STATISTICS OF EXTREME EVENTS AMS Probability and Statistics Committee January 11, 2009 WELCOME! AMS SHORT COURSE Outline Welcome Participants Introduction Introduction to the course topic Definitions Course structure overview Participants Introduction Please state: Your name Affiliation Work focus Expectation from the course Intro to the Course Topic Extreme events: the furthest or highest degree of something; far beyond a norm in quantity or amount or degree; the greatest possible degree or extent or intensity; the most distant in any direction (http://wordnet.princeton.edu/perl/webwn?s=extreme )http://wordnet.princeton.edu/perl/webwn?s=extreme In climatology, the highest and, in some cases, the lowest value of a climatic element observed during a given time interval or during a given month or season of that period (http://amsglossary.allenpress.com/glossary/ )climatologyclimatic elementseasonhttp://amsglossary.allenpress.com/glossary/ Statistics of extreme events: The systematic analysis of random phenomena (http://amsglossary.allenpress.com/glossary/ )analysisrandomhttp://amsglossary.allenpress.com/glossary/ Intro to the Course Topic Some Examples of Extreme Events in Meteorology, Climatology and Hydrology: ENSO events Hurricanes Tornadoes Climate Variability Extremes versus Climate Change Low River Flow Flood Drought A Threshold Definition: ENSO El Nio has tremen- dous effects on global climate and weather due to the eastward migration of the warm pool. How do we define El Nio? A Threshold Definition: ENSO El Nio: A phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the base period) in the Nio 3.4 region greater than or equal in magnitude to 0.5C, averaged over three consecutive months. La Nia: A phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface temperature departure from normal (for the base period) in the Nio 3.4 region greater than or equal in magnitude to 0.5C, averaged over three consecutive months. A Threshold Definition: ENSO Note: the standard deviation of this series is 0.83C and the threshold is 0.50C 1982/1983, 1997/1998 are extreme El Nino events 1988/99 is an extreme La Nina. Others? A Probabilistic Definition River flow recessions occur in May-Jul, and Oct Jan A Probabilistic Definition Low Flow statistics can include: Recession daily averages Minimal 30-day discharge 75% Probability of Exceedance (POE) Discharge Mean Median Mode Low flow Probabilistic & Threshold Definitions Drought Monitoring Categories: D0: Abnormally Dry D1: Moderate D2: Severe D3: Extreme D4: Exceptional Category Description Palmer SPI%tiles D0Abnormally Dry-1 to to D1Moderate Drought-2 to to D2Severe Drought-3 to to D3Extreme Drought-4 to to D4Exceptional Drought