Abstract: For environmental and economic conditions, precipitation can be considered as the most important climatic element. its drought and wet periods are known to change the natural water suply, river discharges and crops yields, as well as natural vegetation. Argentine agriculture was and surely will drive the national economy and the most important agriculture region is the Pampa or pampean flatlands, mainly because it allows the rain - fed crops production. The grain production increased from 23 to 90 million tones during the period 1970 - 2010 by means of the best available technology application and this growth had two components: a) the soybean which has now a ratio of 6 to 1 with respect to corn and b) the increase of precipitation amounts during the last decades of XX century. There is a need to maintain agricultural sustainability and for that changes in production patterns would be considered. On the other hand, the pampean flatlands experienced a succession of extreme hydrological events related to precipitation. Droughts and floods were a constant, according ancient documents during the Spanish domain, the argentine goverment and the installation of meteorological stations near 1870. Documented droughts occurred during 1604, 1614, 1620 and 1824 and floods in 1636, 1770, 1817, 1857 and 1900 can be mentioned as examples. The climate of the studied region according Thornthwaite classification is Perhumid, Humid and Subhumid from East to West, with fluctuations in their limits answering climate variability. And so, the agriculture was influenced. The surface of croplands is greater in the Perhumid and Humid climates regions then in the last one, where livestock is important. Subhumid region has suffered important changes in its land uses and surely, it will be vulnerable in the future. In this paper the three zones are studied using meteorological data, soil water balance and crops data. More recently there were important floods in 1980, 1985, 1993, 2001 and 2002 and severe droughts in 1978, 1983, 1989, 1995 and 2008. Extreme hydrological events acted in short periods but the losses reached high importance because precipitation variability acts over the soil water balance influencing its parameters and the water table depth.