Climate Change Research Spotlight

Rethinking How Water Circulates Between the Oceans and Land

A reexamination of the global water cycle shows that tropical coastlines exert a profound influence on atmospheric water circulation by wringing water vapor from the atmosphere.

Source: Geophysical Research Letters


By

Water plays a crucial role in modulating Earth’s climate by regulating the transfer of energy between Earth’s surface, the atmosphere, and space. Although previous studies have offered a general global overview of water circulation between the oceans and land, this traditional two-region model does not take into account the considerable precipitation that occurs over tropical coastal regions, including the Indonesian maritime continent, the Indian subcontinent, and the Bay of Bengal. To fully understand Earth’s energy budget, the role these boundary regions play in transferring water between the oceans and land needs to be clarified.

Here Ogino et al. reexamine the role of precipitation along tropical coasts in the global water cycle. The team estimated evaporation, precipitation, and the amount of water vapor transport relative to the distance from the coastline in the tropics and the northern and southern extratropics for the 30-year period from 1981 to 2010.

The results show that about half of the water vapor transported inland from the oceans precipitates out along a coastal region, which the team assumes to stretch from 200 kilometers inland to 300 kilometers seaward, and that this effect is most pronounced in the tropics. The researchers also found that the landward transport of water vapor is not symmetric relative to the coastline; instead, it peaks about 300 kilometers offshore and decreases more rapidly landward than seaward. To account for this rapid dehydration of the atmosphere along tropical coasts, the authors propose that the traditional two-region model of ocean-land water circulation should be updated to a three-region concept that separately defines this crucial coastal region.

Because of the magnitude of the freshwater contribution to coastal waters via precipitation, this research may offer additional insights into the distribution of salinity in the ocean, which influences the density gradients that drive circulation. In fact, the team estimates that precipitation along tropical coastlines contributes as much freshwater to oceans as global river discharge. The research also points to the importance of understanding how changes in sea level will impact the lengths and shapes of coastlines and how these differences could, in turn, affect the circulation of water around the globe. (Geophysical Research Letters, https://doi.org/10.1002/2017GL075760, 2017)

—Terri Cook, Freelance Writer

Citation: Cook, T. (2018), Rethinking how water circulates between the oceans and land, Eos, 99, https://doi.org/10.1029/2018EO090425. Published on 11 January 2018.
© 2018. The authors. CC BY-NC-ND 3.0
  • There have been studies on the recirculation of pollution with land and sea breezes. They find air is recirculated so that air pollution moves back and forth. So air comes off the land and makes the air drier near the land even if over the ocean (the air over the ocean is partly from the land). Could this account for the findings above that say, “The researchers also found that the landward transport of water vapor is not symmetric relative to the coastline; instead, it peaks about 300 kilometers offshore and decreases more rapidly landward than seaward.”?

  • nor ne’ Erg

    The article neglects to mention the 960 000 tonnes of Hydrogen’,lost to outer space, from planet Earth. every year/ The hydrogen is derived by the splitting of water vapor by incoming Cosmic rays. The higher [up to 10**20 eV] energy Cosmic Rays are able to split any [email protected] in the outer limits of the Earth’s atmosphere into Carbon and Oxygen; both of which fall back to Earth, for the benefit of animals. The C)2 at ground level is vital for all Plants. Every green shoot or leaf you see this Spring was CO2 from the atmosphere last Fall.