United States: Water surpluses will persist in the Dakotas

17 April 2020

THE BIG PICTURE
The 12-month forecast ending December indicates a vast block of water surplus in the southern states bounded by eastern Oklahoma into North Carolina and southern Illinois through Mississippi. Surpluses will be extreme to exceptional in the southern Appalachian region extending well into Mississippi.

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Surpluses are also forecast in a wide area across the Northern Plains and Upper Midwest. Moderate to extreme surpluses are expected in the Dakotas, particularly widespread in South Dakota with some areas reaching exceptional intensity. Surpluses will reach well into Nebraska; pockets of surplus also forecast in southern Montana and several areas of Wyoming. Primarily moderate surpluses are expected in southern Minnesota, Wisconsin, and Michigan.

In the West, deficits of varying intensity are forecast for much of California north of Los Angeles, most of Nevada, the Pacific Northwest, and northern Idaho. Areas of exceptional deficit include the San Francisco Bay Area, the Columbia River region in central Washington, and the Salmon River Mountains of Idaho. Intense deficits are expected in central and southwestern Colorado, pockets of deficit in Utah and New Mexico, and pockets of surplus in Nevada’s northeastern corner and in Arizona.

Southern Texas can expect deficits, primarily moderate but severe around Houston. Severe deficits are also forecast for much of Florida outside of the Panhandle and will be even more intense south of Lake Okeechobee. Nearly normal conditions are expected in the U.S. Northeast and Mid-Atlantic with some deficits in northern Virginia and exceptional anomalies in southern Delaware.

Outside the contiguous U.S., surpluses are forecast for much of Hawaii. Alaska can expect surpluses from the base of the Alaska Peninsula leading inland, in the southwest near Bethel, and in the Koyukuk and Kobuk River regions in the north. Deficits are forecast from Anchorage past Valdez, and east of Fairbanks.

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

From April through June, surpluses will shrink overall in the U.S. but will persist in several wide-reaching areas. Moderate-to-exceptional surpluses will persist in the Dakotas and Nebraska, extending westward into pockets of Wyoming and southern Montana while moderate surpluses reach eastward through northern Michigan. Conditions will normalize in the northern portion of the Ohio River Valley. Widespread, intense surpluses in the South will moderate overall, but persist in a large block from Oklahoma and northeastern Texas through Tennessee and south through Mississippi. Anomalies will be severe in the southern Appalachian region. Surpluses will increase in Arizona from the center of the state through the southeast.

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Deficits of varying intensity are forecast in the West in California’s northern half, western Oregon, central Washington, northern Idaho, and pockets in Nevada, Utah, Colorado, and New Mexico. Deficits will persist in most of Florida but will downgrade, becoming moderate to severe. Deficits in Delaware will retreat and anomalies in northern Virginia will shrink considerably.

From July through September, anomalies east of the Rockies will shrink, but intense surpluses are forecast for South Dakota and its neighbors, and moderate surpluses from Oklahoma into Texas and in Mississippi, northern Alabama, and south-central Tennessee. In the West, deficits are expected to increase, covering nearly all of California and much of the Pacific Northwest, Nevada, and western Idaho. Areas with intense anomalies include north of San Francisco Bay and the Humboldt River Basin in northern Nevada. Deficits will persist in southwestern Colorado and increase in Utah and Arizona.

The forecast for the final months – October through December – indicates normal water conditions for much of the country, intense surpluses in South Dakota and into neighboring states, and mild to moderate deficits in the Mid-Atlantic, skirting the Gulf Coast, and in central California.

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

IMPACTS
The drought that has plagued the U.S. Southwest since 2000 is now being characterized as “an emerging megadrought” by researchers at Columbia University in a study that firmly places some of the blame on anthropogenic warming. Using tree growth as a proxy for soil moisture content scientists were able to determine that, without the boost from human-induced climate warming, the drought would likely be of only moderate severity. Instead, it could well be one of the worst in 1,200 years.

As of early April, around 43 percent of California is experiencing moderate drought and some parts of Northern California are in severe drought, according to the U.S. Drought Monitor. The statewide snow water equivalent measured just over half of the April average despite a few late winter storms. California’s snowpack is usually at its highest on April 1 and the state depends on it for about 30 percent of freshwater supply.

In the Upper Midwest, the U.S. Army Corps of Engineers warns that many levees on the Missouri and Kansas Rivers still remain compromised from widespread flooding in 2019. The threat of Spring 2020 flood is a concern for Nebraska, Kansas, Iowa, Missouri, and eastern North and South Dakota as soil saturation remains high. And, high water levels have persisted on the James River in South Dakota for over a year.

Like a bathtub with the water left running, the Great Lakes are full. Water levels in the “big lakes” are already higher than average, and many Michigan water officials are increasingly concerned about spring precipitation. Shorelines are eroding, houses slipping into Lake Michigan, and beaches disappearing. The small resort town of South Haven has already tallied $16 million in damages and the head of the Michigan Municipal League estimates $63 million in repair costs to cities.

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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