans, melting glaciers and polar ice.
The last component is the least certain; at the extremes, melting polar ice could take the total sea rise as high as two metres, though this is extremely unlikely. Scientists warn that more research is needed here.
But the findings also show that current predictions for sea-level rise in the Thames Estuary are realistic, and show that the current ‘worst-case scenarios’ of maximum water levels can be reduced from 4.2 to 2.7 metres. Such a reduction means that the Environment Agency should be able to manage water levels in the tidal Thames without having to resort to a tide-excluding estuary barrage this century.
Likewise, climate change now looks less likely to increase the height and frequency of storm surges in the North Sea than previously feared.
The research was carried out by the Met Office Hadley Centre, the Proudman Oceanographic Laboratory (POL) and the Centre for Ecology and Hydrology (CEH).
Among the findings of CEH’s river modelling is that peak freshwater flows for the Thames could increase sharply. For example, at Kingston the flow of water at peak times could increase by around 40% by 2080. But the model’s results vary from river to river; some areas in the Thames Basin may experience only minor changes while in others the change may be considerably larger.
Even using state-of-the-art models, the conclusions are uncertain. But they suggest a large increase in risk compared to the previous consensus; until now flood planning has been done on the basis of a 20% increase in river flows over the century. The Environment Agency will now be testing its flood management plans against a possible 40% rise.
Many of the findings went against received opinion. For example, the Hadley Centre used POL’s storm surge computer model to identify that climate change is less likely to increase storm surge height and frequency in the North Sea than previously thought.a from the US Gravity Recovery and Climate Experiment satellite (GRACE) which essentially weighs the ice sheet.
Results from the two completely independent methods were extremely similar. ‘This gives us confidence when separating out the components,’ says one of the study’s co-authors, Professor Jonathan Bamber from the University of Bristol.
They found that between 2000 and 2008, Greenland lost around 1500 billion tons of ice, which is equivalent to 166 billion tons a year or 0.46 millimetres a year of global sea level rise. But in each year between 2006 and 2008, the ice sheet lost 273 billion tons of ice per year, equivalent to 0.75 millimetres of sea level rise.
‘This is down to increased surface melting as well as glaciers speeding up in recent years,’ says Bamber.
Sea level has been rising on average by around 3.2 millimetres per year since the 1990s, with the latest estimates suggesting that Greenland contributes 0.5 millimetres per year to sea-level rise. ‘It’s clear this number has been rapidly increasing and will be nearer one millimetre a year by the end of the decade if the trend continues unabated,’ says Bamber.

Climate & The ThamesRising sea levels and fuller rivers are likely to increase the risk of flooding around the Thames Estuary over the next century.

Scientists, using sophisticated computer models and data from long-term monitoring projects, have been investigating whether extreme weather would get more or less common in future, and by how much. Their work has reduced uncertainty around the probable effects of climate change on the Thames.

Their results suggest that potentially the biggest problem, and the biggest area of uncertainty, will be sea level rise in the Thames Estuary over the next century. This rise is likely to be between 20 and 90 centimetres by the end of the century, largely due to thermal expansion of the oceans, melting glaciers and polar ice.

The last component is the least certain – at the extremes, melting polar ice could take the total sea rise as high as two metres, though this is extremely unlikely.

But the findings show that current predictions for sea-level rise in the Thames Estuary are realistic, and that the current ‘worst-case scenarios’ of maximum water levels can be reduced from 4.2 to 2.7 metres.