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ABSTRACT: The present work aims to assess the likely effects of climate change on the length of growing period (LGP) of crops in Marina Baixa (SE, Spain). LGP can be assessed by a balance between preci- pitation and reference evapotranspiration. Less rainfall and an increased evapotranspiration, forecast by Global Climate Models (GCMs), are considered as a high risk for agriculture. This area is located in a semiarid climate region where water is a very limited resource. It is a typical example of areas where the agricultural sector has to compete for water with the tourism industry. In this context, by using observed and projected precipitation data set (model HadCM3, Scenario A2), calculating reference evapotranspiration (ETo), and applying the frequency analysis of a probability-type method, we estimated the growing period length in the observed period (1961-1990) and three 30-year future periods (2011-40, 2041-70 and 2071-99) in the study area. The results show a drop in annual precipitations (ᆲ%) and an increased ETo (+18%) towards the end of this century with respect to the observed period (mean annual rainfall: 356 mm; mean ETo: 1476 mm). The results also show a decrease in the number of decades (10 days) when precipitation exceeds half of the ETo, which means shorter growing periods as the 21st century advances. This expected reduction in growing period length towards the end of the present century will imply that many rainfed crops, like olives, almonds and cereals, will require a higher irrigation water supply to maintain suitable growth and performance levels. The results are an early warning to manage water resources in Marina Baixa in a sustainable way.