Climate change may dry out water cycle, Clark scientist co-reports

A new international study in the journal Nature reveals that global water evaporation from land and plants has been weakening over the last decade, as the soil dries up in many southern regions.  The study suggests that limitation in moisture supply in the Southern Hemisphere has contributed to falling rates of evapotranspiration. This slowing trend could have an impact on vulnerable ecosystems, water resources and climate feedbacks.

Evapotranspiration — the combination of evaporation from land surfaces and transpiration from plants — is a fundamental flux of water and energy in the climate system. It is also a strong determinant of water availability for plant growth and human consumption. Climate change is expected to intensify the hydrological cycle and to alter evapotranspiration, but direct observations of such patterns have been lacking at the global scale.

WilliamsChristopher Williams, an assistant professor in Clark University’s Graduate School of Geography and George Perkins Marsh Institute, is among a multinational group of authors contributing to the global study titled “Recent decline in the global land evapotranspiration trend due to limited moisture supply.”   

Williams, along with principal author Martin Jung from the Max Planck Institute for Biogeochemistry and other colleagues, model global evapotranspiration over a large variety of ecosystems using data from global monitoring combined with meteorological and remote-sensing observations. From 1982 to 1997, evapotranspiration increased persistently by about 7.1 millimeters per year per decade. But since 1998 this increasing trend has flattened, probably due to limits on moisture supply, particularly in Africa and Australia.  In other words, parts of the globe have been drying up and the supply of water to the atmosphere has been consequently decreased.

The authors stress that it is too soon to tell whether the changing behavior of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle.

Nature is a weekly, international, interdisciplinary journal of science, and recognized as the world’s most highly cited.

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