Rains Come and Come Again the Next Day
by Bill Chameides | March 24th, 2010
posted by Erica Rowell (Editor)
Do you find that raindrops keep falling on your head? You may be right.
More Refrains of ‘Here Comes the Rain Again’ Likely in Store
Scientists have been predicting for some time that global warming is about a lot more than increasing global temperatures. It’s really about climate disruption: changes in almost all aspects of our climate, including the thing we probably care the most about, rainfall.
We don’t like it when it never rains, because we need that water for drinking and growing things. And we don’t like it when it rains too much because it can lead to flooding and, well, too much rain is just a drag.
The consensus in the scientific community has been that global warming means more rain — more rain and intense rainstorms. (For all you folks who got buried by blizzards this past winter, this includes more snow, when temperatures are below freezing.)
There are probably a number of reasons for this, here’s the most basic one: Higher temperatures cause the amount of water vapor in the atmosphere to increase, and more water in the atmosphere should bring about more water falling out of the atmosphere.
The idea of more rain with global warming is not some wild idea cooked up by a bunch of ivory-tower climate scientists. Data from weather stations show that rain amounts and rain intensity have in fact increased over the past few decades. And by the way, the increase in overall precipitation has been accompanied by longer, more intense dry periods (aka droughts) as well. More wet when it’s wet; more dry when it’s dry; less of when it’s just right.
Paper: Longer Stretches of Wet Periods Found
Now comes a new paper in Geophysical Research Letters by Olga Zolina, of the University of Bonn’s Meteorological Institute, and colleagues, that adds a new twist to the global warming-increasing rainfall story. These investigators used data from European daily rain gauges to assess the length of rainfall events between 1950 and 2008. They defined a wet period (WP) as the number of consecutive days with rain in excess of one millimeter a day (or 0.04 inches/day).
Not surprisingly, most precipitation events (i.e., ~ 50 percent) in Europe last only one day. (More than likely, wherever you are, the same is true in your neck of the woods.) And about 90 percent of all wet periods last about 3 to 4 days or less. Only about one percent of precipitation events last 10 days or more.
All well and good, and sort of ho hum. But things get interesting when the authors looked at the temporal change in the distribution of wet periods from 1950 to 2008:
- the frequency of short WPs (i.e., 1, 2, and 3 days) decreased significantly,
- the frequency of long WPs increased significantly,
- one-day WPs declined by about 0.5 percent per decade,
- 12-day WPs increased in frequency by about 0.4 percent per decade, and
- WPs of 5–11 days increased by about 0.2–0.3 percent per decade.
There’s one more thing worth noting: the trends also show that heavy precipitation events not only increased in frequency but they increasingly occurred during longer WPs.
So some might argue that more consecutive rainy days are a drag but it’s not that big of a deal — after all, look at the folks in Seattle — they’re wet but they’re happy. (Tip of the hat to Yusuf, the artist who used to be known as Cat Stevens.) And if you’re in the rain slicker business, what could be better?
Well, in fact the trend could be trouble and it’s spelled F-L-O-O-D. Rainfall events that last for days at a time can saturate soils, push rivers over their banks, and overwhelm urban sewer systems. And one more thing: the trend is consistent with humongous snowstorms. Hmmm, any evidence of that occurring?filed under: climate change, faculty, global warming, rainfall
and: climate, climate disruption