United States: Exceptional water surpluses forecast for S. Dakota

19 June 2019

THE BIG PICTURE
The 12-month forecast ending February 2020 indicates that water surpluses of varying intensity will affect a broad path down the middle of the nation through the Mississippi River Basin as well as westward well into the Missouri, Arkansas, and Red River Basins, and north through much of Michigan. Surpluses are expected to be extreme to exceptional in South Dakota, Kansas, and along portions of the Missouri and Arkansas Rivers. Extreme surpluses are forecast along the Mississippi River. Texas, too, can expected surpluses in the western Edwards Plateau and in the northeast.

Surpluses are also forecast scattered throughout the Rockies and in Nevada and Arizona and will include pockets of intense anomalies in southern Wyoming and eastern Nevada. Primarily moderate surpluses are forecast for the bulk of California and some scattered pockets in Oregon. On the opposite coast, moderate surpluses are forecast for the U.S. Northeast.

Some deficits are expected in south-central Florida, northwestern Wyoming, pockets of Washington, northwestern Montana, northern North Dakota, and north-central Minnesota.

Outside the contiguous U.S., surpluses are forecast for much of Hawaii. In Alaska, surpluses are forecast from the Alaskan Peninsula northward through the center of the state into the Koyukuk River watershed in the north. Moderate to severe deficits are forecast in the Tawana River region east and south of Fairbanks, and moderate deficits are expected near Anchorage, Valdez, and at the tip of the Alaskan Panhandle. Severe deficits are forecast for western Puerto Rico and moderate deficits in the east.

FORECAST BREAKDOWN
The 3-month maps (below) show the evolving conditions in more detail.

From June through August, relatively normal conditions are forecast east of the Mississippi, with some scattered deficits in the U.S. Southeast and some scattered surpluses in the Northeast. But a wide path of water surplus is forecast in the center of the country throughout the Mississippi River Basin and well into the Missouri, Arkansas, and Red River Basins. Anomalies will be exceptional in South Dakota, pockets of western Oklahoma, and in the western Edwards Plateau in the heart of Texas, and will be extreme from Nebraska south through Kansas, Oklahoma, and into northern Texas. Anomalies will also be extreme on the Arkansas River. States on the western bank of the Mississippi will see moderate to severe surpluses.

Surpluses of varying intensity are forecast in the Rockies. Primarily moderate surpluses are expected in central Arizona, most of California, and into southern and eastern Oregon. Deficits are forecast for northwestern Washington, north-central North Dakota and Wisconsin, and scattered pockets of the U.S. Southeast.

Surplus anomalies will diminish considerably September through November in the center of the country, but anomalies are forecast for South Dakota, Nebraska, western Iowa, Kansas, Oklahoma and into north-central Texas. Surpluses will be particularly widespread and intense in South Dakota with extreme to exceptional anomalies. Surpluses of varying intensity are forecast for the Rocky Mountain States, eastern Nevada, western Utah, central Arizona. Surpluses will shrink in California, leaving moderate surpluses in the state’s southern half, and surpluses are also forecast for eastern Oregon. Conditions are expected to be relatively normal in much of the remainder of the country, with some moderate surpluses in southern Louisiana and pockets of the Northeast.

The forecast for the final months – December 2019 through February 2020 – indicates persistent, widespread surpluses in South Dakota, Nebraska, western Iowa, Kansas, and central Oklahoma, and will include intense surpluses, especially in South Dakota. Surpluses are also forecast for the Rockies, Nevada, Utah, and southern California. Mild to moderate surpluses will emerge in southern Michigan and nearby states in the northern Ohio River Basin and will increase in New York.

(It should be noted that forecast skill declines with longer lead times.)

IMPACTS
June 2018 to May 2019 was the wettest 12-month period in recorded history for the contiguous United States. Drought relief in the West accompanied disastrous flooding in the Great Plains and Midwest; May 2019 was the wettest month on record for Nebraska, Kansas, and Missouri.

Massive snowmelt is running through the Colorado River, putting Lake Powell on track to rise 50 feet this year. The influx of water will allow the Bureau of Reclamation to release enough water downstream to Lake Mead to avoid a water shortage that was predicted for Arizona with a 50 percent chance last year.

Rain has lasted for weeks on end in the grain belt, preventing farmers from planting crops, flooding fields, and halting river freight. The largest corn-producing states planted only 60 percent of their acreage as of early June, making this the slowest corn planting season in United States history. The halting of barge traffic, combined with competition from South American corn led to a 98 percent drop in corn exports week on week at the end of May, and are down 13 percent year-on-year.

An Arkansas River levee breach prompted evacuation of an area northwest of Little Rock in late May. The state made a federal disaster declaration for 16 counties affected by flooding. The Arkansas River rose over two feet above its prior all-time high in Fort Smith, Arkansas.

As the deluge continued into June, a month’s worth of rain, up to 14 inches, fell in a 24-hour period in parts of Texas and Louisiana, resulting in flash flooding that killed at least one person in Baton Rouge.

The Army Corps of Engineers decided this month to open the Morganza Spillway to divert the swollen Mississippi River down the Atchafalaya for the third time in its history, flooding 24,000 acres of rural Louisiana and Morgan City. The Mississippi River has been above flood stage for the most consecutive days in modern history.

The high river flows could make for the largest dead zone in the Gulf of Mexico seen to date. Eutrophication from the high concentrations of nutrient pollution in the Mississippi River causes the dead zone annually, but with most Mississippi tributaries above flood stage, this year’s zone of oxygen-depleted waters along coastal Louisiana will likely be magnified.

Flash flooding at a Tennessee gorge killed a two-year-old Kentucky boy and prompted crews to evacuate the park of 64 people this month. Fourteen people had to be swift-water rescued during the evacuation.

Massive flooding in Pittsburgh’s northern suburbs closed a few schools and prompted a state of emergency declaration in the small borough of Zelienople, which was submerged in up to three feet of water.

Temperatures reaching above 100 degrees fueled drought conditions in the Southeast in May, encouraging 66 wildfires to burn in Florida at the close of the month.

Southeast Alaska reached extreme drought, as classified by the U.S. Drought Monitor, for the first time last month. Washington State Governor expanded his state’s drought emergency declaration to cover roughly half the state late last month.

NOTE ON ADMINISTRATIVE BOUNDARIES
There are numerous regions around the world where country borders are contested. ISciences depicts country boundaries on these maps solely to provide some geographic context. The boundaries are nominal, not legal, descriptions of each entity. The use of these boundaries does not imply any judgement on the legal status of any territory, or any endorsement or acceptance of disputed boundaries on the part of ISciences or our data providers.

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Many analyses reported in ISciences-authored blog posts are based on data generated by the ISciences Water Security Indicator Model (WSIM). Other sources, if used, are referenced in footnotes accompanying individual posts. WSIM is a validated capability that produces monthly reports on current and forecast global freshwater surpluses and deficits with lead times of 1-9 months at 0.5°x0.5° resolution. This capability has been in continuous operation since April 2011 and has proven to provide reliable forecasts of emerging water security concerns in that time-frame. WSIM has the ability to assess the impacts of water anomalies on people, agriculture, and electricity generation. Detailed data, customized visualizations, and reports are available for purchase.

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