Water deficit in San Antonio Oeste, Argentina

Water balance components were calculated in San Antonio Oeste (SAO), Argentina. SAO is located in the North-West of Patagonia, in a semiarid zone of low agricultural productivity due to high annual deficit and the lack of surface drainage. The main aim of this study is to evaluate the deficit in SAO using methodologies adapted to local site conditions. For this, climatic water balances (normal and sequential) according to Thornthwaite and Matter (1955) were calculated based on data from SAO station pertaining to National Meteorological Service. An adequate method to estimate potential evapotranspiration was selected and calibrated through a comparison of four empirical methods and FAO Penman-Monteith. Soil conditions on the terrain were evaluated from texture and organic matter content of soil in three representative sites near the station SAO. The potential evapotranspiration method of Christiansen showed the highest correlation (r(2)=0.994) which mean relative error is 1.1 and 24.2 % in summer and winter, respectively. Interrelationships between precipitation and potential evapotranspiration under normal water balances showed a loss for all periods analyzed (1961-2000) of approximately 1170 mm year(-1). More than 80 % of the annual losses occur mainly from September to March. The period that showed the greatest deficit was between the years 1971 and 1980 (1258 mm year(-1)). In contrast, in the period 1981-1990 and 1991-2000 the values of deficit were slightly lower (approximate to 12 %). Methodological contributions and results should be considered in planning and management of irrigated, especially in an economic context of growing diversification.