Soaking Wet U.S. Soils Leads To Immense Spring Flood Risk

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U.S. flood risk is increasing steadily due to historic wet soil moisture, heavy precipitation events and snowmelt. Worsening flood conditions evolve during spring.

Highlight: Wettest early meteorological spring U.S. soil moisture on record.

Fig. 1: Percent ranking in 1895-2019 climatology of current U.S. soil moisture.

Discussion: The wettest early meteorological spring U.S. soil moisture signature on record is present (Fig. 1). Near or record soil moisture is observed in north-central California, the entire Midwest and Mid-South to Mid-Atlantic U.S. The seasonal trend indicates sharp drying in the Gulf of Mexico region including the Southeast U.S. with marginal drying in the coastal Northeast Corridor (Fig. 2). Prohibitive wet seasonal changes are occurring in California.

Fig. 2: The U.S. seasonal soil moisture anomaly change.

River flooding risk is developing quickly as a result of very wet soils, heavy precipitation events and melting snow in the Midwest U.S. to central and southern Great Plains (Fig. 3). Flooding is ongoing and worsening in the central and southern Mississippi River Valley. Palmer Drought Severity Index also identifies the widespread historically wet soils in the Mid-South U.S. to Mid-Atlantic States and into the Northeast U.S. (Fig. 4) where spring flooding is also likely to emerge with heavy rain events and spring snowmelt.

Fig. 3: NOAA flood risk outlook. The “possible” and “likely” areas in the Central U.S. emerged suddenly over the weekend.

Fig. 4: U.S. Palmer Drought Severity Index (PDSI) reveals soaking wet soils and the attendant evolving flooding in the Central U.S. High flood risk in the East is also present.

Fig. 5: Snow water equivalent of still-present snow cover across the West and North U.S.

Fig. 6: Percent of normal snow water equivalent across the West U.S.

Yet to contribute to ongoing flooding in the Central U.S. is abundant water stored in snow cover across the northern Great Palins and Upper Midwest (Fig. 5). Similarly, immense snow water equivalent is present across northern New England and Quebec and all of the Western U.S. Mountain areas. Nearly 200% of normal snow water equivalent is present in much of the West (Fig. 6).

Summary: The aerial coverage of historic soil moisture across the U.S. is prohibitive. The amount of snow and water equivalent remains immense. Historic flood risk in the Central/East-central/Mid-South U.S. is evolving. Flood risk in the Northeast is present due to as yet un-melted deep snow cover and attendant water equivalent. Flooding due to spring heavy rain events in the Tennessee Valley to Mid-Atlantic region is closely monitored.