Annual maximum and peaks-over-threshold analyses of daily rainfall accumulations for Austria

Abstract

[1] Daily rainfall data from 31 rain gauges in Austria with a record of at least 50 years are used to perform annual maximum and peaks-over-threshold analyses to address question concerning: (1) temporal nonstationarities in extreme rainfall; (2) dependence of extreme rainfall on elevation; (3) changes in the frequency, duration, and accumulation of extreme rainfall; and (4) relation between the occurrence of extreme rainfall and the North Atlantic Oscillation (NAO). Nonparametric tests are used to check for the presence of abrupt and slowly varying changes in annual maximum daily rainfall. The Pettitt test is used to detect change-points in the mean and variance of the quantity of interest, while Mann-Kendall and Spearman tests are used to detect monotonically increasing or decreasing patterns. Annual maximum daily rainfall from these 31 Austrian rain gauges provides limited evidence of the violation of the stationarity assumption, and we cannot make conclusive statements about the presence of a possible climate change signal. The parameters of the Generalized Extreme Value (GEV) distribution are used to examine the dependence of extreme rainfall on elevation. The results of this study do not suggest a strong relation between elevation and the GEV parameters. Changes over time in the frequency, duration, and intensity of extreme rainfall days, defined as days exceeding the 95th, 99th, and 99.5th percentiles, are tested using monotonic trend tests and change-point tests. There is little evidence of changes in these quantities. By modeling the frequency of extreme rainfall days in terms of the NAO with a Poisson regression model, we found that NAO is a more significant predictor of the occurrence of extreme rainfall days in western Austria.