Vol.:(0123456789) 1 3 Clim Dyn (2018) 51:433–442 DOI 10.1007/s00382-017-3932-2 Characterizing the exceptional 2014 drought event in São Paulo by drought period length Yong Zou 1  · Elbert E. N. Macau 2  · Gilvan Sampaio 3  · Antônio M. T. Ramos 2  · Jürgen Kurths 4,5,6   Received: 5 March 2017 / Accepted: 21 September 2017 / Published online: 30 September 2017 © Springer-Verlag GmbH Germany 2017 the extreme climate conditions. The unprecedented increas- ing trend of the SST in 2014 was not observed in other cli- mate variables representing a high pressure center. There- fore, we conclude that the exceptional drought 2014 was enhanced by the feedback mechanism of anomalous warm- ing of SST in the South Atlantic Oceans, which was resulted from the anomalous high pressure. Keywords Drought period length · Precipitation · Southeast Brazil · Sea surface temperature · Sea level pressure · South Atlantic ocean 1 Introduction Water availability is crucial for the São Paulo area since this region is the most populated area in Brazil and around 61% of Brazil’s electricity is currently produced by hydro- power plants according to the Brazilian Electricity Regula- tory Agency (http://www2.aneel.gov.br/aplicacoes/capaci- dadebrasil/OperacaoCapacidadeBrasil.cfm). Drought events caused a number of impacts on water availability for con- sumption, agricultural irrigation and hydropower produc- tion. As it has been reported in the literature (Coelho et al. 2016b), starting from 1998 till the early 2015, the southeast region of Brazil was predominated by a precipitation defcit in the austral summers. The entire austral summer of 2014 experienced the largest negative precipitation anomaly of -249.7 mm with respect to the 1981–2010 climatologi- cal mean value for the southeast Brazil region (574.3 mm) (Coelho et al. 2016a, b). Due to the defcit rainy season accompanied by record high temperatures and subsequent increase in water demand by the large population in this region, the largest reservoir system Cantareira reached the unprecedented lowest levels in early 2015 since 1951 (Nobre Abstract In the last decade, the southeast region of Brazil has been sufering severe water shortages. Here, we propose to compute the expected drought period length to charac- terize the drought events in the region of São Paulo. We report the unique properties of the exceptional drought event during the austral summer 2014 by showing the diferences and similarities to the very dry season in 2001 and the mild dry seasons in 2006 and 2015. Furthermore, we investigate the correlations of the abnormal precipitation defcit with the ocean and atmospheric patterns. In comparison to other drought events, we validate the hypothetical mechanism that underlies the exceptional drought 2014: (1) The existence of an anomalous high pressure center in the area acts as a blocking mechanism that prevents moisture transport from the Amazon and passage of cold front systems from south Brazil. This blocking high has been observed in all dry sea- sons considered, with much larger magnitude in 2014. (2) The much faster increasing trend of the anomalous sea sur- face temperature acts as a strong feedback which intensifed * Yong Zou yzou@phy.ecnu.edu.cn 1 Department of Physics, East China Normal University, Shanghai 200062, China 2 Instituto Nacional de Pesquisas Espaciais, São José dos Campos, São Paulo, Brazil 3 Instituto Nacional de Pesquisas Espaciais, Cachoeira Paulista, São Paulo, Brazil 4 Potsdam Institute for Climate Impact Research, 60 12 03, 14412 Potsdam, Germany 5 Department of Physics, Humboldt University Berlin, Newtonstraße 15, 12489 Berlin, Germany 6 Institute for Complex Systems and Mathematical Biology, University of Aberdeen, Aberdeen AB243UE, UK