Tuesday, 24 January 2012
Empirical Examination of the Changes in the Frequency of Extreme Rainfall in the Central United States
Hall E (New Orleans Convention Center )
Long records of daily rainfall accumulations from 311 rain gage stations over the central US (this area includes Iowa, Illinois, Indiana, Missouri, Kentucky, Tennessee, Arkansas, Louisiana, Alabama, and Mississippi) are used to assess possible changes in the frequency of extreme rainfall. Each station has a record of at least 50 years, and the data cover most of the twentieth century and the first decade of the twenty-first century. Analyses are performed using a Peaks-Over-Threshold approach, and, at each site, the 95th and 99th percentiles are used as threshold. Both abrupt and slowly varying changes in the frequency of extremes are considered. A Bayesian change-point test for count data is used to detect abrupt changes in the rate of occurrence of extreme rainfall. Because of the count nature of the data, the presence of slowly varying changes is assessed by means of a Poisson regression model, in which we examine whether the rate of occurrence parameter is a linear function of time (by means of a logarithmic link function). We will show results concerning the presence and nature (abrupt or slowly varying) of changes in the frequency of extreme rainfall over this area, and examine whether they are associated with human-induced climate change.