Historical and future trends in evapotranspiration components and irrigation requirement of winegrapes

Background and Aims: An understanding of the dynamics of the components of evapotranspiration and irrigation requirements in response to climate variation and change is essential to manage vineyards sustainably. 

Methods and Results: Winegrape evapotranspiration (ET_{C adj}), seasonal transpiration (T_{p adj}), soil evaporation (E_s) and irrigation requirement (I) were evaluated with the FAO-56 dual-crop coefficient, across a range of soil types, in response to historical (1970–2017) and future (2018–2050, Representative Concentration Pathway 4.5) climate projections. The Mann–Kendell non-parametric test and Sen's slope were used to detect any trends regarding historical and future climate. A statistically significant increasing trend was observed in the annual ET_{C adj}, T_{p adj} and I under both climate scenarios, and E_s showed a significant negative trend for the historical projection. Average daily ET_{C adj} ranged from 1.2 to 4.3 mm under historical climate and increased to 1.5–4.6 mm under the future climate projection. Estimated I was 240–528 mm depending on the soil type and rainfall during the growing season, with the largest increase in irrigation predicted during October and November. 

Conclusions: The increase in irrigation requirements was within half a standard deviation of historic values, and the largest increase did not coincide with the months of maximum demand. 

Significance of the Study: The predicted increase in irrigation requirements is likely to be within the adaptive capacity of the existing infrastructure and growing systems but will need ongoing monitoring as climate projections are revised.