Extreme precipitations in Argentina

According to media reports, the frequency and intensity of extreme weather events seem to have increased in Argentina. However to arrive to clear conclusions good analytical procedures are needed to model behaviors and detect trends in of the extreme values. Therefore, extreme precipitations over Argentina were analyzed considering different thresholds and time duration of the events. Series of overlapping two-day precipitation were used to avoid loosing events that were spitted in two consecutive days. Since the 1970 decade, in the East and Centre of Argentina, increasing trends have been observed in the frequencies of these extreme precipitations. The number of cases of twoday precipitation bigger than 100 or 200 mm in the period 1983-2002 were about three times higher than those occurred in the period 1959-1978. There is much evidence that the probability distribution of daily precipitation is heavy tailed. The tail of the probability distribution is of special interest because extreme events characterized by high return periods can cause floods, especially if the conditions of the area do not facilitate the runoff or concentrate it in certain places. As an alternative to the block maxima method, it was used the Peak Over Threshold (POT) approach. The POT method is based on a statistical model, consisting of a Poisson process for the occurrence of an excess over a high threshold and a Generalized Pareto Distribution (GPD) for the excess over the threshold. The GPD is an asymptotic distribution which is fitted to the extreme upper tail of the data. To detect non-stationary processes due to long-term climate changes, the GPD is fitted with a linear trend. With the daily precipitation information of 45 meteorological stations of the Meteorological National Service (SMN), it was developed a statistical model to estimate long-term trends in the frequency and intensity in Argentina. Regional analyses were performed combining data from stations over regions were data from different stations present similar features. All the computations were carried out using the Extremes Toolkit (extRemes), which is an add-on package for the R system, a free and available via the internet language and environment for statistical computing and graphics. As results, there are no statistical significant trends in the intensity of extreme precipitation events. However, there are strong positive and significant trends in the frequencies of extreme precipitations. The last explains the increasing social and economic vulnerability to sudden floods that has been reported by the media.Pages: 1575-158