United States: Water deficits in the west & SW will shrink

21 November 2020

THE BIG PICTURE
The 12-month forecast ending July 2021 indicates widespread water deficits in the southwest quadrant of the continental U.S. Deficits are expected to be exceptional in New Mexico, Arizona, and Utah. Deficits of varying intensity, including exceptional, are forecast for West Texas, California, Nevada, and Colorado, bleeding into Wyoming, Nebraska, Kansas, and western Oklahoma. Deficits will also follow the Gulf Coast in Texas reaching well into the south and southeast regions of the state.

The Pacific Northwest can expect deficits in southern Oregon, and pockets of surplus in Washington, northern Idaho, and western Montana along with a few small pockets of deficit as well.

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Iowa will experience deficits. Around the Great Lakes, surpluses are forecast for southern Wisconsin and from northeastern Wisconsin into northern Michigan. A few pockets of surplus are also expected in northwestern Minnesota. Some moderate deficits will skirt Michigan’s southern border and reach into northern Indiana. Moderate surpluses are forecast in central Ohio, but deficits are expected in the east, becoming intense and widespread in western Pennsylvania. Deficits of varying intensity are expected in the U.S. Northeast with exceptional deficits in the St. Lawrence River region of Upstate New York and pockets in Vermont, New Hampshire, and Maine.

Surpluses are forecast from Washington, D.C. past Richmond, Virginia into North Carolina, and will be exceptional in the Chesapeake Bay Area and south of Richmond. Surpluses will lead inland through Virginia and the southern Blue Ridge Mountains where anomalies will reach exceptional intensity in a few pockets of North Carolina. Reaching through the southern portion of the Ohio River Watershed, surpluses will moderate. Arkansas can also expect surpluses and some pockets are expected in Louisiana, though intense deficits are forecast south of Lake Pontchartrain.

Deficits are expected in much of Florida outside of the Panhandle with exceptional deficits north of Orlando and south of Lake Okeechobee. Pockets of deficit are also forecast in southeast Georgia.

Outside the contiguous U.S., surpluses are forecast for much of Hawaii. Alaska can expect deficits west of Kodiak and from Anchorage past Valdez; in the northeast; and in pockets of the west. Surpluses are forecast north of Iliamna Lake; some pockets in the center of the state; and from Denali east to the Canadian border.

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

From November 2020 through January 2021, widespread intense deficits in the West and Southwest will shrink and downgrade considerably, as will widespread surpluses from the Lower Mississippi region through Virginia and the Carolinas to the Atlantic Coast. Intense deficits will persist in Colorado and pockets of Wyoming, deficits will increase Nebraska, and moderate to exceptional deficits will emerge in much of Kansas. Deficits will downgrade in West Texas but increase across southern Texas with extreme deficits along the Gulf Coast.

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In the U.S. Northwest, surpluses will emerge in Washington, Idaho, and Montana. Surpluses will persist in central South Dakota flanked by deficits in the state’s southern corners. Intense deficits will emerge in a pocket of North Dakota east of Bismarck; deficits in Iowa will downgrade. Moderate surpluses will persist in southern Wisconsin and northern Michigan and will emerge in north-central Ohio. Deficits will downgrade in western Pennsylvania and will recede considerably in New England. Moderate surpluses are forecast from southern Delaware through eastern Virginia and into the southern Blue Ridge Mountains. Deficits will be intense in Peninsular Florida but moderate in southeastern Georgia.

From February through April 2021, normal water conditions will return to many regions. However, deficits will increase in Peninsular Florida; persist south of Lake Pontchartrain; intensify along the Gulf Coast of Texas and south of Amarillo; persist in New Mexico, intensifying in the southeast; and persist in central Colorado. Surpluses will shrink in the Pacific Northwest, persist in western Montana and south-central South Dakota, and re-emerge in north-central Nebraska. Moderate surpluses are forecast in the Ohio River Watershed, southern Wisconsin, southeastern Michigan, and Arkansas.

The forecast for the final months – May through July 2021 – indicates moderate deficits in Florida and along the South Atlantic Coast, and deficits of varying intensity in western Texas, the Southern Rockies, and Southwest. Pockets of surplus are forecast in the Northern Rockies, Pacific Northwest, and around the Great Lakes.

Please note that WSIM forecast skill declines with longer lead times.

IMPACTS
While drought and wildfires in the western US have commanded media attention, New Englanders are also suffering the affects of precipitation deficits. Maine’s potato harvest is down 18 percent from last year due to severe drought conditions and some growers are expected to see losses of up to 30 percent. In New Hampshire, at least 1,000 residential wells are running dry. Increased rainfall in October has not been enough to compensate for rainfall shortages in prior months. The state has offered emergency drought assistance.

Hurricane Eta, posing as a somewhat less intense Tropical Storm at some points in its development, pushed water over the seawall protecting St. Petersburg in mid-November, flooded Bayshore Boulevard in Tampa, and dumped sailboat on the beach in Gulfport. One death was reported in Bradenton due to electrocution, and more than 35,000 accounts lost electrical power.

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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