Characterizing the exceptional 2014 drought event in Sao Paulo by drought period length

摘要

In the last decade, the southeast region of Brazil has been suffering severe water shortages. Here, we propose to compute the expected drought period length to characterize the drought events in the region of So Paulo. We report the unique properties of the exceptional drought event during the austral summer 2014 by showing the differences 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 deficit 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 seasons considered, with much larger magnitude in 2014. (2) The much faster increasing trend of the anomalous sea surface temperature acts as a strong feedback which intensified the extreme climate conditions. The unprecedented increasing trend of the SST in 2014 was not observed in other climate variables representing a high pressure center. Therefore, we conclude that the exceptional drought 2014 was enhanced by the feedback mechanism of anomalous warming of SST in the South Atlantic Oceans, which was resulted from the anomalous high pressure.