Agradecimentos: This work was supported by: FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo), Grant Numbers 08/58161-1, 15/11035-5 and 14/50848-9; INCT (Institutos Nacionais de Ciência e Tecnologia), Fase-2 INCT-MC 2, Grant 465501/2014-1; CAPES (Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) Grant 88887.136402-00INCT; RED-CLIMA (Red Española e Iberoamericana sobre Variabilidad Climática y Servicios Climáticos en Ecosistemas Terrestres y Marinos): RED-CLIMA Project, Grant INCCLO0023, from the Consejo Superior de Investigaciones Científicas LINCGLOBAL CSIC, Spain Ver menos

Abstract: The study assessed changes in rainfall variability and the frequency of extreme events (very wet and very dry) in the state of S ?o Paulo, Brazil, for a 40-year period that divided into two sub-groups: 1973-1992 (P1) and 1993-2012 (P2). Data of 79 rain gauge stations were selected to represent the different climatic and geomorphological domains of the state. The annual pattern was evaluated through the scale and the shape parameters of the gamma distribution and the 95th and the 5th percentiles thresholds, the latter also employed to evaluate the seasonal spatial patterns (rainy season, Oct.-Mar. and sub-humid to dry season, Apr.-Sep.). Results showed that the average precipitation was similar in P1 and P2, but S ?o Paulo evolved to a pattern of increased irregularity in the rainfall distribution, with a rise of approximately 10% in the number of extremes between 1973 and 2012, especially in the very dry occurrences, and in the north and west of the state, which are the least rainy regions. Moreover, while 55% of the evaluated rain gauges recorded more extreme wet episodes in P2, 76% registered more dry extreme episodes in the same period. Some very dry or very wet events recorded after the 40-year period evaluated were discussed in terms of the associated weather patterns and their impacts on society and attested to the validity of the results found in the quantitative assessment. The qualitative analysis indicates that if the trends of more irregular distribution of rain and increase in extreme events persist, as pointed out by the gamma and percentile analyses, they would continue to bring serious effects on the natural and social systems in the state, which is the most populous and has the strongest and most diversified economy in Brazil Ver menos