Long Term Rainfall Variability in Argentinean Buenos Aires Plain Region

GONZÁLEZ, MARCELA HEBE; ROLLA, ALFREDO

montevideo

Congreso; WCRP-Conference for Latin America and the Caribbean, developing, linking, and applying climate knowledge; 2014

wcrp

The Argentinean Buenos Aires plain region has a relevant biodiversity and it has experienced important changes in annual rainfall during the last century. It is a relevant region because a great part of the economic resources are generated by agricultural practices in this area. Data used were monthly-accumulated rainfall in 22 stations, with different record during the period 1950-2012. Annual precipitation low frequency variability was analyzed using a linear trend method of minimum squares, and statistics significance was tested using a T-Student test. Results depend on the region and seasons. Annual trends were positive in northern and eastern part of Buenos Aires meanwhile they were negative in western-southern and central area of the province. Other rainfall variabilities were analyzed to better understand its behavior in scales greater than a year. The dominant frequencies related with annual rainfall variability were identified through spectral analysis. The spectral analysis and its significance, depending on the spectrum adjusted a white or red noise model, were performed using the Blackman-Tukey method. This method was applied to series and a confidence level of 95% was used to detect significant peaks. When analyzing actual data, one would like to find the frequencies with the greatest spectraldensities, that is, the frequency regions, consisting of many adjacent frequencies that contribute most to the overall periodic behaviour of the series. This can be accomplished by smoothing the spectral values using a weighted moving average transformation. In this work a Hann window was used for that purpose. The annual cycle, with maximum in summer and a double relative peak in transition seasons (Autumn and Spring) is present all over the region and more pronounced towards the west. After filtering the annual cycle, a cycle of around 12 years was found in stations widely distributed all over Buenos Aires province and other of around 4 years was also present especially in northeastern region. A harmonic analysis was applied to annual rainfall series in order to isolate the individual waves present in rainfall series. The most important harmonics were used to reconstruct rainfall series in order to describe the mean behavior in different periods on each station.