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How More Rain Will Worsen Water Woes

As snow becomes history, a smaller proportion of the planet's precipitation will reach the streams that feed water reservoirs.
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(Photo: Bidgee/Wikimedia Commons)

(Photo: Bidgee/Wikimedia Commons)

As fossil fuels and deforestation continue to ratchet up global temperatures, less precipitation is forecast to fall as snowflakes. Instead, greater proportion of moisture is expected to tumble out of the clouds as raindrops.

It's long been known that this will worsen climate change's woes for water managers and hydroelectric operators. That's because snowpacks can act as water batteries, gradually discharging their aqueous bounties into streams that feed reservoirs during warmer months, when demand for water is often greatest. That means reservoirs may need to be expanded to help cope with the loss of these frigid montane water reserves—an expensive and environmentally damaging strategy.

But new research suggests that the problems could go even deeper than that.

We need to be bracing for a different type of interruption to our water supplies than had already been anticipated.

Research published Sunday in Nature Climate Change revealed how a bucket of snowmelt can act differently in the environment than a bucket of rain. As rainfall subs in for snowfall, scientists discovered that the amount of water flowing down streams is often reduced, even when the amount of precipitation remains the same.

The finding is worrying—and, frankly, perplexing.

"As far as why this happens, we don't know yet," says Wouter Berghuijs, a University of Bristol hydrology researcher and the study's lead author.

Berghuijs was part of a small team of European researchers that analyzed the effects of snowfall on streamflow using data from 420 water catchments across the United States between 1948 and 2001. They found that a higher ratio of snowfall to rainfall was associated with higher streamflow averages when compared with catchments that received little or no snow. "Furthermore," they write in the paper, "the fraction of each year’s precipitation falling as snowfall has a significant influence on the annual streamflow within individual catchments."

The researchers speculate that these differences could be related to water storage dynamics, evaporation rates, and the way water flows through different environments.

"An example mechanism could be the freezing of the ground," Berghuijs says. "When you have a snowpack that sits on the ground for a long time, the soil underneath can become frozen. Later on, in spring time, when the snow melts, the ground underneath is frozen and the meltwater flows through to the river quickly. When you warm that soil, the soil may better hold the water—and evaporate it before it gets a chance to reach the river."

Much more research is needed to help clarify the possible causes of the altered streamflow rates, including field measurements and computer models, according to Berghuijs. What the new research appears to make clear, though, is that we need to be bracing for a different type of interruption to our water supplies than had already been anticipated.

"If the amount of water in a river goes down, this may put pressure on hydropower production, irrigation schemes, and municipal water supply," Berghuijs says. "For some, a change in total runoff may not cause much harm—while other region will be much more severely affected."