How much rain is needed to end drought?

Tue, May 1, 2012

Climate Change, UK Climate Change

Floods and swollen rivers are not a sign that our water supply is being restocked and the hose pipe ban will suddenly be cancelled.This chart showing  rainfall in the UK over past 3 years reveals just how little rain has fallen and as a result ground water stocks are exceedingly low.

The combination of low rainfall in winter especially and our dependence on ground water  is creating the ongoing drought despite the wettest April on record for some areas of UK.

“One of the main reasons for concerns over water availability in southern and eastern England and the Midlands – which are officially in drought – is their dependence on groundwater from aquifers.

“Weeks of rain are needed to wet the ground enough for rainwater to percolate down and begin filling up the aquifer. After the wettest April on record, this is starting to happen. However, most of rain in recent weeks has run off directly into rivers, which is why we are experiencing flooding in some places at the moment.”

Water levels in those areas are around 10m below average for this time of year.

“Crudely, the amount of water needed to ‘fill’ or saturate the rock – usually chalk – is about 1% of its total volume, therefore to raise the water table by 10m requires approximately 100mm of water. However, you need to take into account as the weather warms up, water evaporates more readily from the soil,” he says

http://www.bbc.co.uk/news/magazine-17875456

 

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