Analysis of Extreme Reversals in Monthly, Seasonal, and Annual Precipitation Anomalies across the United States, 1895–2014

As population and urbanization increase across the United States, the effects of natural hazards may well increase, as extreme events would increasingly affect concentrated populations, and therefore a greater number of people and the infrastructure upon which they rely. Extreme precipitation is one natural hazard that could stress concentrated populations, and this research focuses on extreme precipitation reversals - defined as an unusually wet (dry) period that is preceded by an unusually dry (wet) period. The magnitude of the extreme precipitation event is determined by the difference in the percentile expression of the two consecutive events. This concept has been documented only once before in a study that analyzed extreme precipitation reversals for a region within the southwestern United States. That study found that large differences in winter-to-winter precipitation occurred more frequently than what would be expected from random chance, and that extreme precipitation reversals have increased significantly since 1960. This research expands upon the previous work by extending the analysis to the entire continental United States and by including multiple temporal resolutions. Climate division data were used to determine monthly, seasonal, and annual precipitation for each of the 344 climate divisions of the continental United States from 1895-2014. Precipitation values were then ranked and given percentiles for the monthly, seasonal, and annual data. The monthly analysis examined percentiles for consecutive months (e.g., January–February, February–March). The season-to-season analysis was performed in two ways. The first examined consecutive seasons (e.g., winter–spring, spring–summer) while the second analyzed the seasonal data from consecutive years (e.g., spring 2014–spring 2015). The annual data represented precipitation for the period October 1–September 30, or the “water year” used by water resource managers. Following the approach of the previous study, a secondary objective of the research was to examine large-scale climate teleconnections for historical relationships with the occurrence of precipitation reversals. The teleconnections chosen were previously found to have relationships with precipitation patterns across the United States. Results indicate regional expressions of a propensity for extreme precipitation reversals and relationships with teleconnections that may afford stakeholders guidance for proactive management.