Every Day Is Special: Rain
Even though sometimes on Rain Day (July 29 each year) we want to shake our fist at the sky and shout, “Enough, already!” the fact is we humans need rain to survive.
We require not just stationary water (97 percent of the world’s supply is undrinkable salt water), but the whole hydrologic cycle, including evaporation, condensation and precipitation.
We learned in school how the water cycle works. Water evaporates from the ocean (leaving its salt behind) and other bodies of water, ascends into the wind stream to be carried inland, and the water particles coalesce until gravity can no longer keep them airborne, thus creating rain, sleet or snow.
The water then completes its journey to surface bodies of water or underground aquifers via several routes. About 70 percent of the precipitation returns to the atmosphere through evaporation off the surface and from vegetation. The remainder finds its way back to a stream, lake or ocean by runoff or underground infiltration.
Such movement of water is unique to Earth, as far as we know, owing to the precise balance of four critical factors: the amount of water, temperature range, gravitational force and atmospheric composition and pressure.
Life under any other circumstance is highly unlikely, as creatures create waste, and stagnant water would eventually become too polluted to sustain a viable living population.
Rain provides a fringe reward. Moving water produces negative ions which enter the bloodstream and trigger biochemical reactions that relieve stress, alleviate depression, enhance concentration and boost energy levels.
And that clean, fresh fragrance after a rain? It has had a name since 1964: petrichor (Greek for “rock fluid”). During dry seasons, plants exude an oil which is absorbed by rocks and clay-based soils. Rain releases those oils, which mingle with a bacterial by-product emitted by wet soil, thus producing the distinctive aroma.
[mlw_quizmaster quiz=11]