资源环境科技发展态势分析平台

Extreme precipitation studies commonly link anomalies to specific episodes of drought or flooding, while studies of precipitation volatility typically employ statistical measures of variability. This study addresses the concept of an extreme precipitation reversal (EPR), defined as an unusually wet or dry period that precedes a large precipitation anomaly of opposite sign, or more specifically the difference in the percentiles of precipitation for consecutive periods. The focus of this study is EPRs over the past 121years for the hydrologically critical winter season across the Western United States. Results show that EPR values are of a greater magnitude during the second half of the historical record than during the first half, indicating increased volatility in extreme winter-to-winter precipitation. Historically, the direction of reversals (wet-to-dry or dry-to-wet) corresponds to a similar reversal in the nature of the El Nino-Southern Oscillation (ENSO) phenomenon, although EPRs are not systematically aligned with extreme ENSO reversals. While a greater frequency and intensity of winter season EPRs in recent years is potentially problematic for water managers, the relationship with ENSO may afford proactive management and mitigation of the impacts.