United states: Water deficits Persist throughout California, PNW

22 December 2022

THE BIG PICTURE
The 12-month forecast ending in August 2023 indicates significant water anomalies in Idaho, the Pacific Northwest, California, the Upper Midwest, and Florida.

Exceptional deficits are expected in the following areas:

Central Idaho, near the Salmon River Mountains.
Northwestern Washington, throughout the Cascade Range into western Oregon.
Southern California, in the southernmost region of the Central Valley.

Moderate to extreme deficits can be expected in:

North-central Iowa, near the cities of Humbolt and Pocahontas.

Severe deficits are forecast in:

Northwestern Florida, in pockets occurring in and to the east of the Apalachee Bay.
Northern California, throughout the Klamath Mountains and the surrounding area.
Western Washington, widespread in the Olympic Peninsula.
Northeastern North Dakota, near the Upper James River region.
Southeastern North Carolina, in the Coastal Plain.
Western Puerto Rico, along its coastal regions.

Mild to moderate deficits are forecast in the following regions:

Eastern Oregon, near the northern regions of the Columbia Plateau.
California, throughout the northern and central areas of the Sierra Nevada.
Much of central, western, and eastern Nebraska.
Southeastern Missouri, into the Ozark Plateau into the Ouachita Mountains.

Areas experiencing severe to exceptional surpluses include:

Northwestern and southeastern Alaska, as well as widespread throughout the Wrangell Mountains, northern and western coasts of the North Slope, southern coast of Seward Peninsula, and the Alaska Peninsula.
Hawaii; the main island, as well as the islands of Moloka’i and Lana’i.

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

The forecast through February 2023 anticipates exceptional deficits in the Pacific Northwest to subside, with some intense deficits remaining near the Salmon River Mountains. Extreme to exceptional deficits will occur in the Great Plains, primarily around northwestern Kansas, extending into eastern Colorado, southern Nebraska, and north-central Iowa. North and South Dakota can expect transitional conditions across the states’ eastern regions into western Wisconsin. Northern Florida can anticipate pockets of moderate to severe deficits along the coast of the Apalachee Bay. Coastal regions in western Puerto Rico can expect similar deficits.

Alaska can expect widespread, intense surpluses along its southern, western, and central regions. Mild to moderate surpluses are forecast in the U.S. Northeast, beginning in northern Maine and into New Hampshire, extending south through much of the Appalachian Mountains, down to western North Carolina.

From March through May 2023, many of the previous anomalies are expected to lessen to normal conditions, with some exceptions. Mild water deficits are expected to persist in Florida; moderate to severe deficits in California, southeastern Nebraska, Iowa, and the base of the Texas Panhandle; and more intense deficits in northwestern Wisconsin and central Idaho. Scattered pockets of moderate surplus are forecast elsewhere in Idaho and in northern Nevada, Utah, western Wyoming, and Colorado. Anomalies in Alaska are expected to decrease in intensity, though moderate to severe surpluses are forecast in southern, northern, and western regions.

The forecast for the final months – June through August 2023 – indicates widespread deficits of varying intensity in California, and surpluses continuing throughout northwestern, southwestern, and eastern Alaska.

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

IMPACTS
As a result of persistent drought and low reservoir levels, the Metropolitan Water District of Southern California (MWD) declared a drought emergency for the region. MWD is the nation’s largest water supplier, providing water to 26 different agencies, which include heavily populated regions like Los Angeles and San Diego counties. State officials stated that agencies like MWD should expect to receive only 5% of their requested supplies for the start of 2023, with a potential for more, if necessary for their communities’ health, sanitation, or safety purposes. This declaration brings potential mandatory water restrictions that could impact up to 19 million people.

Intense winter storms have impacted several states in the western United States, bringing dangerous blizzards and floods in many drought-stricken areas, including California. On December 17th, Soda Springs, a mountainous, drought-affected area in northern California, had received 60 inches of snow in just 48 hours. According to the National Weather Service, snowpack in the Sierra Nevada region is already above average, with expected levels to be 225% above normal, more than twice of what is normally expected in December. Officials at the National Weather Service have commented as being “cautiously optimistic” regarding the snowfall helping with regional drought.

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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