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The objective of this paper is to analyse the impact of temperature increases and irregular rainfall distribution, associated with climate change, on water availability for rainfed vineyards cultivated in a Mediterranean climate area. The study includes the analysis of the interrelations between precipitation distribution, temperature, evapotranspiration and runoff rates, and the resulting water storage in vineyards soils of the Penedès region (NE Spain). A hierarchical cluster analysis was applied to classify the years according to water availability. The influence of water stored into the soil on yield for some one of the main vine varieties cultivated in the area is analysed. A vineyard, representative of the land management practices in this area, was selected for soil moisture monitoring and runoff evaluations, as well as for grape yield, which was compared with yields recorded in other plots.
According to rainfall distribution and water availability, the 12 analysed years represent five different situations: wet years with positive and negative water balance; dry years; years with average annual rainfall but irregularly distributed throughout the year leading to a negative water balance; and extreme situations. Significant water deficits were observed in years in which total rainfall amount was above the annual average in the area, being similar to those observed in dry years: in 8 of the 12 analysed years deficits higher than 100 mm (up to 309 mm) during the growing period (budbreak�harvest) were recorded. At annual scale, 42% of the analysed years recorded deficits ranging between 27.7 and 191.4 mm. In the driest years, and those with more irregular rainfall distribution, soil moisture contents below the wilting point were reached. The high intensity rainfalls, producing important runoff losses (in many cases out of the periods in which crop water needs are higher), together with the increasing temperature trends, which give rise to significant evapotranspiration increases (values up to 32% higher than the average were recorded during the study period), are the main responsible factors for the water deficits recorded during grape development. Winegrape yield was influenced by the water stored into the soil, bloom�veraison or during budbreak�bloom depending on the variety
