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23 March 2008

Drip Dry - What is a Desert?

Walking around Pasadena, most people probably don't think of the city as part of a desert - a place of vast sands, mouth-drying winds and devastating heat. But perhaps we would all be better off if they did.

With the so-called "perfect drought" of last summer and the autumn firestorms that followed, fears of global warming have hit Southern California hard, including Pasadena, which isn't yet a desert, but is well on its way to becoming one.

According to Tapio Schneider, an assistant professor of environmental science and engineering at Caltech, just what a desert actually is isn't easily defined.

"Desert has many different and quite vague meanings. The meaning you are probably thinking about is a very arid region [little rainfall, evaporation exceeds precipitation] with a barren landscape and sparse vegetation," Schneider explained recently via email. "Climatologically, deserts can be defined and sub-classified in several ways, but usually the term desert is applied if annual rainfall is less than about 10 inches," Schneider explained. "We receive about twice that amount on average, so according to that definition, Pasadena is not a desert. But in other classifications, the term ‘desert climate' refers to any climate in which evaporation exceeds precipitation, and this is the case in Pasadena."

If you look at a map drawn Sept 25 at the University of Nebraska-Lincoln's Drought Monitor, you'll see that most of California was under a moderate to extreme drought, with almost all Southern California under extreme drought conditions. Yet, there were no statewide mandatory water conservation measures taken.

Nationwide, California wasn't the hardest hit area last year. A large portion of the Southeast United States suffered from extreme to exceptional drought conditions during that time.

Certainly things have improved this year and the current drought map shows Southern California as being abnormally dry to under severe drought conditions. Northern California also appears to be sitting pretty. But does this mean water usage is now only a Southern California issue?

Schneider explained in a phone interview that while many regions across the US are now suffering from drought and "we [scientists] see pretty clear changes," some people will argue that "the drought we are seeing here is a sign of climate change." But, he cautioned, it is too early to come to that conclusion.

After all, he continued, "A few years ago was one of the most humid years on record. And three years later, it was the driest year on record." He does still feel that "on average, it will get drier here," yet we must also consider that during a period of time there will be "variability" in weather patterns.

However, he was sure that "it is very likely it will get drier in the coming decades," but "whether that is due to human activity that is too early to tell. We'll know in a decade or two."

While scientists can wait that long to figure out whether last year's perfect drought was a sign of things to come or just a normal variation in the weather, he also acknowledged that, as a community, we can't wait much longer.

"We have to do two things: Find ways of producing energy with lower emission of greenhouse gases," he said. "At the same time, climate change will happen, part of it is inevitable, yet we do have a choice in it. We can adapt and conserve water as a resource by using energy technologies on an individual level and by being more aware in order to put pressure on our institutions to change on larger scale."

As the current drought monitor maps show, despite the rain, Southern California is still under drought conditions.

And "Water policies need to adapt now," Schneider said, "Climate will change in the next 50 years" and the reality is we will have to "use less water to adapt."

--Originally published in the Pasadena Weekly

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