20 May 2014 Last updated at 22:03 ET
By Jonathan Amos Science correspondent, BBC News 
Natural ‘”water towers” – places that hold and release water for society
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A new study finds that if temperatures rise and more precipitation falls as rain rather than snow, it will reduce the total amount of water in rivers.
It is a surprising observation. One might expect the timing of water flow to change but not the overall volume.
But this is precisely what scientists discovered when they examined the histories of 420 catchment basins in the US spanning the period 1948-2001.
The researchers report their work in the journal Nature Climate Change.
The study compares places of similar climate and precipitation, but with differing fractions of that precipitation falling as snow and as rain.
And it seems there is a significant difference in total streamflow if the fraction shifts from snow to rain.
“At first we thought there could be all kinds of explanations for this, so we better dig a bit deeper and make sure that this difference between places wasn’t being caused by something else,” explained Dr Ross Woods from Bristol University, UK.
…(read more).
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