Science Sunday: What’s That You Say? Stationarity Is Dead?

We’re always sorry to hear that anyone has died. This death is attributed to human-induced climate change, which is altering the fundamental assumptions of water management in the West and worldwide — potentially imperiling a half-trillion dollar annual investment.The average temperature of the Rockies has increased by 2 degrees Fahrenheit over the last 50 years. By 2040, most of the snow that falls over the winter in the Rockies and California’s Sierra Nevada will melt by April 1. Snowpack in the Sierras has already declined by 20 percent.

The cause for these changes is human-caused climate change, according to a paper published in this week’s journal Science.

“We looked at whether there is a human-caused climate change where we live, and in aspects of our climate that we really care about,” said Benjamin Santer of LLNL and co-author of the paper. “No matter what we did, we couldn’t shake this robust conclusion that human-caused warming is affecting water resources here in the Western United States.”

Furthermore, worldwide changes in the water budget are undermining the basic assumptions of water management, according to another paper in Science. Water management is based on the principle of “stationarity,” which means that water availability factors — like streamflow and precipitation — vary within an “unchanging envelope of variability.”

But according to a paper by the U.S. Geological Survey’s Christopher Milly and colleagues:

“But anthropogenic change of Earth’s climate is altering the means and extremes of these factors so that this paradigm of stationarity no longer applies.”

This means that when planning worldwide investments in water infrastructure — an exercise that costs nations about $500 billion a year — engineers can’t be guided by historical variability of water availability and flow. So the adequacy of those structures to handle their intended jobs is called into question.

“The assumption that the past is the key to the future has lost much of its value for water management,” says Zbigniew Kundzewicz, leader of the Potsdam Institute for Climate Impact Research and co-author of the Sciencearticle.

Courtesy Science

The water changes worldwide will not be uniform. Water availability will probably increase in the northern latitudes and in some tropical regions, while decreasing substantially in the Mediterranean basin, southern Africa and southwestern North America. “These drying regions are likely to experience increasing drought frequency in the future,” says the USGS’s Milly.

Previous regional studies have indicated that the southwestern U.S below the 40th parallel — the 40th parallel is the Kansas-Nebraska border and runs along Baseline Road in Boulder — will experience less rainfall and greater droughts in the coming century as a result of anthropogenic climate change.

In the intermountain West, water storage is less of a problem, because the region already relies on reservoirs for much of its summer and fall water supply. On the Pacific Coast, however, this is less true. Those areas may face a large infrastructure bill to build reservoirs to capture runoff for later season use, and to prevent flooding, which is already a problem in some seasons.

But it’s also been projected that the mountainous regions of Colorado may get more precipitation. The pattern of that moisture is expected to change. Snowline should be higher. Previous studies have also projected like this one in Science  that the snowfall may melt earlier in the season, creating potential water storage problems.