Why was the Paraná flood of 2016 weaker than that of 1998

Although the 2015-2016 El Nino was expected to cause a severe Parana River flood similar to that associated with the 1997-1998 El Nino, the Parana flood of 2016 was considerably weaker than that of 1998. Here we explain this by analysing Parana discharge data (1904-2017) to assess the contributions of discharge cycles with different frequencies and with different associated climate modes to the formation of the 1998 and 2016 floods. We found that the 2016 flood was relatively weak mainly because the following Parana discharge cycles contributed less to form the 2016 flood than to form the 1998 flood: (a) a 3-5-year cycle linked to El Nino/Southern Oscillation (ENSO), (b) a 9-year cycle related to the North Atlantic Oscillation (NAO), and (c) a 31-85-year cycle associated with the Interdecadal Pacific Oscillation (IPO). This finding suggests that, besides ENSO, two other climate modes (NAO and IPO) may have acted to weaken the 2016 flood.