May 27, 2021 report
Global evapotranspiration rose by 10% from 2003 to 2019
A team of researchers at NASA's Jet Propulsion Laboratory at the California Institute of Technology has found that global evapotranspiration rose by 10% from 2003 to 2019. In their paper published in the journal Nature, the group describes the original approach they took to measuring global evapotranspiration.
Evapotranspiration is the transfer of water from the ground to the air from both evaporation and transpiration, water emitted by plants. It is one of the main components of the planet's water cycle. Scientists have been predicting for several years that Earth's water cycle will gain energy as the planet heats up due to global warming—but proving it has been difficult because there is no reliable way to measure changes in evapotranspiration—until now, most efforts have been far too localized. In this new effort, the researchers found a way to calculate global evapotranspiration over periods of time using information from satellites.
Instead of attempting to measure evapotranspiration directly, as has been done in other efforts, the researchers used satellite data to measure other parts of the water cycle and then used that data to calculate the degree of evapotranspiration. And rather than using satellite imagery of clouds and groundwater, the researchers used data collected by the Gravity Recovery and Climate Experiment and its follow-up study GRACE-FO. Both were involved in measuring changes to large amounts of water on the surface. Notably, neither system needed to be able to see the ground below, which meant that measurements were not interrupted by cloud cover. The data from the satellites was in the form of changes in gravity that correspond with changes in large amounts of water—the satellites were actually pulled by such changes. Next, the researchers obtained data for the other parts of the water cycle. Then, using data from both sources, they were able to calculate the rate of evapotranspiration for the years 2003 to 2019. And as they did so, they noted that the rate rose slightly each year, and that over the entire span of time, the rate had risen by approximately 10 percent.
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