Conversely, the extremely dry region, which occupies most of the South-Central area at time scales

of 6 and 12 months, increases toward the north and decreases in the SW extreme at the low frequency scale of 18 months. The most vulnerable area to extraordinary extreme hydrological droughts, represented by the portion with SPI18 (t) < −2 (Fig. 9c), includes the North-Central zones of Entre Rios, Santa Fe and Córdoba, South Smad inhibitor of Santiago del Estero and SW of Corrientes provinces. The Southwestern corner shows average normal conditions during critical months of the study period, similar to the scale of 12 months (Fig. 9b). Most of the region, except for the northern portion above 28° S, shows a significant vulnerability to extreme dry events at intra-annual time scale, relevant for agriculture (Fig. 9a), with a large area experiencing extraordinary extreme droughts in critical months between 1901 and 2010. Our results showed

that low-frequency behavior of EPE in the NEA was differentiated into two distinct periods: a dry one between 1901 and 1960 and a wet one between 1970 and 2003. This behavior is associated with well-known find more long-term changes in precipitation starting in the 1950s and reported by several authors (e.g., Minetti and Vargas, 1998, Krepper and Sequeira, 1998 and Krepper and Garcia, 2004). The time series of SPI and wetness area coverage analyzed at different time scales, presents signs of stabilization and a trend reversal toward drier conditions since 2007. These results are consistent with those reported by Seager et al. (2010) for the whole SESA region. They argue that while the long-term trend toward wetter conditions in SESA was of great benefit to regional agriculture, there is no reason to expect this to continue since it seems to have been influenced by tropical SST anomalies associated with the AMO. This index is presumed to be shifting toward a positive phase (Ting et al., 2009) HSP90 that may force

a decrease in SESA precipitation in the coming years. This implications and the results presented in this paper presumably indicate that hydrological wet EPE of high intensity, duration and spatial extent noticed between 1970 and 2003 could decline in the coming years. Viglizzo and Frank (2006) described a large drought episode in the 1930s and 1940s denoted as the “Pampas Dust Bowl” in the Western Pampas of Argentina. In our paper, the behavior of SPI fields and the area covered by droughts showed a dry period in the center of the study region between about 1925 and 1940 and for the Northwest extreme between 1930 and 1950 that might extend the “Pampas Dust Bowl” to the bulk of the NEA. The 1930s drought appears within a hemispherical symmetric pattern of precipitation anomalies across the Americas with drought in both the northern and southern extratropics.