When a drought is not a drought
Despite recent rains, overall precipitation has been somewhat below normal here since February. Most of us, however, would not construe the current weather pattern as anything close to being a "drought." We tend to reserve that term, along with the expected heat and humidity, for use during the summer.
But although we in the D.C. area usually experience at least one or two rainless stretches each summer, does the long-term average really substantiate the perception held by some that summertime drought is common here? The answer may surprise you.
Keeping reading for more on what a drought really is...
Most dictionaries define drought as something like "an extended period of dry weather, relative to normal, especially when injurious to crops." But average summer rainfall in the D.C. area is actually quite plentiful. June, with 3.13 inches, July, with 3.66 inches, and August with 3.44 inches, constitute the fourth rainiest three-month period of the year here (as measured at Reagan National Airport).
Obviously, to really define the word properly, we need to consider such factors as soil moisture, river levels, and local weather history. (The 39 inches of annual DC rainfall would be an extreme drought for southern Florida, which usually gets about 60 inches, but a bonanza for much of the West, where 10 to 30 inches is more common.)
Locally, even with the above-stated average amount of rainfall, drought-like conditions can still develop quickly under a strong summer sun, depending on rainfall distribution and intensity. Unfortunately, much of our summer precipitation is erratic and comes in the form of sudden, violent storms, which unleash very heavy rains over a short period of time. Some communities get deluged (the exception), while others remain parched. If you happen to live in one of those parched areas and a thunderstorm skirts by, well, you're still in a drought.
Sometimes a week, or even two or three, will pass before it rains again. Since vegetation needs about one inch of rain per week during the growing season, plants can quickly deteriorate without watering.
Though some may complain about the streaky summer rainfall pattern here, it does mean there are many fine, sunny days (roughly 2 out of 3) that are custom-made for the beach or other outdoor activities. Residents of other areas, such as the Pacific Northwest coastal strip from San Francisco northward, are not nearly so lucky (assuming they like beach weather). There, although rain is not the summer spoiler, fog is. And even though the sun usually breaks through for at least a few hours each day, summer weather can be a cool and invigorating experience, with the heat usually held at bay in the inland valleys. Mark Twain once said, "The worst winter I ever experienced, was summer in San Francisco."
Local residents are often surprised to learn that Portland, OR, among other West Coast locations, actually receives slightly less annual rainfall than Washington, DC. And in terms of summer rain, despite Portland's many foggy (and soggy) days, total rainfall is scarcely 3 inches, compared with Washington's 10.
The comparison with San Francisco is even more striking, as it receives little more than half our annual rainfall and only 1-2 percent of our summer moisture. Does such meager seasonal and annual rainfall constitute a drought? Probably not, since that's normal for those areas during those time periods.
As to whether drought (which rhymes with pout, not mouth) is really the weather villain that we seem to make it out to be, I suppose it all depends on your point of view. If you're a farmer or a water supply official, it's a worrisome issue. If, on the other hand, you're a sun-bather or vacationer, a drought presents no problem at all, at least in the near-term, you believe.
Personally, I agree with John Ruskin, the English writer, who said, "There is no such thing as bad weather, only different kinds of good weather." How about you? Do you agree?
[Officially, the driest calendar month on record in D.C. was October 1963, when only a trace of rain fell. The driest year was the dust bowl year of 1930, which could only muster 21.66 inches of precipitation (45% below normal). For more information on drought measurement, refer to the National Drought Monitor]
| May 26, 2010; 11:00 AM ET
Categories: Droughts, Lipman, Local Climate
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