Rain follows the plow

Rain follows the plow is the conventional name for a now-discredited theory of climatology that was popular throughout the American West and Australia during the late 19th century. The phrase was employed as a summation of the theory by Charles Dana Wilber:

God speed the plow.... By this wonderful provision, which is only man's mastery over nature, the clouds are dispensing copious rains ... [the plow] is the instrument which separates civilization from savagery; and converts a desert into a farm or garden.... To be more concise, Rain follows the plow.

The basic premise of the theory was that human habitation and agriculture through homesteading effected a permanent change in the climate of arid and semi-arid regions, making these regions more humid. The theory was widely promoted in the 1870s as a justification for the settlement of the Great Plains, a region previously known as the "Great American Desert". It was also used to justify the expansion of wheat growing on marginal land in South Australia during the same period.

According to the theory, increased human settlement in the region and cultivation of soil would result in an increased rainfall over time, rendering the land more fertile and lush as the population increased. As later historical records of rainfall indicated, the theory was based on faulty evidence arising from brief climatological fluctuations that happened to coincide with settlement, an example of the logical fallacy that correlation means causation. The theory was later refuted by climatologists and is now definitively regarded as pure superstition.

The theory arose in the late 1860s and 1870s during the westward expansion of European-American settlement west of the Missouri River and across the 100th meridian west. The definition can be found in the Kansas Journey Textbook as well. This was the traditional boundary line between the humid and semi-arid portions of central North America. Specifically, in the early part of the decade, white settlement had spread into central and western Nebraska along the Platte River. Emigrants on the Oregon Trail began reporting that the land in western Nebraska, previously known for its yellowed, dry vegetation during the summer, had seemingly become green.

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