Blame California’s mega‐fires on global warming. Or at least that’s what Senate Majority Leader Harry Reid (D-NV) said last week in the Hill.
Global warming affords endless opportunities to test glib hypotheses by politicians who have no training whatsoever in fields of which they claim pontifical knowledge. And Reid’s statement is easy to test.
By the end of each and every summer, Southern California is drier than the world’s best martini. A couple weeks ago, I took a drive up San Gabriel Canyon, an arroyo typical of the mountains surrounding the Los Angeles basin. The steep hillsides were studded with crackling‐dry vegetation, and it was obvious that the area was sitting on the precipice of a massive fire season.
California’s big wildfires are, ironically, caused by excessive winter rains. Normally, the region that’s been ablaze averages about a foot from December through March. Owing to the fact that just about every day after the rainy season is warm and sunny, it’s only a matter of a month or two before the surface dries out to the point that there’s not enough water to support additional plant growth. The more it rains in the winter, the more vegetation grows, and the more there is to burn in the summer, which is invariably hot and dry.
The distribution of rainfall between years is a bit unusual. The vast majority of the years have below normal precipitation — about four or so inches below the average of a bit over a foot, as shown in our attached graph. In the fewer years that are above average, when it rains, it pours, with rainfall often 100% (one foot or more) above the mean.
Some of the very wet years are caused by El Nino, a reversal of winds over the Pacific Ocean that has been going on every few years ever since there was a Pacific Ocean. People like Senator Reid (and Vice President Gore) will cite computer models predicting that El Ninos should become stronger or more frequent with global warming, but there are an awful lot of other models showing that they won’t change or that they might even lessen in frequency. The Nobel Prize‐winning United Nations Intergovermental Panel on Climate Change says “There is no consistent indication of discernible future changes in ENSO [an acronym for El Nino] amplitude and frequency.”
When things get very wet, there’s plenty more time for the soil to remain moist, producing a much longer growing season in the hills where suburbs and very expensive homes are proliferating. The problem is that these rooms‐with‐a‐view are also houses‐with‐a‐risk; i.e., they’re in the path of wildfires. Rain adds fuel to the fire, by bulking up the vegetation mass.
If Senator Reid is right, then rainfall, or the frequency of rainy years, must be increasing in the fire zone. Here is the total December‐March precipitation for the California South Coast Drainage Climatological Division from 1895 through 2007. Data are from the National Climatic Data Center, a part of the U.S Department of Commerce.
What’s noted in the graph is pretty obvious. Most of the years are below the long‐term average of about 12 inches, but the relatively few that are above the mean are often way above it. If global warming is causing the increase in Southern California wildfires, then the frequency of very wet years has to be increasing in a significant fashion, because excessive moisture is required to create excessive vegetation.
Obviously it is not. In fact, the biggest agglomeration of far above‐normal years was a 12‐year period beginning in 1905.
Ironically it was these rains that prompted some of the massive westward migration of U.S. population, as both California and Arizona were touted as green paradises, which they were, thanks to all that vegetation. Sure, there were wildfires then, but very few people lived within their reach.
Now that the paradise of the Los Angeles Basin is home to so many more people, whenever we have a very wet year (2005 being the last big one), it’s only a matter of time before thousands of homes get torched.
But don’t blame this on global warming. There’s no trend whatsoever in the frequency of heavy‐rainfall years that would promote wildfires. And our officials should especially avoid making untested statements on global warming to papers like the Hill, which other Senators and Congressmen accept as gospel.