Climate change and shrinking water supply

A 2008 study shows that climate change has caused available water to shrink in the western U.S. during the last half century.

And even bigger changes lie ahead, according to lead author Tim Barnett of Scripps Oceanographic Institution in San Diego.

Tim Barnett: It’s a 20 percent decrease on average over the western U.S. in the snowpack as it exists on the first of April.

Barnett’s study compared 50 years of river and climate data with computer models. It showed that in the western U.S., about 60 percent of changes, such as shrinking snowpack, can only have a non-natural explanation: a human-induced rise in temperature caused by greenhouse gases. Barnett added that water supplies in the western U.S. might be disrupted within 20 years.

EarthSky asked Barnett how people will adapt.

Tim Barnett: Some of the adaptations will be conservation. Some will be taking it from farmers and giving it to a growing population. A decent adaptation would be to limit the population growth and development in the western United States. I don’t think that will ever happen. But those are the kinds of things that we’re going to have to do.

Barnett is concerned about the environmental future we’re leaving for the coming generations.

Tim Barnett: We’re altering the climate of planet in ways that we know, and in lots of ways that we don’t know. We’re making a world for today’s children and grandchildren that they’re going to have to live in, in the future. And if they don’t like it, there won’t be a thing they can do about it.

Barnett warns that dam capacity will be insufficient to hold the water coming rushing down.

Tim Barnett: What it means is that the bulk of your water that you receive, say from the melting snow, is going to come in the first three months of the year: January, February, March. By the time that you get to April, you’re largely out of snow in many areas. So what happens then is that you have to have enough dam capacity to hold all that water that comes – swish – down there in the early part of the year. If you don’t, you have to let it go. In the case of California, and in the case of the Columbia basin, they do not have the dam capacity to capture all of that water. So a lot of good water that we could use will go to waste.

How does Barnett’s study show this climate change is human-caused, rather than part of a natural climate cycle?

Tim Barnett: Well, of course that’s the trick. We do compare the signal, the fingerprint, with that we get from natural variability. We estimate natural variability from computer models. We think, from the computer models, that we’ve got a pretty good idea of what the natural variability of a system is like. We then compare that with what happens when you add greenhouse gases into the model. And they’re just night and day. They just don’t look alike.

What does he expect of water supplies in the American west over the coming two decades?

Tim Barnett: Things will get increasingly tighter, and tighter, and tighter.

Our thanks to:
Tim Barnett
Research Marine Physicist
Scripps Institution of Oceanography, UCSD
La Jolla, CA