Water Goes 'Missing' as More Rain, Less Snow Falls

A new study finds that as temperatures rise, it will rain more and snow less, causing the total amount of water in rivers to decline.

Researchers compare in the journal Nature Climate Change areas of similar climate and precipitation, but with differing fractions of that precipitation falling as snow and as rain.

After examining the histories of 420 catchment basins in the US spanning the period 1948-2001, scientists discovered there is a significant difference in total streamflow if the fraction shifts from snow to rain, something they did not expect.

"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," Dr. Ross Woods from Bristol University, UK, explained to BBC News.

"We also checked out what happened at the same place between different years, and we found that the years with more snow also produced more streamflow than the years with less snow," he added.

The team hypothesizes that the ground may be changing in response to temperature rises. Warmer conditions means the ground can absorb more water, to be later evaporated or transpired by plants, meaning less will run into nearby streams and rivers.

"This issue is important because quite a lot of the snow at the moment is in the places we call the 'water towers' - the places that provide water to the great bulk of society," Woods said.

He fears that people in such areas will be scrambling for a larger water source. Irrigation systems or hydropower systems or municipal water supply systems rely on water availability to function.

"Those communities or systems would need then to adapt to that - to find a way to get by with less water, or else find alternative water sources," Woods concluded.

As global warming warms up the Earth, the overall patterns of precipitation are likely to change as well, but clearly affect certain areas more than others.