Researchers put a bit of old folk wisdom to the test by investigating whether water droplets on the top of leaves actually can focus the sun's rays and burn them. The result? Score one for folk wisdom.
That line of logic is why many gardeners advise against watering plants at midday, when the sunlight is at its fiercest. However, there'd never been any scientific basis for this assertion. Biophysicist Gabor Horvath and his team at Hungary's Eotvos University set out to determine the validity of this notion both through direct experimentation and computer modeling.
They discovered that, depending on the type of leaf, it really was possible for water droplets to burn leaves. In particular, leaves with tiny wax hairs, like those on a fern, were able to hold the droplets just above the leaf surface. Much like a magnifying glass, the droplet focused the light directly onto the leaf, which left an unmistakable burn. On the other hand, smooth leaves, like the maple, displayed no such burn effects.
Horvath points out why the results of the study might be surprisingly important:
The prevailing opinion is that forest fires can be sparked by intense sunlight focused by water drops on dried-out vegetation.
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So, what's the verdict? Is the prevailing opinion correct? Horvath continues:
If the focal region of drops falls exactly on the dry plant surface intensely focused sunlight could theoretically start a fire. However, the likelihood is reduced as the water drops should evaporate before this, so these claims should be treated with a grain of salt.
In other words, it's possible, but not exactly likely. That verdict should be more than good enough for Roland Emmerich to make a movie where water starts massive forest fires. FIRES THAT DESTROY THE EARTH!!!