The top 2 inches of topsoil on all of Earth’s landmasses contains an infinitesimal fraction of the planet’s water — less than one-thousandth of a percent. Yet because of its position at the interface between the land and the atmosphere, that tiny amount plays a crucial role in everything from agriculture to weather and climate, and even the spread of disease.
The behavior and dynamics of this reservoir of moisture have been very hard to quantify and analyze, however, because measurements have been slow and laborious to make.
The top 2 inches of topsoil on all of Earth’s landmasses contains an infinitesimal fraction of the planet’s water — less than one-thousandth of a percent. Yet because of its position at the interface between the land and the atmosphere, that tiny amount plays a crucial role in everything from agriculture to weather and climate, and even the spread of disease.
The behavior and dynamics of this reservoir of moisture have been very hard to quantify and analyze, however, because measurements have been slow and laborious to make.
That situation changed with the launch in 2015 of a NASA satellite called SMAP (Soil Moisture Active Passive), designed to provide globally comprehensive and frequent measurements of the moisture in that top layer of soil. SMAP’s first year of observational data has now been analyzed and is providing some significant surprises that will help in the modeling of climate, forecasting of weather, and monitoring of agriculture around the world.
These new results are reported in the journal Nature Geosciences, in a paper by SMAP Science Team leader Dara Entekhabi, recent MIT graduate Kaighin McColl PhD ’16, and four others. Entekhabi is a professor in the Ralph M. Parsons Laboratory for Environmental Science and Engineering in MIT’s Department of Civil and Environmental Engineering.
The SMAP observations are providing an unprecedented level of detailed, worldwide information on the amount of water in those top 2 inches (5 centimeters) of soil, collected globally every two to three days. Entekhabi says this is important because this thin layer is a key part of the global water cycle over the continents, and also a key factor in the global energy and carbon cycles.
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