Record flooding along the Souris River near Minot, N.D. and record drought at O.C. Fisher Lake near San Angelo, Texas have more than their contrasting water conditions in common.
These places, nearly 1,000 miles apart, are situated almost exactly north and south of each other near the100th meridian of longitude. On average they have similar amounts of precipitation. Minot typically receives 17.5 inches per year while San Angelo customarily tallies 22.5 inches annually.
"The upper Souris Basin has been quite moist since last fall," said Steve Robinson from the U.S. Geological Survey North Dakota Water Science Center. "An above normal winter snowpack in addition to much above normal precipitation in May and June led to the record flooding along the Souris River."
Meanwhile, Texas is experiencing near record drought conditions four states south of North Dakota. Jason Johnson of the National Weather Service in San Angelo said that this is the driest nine-month period in Texas since record collection began more than 100 years ago.
Cary Carman of the USGS office in San Angelo grew up in west Texas where many of his relatives still recall the historic drought of the 1950s. Carman said that although O.C. Fisher Lake has been dry before, he has not seen such parched conditions.
"It is a challenge to keep streamgaging instrumentation working properly because many streams and reservoirs are so low," said Carman.
In the late nineteenth century, the 100th meridian, one hundred degrees of longitude west of Greenwich, England, emerged as a widely-recognized line that represented the boundary in the central United States between the moist east and the arid west. In his 1878 "Report on the Lands of the Arid Region of the United States," John Wesley Powell, the second Director of the USGS, noted the boundary that has resonated to this day.
The 100th meridian was not solely selected for its neat round number; it actually approximates the north-south line of twenty inches of annual average precipitation. When an area receives more than twenty inches of precipitation, irrigation is often not necessary. Thus, this line of longitude marks the approximate boundary between the non-irrigated east and the irrigation-needed west.
Log in to the USGS WaterWatch site to stay apprised of both floods and drought across the country. WaterWatch displays maps, graphs, and tables that describe real-time, recent, and past streamflow conditions for the United States. The real-time information generally is updated on an hourly basis.