Irrigation management or climate change ? Which is more important to cope with water shortage in the production of table grape in a Mediterranean context

Table grape production requires large amount of water, which can be problematic in semi-arid Mediterranean regions, where climate change projections anticipated reductions in water availability associated to decreases in precipitation and increases in temperature. In this context, this study aims to evaluate the effect of contrasting irrigation strategies and climate change scenarios on key water balance variables using a Chilean Table grape crop as case study. A standard and an improved irrigation management treatments were implemented in situ during the 2015/2016 and the 2016/2017–2017/2018 observed growing seasons, respectively. Then, the HYDRUS-1D water transfer model was run to simulate the three observed growing seasons and 27 near future growing seasons (2019/2020–2044/2015) under climate change conditions. Satisfactory calibration and validation results against soil moisture and water storage measurements were obtained within the first and the second observed growing seasons respectively (RRMSE values below 5%). Results during the observed seasons showed that by changing the standard irrigation by the improved irrigation management, the water use efficiency (WUEi) increases from 49.5% to 55.7%. For the near future, the calibrated model shows that under all the tested climate change scenarios, irrigation strategies based on supplying 80% and 50% of the crop evapotranspiration (ETc) (deficit irrigation scenarios) have larger efficiencies compared to the standard irrigation management (presenting a higher actual basal crop coefficient and lower percolation). Similar results were obtained under future extreme climate change years, defined as the ratio between model-based projections of reference evapotranspiration (ET0) and precipitation, with the deficit irrigation scenarios having larger efficiencies than the standard irrigation management. Based on these results, it is concluded that by mid- century, the irrigation management has more relevance than climate change impacts for tables grapes growing under a Mediterranean climate in central Chile.