Rain follows the plow

Rain follows the plow is the conventional name for a now-debunked theory of climatology that was popular throughout the American West and Australia during the late 19th century. The basic premise of the theory was that human habitation, in particular 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", and the expansion of wheat growing on very marginal land in South Australia during the same period.

According to the theory, increased human settlement in the region 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 would indicate, the theory was based on faulty evidence arising from brief climatological fluctuations. The theory was later refuted by climatologists and is now regarded as a serious error. In South Australia, George Goyder warned as early as 1865 in his famous report on farming in the state that rain would not follow the plow. Despite this, there was talk of cereal crops spreading to the Northern Territory border up until further droughts in the 1880s. Today, grain crops do not grow further north than Quorn and climate change could possibly remove them from South Australia entirely.  

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History

The theory arose in the late 1860s and 1870s during the westward expansion of white settlement west of the Missouri River and across the 100th meridian west, the traditional boundary line between the humid and semi-arid portions of central North America. At the same time, there was a spread of farming from the area near Adelaide northwards to areas of much lower rainfall. 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. Out of this evidence, some scientists of the day concluded that change was due to the settlement and the effects of cultivation. One of the most prominent exponents of the theory was Cyrus Thomas, a noted climatologist of his day who made a study of the recent history of Colorado, concluding the increase in moisture was permanent, and that it coincided exactly with the first homesteaders. Other prominent advocates of the theory were Ferdinand Vandeveer Hayden, the noted geographer who had explored and surveyed parts of the Rocky Mountains of Colorado, and Samuel Aughey, a professor at the University of Nebraska.

Thomas and other climatologists offered a variety of explanations for the theory. A common idea was that the plowing of the soil for cultivation exposed the soil's moisture to the sky. In addition, newly planted trees and shrubs increased rainfall as well, as did smoke from trains. Another hypothesis stated that the increased vibrations in the atmosphere due to human activity created additional clouds, from which rain fell, an idea that led to the widespread dynamiting of the air across the Great Plains in the 1870s.

The theory was widely embraced in its day, not only by scientists, but land speculators and emigrants. Some historians have argued that the theory was embraced readily as an outgrowth of Manifest Destiny, the idea that the United States had a mission to expand, spreading its form of democracy and freedom. The theory is regarded as partially responsible for the rapid settlement of the Great Plains in the later 19th century.

It is now understood by climatologists that increased vegetation and urbanization can indeed result in increased precipitation. The effect, however, is local in scope, with increased rainfall typically coming at the expense of rainfall in nearby areas. It cannot result in a climatological change for an entire region.

In 2007, Richard Raddatz, a climatologist at the University of Winnipeg, published results of his studies on the conversion of Canadian grasslands to cropland. His theory is that, because corn crops transpire moisture into the atmosphere at a faster rate than the grass they have replaced, crops can generate storms and intensify the season during which water is cycled through the atmosphere. ^[2]

See also

• Dust Bowl
• Obsolete scientific theory

References

• Cadillac Desert, Marc Reiser.

Notes