Water droplets can cause forest firesJanuary 11th, 2010 - 2:49 pm ICT by IANS
London, Jan 11 (IANS) Those with green fingers may have known that watering a garden in the midday sun can burn plants, but science has only now caught up with the fact.
“The problem of light focusing by water droplets adhered to plants has never been thoroughly investigated, neither theoretically nor experimentally,” said Gabor Horvath, from Hungary’s Eotvos University, who led the research.
“However, this is far from a trivial question. The prevailing opinion is that forest fires can be sparked by intense sunlight focussed by water drops on dried-out vegetation.”
The team conducted both computational and experimental studies to determine how the contact angle between the water droplet and a leaf affects the light environment on a leaf blade.
The aim was to clarify the environmental conditions under which sunlit water drops can cause leaf burn. These experiments found that water droplets on a smooth surface, such as maple or ginkgo leaves, cannot cause leaf burn.
Conversely, the team found that floating fern leaves, which have small wax hairs, are susceptible to leaf burn. This is because the hairs can hold the water droplets in focus above the leaf’s surface, acting as a lens.
“In sunshine, water drops residing on smooth hairless plant leaves are unlikely to damage the leaf tissue,” summarised Horvath and co-authors.
“However, water drops held by plant hairs can indeed cause sunburn and the same phenomenon can occur when water droplets are held above human skin by body hair.”
While the same process could theoretically lead to forest fires if water droplets are caught on dried-out vegetation, Horvath and colleagues added a note of caution:
“If the focal region of drops falls exactly on the dry plant surface intensely focussed sunlight could theoretically start a fire,” Horvath said, according to an Eotvos University release.
“However, the likelihood is reduced as the water drops should evaporate before this, so these claims should be treated with a grain of salt.”
These findings were published in the New Phytologist.
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