United States: Intense water deficits in AZ, NM, CO, WY, CA

22 January 2021

THE BIG PICTURE
he 12-month forecast ending September 2021 indicates widespread water deficits in the western U.S. deficits are expected to be exceptional in many areas, especially California and Arizona.

Large pockets of intense deficit are also forecast in Nevada, Utah, Colorado, New Mexico, and northwestern Texas. deficits of varying intensity are expected in many other regions of Texas including exceptional deficits in the state’s southern tip. Generally moderate deficits are forecast in pockets throughout Wyoming, and to a lesser extent, in the Plains States.

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Some small, isolated pockets of surplus are forecast from the U.S. Northwest into Montana, along with deficits in Oregon and the Salmon and Snake River regions of Idaho. Surpluses are forecast in a small central pocket on the Montana/Wyoming border.

A few small pockets of surplus are expected in Wisconsin and the northern reaches of Michigan’s Lower Peninsula. In Arkansas, surpluses will converge where the White and Black Rivers meet in the northeast, and a few small pockets are forecast further south and in Louisiana, though deficits are expected in the Mississippi Delta. Deficits are forecast for southern Alabama, southeastern Georgia, and Florida, and will reach extreme intensity in the Alabama River region, near Savannah, and south of Jacksonville. Generally moderate deficits will surround Lake Okeechobee, and surpluses will skirt Florida’s southern coast.

In the Mid-Atlantic, surpluses are forecast from New Jersey’s southern tip through northern North Carolina. Surpluses will be intense in the Roanoke River Basin in Virginia and the Delmarva Peninsula. Moderate deficits are expected in western Pennsylvania, but some small exceptional pockets are forecast in Upstate New York along the St. Lawrence River and also south of Burlington, Vermont. Severe deficits are expected in New Hampshire near Lake Winnipesaukee.

Outside the contiguous U.S., surpluses are forecast for Hawaii’s Big Island. Alaska can expect deficits from Anchorage past Valdez; in the center of the state at the confluence of the Yukon and Tanana Rivers; in the northeast; and in large pockets of the west. Surpluses are forecast near Iliamna Lake and near Juneau. Moderate deficits are expected in western Puerto Rico.

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

Though deficits in the West will shrink overall through March 2021, anomalies will remain widespread from California’s southern half through the Southwest and southern Rocky Mountain States. Deficits will be intense in Arizona, New Mexico, central Colorado, western Wyoming, and pockets of Southern California. In Texas, deficits are forecast west of Lubbock, from San Antonio to Houston, and in the Rio Grande region from Big Bend past Amistad Reservoir. Deficits will shrink and downgrade in Nebraska, Kansas, and Iowa, but will become exceptional in North Dakota. In the U.S. South, deficits are forecast for the Mississippi Delta, southern Alabama, southeastern Georgia, northern Florida and around Lake Okeechobee in the south. Surpluses will persist from Miami through the Keys.

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Surpluses will increase somewhat from the Pacific Northwest through western Montana and on the Missouri River, and will persist from Nebraska into South Dakota. Generally moderate surpluses will increase in Wisconsin, Michigan, and pockets of Minnesota, and will emerge in eastern Iowa, northern Illinois, northeastern Ohio, and Oklahoma. Pockets will persist in Arkansas. Deficits will recede in the Northeast, persisting in northwestern Vermont and northern New York, as surpluses emerge in Pennsylvania, New York, New Jersey, Connecticut, Massachusetts, Vermont, New Hampshire, and Maine. Surpluses in the Mid-Atlantic states will shrink and moderate, persisting in Virginia.

From April through June 2021, normal water conditions will return to many regions as surpluses nearly disappear. However, deficits will persist in the West and Southwest and exceptional deficits will increase in the Southwest. Deficits will increase in Texas; emerge in Pennsylvania, southern North Carolina, and South Carolina; and generally downgrade in Georgia, Florida, Alabama, and the Mississippi Delta.

The forecast for the final months – July through September 2021 – indicates that deficits will shrink and downgrade in the Southwest but increase in the Northwest and Rockies. Moderate deficits are forecast for the Arkansas and Canadian Rivers, Mississippi Delta, northern Michigan, and pockets in Maine, North Carolina, and Florida.

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

IMPACTS
Drought in the West continues to command headlines. The 2020 Southwest monsoon season - June through September - earned the moniker “non-soon” when it failed to deliver desperately needed precipitation.

Annual precipitation last year in Colorado, Arizona, Wyoming, Utah and New Mexico was the lowest in over four decades. Snowpack, which acts like a natural reservoir, has been disappointing. Even a normal snowpack season wouldn’t be enough to offset drought conditions, but Colorado’s snowpack in early January was only 74 percent of median.

California snowpack in mid-January was just 40 percent of average. The state is dependent on snowpack for 30 percent of its water needs. Levels in the Sierra Nevada Range are running well below normal due to hot, dry conditions.

Lake Powell, the well-known reservoir in Arizona and Utah on the Colorado River, was at 42 percent of capacity in early January while Lake Mead near Las Vegas was at 39 percent.

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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