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.
Highlights
In the Mediterranean basin, rice is grown on a surface of 1,300,000 hectares
Where paddy areas are not perfectly flat, local topography may activate lateral water exchanges. All these peculiar aspects lead to a strong interaction between irrigation and surface groundwater dynamics, activated by the huge percolation fluxes from the rice paddies and the unlined canal networks, by the presence of a very shallow aquifer, and to a partial reuse of irrigation water, since water losses from fields and canals are partially recovered for irrigation in the downstream agricultural areas
Even if the irrigation district (500 ha) was not exactly representative of the Lombardy–Piedmont rice area, and the model developed was quite simplified, the results clearly show that the strong interaction between irrigation water and groundwater levels may reduce the ‘water saving potential’ of alternative irrigation techniques, due to the important drawbacks that a widespread modification of irrigation methods could have on global water dynamics when considering a large portion of territory
Summary
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. Water 2019, 11, 1833 basin, rice is traditionally grown in fields flooded from before sowing to a few weeks before harvest: this technique requires much more water than irrigation techniques adopted for other cereals [1,2] This area is characterized by many peculiarities: a historical abundance of surface water, an ancient and extensive network of unlined irrigation and drainage channels, a complex geo-morphologic and hydro-geologic structure formed by wide fluvioglacial conoids (Pleistocene) cut by river valley lowlands (Holocene) hosting one of the largest aquifers in Europe. Multi-functionality and eco-system services are provided by irrigation systems in many areas (e.g., landscape quality and profitability, ecosystem biodiversity)
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