In 1878, explorer John Wesley Powell travelled east to west across the US and noticed a change in the plants around him. Over a relatively small transect of land, prairie flowers gave way to drier shrubs, which in turn gave way to cacti. This gradual but strong transition, between the humid east and the dry west, extended in a straight line from north to south of the US, roughly following the 100th meridian. New research has now confirmed that this climate divide is gradually moving towards the east.
The divide can be seen from space, on Google Earth, and ‘is also plain to window seat passengers flying on airplanes across the continent’ say researchers from the the University of Columbia who have been looking into this territorial shift.
Though scientists largely agree that the climate divide along the 100th meridian exists, the Columbia study is the first to examine its causes. By looking at precipitation models, the team discovered the divide occurs for three reasons: the east is kept wetter by winter storms from the Atlantic and summer storms from the Gulf of Mexico that bend northeast. Meanwhile storms from the Pacific are wicked away by the Rocky Mountains, leaving the west dry.
According to the findings, these dry conditions are moving eastwards. By analysing climate data from 1979 to 2015, the researchers found there had already been a noticeable trend eastwards of the arid climate, now putting the divide roughly at the 98th meridian. ‘There have also been contributions from declining precipitation but we think those might mostly be due to natural variability,’ says Richard Seager, lead author of the study. He believes it is rising temperatures that will increase evaporation and move the arid conditions further eastward. By linking these findings with climate change models, the team predicts that the easterly trend will continue to become more noticeable throughout the 21st century.
If the predictions become true, it could amount to big repercussions for land use along the 100th meridian. Already farming is largely dictated by the divide: moving west across it, farms become fewer and larger by land area, reflecting less available quantities of water. The majority of crops also change from moisture-loving corn, to plants that cope better with dry conditions, such as wheat. The researchers predict that these characteristics will need to be incorporated into the land around the 98th meridian in order to handle the warming conditions to come, potentially redrawing the agricultural maps of North and South Dakota, Nebraska, Kansas, Oklahoma and Texas.
This was published in the June 2018 edition of Geographical magazine
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