Credit: CORBIS

Rain follows the plough, people said knowingly in late-nineteenth-century America. The phrase was promulgated in a book published in 1881 by one Charles Dana Wilber, a land speculator who was au courant with the climatology of his day. It distilled the theories of some prominent Earth scientists that settlement and cultivation, especially the planting of trees, would transform arid regions, notably the Great Plains beyond the hundredth meridian, into fertile, loamy expanses bathed in rain, like the agriculturally fecund Mississippi Valley.

Publications by European scientists on forests and rainfall formed a major source of theorizing. Their ideas were brought to the attention of US readers by George Perkins Marsh in his remarkable treatise of 1864, Man and Nature; or, Physical Geography as Modified by Human Action. Marsh, a polymathic businessman, diplomat and writer, was a New Englander appalled by the deforestation of his native region and an advocate of planting and preserving trees. While Marsh faithfully acknowledged that the rainmaking power of trees was “not entirely free from doubt,” he reported that the balance of European scientific judgement believed that forests exercise a “certain and undisputed” meteorological influence.

That was enough for Ferdinand V. Hayden, a geologist and explorer of the American west and, beginning in the late 1860s, the head of the US Geological Survey of the Territories. In 1867, in his agency's first report, he announced that the timber increase arising with settlement had already elevated rainfall in Nebraska, and that similar change would “extend across the dry belt to the foot of the Rocky Mountains as the settlements extend and the forest-trees are planted in proper quantities”. Hayden's assistants at the survey enlarged on the claim, declaring that rainfall increased not just with trees, but with ploughing, and possibly even with the laying of telegraph lines and railroad tracks.

During the 1870s, as settlement spread westward across the Great Plains, rainfall happened to increase, giving a seeming plausibility to the arguments of Hayden and his colleagues. But the geologist John Wesley Powell was unconvinced. “In what manner rainfall could be affected through the cultivation of the land, building of railroads, telegraph lines, etc., has not been shown,” he wrote in 1878, in a Report on the Lands of the Arid Region of the United States.

Powell argued that rainfall in the arid region could never sustain agriculture based on the traditional 160-acre homestead. That system of apportionment had to give way to one that allowed for much larger sections suitable for dry-land ranching and irrigation farming. Their contours would be shaped by their access to water, and their size — up to 2,500 acres — would be determined by the use to which the land could be put. Powell's ideas were the basis of legislation for the arid region introduced in Congress in February 1879, and commended by easterners of all political persuasions as wise, realistic, and scientifically authoritative.

Land up for grabs: but many homesteaders were ruined when rain stopped ‘following the plough’. Credit: CORBIS/BETTMANN

But representatives from the west derided and killed the measure. To them, ambitious inhabitants of a developing region, Powell's initiative resembled a kind of environmental colonialism. Theorists had pronounced the homestead system dead before, cried the delegate from the Montana Territory, yet settlers had gone west and, “practical men” all, had “seen the capabilities of this land which had escaped the notice of our scientists and statesmen”. A congressman from Kansas admonished scientists who explored the west: “If you please, while you are out there acting in the interest of science and in the interest of professional bug-hunting, leave the settlers upon our frontier alone.”

Powell nevertheless had the science essentially right. According to modern views, trees do bear some relationship to the moisture content of the air in their neighbourhood, but not to rainfall. On the Plains during the 1880s, rain stopped ‘following the plough’, ruining numerous settlers; irrigation would prove indispensable to farming in the region. But, at the height of the dispute, opposition to the kind of land reform advanced by Powell had on its side the scientific theorizing of Hayden and its links to the interests of small farmers by Wilber, who characterized the proposed departure from the “equable” 160-acre homestead system as the work of a “powerful ring” in Washington bent on serving the “aristocratic tastes” of the cattle barons. The episode would not be the last to combine contested theories of climate with passionate convictions of political economy.