59, August 2007
What's so special about drylands?
|This picture, from the article Where rivers run dry or ten feet high: Variation and predictability matter more than averages for desert ecosystems, by Mary Price and Nick Waser, is a perfect illustration of the kind of huge variations in water availability that characterize deserts everywhere. The Rillito "River" of Tucson, Arizona, is normally completely dry; in fact, it's a favorite location for Tucson residents to let their dogs run and play, or to go horseback riding. But when the summer rains come, such activities have to be put on hold. Not only can the rains be torrential, but once the ground becomes saturated, further rainfall can cause serious flooding and even flash floods. This picture is from July 2006, but the rains in July 2007 were equally extreme and dangerous: tragically, three people were swept away and drowned during flash floods in Tucson that month. Although visitors sometimes laugh at local road signs that say "do not enter when flooded" where there is not a drop of water in sight, these signs mean what they say!|
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