THE USE OF WATER IN THE AGRICULTURAL SECTOR: A PROCEDURE FOR THE ASSESSMENT OF LARGE-SCALE IRRIGATION EFFICIENCY WITH GIS

Large-scale water assessment models can be valid decision support systems for water management institutions. We developed a spatially distributed model in order to evaluate efficiencies of irrigation scenarios. Model development required four stages: questionnaire data collection from farmers, integration of questionnaire data with water supply and physical soil characteristics data, cluster analysis with Management Zone Analyst, and GIS for spatial distribution. Four irrigation scenarios in the north-east of Italy were compared: (i) the current condition (three turns of 24h of supplied water per month), (ii) scenario 2 (three turns of 16h of supplied water per month), (iii) scenario 3 (four turns of 12h per month); and (iv) scenario 4 (4 turns of 10h per month). In the current irrigation scheme, results show high potential water excess in every month of the irrigation season. Shifting from three to four irrigation turns per month increased the probability of water excess, because water losses decreased and water availability for plants increased. For the same reason, potential water excess increased when the duration of each turn decreased, even when the total water supply was reduced. The irrigation efficiency index, therefore, was lowest in scenario 1 compared to the other scenarios. Scenario 4, in contrast, was the most efficient.