Assessing the Impact of the El Nino Southern Oscillation Phenomenon upon Extreme Weather/Climate Events at the Local and Regional Level Across the Contiguous United States

摘要

Aim Increasing body of literature suggests that some characteristics of extreme events (e.g., frequency, duration, and intensity) are affected by a changing climate. Large-scale weather phenomenon, such as the El Nino Southern Oscillation (ENSO), is known to affect weather events at regional and local level, globally. No studies to date have investigated how ENSO may modulate the frequency of extreme heat and precipitation events at a local level. In this study, we utilized a historical weather/climate dataset to provide quantitative estimates on how ENSO has influenced extreme heat and precipitation events at the local and regional level across the contiguous United States. This information is of particular importance for understanding the impact and risk of these events on human health, for preparedness, recovery, and long-term adaptation measures. Methods We used a 30-year baseline (1960-1989) dataset to derive extreme heat and precipitation events for counties within the contiguous U.S. from 1960 to 2010. We obtained information regarding the phases of ENSO (El Nino, La Nina, and Neutral condition) from the National Weather Service Climate Prediction Center. Stratifying across the ENSO phases, we computed descriptive statistics of the spatial (Census division) and temporal (seasonal, inter-annual, as well as longer time periods) characteristics of extreme heat and precipitation events. We also determined the difference of extreme heat and precipitation events for the three phases of ENSO for each climate region within the U.S. Results We found the Northwest, Upper Midwest, Central, and Northeast climate regions of the U.S. to have less extreme precipitation events during El Nino, relative to the ENSO Neutral phase. In contrast, the West, Southwest, Southeast, and South climate regions showed more extreme precipitation events during El Nino relative to the ENSO Neutral phase. During La Nina events, the Northwest, Central Northwest, and Upper Midwest climate regions showed more extreme precipitation during La Nina relative to the ENSO Neutral phase. However, the West, Southwest, South, Southeast, and Northeast climate regions showed less extreme precipitations events during La Nina in comparison to the ENSO Neutral phase. ENSO's impact upon extreme heat events also varied considerably by climate region. Conclusion Our study demonstrates that the frequency of extreme weather events varies considerably during ENSO phases, which has a strong but uneven influence on weather across the globe. Studies investigating the link between climate change and mitigation/adaptation measures, including those focused on assessing impact to human health, need to account for this phenomenon.