Understanding Drought: Lesson One

From a useful op-ed in today’s Los Angeles Times:

In January, it rained a lot in Southern California. The usual street
intersections flooded. Water tumbled down the Los Angeles River. And
houses in areas ravaged by fires last fall seemed in danger of sliding
off their hilltop perches.

It
was chaotic, as always — but desperately needed. The wet weather came
after the driest year on record in the L.A. Basin — less than 3.5
inches of rain. Coupled with below-average rainfall in 2006, lack of
rain in 2007 had fed fears of a drought. Do last month’s downpours mean
we can stop worrying now?

There is no simple, single
definition of drought. In any region, there are periods of below-normal
precipitation. These dry periods become a drought when demand for water
exceeds supply. In this sense, we may be in a permanent drought
throughout the Western United States.

Was chatting with a scientist friend about this topic a couple of months ago. Though not a hydrologist, he was sure there was a good scientific definition of drought. And he’s right: there are several scientific measures of drought, which NOAA blends (like scotch) in various drought index formulations.

But the fact remains: because drought is in part a measure of demand, as well as supply, it’s surprisingly difficult to say when in a thirsty region like Southern California when a drought begins…or ends.

Published by Kit Stolz

I'm a freelance reporter and writer based in Ventura County.

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