Spatial modelling of the impact of climate variability on the annual soil moisture regime in a mechanized Mediterranean vineyard

Some vineyard areas located in NE Spain are undergoing important land transformations to adapt fields to mechanisation. In addition to the high variability of the Mediterranean climate and the characteristics of Mediterranean precipitation, which in many cases affect water availability for drylands crops, those land transformations are also affecting the water balance and may be accelerating soil degradation processes. This study evaluates the effect of different rainfall quantities and temporal distribution patterns on soil hydrological processes and water balance in highly mechanized vineyards in which important soil movements were carried out before planting. The simplified two-dimensional version of the PATTERN SVAT-growth model (PATTERNlight) is used here to simulate the field-scale water balance in order to understand the hydrological implications of the soil physical conditions generated by mechanical soil re-distribution within the field. The great variability of the rainfall in the Mediterranean causes significant differences in soil moisture and recharge under vine culture. Furthermore, the different soil thicknesses produced by mechanized soil movement generate irregular distributions of soil moisture conditions and thus crop water availability within the fields. In shallow soils, saturation occurs quickly during events and the soil often dries completely between them, whilst deeper soils show a less variable moisture behaviour. Runoff production is higher on shallow soils and this produces a positive feedback of increased soil loss and thus progressively decreased plant water availability.