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Title: Are extreme rainfalls in northeastern USA becoming more frequent, or bigger, or both? Authors:  Holger Rootzen - Chalmers (Sweden) [presenting]
Helga Olafsdottir - Chalmers (Sweden)
David Bolin - Chalmers (Sweden)
Abstract: Records may become more extreme because the underlying distribution changes, or because one makes more tries, or both. We use NOAA data from 17 stations to study large rainstorms in northeastern USA. The stations were selected because they show an increasing trend in annual maxima. These trends did not appear in some nearby stations. Data on individual rainstorms provide the most direct path to understanding the development of rainstorms. However, annual maxima data are more widely available, and often of higher quality. We hence use both kinds of data, together with the close relation between the PoT method with generalized Pareto distributed excesses and the annual maxima method with the generalized extreme value distribution. This relation is closely related to Langbeins formula, which is widely used in hydrology to connect partial duration series with annual maxima. A (very) preliminary answer is that rainstorms are becoming more frequent, but that the distribution of the total amount of rain in individual rainstorm is not changed.