Identifying the future water and salinity risks to irrigated viticulture in the Murray-Darling Basin, South Australia

Abstract

Water and water related salinity risks to viticulture were assessed by running the HYDRUS-1D model with 100 ensembles of downscaled daily meteorological data obtained from the Global Climate Model (GCM) for 2020–2099. The modeling output was evaluated for seasonal irrigation requirements of viticulture (Ir), root zone soil salinity at the beginning of the new season (ECswi), and the average seasonal salinity (ECsw) for all 100 realizations for four 20-year periods centred on 2030 (2020–2039), 2050 (2040–2059), 2070 (2060–2079), and 2090 (2080–2099). The model showed a 4.2% increase in the mean seasonal Ir of viticulture during 2020–2039 as compared to Ir of 350.9 mm during 2004–2015. Similarly, the mean seasonal Ir increased by 7.5, 10.9, and 16.9% during 2040–2059, 2060–2079, and 2080–2099, respectively, as compared to 2004–2015. These projections indicate that viticulture can face significant deficit conditions, which may have a drastic impact on the sustainability and productivity of the grapevine. Likewise, the average median ECswi increased by 40% during 2020–2039 as compared to the 2004–2015 mean ECswi value of 1.63 dS/m, but remained below the threshold (ECsw = 4.2 dS/m) for viticulture. The median seasonal ECswi almost doubled (3.15 dS/m) during 2040–2059, varied from 1.73–8.15 dS/m during 2060–2079, and increased more than three times during 2080–2099 to surpass the threshold salinity for grapevines. Similarly, the seasonal average root zone salinity (ECsw) showed a 47% increase during 2020–2039 over the baseline salinity. It continued increasing at a growing pace during 2040–2059 (1.5–8.64 dS/m) and 2060–2079 (2.78–9.52 dS/m), and increased to almost three times (6.04 dS/m) during 2080–2099 compared to the corresponding baseline salinity (1.97 dS/m). The continued presence of high salt concentrations in the root zone can significantly affect the growth, yield, and wine quality. The modeling results indicate that soil salinity at the beginning of the vine season and the average seasonal salinity are crucial factors that may need special management to sustain the viticulture in this region.