United States: Intense water deficits forecast for Lower Mississippi Valley

19 December 2017

THE BIG PICTURE

The 12-month forecast (above) indicates significant deficits in Maine, the South Atlantic States, the Lower Mississippi Valley, Texas, the Southwest, and California. Surpluses are forecast for Idaho, the Ohio River Valley, and parts of the Upper Midwest. Outside the contiguous US, surpluses are forecast for western Alaska and deficits in the east; intense surpluses are forecast for Hawaii; and, deficits are expected in western Puerto Rico with mild surpluses in the east.

IMPACTS
Newly released NASA research shows that drought in California between 2011 and 2015 caused the Sierra Nevada range to lose water, and consequently rise in height by 24 millimeters (about one inch) after shedding the water weight. Increased precipitation since 2015 has refilled mountainous stores, creating additional weight and causing the mountains to shrink in height by 12mm. The new research advances knowledge of the water storage capacity of mountain rock fractures.

Other new geological research reports that standing floodwater from Hurricane Harvey rainfall, which weighed an estimated 127 gigatons, depressed the Earth’s crust beneath it by up to 1.8 cm (0.7 inches). The ground slowly rebounded as floodwaters dissipated, according to supersensitive GPS stations, which signaled that excess water had completely drained or evaporated by three weeks after the storm had made landfall. The researchers hope to use similar technologies to predict downstream effects of floods and inform dam managers concerned with safety limits and storage capacities.

The Thomas Fire burning in Southern California is on course to become the largest wildfire in California state history. As of December 17 it burned 270,000 acres, and is the third most destructive in structure loss. Reflecting on several years of weather extremes and lengthening fire seasons, California state regulators have toughened fire prevention rules by increasing the minimum allowable distance between power lines and vegetation. Power lines may have contributed to a forest fire in Northern California in October of this year, which killed 44 people and caused over $9 billion in damages.

Scientists warn that by not taking into account the flood risk contribution made by small tributaries of larger rivers, the U.S. Federal Emergency Management Agency (FEMA) underestimates the number of people living in 1-in-100 year floodplains by two-thirds. While FEMA maps 13 million people at risk, British researchers estimate 40 million people, and expect those numbers to grow in the coming decades.

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

Please note that we are well aware of the recent devastation wrought by hurricanes. Readers are advised that inputs used in our Water Security Indicator Model (WSIM), the model used to generate “Global Water Monitor and Forecast Watch List,” have been proven reliable in forecasting broad precipitation patterns, but are not effective for predicting singular events such as tropical storms. Detailed outlooks and analyses of tropical storms are available from NOAA National Hurricane Center.

The forecast for December through February indicates a column of exceptional deficits in the Lower Mississippi Valley encompassing southern Missouri, Arkansas, Louisiana, Mississippi, and western Alabama. Deficits nearly as intense trace a wide path down through the South Atlantic States from Virginia through Georgia and into the Florida Panhandle. Deficits are expected to be exceptional in North Carolina. Widespread moderate deficits are forecast in southern California, Arizona, New Mexico, and eastern Texas, where deficits could be severe near Houston. Deficits of varying severity are forecast in Utah, Colorado, Kansas, and Oklahoma. Primarily moderate deficits are expected in Montana, North Dakota, South Dakota, and northern Minnesota.

Surpluses reaching exceptional severity are forecast during this period for eastern Nebraska, central Minnesota, and southeastern Idaho. Moderate to severe surpluses are forecast for northern Wisconsin, Michigan, northern Indiana, Ohio, and western New York.

From March through May deficits in the Lower Mississippi Valley should begin to normalize, though moderate to severe deficits may persist in southern Louisiana. Likewise, deficits in the South Atlantic States are expected to moderate, but severe conditions may persist in the Florida Panhandle. Moderate deficits are forecast to linger in eastern Texas, will spread throughout California, and will intensify in southwestern Arizona. Surpluses ranging from severe to occasionally exceptional will emerge in parts of the Oregon, throughout Idaho, in western Montana, and along the Columbia, Missouri, and Yellowstone Rivers. Some moderate surpluses will continue to emerge in southwestern Minnesota, and mild surpluses in Michigan and the Ohio River Valley. Michigan’s Upper Peninsula is expected to transition from surplus to deficit conditions along with northern Wisconsin.

The forecast for the final months – June through August – indicates a distribution of water anomalies similar to the prior three months but with a transition from surplus to moderate deficit in the Northwest.

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

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.