Soil moisture is an essential variable for both the agricultural production and the functioning of natural ecosystems, as well as one of the main variables regulating the climate system. Like precipitation, soil moisture has a marked annual cycle that depends mainly on the behaviour of precipitation and evapotranspiration. In this study, we developed a methodology that allows describing and characterizing the annual cycle of soil moisture in Argentina. For this purpose, we estimated soil moisture at 121 sites of Argentina by means of a simple hydrological balance (the BHOA, an acronym for its name in Spanish: "Balance Hidrológico Operativo para el Agro") and analysed its intra-annual variability by means of different indices. This methodology allowed recognizing five different annual behaviours, with a consistent geographical pattern throughout Argentina. The characterization was based mainly on the time of occurrence of the annual maximum and minimum values of soil moisture, and secondly by the annual soil moisture content and seasonality. The northwest and part of the centre of Argentina present the minimum soil moisture values in spring and the maximum ones in autumn, while the east and south present the minimum values in summer and the maximum ones in winter. In general, sites with higher soil water content were found to have lower seasonality and vice-versa.

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Abstract. Surface soil moisture (SSM) dry-downs have been employed to compare independent data sources on the dynamics of water in soils, including such remote sensing, land surface models and in-situ measurements, which are often difficult to contrast with standard methodologies. The soil drying approach summarizes the soil response to climate as well as surface conditions during a dry period. In this work it is estimated as the SSM e-folding decay, named as dry-down time scale. This is the first assessment over eastern Cordoba, Argentina, a region with a very high cultivated land fraction that was subject of important agricultural changes in the last decades. SMOS SSM product (derived from microwave measurements at L band) is validated with in-situ SSM measurements provided by the National Commission for Space Activities during 2012–2018. Both products agree in showing that the austral spring season has the largest number of dry-down events for the whole period. The dry-down time scale sensitivity to the chosen detection method as well as the data sampling frequency is larger in summer than in spring. A faster soil drying in SMOS than in In-situ SSM is found, likely as a consequence of the shallower sensing depth of the first. This dependency seems to be more important than the temporal sampling frequency in the SSM data.