Colorado flooding

For four years back in the early 1970s, Lynda and I lived in Boulder, Colorado.  It's been a while since we've been back, but i can still sort of recall the little stream that came down out of Boulder Canyon.  So the videos and pictures of the recent flooding are that much more remarkable, if not incredible.  The New York Times reports that 4,000 people in Boulder Canyon were told to evacuate immediately; and another 4,000 were told to move to higher floors.  The main campus of the University of Colorado has been closed.  Early estimates report that 20 percent of the university's buildings have had some amount of water damage, including the theater and main library.  There have been three reported deaths so far and more flood damage in and around canyons all along the Colorado front range.  The state's governor, John Hickenlooper, has referred to it as among the worst flooding in the state's history.

How could that much water collect and roar down the canyon and cause all that damage?  The Times reports 15 inches of rainfall in the past few days.  And where the rain fell on hillsides above Boulder and other canyons that had been burned by recent forest fires, there was nothing to absorb it.  Worse, heat from the fires had created a layer of soil that is virtually waterproof.  The rain falls and virtually all of it immediately heads downhill, collecting dirt, rocks, and all sorts of debris as it goes.  It knocks down and sweeps along almost everything in its path and doesn't stop until it looses energy on the plains beyond the mouths of the canyons.

After people recover as best they can from the shock, and after the cleanup, I hope the papers will continue to cover how, if at all, Boulder and the other communities respond.  It's a version of the situation following almost any weather-related disaster.  It's on-going in New York and New Jersey in the aftermath of Hurricane Sandy.  Is this combination of bare hillsides after forest fires and heavy rains an extraordinary, highly unlikely ever-to-be-repeated event?  Or does climate change make such extreme weather, even without the forest fires, more likely?  Is there a need to take steps to mitigate damage from similar floods in the future?  Would this influence land use decisions in the canyons?