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What is the percentage of the global water cycle (evaporation, precipitation) that occurs over the ocean?

Most of the water cycle studies focus on the processes and changes occurring over land with little emphasis on the ocean. Meanwhile, the ocean covers almost 3/4 of the surface of Earth. How much of the global precipitation and evaporation takes place over the ocean? Is it 75% of the total? If the percentage is higher, why does that occur?

Answer

The bulk of the planet's precipitation falls from convective storms that develop throughout the Intertropical Convergence Zone (ITCZ). The ITCZ transits north and south of the equator due tracking the sun's zenith throughout the year and is skewed by the position of land, but is generally situated near the equator over the ocean. ![Wikipedia ITCZ][1] ![Global Precipitation][2] [Trenberth et al (2006)](http://acd.ucar.edu/~lsmith/GEWEX-JHydroMet8.pdf) go into detail describing the different components of the global hydrological cycle, but the core of their research can be summed up in the image below. ![Hydrologic Cycle from Trenberth et all (2006)][3] - ~96.5% of the world's water is held in the oceans. - ~90% of evaporated ocean water leads to precipitation over the oceans. - ~77% of precipitation falls over the ocean. - ~10% of evaporated ocean water leads to precipitation over land. This equals the roughly ~10% of runoff that returns to the oceans. - Envirotranspiration from plants plays a noticeable role in the water cycle over land. Personally, I do wonder about the ~77% falling over the ocean. That number seems a slight bit low given recent remote sensing data of global annual precipitation. [1]: http://i.stack.imgur.com/1tBJA.png [2]: http://i.stack.imgur.com/EWxEk.png [3]: http://i.stack.imgur.com/4OoEj.png

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