资源环境科技发展态势分析平台

In this study we have examined changes in frequency and intensity of extreme rainfall events for the state of Santa Catarina (SC) in southern Brazil during austral spring and summer. The results show that changes in El Nino-Southern Oscillation (ENSO) between 1979-1999 and 2000-2015 due to different phases of Interdecadal Pacific Oscillation have an impact on the teleconnection patterns from the Pacific to South America. As a consequence, precipitation over SC in the late period is less likely to be linked to ENSO. Moreover, there have been changes not only in the frequency and intensity of extreme events between the two periods but also in the mechanisms that cause the extremes affecting the spatial distribution of the extremes. In spring, the extreme events are less likely to occur during El Nino events and more frequent during La Nina and neutral years. The classical mechanism, of an enhanced South Atlantic Lower Level Jet (SALLJ) bringing moisture to SC, is no longer responsible for the extremes in the spring. The current main mechanism is associated with the presence of frontal systems during ENSO years and the presence of the South Atlantic Convergence Zone (SACZ) to the north combined with an anticyclonic system off the South American coast during neutral years. As a consequence the extreme events are currently more frequent at stations in the eastern side of SC. In summer during neutral years, SACZ events have become less frequent at the same time that atmospheric blocking events have become more frequent, explaining the decrease in extremes. On the other hand, SACZ events have become more frequent during La Nina years and so do the extremes in SC, with El Nino events playing a less important role.