Climatology of the annual maximum daily precipitation in the La Plata Basin

Abstract

Important features of extreme precipitation in the La Plata Basin are studied on daily, seasonal, and annual time scales, using information from 1861 to 2005 and a common period from 1959 to 1998. A relation between the daily precipitation annual maximum and different time scales is developed. The points that make up part of the association field, the location of the maximum annual frequencies, the maximum annual precipitation totals, and the years in which they occur in the basin region are also presented. Owing to the increase in precipitation documented in the region during the last decades of the twentieth century, this work will attempt to estimate the trends during the time periods studied in each of the basin stations prior to analysing the trend estimators calculated for different periods. Conditioning over the physical inference of the trends is related to the previous estimation results. Indeed, trend estimators may identify a long wavelength with a small amplitude at a physical level or the presence of waves during the calculation period with wavelengths longer than the period itself. Due to the fluctuations present in the selection of the daily precipitation maximum, the three annual maxima and the mean of the three absolute maxima for each year are analysed. This procedure is sound, whereby the frequency distribution models are the same for the individual maxima as well as for the mean values. The most suitable models for the adjustmentof extreme precipitation events in the basin are the GEV and Gamma distributions.