Modelling of Soil Hydrological Dynamics along the Ticino Valley Irrigation Cascade in Lombardy

The doctoral research project explores the complex soil hydrological dynamics along the irrigation cascade in Lombardy's Ticino Valley, aiming to model hydrological processes within an agricultural landscape. This PhD thesis is part of the CE4WE project (Circular Economy for Water and Energy), funded by the Lombardy Region, dedicated to advancing sustainable water cycle management through the development of technologies, knowledge, and specific skills. The application of SWAT (Soil Water Assessment Tool), a basin-scale, physically based model that simulates water dynamics in the soil, is a central focus of this project. SWAT was chosen because it allows to incorporate agricultural management practices such as irrigation, essential for the intensive agricultural study area. SWAT's water balance calculations are based on various input data, including topography, land use, soil types, and climate data. The project's initial focus was on data research, creating a "hybrid" Digital Elevation Model (DEM) and using land use and soil information from DUSAF 2018 and ERSAF pedologic maps respectively, and collecting meteorological data from ARPA Lombardia stations. The following task was to define the sub-basins for the SWAT model in the study area characterized by artificial drainage channels. The flat terrain emphasizes vertical connectivity, while the absence of natural watercourses and the dense network of irrigation channels pose unique challenges. Once the SWAT model was set-up, it conducted simulation from 2004 to 2022, on a monthly scale. SWAT was calibrated using satellite actual evapotranspiration data (MOD16) through SWAT-CUP software. The model demonstrates to achieve a Kling-Gupta Efficiency (KGE) of 0.59, implying its adeptness in simulating the intricate dynamics of the study area, with some HRUs reaching more than 0.85 KGE. However, it's important to note that both the uncalibrated and calibrated representations of actual evapotranspiration exhibit a tendency to underestimate during winter periods. This discrepancy may be attributed to the resolution disparities between Hydrological Response Units (HRUs) and MOD16 data, revealing a potential limitation in accurately representing seasonal variations. Following validation, analyses focused on climatic changes, over the past 18 years, revealed a significant increase in rainless days. Furthermore, the study explored variations in temperature (T) and actual evapotranspiration (AET) highlighting an increase, and a consequential decrease in soil water content (SWC), impacting water resource availability and crop productivity. This also caused an increased water stress for crops and the ecosystem, highlighting the direct impact of adverse climate conditions on soil hydrology and agriculture. These results contribute significantly to the understanding of regional hydrological processes, as it specifically addresses recent droughts in the Lombardy lowlands, ensuring that the system's stability is maintained. Furthermore, the project conducted an assessment of potential future scenarios involving climate change and sustainable agricultural management