https://www.earthmagazine.org/article/dividing-line-past-present-and-future-100th-meridian
"The researchers then calculated and plotted the aridity index across the U.S. from 1979 to 2016. They found that a sharp aridity gradient still exists, but that it’s now centered around the 98th meridian. “After examining the individual components that led to the gradient’s formation,” Lis says, “we determined that precipitation and relative humidity are the most significant contributors to the present gradient.” Those factors are in turn controlled by the rain shadow of the Rocky Mountains to the west (as Powell had surmised), as well as the flow of moisture from the Gulf of Mexico to the southeast."
Evapotransporation has changed over time and what was the line of drastic dryness changes around the 100th meridian is now at the 98th. It is shifting and should continue until it reaches about the 95th or 96th.
"The researchers then calculated and plotted the aridity index across the U.S. from 1979 to 2016. They found that a sharp aridity gradient still exists, but that it’s now centered around the 98th meridian. “After examining the individual components that led to the gradient’s formation,” Lis says, “we determined that precipitation and relative humidity are the most significant contributors to the present gradient.” Those factors are in turn controlled by the rain shadow of the Rocky Mountains to the west (as Powell had surmised), as well as the flow of moisture from the Gulf of Mexico to the southeast."
Evapotransporation has changed over time and what was the line of drastic dryness changes around the 100th meridian is now at the 98th. It is shifting and should continue until it reaches about the 95th or 96th.
