United States: Water surpluses to shrink and downgrade

20 May 2020

THE BIG PICTURE
The 12-month forecast ending January 2021 indicates water surpluses of varying intensity in a vast block bounded by eastern Oklahoma into North Carolina and southern Illinois through most of Mississippi. Surpluses will be extreme to exceptional in Mississippi, Tennessee, and pockets of central Georgia.

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Surpluses are also forecast in the Northern Plains and parts of the Upper Midwest. Moderate to extreme surpluses are expected in the Dakotas in a checkerboard pattern interspersed with normal conditions. Anomalies will be more prevalent in South Dakota where some relatively small areas will reach exceptional intensity and surpluses will reach into north-central Nebraska. Some pockets of surplus are also forecast for Montana, but scattered deficits are expected in western regions of the state. Scattered pockets of anomalies, surplus and deficit, are forecast in Wyoming. In the Upper Midwest, moderate surpluses are expected in eastern Wisconsin and moderate to extreme surpluses in the northern portion of Michigan’s Lower Peninsula.

In the West, deficits of varying intensity are forecast for much of California from Fresno north, most of Nevada, Utah, Colorado, Oregon, central and eastern Washington, and central 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. Some isolated pockets of surplus are forecast in the Pacific Northwest. Deficits are expected in northern and central New Mexico. Surpluses are forecast for southeastern Arizona and near Phoenix, with deficits in the southwest.

Southern Texas can expect some deficits, while pockets of moderate surplus are expected in the northeast. Deficits are forecast for much of peninsular Florida and will be especially 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 severe to exceptional deficits in the Delmarva Peninsula.

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 to the center of the state and in the southwest near Bethel. Deficits are forecast on the Seward Peninsula, from Anchorage past Valdez, east of Fairbanks, and in the far northeast.

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

From May through July, surpluses will shrink considerably in the U.S. with nearly normal conditions returning to many parts of the Upper Midwest, Central Plains, northern Ohio River Basin, and the Northeast. However, moderate to extreme anomalies will persist in the Dakotas and north-central Nebraska, and moderate anomalies in Tennessee, Mississippi, northern Alabama, and pockets to the west. Surpluses will also persist across central Georgia but will be more intense.

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Deficits of varying intensity are forecast in many areas of the U.S. West, Southwest, and Pacific Northwest, though southern California will be largely spared and can expect some surpluses around San Diego. Areas with a forecast of severe to exceptional deficit include northwestern California into Oregon, central Utah, and Colorado’s southwest quadrant. Deficits will shrink and downgrade in Florida, northern Virginia, and the Delmarva Peninsula. Relatively mild anomalies are forecast for Texas: some surpluses in the northeast and deficits in the west.

From August through October, normal water conditions will return to much of the country east of the Rockies, but surpluses will persist from South Dakota into north-central Nebraska and in pockets of North Dakota, and relatively mild deficits will emerge in the upper Great Lakes region and Mid-Atlantic. In the West, deficits will shrink and downgrade overall in the Rockies, Southwest, and Pacific Northwest, but increase in California, covering much of the state north of Santa Barbara. Deficits will remain intense in the state’s northwest corner and into Oregon. Surpluses will persist in central and southeastern Arizona and pockets of southwestern California.

The forecast for the final months – November through January – indicates normal water conditions for much of the country including the West; surpluses in the Dakotas, Nebraska, and southern Wisconsin; and moderate deficits in Delaware, Virginia, North Carolina, and pockets of Florida.

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

IMPACTS
At the end of April, Hawaii’s governor issued an official disaster declaration for Kauai after heavy rainfall caused major flooding a month earlier. The declaration opens up relief funds to address widespread property damage on the island. Overnight flooding launched debris into the Wailua River, creating a dam at the Wailua Bridge and sending floodwaters into the surrounding neighborhood, business area, and local golf course. One resident described it as the worst flooding in 30 years.

Michigan’s governor issued an emergency declaration on 20 May after intense rainfall compromised two dams, flooding downtown Midland. An evacuation was ordered for 10,000 people in Midland and residents of nearby villages. The deluge pushed the Tittawabasee River above flood stage and sent floodwaters racing toward the international headquarters of the Dow Chemical Company and a Superfund toxic cleanup site downriver.

A drought emergency declaration was issued by Oregon’s governor for Klamath, Jackson, and Curry Counties in an effort to steer clear of a devastating fire season like 2018’s that burned 38,000 acres and left one person dead.

As the coronavirus pandemic adds a “threat multiplier” to disaster response and preparedness, authorities are faced with the new challenge of how to collectively train for disasters or evacuate disaster sites and still maintain recommended COVID-19 protocols for social distancing to prevent the virus’ spread.

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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