A FROST REGIME MICROCLIMATOLOGICAL STUDY IN SOUTHERN ARGENTINA (AÑELO, PROVINCE OF NEUQUÉN)

Frosts constitute a main hazard for most of the Argentine olive growing area. As a component of a feasibility assessment, financed by the Argentine Federal Investment Council (CFI) to introduce olive growing in southern Argentina (Neuquén), a microclimatological study of the frost regime in 3760 ha was conducted. The field occupies a band, with moderate gradient, which runs between the limit of the Patagonian plateau and the Neuquén River that flows in the lower part of a narrow valley, thus allowing cold air to drain, mitigating frost intensity. To evaluate frost hazard, a meteorological automatic station with capacity to transmit data, and 30 registering temperature sensors were installed, making observations from March to November 2010. Those registers were correlated with data from two neighbor climate stations, reconstructing the local series for the 2001-2010 decade. Those reconstructed data were introduced in a model developed taking as a basis the NCEP (National Centers for Environmental Prediction of NOAA) Climate Forecast System Reanalysis a downscaling process was carried on, for a 2.5 by 2.5 m grid, covering the area in study to a high degree of resolution. Maps of mean value, beginning, end and duration of the annual periods with temperatures equal or less than 0, -1, -3, -7, -10 and -12°C, were elaborated. For all thermal levels, it was observed that the lower portions of the fields are prone to suffer longer lasting and more intense frosts, making evident the importance of two main microclimate factors: (a) upper portion of the area, higher wind speed, impedes air stratification avoiding the thermal inversion necessary for radiation frost development; and (b) lower portions of the field, cold air drainage ads to thermal loss increasing cooling. Those criteria allowed dividing the field in sub-areas with different levels of frost hazard.