As I write this, storm clouds are gathering in the west. That's a pretty common situation here in Boulder, Colorado, in the summer. We get fine, clear mornings, and sometimes rain in the afternoon. In general big storms aren't exactly rare, but this summer we've been getting pounded. On my bike rides it's been routine to see the creeks in the area swollen to the point of overflowing.
But this summer, that situation has turned more dangerous. We've been getting some serious flood scares, and the reason may not be obvious to people who don't live in the area: fires.
Last year, the Fourmile Canyon area north and west of Boulder burned pretty vigorously for many days. The smoke plume was visible from space, and it caused a lot of local grief. What wasn't clear to me at the time was how this would affect flooding.
The image above, taken on June 7, 2011, is from NASA's Earth Observing-1 satellite, and is a combination of far-infrared and visible light. Water (reservoirs and lakes) shows up as purple in this false-color image, vegetation is mostly green, and red/orange shows the fire damage. You can see Boulder to the lower right of the burned area.
When fire burns off all the plants, there's nothing to hold the rain water in when we get storms. The water all washes downhill, in this case into the Fourmile Creek. That runs into the Boulder Creek, and that, well, here's a natural color image which shows why that's bad:
You can see the wiggly line that's the Boulder Canyon, and the creek runs along it, out of the Foothills, and right through the heart of Boulder, which sits on what is essentially a flood plain. It's been a while since there's been a devastating flood here, but you can see that the creek opens up right at the western edge of town.
This year, as I said, we've been getting pummeled. A couple of weeks ago a storm dumped a lot of rain right on the Fourmile area. The creek surged, merged with the Boulder Creek, and a swell well over a meter high ran down into town. The damage was surprisingly minimal, but it was touch and go there for a while (some low-lying areas were evacuated, for example).
When I moved here, I thought Boulder was immune to the natural disasters I was used to: hurricanes (I grew up in Virginia), tornadoes (my wife's family is from Kansas) and earthquakes (for six years we lived within a few klicks of the San Andreas fault). Floods didn't occur to me at the time, but they're on my mind now. I am nowhere near the flood plain, but I'm really fond of this little town, and I'm hoping things ease off soon.
My office window faces west, toward the mountains, and all I can think is that it's going to be a long summer.