Last updated October 18, 2018

Whither the 100th Meridian? The Once and Future Physical and Human Geography of America’s Arid–Humid Divide. Part II: The Meridian Moves East

  • States that the 100th meridian bisects the Great Plains of the United States and effectively divides the continent into more arid western and less arid eastern halves and is well expressed in terms of vegetation, land hydrology, crops, and the farm economy.
  • Considers how this arid–humid divide will change in intensity and location during the current century under rising greenhouse gases.
  • Shows that state-of-the-art climate models from phase 5 of the Coupled Model Intercomparison Project generally underestimate the degree of aridity of the United States and simulate an arid–humid divide that is too diffuse.
  • Develops bias-corrected future projections that modify observationally based measures of aridity by the model-projected fractional changes in aridity.
  • Finds that:
    • Aridity increases across the United States, and the aridity gradient weakens. The main contributor to the changes is rising potential evapotranspiration, while changes in precipitation working alone increase aridity across the southern and decrease across the northern United States.
    • The “effective 100th meridian” moves to the east as the century progresses.