ENSO EVENTS , RAINFALL VARIABILITY AND THE POTENTIAL OF SOI FOR THE SEASONAL PRECIPITATION PREDICTIONS IN THE SOUTH OF CORDOBA-ARGENTINA

Weather conditions and soil moisture along the coming crop season are common and persistent questions of the farmer throughout the year. Uncertainties about the future weather promote a high demand of weather information at the time close to planting, to define the best cultural practices and sustainable combinations for their agricultural production systems (Rivarola et al., 2002) Climate change and climate variability are more evident every day through the changing in the weather variables and also in the responses of the biological systems. The inter-annual variability of the precipitations poses the main restriction to any farm size or farming system and increases the risk associated to the agricultural decisions. In the agricultural areas of Argentina and particularly in the south of the province of Cordoba, climate variability has become a very significant feature of the farming system. During the cropping season of the summer crops (September-March), corn, soybean, and peanut are the main options in this region. These crops are sensitive not only to the availability of water at planting but also during crop development (December to February), when the water demand is normally the highest of the season (Seiler et al., 1995). El Niño is one part of a multi-year cycle of the coupled ocean-atmosphere interaction in the tropical Pacific, called El Niño-Southern Oscillation (ENSO) (WMO, 1995) and it has been recognized as one of the controls of the precipitation variability. The ENSO phenomenon involves two extremes phases: a warmer (El Niño) and cold (La Niña) ocean events, that affect atmospheric circulation, disturbing normal pattern of air pressure, tropical rainfall, and winds, leading to changes in the weather around the globe (Ropelewski and Halpert, 1989; NOAA, 1997). Years that do not fall in these extreme phases are referred as Neutral. In the main agricultural area of Argentina warm ENSO events were associated with enhanced likelihood of higher than the median precipitation anomalies during October-February, while lower than the normal precipitation during the same period was typical of cold ENSO events (Messina, et al. 1999; Ropelewski and Halpert, 1989). Seiler and Kogan (2002) working with NOAA-AVHRR indices found significant responses of crops and vegetation to El Niño and La Niña years. Although strong ENSO related precipitation signal over central-eastern Argentina was found for November-January precipitation (Ropelewski and Halpert, 1989; Podesta et al., 1999), Ropelewski and Halpert, (1996) and Tanco and Berri (1996) found the association between rainfall anomalies and the cold phase stronger than for warm events in the region. In the west of that region and particularly in the south of Cordoba little is known about the magnitude of the ENSO signal where precipitation occurrences may be also affected by local factors and processes. This study attempts to quantify the regional signal of the ENSO phases in the rainfall anomalies and its potential for the application in seasonal climate forecasts in agriculture.