The Effect of Soil and Vegetation Spatial Variability on Modelling Hydrological Processes for Irrigation Optimisation at Large Scales

Spatial variability of soil and vegetation parameters are crucial in agrohydrological models concerned with optimizing irrigation volumes at large scales. Measuring aforementioned parameters can be time consuming and laborious, so it is more efficient to aggregate their spatial variability without significantly affecting the optimal irrigation fluxes at large scales. The main purpose of this paper is to study the effect of spatial variability of soil hydraulic parameters and vegetation indices (i.e., leaf-area index, LAI, and crop coefficient, Kc) and soil profiles’ hydraulic parameters on the optimal irrigation volumes. Here we analyse the effect of aggregating the spatial variability of soil and vegetation parameters on a 140-ha irrigation sector in “Sinistra Ofanto” irrigation system in Apulia Region, Southern Italy. Five soil profiles were excavated and their hydraulic parameters were measured. Remote sensing applications were used to obtain LAI and Kc using European space agency’s Sentinel-2 images. Optimal irrigation volumes were calculated using FLOWS-HAGES agrohydrological model at field scale using variable vegetation and soil inputs. Then, a sensitivity analysis was carried out by aggregating soil and vegetation parameters into sector scale. Aggregating vegetation parameters was carried out while preserving soil parameters variability. Aggregating soil parameters variability was carried out five times by applying each of the five measured profiles while preserving vegetation parameters. Aggregating vegetation parameters did not significantly change the optimal irrigation volumes and the resulting deep percolation volumes. However, aggregating soil parameters variability significantly affected the optimal irrigation volumes and the corresponding deep percolation volumes. Aggregating soil vegetation parameters is possible to facilitate irrigation management provided that soil parameters variability is preserved and the cropping pattern is relatively uniform.