water Article A Comprehensive Modelling Approach to Assess Water Use Efficiencies of Different Irrigation Management Options in Rice Irrigation Districts of Northern Italy Alice Mayer 1, *, Michele Rienzner 1 , Sandra Cesari de Maria 1 , Marco Romani 2 , Alberto Lasagna 3 and Arianna Facchi 1 1 Department of Agricultural and Environmental Sciences, University of Milan, 20133 Milan, Italy 2 Centro Ricerche sul Riso, Ente Nazionale Risi, 27030 Castello D’Agogna, Italy 3 Consorzio di Irrigazione e Bonifica Est Sesia, 28100 Novara, Italy * Correspondence: alice.mayer@unimi.it Received: 31 July 2019; Accepted: 31 August 2019; Published: 4 September 2019   Abstract: European rice production is concentrated in limited areas of a small number of countries. Italy is the largest European producer with over half of the total production grown on an area of 220,000 hectares, predominantly located in northern Italy. The traditional irrigation management (wet seeding and continuous flooding until few weeks before harvest—WFL) requires copious volumes of water. In order to propose effective ‘water-saving’ irrigation alternatives, there is the need to collect site-specific observational data and, at the same time, to develop agro-hydrological models to upscale field/farm experimental data to a spatial scale of interest to support water management decisions and policies. The semi-distributed modelling system developed in this work, composed of three sub-models (agricultural area, groundwater zone, and channel network), allows us to describe water fluxes dynamics in rice areas at the irrigation district scale. Once calibrated for a 1000 ha district located in northern Italy using meteorological, hydrological and land-use data of a recent four-year period (2013–2016), the model was used to provide indications on the effects of different irrigation management options on district irrigation requirements, groundwater levels and irrigation/drainage network efficiency. Four scenarios considering a complete conversion of rice irrigation management over the district were implemented: WFL; DFL—dry seeding and delayed flooding; WDA—alternate wetting and drying; WFL-W—WFL followed by post-harvest winter flooding from 15 November to 15 January. Average results for the period 2013–2016 showed that DFL and WDA would lead to a reduction in summer irrigation needs compared to WFL, but also to a postponement of the peak irrigation month to June, already characterized by a strong water demand from other crops. Finally, summer irrigation consumption for WFL-W would correspond to WFL, suggesting that the considered winter flooding period ended too early to influence summer crop water needs. Keywords: irrigation district; rice irrigation requirement; water-saving technology; agro-hydrological model; groundwater level; irrigation network efficiency 1. Introduction In the Mediterranean basin, rice is grown on a surface of 1,300,000 hectares. Italy is the leading producer of rice in Europe, with over half of the total EU production and a high level of quality, and the second rice producer in the Mediterranean area after Egypt. The most important Italian rice area is the portion of the Po Valley located on the left bank of the Po river and along the river Ticino, straddling the regions of Lombardy and Piedmont in northern Italy (about 213,000 hectares in 2017, 93% of the Italian rice area according to Ente Nazionale Risi). In Italy, as well as throughout the Mediterranean Water 2019, 11, 1833; doi:10.3390/w11091833 www.mdpi.com/journal/water