A distributed agro-hydrological model for irrigation water demand assessment

• Published in: Agricultural water management 2008-02, Vol.95 (2), p.123-132
• Main Authors: Minacapilli, M., Iovino, M., D’Urso, G.
• Format: Article
• Language: English
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agronomy. Soil science and plant productions; albedo (reflectance); Biological and medical sciences; Distributed hydrological model; Freshwater; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; hydrologic models; image analysis; irrigation management; Irrigation scheduling; irrigation water; Irrigation. Drainage; Landsat; leaf area index; multispectral imagery; On-demand irrigation system; Remote sensing; simulation models; soil hydraulic properties; soil water; vegetation cover; water use
• ISSN: 0378-3774; 1873-2283
• DOI: 10.1016/j.agwat.2007.09.008

The actual irrigation water demand in a district in Sicily (Italy) was assessed by the spatially distributed agro-hydrological model SIMODIS (SImulation and Management of On-Demand Irrigation Systems). For each element with homogeneous crop and soil conditions, in which the considered area can be divided, the model numerically solves the one-dimensional water flow equation with vegetation parameters derived from Earth Observation data. In SIMODIS, the irrigation scheduling is set by means of two parameters: the threshold value of soil water pressure head in the root zone, h m, and the fraction of soil water deficit to be re-filled, Δ. This study investigated the possibility of identifying a couple of irrigation parameters ( h m, Δ) which allowed to reproduce the actual irrigation water demand, given that the study area was adequately characterized with regard to the spatial distribution of the soil hydraulic properties and the vegetation conditions throughout the irrigation season. The spatial distribution of the soil and vegetation properties of the study area, covering an irrigation district of approximately 800 ha, was accurately characterized during the summer of 2002. The soil hydraulic properties were identified by an intensive undisturbed soil sampling, while the vegetation cover was characterized in terms of leaf area index, surface albedo and fractional soil cover by analysing multispectral LandSat TM imageries. Irrigation volumes were monitored at parcel scale. A reference scenario with h m = −700 cm and Δ = 50% (corresponding to a mean actual to potential transpiration ratio of 0.95) allowed to reproduce the spatial and temporal distribution of the actual irrigation demand at the district scale. The spatial variability of the crop conditions in the considered area had much more influence to assess the irrigation water demand than the soil hydraulic spatial variability. The proposed approach showed that, under the agro-climatic conditions typical for the Mediterranean region, SIMODIS may be a valuable tool in managing irrigation to increase water productivity.