SUMMER RAINFALL VARIABILITY IN THE ARGENTINEAN CHACO PLAIN

GONZÁLEZ, MARCELA HEBE; NUÑEZ, MARIO

mendoza

Congreso; congremet XI; 2012

The Argentinean Chaco plain region has a relevant biodiversity and it has experienced an important increase in annual rainfall during the last century. However, there is evidence that some rainfall decrease has happened in some sub-regions since 1980; such decrease could be related to deforestation carried out in order to increase the farming area. In this paper rainfall variability was analyzed to better understand its behavior in scales greater than a year. There are indicators of a cycle of 22 years in the west of Chaco and other of 6,6 years in the east. The annual cycle, with maximum in Summer, is present all over the region and more pronounced towards the west. The interannual rainfall variability shows that there are three main summer (from October to April) rainfall anomaly leading patterns, obtained using the principal component method. The first is associated with the sea surface temperature in the subtropical Atlantic Ocean, anomalies of low pressure in low levels in Southern Brazil and with the annular mode associated with the Southern Antarctic Oscillation. The second leading is related to El Niño-Southern Oscillation and a high pressure anomaly centered in central-southern Brazil and the third is associated with positive correlation in the west tropical and subtropical Pacific and with a wave train extended from the western Pacific Ocean towards South America. The results indicate that rainfall must be monitored in order to determine its future evolution and if deforestation has influenced the climate of the region. Likewise, the relation between climate and deforestation must be best studied in order to mitigate the negative impacts over the region. In order to describe a possible situation in the future some simulations are detailed. The regional model MM5 was nested within time slice global atmospheric model experiments conducted by the HadAM3H model. The simulations cover a 10-year period representing present-day climate (1981–1990) and two future scenarios for the SRESA2 and B2 emission scenarios for the period 2081–2090. Both the A2 and B2 simulations show a general increase in precipitation in northern and central Argentina especially in summer and fall and a general decrease in precipitation in winter and spring.