Do the recent severe droughts in the Amazonia have the same period of length?

In Amazonia there remains the largest contiguous tropical forest of the planet. The vegetation, including its deep root system, is efficient in recycling water vapor, which is an important mechanism for the forests maintenance and helps to maintain evergreen canopies during dry seasons (Nepstad et al. 1994; Cox et al. 2008), demonstrating the adaptation of Amazon forest species to seasonal drought (Davidson et al. 2012). However, multi-year or extreme droughts can affect this adaptation to seasonal drought and eventually leading to mortality when roots are unable to extract enough soil water during multi-year droughts (Fisher et al. 2006; Davidson et al. 2012). Understanding drought events in Amazonia has fundamental importance especially because the droughts may result in increased length of the dry season and become more frequent during this century as a result of anthropogenic climate change (Salazar et al. 2007; Saatchi et al. 2013; Phillips et al. 2009). The sea surface temperature (SST) variabilities in both the tropical Pacific and Atlantic Oceans play important roles in forming the climate conditions in the inter-annual rainfall variations over the Amazon (Aceituno 1988; Marengo 1992; Ronchail et al. 2002). Rainfall reductions and droughts in Amazonia have been associated with El Niño Southern Oscillation (ENSO) events, or with Abstract We propose a new measure based on drought period length to assess the temporal difference between the recent two severe droughts of 2005 and 2010 in the Amazonia. The sensitivity of the measure is demonstrated by disclosing the distinct spatial responding mechanisms of the Northeastern and Southwestern Amazon (NA, SA) to the surrounding sea surface temperature (SST) variabilities. The Pacific and Atlantic oceans have different roles on the precipitation patterns in Amazonia. More specifically, the very dry periods in the NA are influenced by El Niño events, while the very dry periods in the SA are affected by the anomalously warming of the SST in the North Atlantic. Our analysis discloses convincingly that the drought 2005 hit SA, which is correlated to the North Atlantic only. Furthermore, it suggests that there are two phases in the drought 2010: (1) it was started in the NA in August 2009