Drought and Pluvial Dipole Events within the Great Plains of the United States

The occurrence of significant precipitation following severe drought periods within Oklahoma and the surrounding Great Plains is critical to the agriculture and economy of the region. Dong et al. (2011) conducted a comparative study over a year of intense drought in 2006 followed by a year of excessive rainfall in 2007 across the Southern Great Plains and found that a dipole relationship exists between drought and pluvial periods. However, the temporal frequency of dipole events has not been documented throughout the climatological record. Thus, the purpose of this study was to quantify dipole events for various spatial scales including the nine Oklahoma climate divisions (CDs), the Southern Great Plains (SGP), the High Plains (HP), and the Northern Great Plains (NGP) of the United States. Analyses revealed that, on average, over twice as many standard deviation (STDEV) dipoles existed in the latter half of the dataset (1955-2013) compared to the first half (1896-1954), suggesting that dramatic increases in precipitation from one year to the next within the Oklahoma CDs are increasing with time. In addition, a gradient existed in the number of significant drought to significant pluvial (SD to SP) dipoles across Oklahoma, with a higher number of SD to SP dipoles in the northwestern CDs compared to the southeastern CDs. For the larger regions within the Great Plains of the United States, the percent chance of a significant pluvial year following a significant drought year was approximately 25% of the time for the SGP and NGP, and approximately 16% of the time for the HP. The STDEV dipole analyses further revealed that the frequency of dipoles were consistent between the first and second half of the dataset for the NGP and HP, but were increasing with time in the SGP. Finally, the temporal periods of anomalous precipitation during relative pluvial years within the STDEV dipole events were unique for each region whereby October occurred most frequently (70%) within the SGP, September occurred most frequently (60%) within the HP, and May occurred most frequently (62%) within the NGP.