Thursday Afternoon: If A Raindrop Falls In The Ocean Does It Make A Splash?

The Evaporation/Precipitation Water Cycle

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A graphical representation of the water cycles
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The "old school" view of the water cycles that mimimally acknowledges the role of the oceans in evaporation and precipitation. (Ray Schmitt, WHOI)

A graphical representation of the new water cycle
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An oceanographer's representation of how the water cycle should be portrayed, with an emphasis on the ocean's role in evaporation and precipitation. (Ray Schmitt, WHOI)

What if your doctor declared you free of skin cancer, but had examined only your little finger? You’d probably want a second opinion. That’s what WHOI’s Ray Schmitt wants, a second opinion on the health of the planet.

An important component of the earth’s climate system is the global water cycle, a concept that quantifies the state of water evaporation and precipitation around the world. Ray’s concern is that most of the global water cycle studies focus almost exclusively on terrestrial sources of water, leaving the oceans largely ignored.

“We know rather little about oceanic freshwater fluxes because water cycle research has focused on land and atmospheric processes, and neglected the much larger oceanic component,” Ray explained to an over-flowing crowd at his talk this afternoon. Oceanographers have been all but excluded from programs designed to study the phenomenon of evaporation and precipitation despite 78% of the globe’s precipitation and 86% of its evaporation taking place on the ocean.

The oceanic water cycle plays a major role in the climate system due to its impact on seawater density. Where evaporation is high, salinity of surface water increases. Salty water has a higher density than fresh water and sinks, taking with it heat from the atmosphere. Understanding this process and the role the oceans play in it is important to the understanding of global warming.

Ray began looking into evaporation and precipitation in the early eighties. He put it aside for awhile but has since renewed his interest, in part due to a collaboration with fellow Physical Oceanography department scientist Lisan Yu who has also been studying fresh water transport. When he compares recent work with that done over the last two decades Ray sees a lot of uncertainty in the estimates for the oceanic water cycle, uncertainties “that dwarf the terrestrial components. We need to start looking at the part of the equation that has the most impact.”

Ray may someday get his wish. The ARGO  float program is now collecting sea surface salinity data from around the globe and in 2009 the first salinity sensing satellite will be operational. Even with these new tools, Ray believes that oceanographers must assert themselves. “The oceanographic community should own the water cycle,” he says.


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Last updated February 24, 2006
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