ORIGINAL PAPER Precipitation diagnostics of an exceptionally dry event in São Paulo, Brazil Caio A. S. Coelho 1 & Denis H. F. Cardoso 1 & Mári A. F. Firpo 1 Received: 15 January 2015 /Accepted: 19 June 2015 # Springer-Verlag Wien 2015 Abstract The State of São Paulo in Brazil experienced in 2014 and early 2015 an expressive precipitation deficit, lead- ing to drought conditions with impacts in water availability for public consumption, hydropower generation, and agriculture, particularly during austral summer. This study performs a de- tailed diagnostics of the observed precipitation during 2014 and early 2015 over a particular region of São Paulo State, which includes the massively populated metropolitan region of São Paulo. The diagnostic was designed to provide answers to a number of relevant questions for the activities, decisions, and strategic planning of several sectors (e.g., general public, media, and high-level governments). Examples of questions such diagnostics can help answer are: How much precipitation has the region received? Has the region experienced drought conditions in the past? When have similar drought conditions been observed in the past? What has been the observed pre- cipitation pattern in the last years? How severe/rare were the 2014 and 2015 droughts? When does the rainy season typ- ically start/end in the region? What happened during the 2013/2014 and 2014/2015 rainy seasons? The performed diagnostics based on historical 1961/1962–2014/2015 re- cords revealed that the 2013/2014 austral summer was a very rare event classified as exceptionally dry. Similar drought events were previously recorded but with smaller magnitude in terms of precipitation deficits, making the 2013/2014 drought event the driest on the examined record. In fact, the region has been experiencing a precipitation deficit pattern since 1999/2000. One of the contributing factors for the expressive precipitation deficit in 2014 was the abnormally early end of the 2013/2014 rainy season in the region. 1 Introduction The State of São Paulo in Brazil suffered a major drought in 2014 and early 2015, leading to a number of impacts in several socioeconomic sectors. Reservoirs around the metropolitan region of São Paulo, the largest city in Latin America, with a population of around 20 million people, reached unprecedent- ed low levels. The largest reservoir (Cantareira), which nor- mally supplies most of São Paulo’s population, reached in January 2015 the level of just 5 % of storage capacity. This situation led the local government to install a pumping system capable of extracting water from deep reservoir levels never reached in the past for mitigating the water deficit for human consumption (Porto et al. 2014). The established water crisis had impacts not only in water availability for public consump- tion, but also for agricultural production and hydropower gen- eration. Given the impacts generated by this major drought event, this paper aims to perform a diagnostics of the observed precipitation conditions over a particular region of São Paulo State. This region is defined by the continental area between 22.5° S, 25° S, 47.5° W, 45° W, as illustrated by the squares in Fig. 1, and includes the metropolitan region of São Paulo. Precipitation variability over São Paulo and southeastern South America has been documented in a number of studies (Kousky 1988; Liebmann et al. 2001; Carvalho et al. 2002, 2004; Dufek and Ambrizzi 2008; Sugahara et al. 2009; Silva Dias et al. 2013). The wet season in this region is influenced by the South American monsoon system (Vera et al. 2006; * Caio A. S. Coelho caio.coelho@cptec.inpe.br 1 Centro de Previsão de Tempo e Estudos Climáticos (CPTEC), Instituto Nacional de Pesquisas Espaciais (INPE), Brazil, Rodovia Presidente Dutra, km 40, SP-RJ, Cachoeira Paulista, SP 12630-000, Brazil Theor Appl Climatol DOI 10.1007/s00704-015-1540-9