Atmospheric and Oceanic Patterns Associated with Extreme Drought Events over the Parana Hydrographic Region, Brazil

The Parana Hydrographic Region (PHR) is one of the main hydrographic basins in Brazil, standing out for its energy generation and consumption, among other ecosystem services. Thus, it is important to identify hydrological drought events and the driest periods inside of these droughts to understand the anomalous atmospheric circulation patterns associated with them (a multiscale study). This study used the standardized precipitation index (SPI) for the 12-month scale to identify hydrological drought episodes in the PHR from 1979 to 2021. For these episodes, the severity, duration, intensity, and peak were obtained, and the SPI-6 was applied to the longest and most severe drought to identify periods with dry conditions during the wet season. Anomalous atmospheric and oceanic patterns associated with such episodes were also analyzed. The results reveal that the longest and most severe hydrological drought on the PHR started in 2016. The end of this episode was not identified by the end of the analyzed period. The SPI-6 revealed three rainy seasons during this drought event marked by anomalous dry conditions: 2016/2017, 2019/2020, and 2020/2021. In general, the circulation patterns identified differ in each period, for example, in 2016/2017, an El Nino event was dominant, in 2019/2020, the tropical Pacific Ocean showed neutral conditions, and in 2020/2021, a La Nina episode was registered. Despite that, in the three periods, the anomalous atmospheric patterns contributed to the weakening of the low-level jet east of the Andes and, consequently, to the decreasing of the moisture transport to the PHR, then leading to dry conditions over the basin.