The chart at right shows the temperature (°F on the left scale, red line) and relative humidity (% on the right scale, green line). For the past four days we've been below 20% relative humidity — much of the time below 10%!
This is extraordinarily dry even for the chapparal country, and it's been quite prolonged as well. Yesterday the wind was from the northeast for much of the day, indicating a Santa Ana condition, though the winds weren't high as they usually are in a Santa Ana.
This is a litle worrisome, as conditions like this are enablers for wildfires. There's one going on right now 150 miles north of us, and much the same weather conditions apply there. The longer the dry air continues, the longer the brush and botanical detritus has to dehydrate — and the drier that fuel gets, the more dangerous the conditions. When the fuel gets very dry — like it was before the Cedar Fires two years ago — then even the smallest spark can turn into a hard-to-stop fire. And because Lawson Valley hasn't burned for over 30 years, we have a lot of fuel on our hillsides.
Just today I ran across a map of San Diego County that was color-coded to show when each area had last burned. Lawson Valley is colored to indicate "1961-1970" — and if that's right, we've got 35 - 45 years of chapparal growth on our hillsides. Yikes!
In the old blog, Anonymous said:
ReplyDeleteWas this map online? If so would you mind posting a link? That sounds very interesting and I’d love to see it.
In the old blog, SlightlyLoony said:
ReplyDeleteThat map was very interesting, but unfortunately I could not find it online. In print it is in the San Diego Bird Atlas, a wonderful resource completely aside from the fire information. I did find some useful stuff at a CDF site, including a very large PDF with a similar, though lower-resolution map as the Bird Atlas, and (more interestingly to me) the raw data freely available for download. You’d have to have appropriate software, or be a bit of a programmer, to make use of that data, though…