Using NDVI-derived vegetation vigour as a proxy for soil water content in Mediterranean-mountain traditional water management systems: Seasonal variability and restoration impacts

This study proposes to use the vegetation vigour, measured by the Normalized Difference Vegetation Index (NDVI), as a proxy of the soil water content in Mediterranean mountain traditional irrigation systems. The Sierra Nevada ditches network (southern Spain), has been used as a representative study case. Vegetation status in the influence area of the ditches has been analysed for the period 1984–2020 using TM, ETM+, and OLI Landsat imagery. In addition, the implications of the restoration, using traditional techniques, of one of the ditches in the area, the Barjas Ditch, was used to assess the changes in vegetation before and after its implementation. The results show that (i) NDVI values have, in the area of influence of the ditches, a strong seasonal pattern link to ditches functioning; (ii) the closer the vegetation to the ditch the higher its NDVI values, NDVI in the immediate ditch area averaged 0.36 compared to 0.29 at distances > 200 m; (iii) the restoration of the Barjas’ ditch has a beneficial impact on the vegetation status, NDVI experiences an increase of 19 % after the restoration resulting from a 0.09 rise. These results highlight the role of ditches in the landscape beyond their use as water resources infrastructure, proving a function to the ecosystems.