Expanding drought concerns in U.S. heading toward Q2/2022!

Highlight: Expanding drought concerns in U.S. heading toward Q2/2022!

Fig. 1: Latest U.S. Evaporative Demand Drought Index (EDDI) analysis identifies extreme ED4 conditions across the West-central U.S.

Discussion: According to NOAA/Physical Sciences Laboratory (PSL), “The Evaporative Demand Drought Index (EDDI) is an experimental drought monitoring and early warning guidance tool. It examines how anomalous the atmospheric evaporative demand is for a given location and across a time period of interest. EDDI can offer early warning of agricultural drought, hydrological drought, and fire-weather risk.” Climate Impact Company began monitoring EDDI last year due to its usefulness in predicting flash drought. The current EDDI analysis indicates harsh ED4 drought conditions in the far western Great Plains and central/south Continental Divide (Fig. 1). Certainly, the devastating Louisville/Superior, Colorado fires occurred in the EDDI/ED4 region. According to NOAA/PSL, ED4 is a drought condition previously observed <2% of the time in the 1979-2016 climatology.

The conventional U.S. Drought Monitor (Fig. 2) utilizing Palmer Drought Severity Index (PDSI) identifies the long-term West U.S. Drought expanding into the Mid-south U.S. plus the Carolina Drought. A closer look at U.S. soil moisture anomalies and the seasonal trend (Fig. 3-4) implies improving conditions in the West, worsening conditions centered on the Mid-south States and much of the East Coast. Are drought conditions emerging east of the Continental Divide an increasing concern for 2022?

Fig. 2: U.S. Drought Monitor issued Dec. 28, 2021.

Fig. 3-4: Daily U.S. soil moisture anomalies for Dec. 30, 2021 and the seasonal soil moisture change.

Fig. 5-7: Northeast Pacific and North Atlantic SSTA patterns and the NOV/DEC 2021 upper air regime across North America. 

As a review, the current climate-motivating Northeast Pacific/North Atlantic SSTA regime is UNIQUE (and consequently generating unusual climate). In the Northeast Pacific, the Gulf of Alaska is cooler than normal (a rare occurrence since 2012) while northwest of Hawaii the Northeast Pacific “warm blob” of 2013-2021 has shifted west and remains super-warm (Fig. 5). The contrast between the warm SSTA northwest of Hawaii and cool SSTA in the Gulf of Alaska has generated one of the strongest cool phase Pacific decadal Oscillation (-PDO) regimes in the 1950-2021 climatology. Meanwhile, in the North Atlantic basin, the Atlantic multidecadal oscillation (AMO) is in the +0.45 to +0.50 range (for December) which is record warm (Fig. 6). The +AMO regime in the +0.45 to +0.50 range for OCT/NOV/DEC 2021 is the warmest on record for quarter 4 in the 1950-2021 climatology. And of course, La Nina is present. Also of interest, and a significant contributor to the South-central U.S. drought and unusual severe weather events just-to-the-north is an evolving warm SSTA region southwest of Baja California. This feature is gaining influence on the position of the subtropical ridge centered on Texas during NOV/DEC 2021 (Fig. 7). Note the wet upper trough into the West U.S. associated with the -PDO pattern. SSTA patterns are used to generate climate forecasts because they generally change slowly. The IMME global SSTA forecast for May 2022 indicates SSTA features in-place now will continue and could strengthen while La Nina weakens (Fig. 8).

Fig. 8: IMME global SSTA forecast for May 2022.

The U.S. soil moisture forecast into early meteorological spring is potentially scary. The most conservative (NCEP CFS V2) outlook amplifies the central/southern Rockies to central Great Plains/Texas drought (Fig. 9). Additionally, drought continues in the Carolinas stretching to Florida and the Western U.S. drought is suppressed into the Southwest States including the southern half of California. There is reasonable potential for a wider area of drought given the expected warming of the North Pacific to the southwest of Baja California and additional warming of the North Atlantic. A more extreme soil moisture forecast (CAN CM4I) projects widespread southern half of the U.S. drought with potential expansion into the U.S. Corn Belt (Fig. 10).

Fig. 9: NCEP CFS V2 U.S. soil moisture projection into early spring. The most conservative forecast.

Fig. 10: CAN CM4I U.S. soil moisture projection into early spring. The “caveat” forecast.

Conclusions: The Evaporative Drought Demand Index (EDDI) is used by Climate Impact Company to project high risk flash drought potential areas. The EDDI certainly identifies a region of concern stretching from the central Rockies to the western Great Plains and western Texas. The EDDI also indicates improving conditions in the West and more-so than conventional Palmer Drought Severity Index (PDSI) used by the conventional USDA/NOAA Drought Monitor. Soil moisture analysis (and trend) clearly identifies a developing dry-to-drought regime in the East U.S. centered on the Carolinas. The pattern(s) described are generated primarily by unique mid-latitude SSTA regimes in the Northeast Pacific and North Atlantic. Other SSTA regions contributing to this pattern are moderate La Nina and an emerging warm SSTA region southwest of Baja California.

The global SSTA forecasts are in general agreement that the Northeast Pacific (cool phase Pacific decadal oscillation) and North Atlantic (warm phase Atlantic multi-decadal oscillation) will continue into mid-year (while La Nina dissipates). Drought expansion is a reasonable expectation given this (SSTA) projection. The conservative forecast is most-focused on West-central to Mid-south U.S. drought expansion/strengthening while also strengthening drought from the Carolinas to Florida. The “caveat” (and more extreme scenario) forecast projects a wider drought stretching across the southern half of the U.S. and possibly into the Western U.S. Corn Belt.

The West U.S drought region should continue to benefit by -PDO generated storms and cool weather (plus spring snowmelt). The Northern Great Plains and southern Canadian Prairies also benefit from above normal precipitation generated in-between the western North America upper trough and eastern U.S. upper ridge.