Teleconnection and the buildup of water storage leading to the 2011 Missouri River flooding

From May through August 2011, the Missouri and Souris River basins experienced widespread record flooding. Damages were inflicted on residences, businesses, infrastructure, transportation, and agriculture amounting to over $2 billion dollars lost. The Gravity Recovery and Climate Experiment (GRACE) observation indicates a buildup of water storage in the Missouri River basin spanning two years leading to the 2011 flooding. This long buildup of water storage signifies the multi-year wet period after a multi-year dry period. The alternation of wet-dry periods, each spanning 2-4 years, is supported by precipitation and groundwater well data. Spectral analyses of precipitation and groundwater level reveal significant power at the 10-15 year frequency, suggesting a quasi-decadal oscillation (QDO). The QDO has been observed in the central tropical Pacific while a similar frequency is found in the annual values of the North Atlantic Oscillation (NAO). Climate diagnostic analyses indicate that the 2008-2011 wet period resulted from a combined effect of the QDO and NAO. While the QDO led to the buildup, the strong negative NAO phase in winter and spring 2011 contributed to the extremeness of the wet anomaly. The fact that GRACE observes the water storage buildup suggests that utilization of GRACE data in real time will provide valuable information for flood preparedness. Moreover, the warm/cold extremes of the Pacific QDO represented by the Nino-4 index tend to lead the wet/dry periods by 2-4 years. This character makes the Nino-4 index a natural predictor for the wet/dry periods in the Missouri River Basin – this capability has been researched and applied for the Great Basin hydrology. The dynamic process driving the phase shift between the QDO and local precipitation anomalies is discussed.