The Role of the Great Plains Low‐Level Jet in Moisture Transport, Streamflow, and Flooding in the Missouri River Basin

Erika K. Wise; Matthew P. Dannenberg; Gregory J. McCabe

doi:10.1029/2024JD041066

The Missouri River Basin, one of the primary agricultural regions in North America, is prone to large hydroclimatic variability and extreme events. The Great Plains low‐level jet (GPLLJ) is one of the major sources of moisture transport into this region, and concerns over moisture extremes already seen in the interior U.S. have been linked to changes in GPLLJ. However, the relationship between GPLLJ and precipitation in this region remains uncertain, with studies showing conflicting results that may be related to distinct types of jet events. Here, we use daily GPLLJ data to study connections between different types of jet events and precipitation, integrated water vapor transport, and synoptic conditions to better understand GPLLJ‐streamflow linkages. We assess GPLLJ conditions during historical flood events and potential future changes using CMIP6 projections. We find: (a) in May–September, GPLLJ is associated with 29%–46% of monthly precipitation and with increased precipitation intensity; (b) GPLLJ has a consistently positive impact on Missouri River streamflow over the warm season; (c) coupled jets have a larger impact on moisture transport than uncoupled jets, but streamflow impact is reduced, likely due to seasonal timing; (d) unusual jet conditions preceded historical warm‐season flood events; and (e) future projections indicate relatively small changes in GPLLJ meridional wind velocities along with large increases in moisture transport driven by humidity increases. Although future streamflow will be partially dependent on snowmelt from the upper basin, the projected intensification of warm‐season moisture transport to the Missouri River suggests possible increases in future flood risk. Plain Language Summary Both floods and droughts are of concern in the Missouri River, which is relied upon for agriculture, fish and wildlife, transportation, and power generation. One of the river's main sources of water is the Great Plains low‐level jet—strong winds near Earth's surface that bring moisture from the Gulf of Mexico to the Missouri River basin during summer months. In this study, we examined how different configurations of jets affect rain, movement of moisture in the atmosphere, and streamflow in the Missouri River, as well as the conditions leading up to flood events. We found that more than a third of monthly rain totals are associated with a jet, and that jet occurrence coincides with higher streamflow in the Missouri River. Atmospheric moisture transport and the number of jets were unusually high in the weeks preceding the 1951, 1986, and 1993 flood events. Although drying associated with global warming has been projected for this region, our results suggest that flooding will remain a concern for the Missouri River due to increasing water vapor content and transport in the atmosphere. Key Points The Great Plains low‐level jet (GPLLJ) has a clear and consistent impact on Missouri River streamflow and peak flows during the warm season GPLLJ is associated with 29%–46% of warm season precipitation and with increases in precipitation intensity and flood events Models project large increases in future moisture transport, a source of concern for precipitation‐driven flooding in the Missouri River

The Role of the Great Plains Low‐Level Jet in Moisture Transport, Streamflow, and Flooding in the Missouri River Basin

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