Atmospheric aspects of the 2008 Midwest floods: a repeat of 1993?

Abstract

This paper identifies and documents the major large-scale atmospheric circulation characteristics that preceded and facilitated the devastating floods across the Midwestern United States along the upper Mississippi, Missouri, and Wabash River basins in the late spring/early summer of 2008. These circulation features were also placed in the context of the 1993 floods that occurred within a similar temporal and spatial domain. This process included investigating the relationship between various atmospheric conditions and the timing of flood-producing rainfall events at monthly and sub-monthly timescales. Unlike in 1993, the 2008 flood event took place 1 month earlier in the year (May), lasted over a much shorter time period, and extended eastwards into Indiana. The comparison confirmed much previous work regarding the factors associated with Midwest flooding during the early warm-season and revealed the possible influence of the state of the North Atlantic Ocean and the North Atlantic oscillation (NAO) on warm-season flooding across the Midwest. Both the 2008 and 1993 events were preceded by an NAO positive phase; the pattern switched phase about 2 months before the onset of the flooding and remained negative for the duration of the floods. While the major atmospheric conditions known to be associated with major flooding across the Midwest were present in 2008 (e.g. a strong Great Plains low-level jet), the level of their development, persistence, and geographic orientation/position was very distinct from those observed in 1993. These conditions were also embedded in different state of the remote hemispheric circulation over the Pacific North American region. Together, these variations contributed to the 2008 Midwest floods that occurred earlier in the warm season, were shorter-lived, and had an impact on a slightly different geographic area.

Eastern U.S. summer streamflow during extreme phases of the North Atlantic oscillation

“…Consequently, eastern U.S. summer streamflow responses are more pronounced during the positive phase of the NAO both in terms of the spatial extent as well as magnitude of impact. Yet, a negative spring NAO often precludes warm season flood conditions along the Wabash River Basin in Indiana [ Coleman and Budikova , ]. The composite analysis (Figure c) shows central and southern Indiana summer streamflow is higher after negative NAO springs, but not lower after positive NAO springs.…”

“…The Atlantic warm pool may abate the southerly Great Plains low‐level jet (GPLLJ) intensity, yet still increase the magnitude of summer moisture transport northward into the upper Mississippi basin from more moisture‐laden air. The GPLLJ is an important factor on warm season hydrometeorological conditions in the central U.S., particularly notable floods events across the Midwest [ Coleman and Budikova , ; Mo et al ., ; Bell and Janowiak , ]. The strength of the GPLLJ and associated moisture changes are related to the positioning of the Bermuda‐Azores High and the state of the NAO [ Weaver and Nigam , ; Ruiz‐Barradas and Nigam , ].…”

Extreme Flood Response: The June 2008 Flooding in Iowa

“…6, top). Clustering of flood occurrences may be due to persistence of atmospheric processes or to land surface processes associated with soil moisture (see Guetter and Georgakakos 1996;Coleman and Budikova 2010;Villarini et al 2013). 7 (see next section for additional discussion of storm properties).…”

“…The hydroclimatology of flooding in Iowa is characterized by seasonal maxima of flood occurrences in the April-June time period (Villarini et al 2011a,b;Wang and Chen 2009;Schumacher and Johnson 2006) and by the occurrence of multiple floods during major flood years like 1993 and 2008 Coleman and Budikova 2010;Villarini et al 2013). Links between climate variability and extremes of the hydrologic cycle in Iowa have been examined in previous studies (Changnon and Kunkel 1995;Guetter and Georgakakos 1996;Kunkel et al 1994;Budikova et al 2010;Villarini et al 2013 systems (MCSs).…”

Future changes in the climatology of the Great Plains low-level jet derived from fine resolution multi-model simulations

“…GPLLJs also influence the intensity and longevity of mesoscale convective complexes 3 , and diurnal variations of the GPLLJ help explain the summertime nocturnal precipitation maximum of the central plains 4 . An anomalously strong GPLLJ contributed to the central U.S. floods of 1993 5 , 2008 6 , and 2015 7 , and increased (decreased) precipitation in the northern (southern) plains observed during 1979–2012 was attributed to a northward expansion of the GPLLJ 8 . Moreover, regional tornado activity is correlated with fluctuations in the GPLLJ’s strength and position 9 .…”