Water Productivity and Sustainability Analysis of Irrigation Schemes Based on Remote Sensing Experimentation in Lis Valley, Portugal

Agriculture is responsible for approximately 70% of global freshwater withdrawals, with the remainder allocated to industrial and domestic uses (UNESCO, 2024). Nearly half of the world's population already experiences severe water scarcity during at least part of the year, a situation expected to worsen under the combined pressures of climate change and population growth. Projections indicate that food demand will increase by 60% by 2050, driven by population expansion and shifting dietary patterns, particularly in developing regions (FAO, 2017). In this scenario, irrigated agriculture emerges as a crucial strategy to meet global food needs due to its superior productivity, yield stability under climatic variability, and suitability for intensive land use. However, the intensification of irrigation often leads to unsustainable water management practices. Inefficient irrigation, groundwater over-extraction, and inadequate drainage contribute to environmental degradation, aquifer depletion, soil salinization, and deteriorating water quality, jeopardizing the long-term viability of irrigated agriculture. At the European level, the European Union (EU) addresses water scarcity and promotes sustainable agricultural water use through key legislation. The Water Framework Directive (2000/60/EC) requires Member States to implement river basin management plans, achieve "good status" for water bodies, and apply the "polluter pays" principle (European Commission, 2000). This is supported by the Groundwater Directive (2006/118/EC) to prevent groundwater pollution (European Commission, 2006) and Regulation (EU) 2020/741, effective since June 2023, setting standards for reusing treated urban wastewater in agriculture (European Commission, 2020). These are embedded within the European Green Deal, Farm to Fork Strategy, and the post-2022 Common Agricultural Policy (CAP 2023-27), which promotes sustainable water use via conditional payments, eco-schemes, innovation funding, and European Investment Bank support (European Commission, 2019a; 2019b; 2021). Portugal aligns with EU directives by modernizing irrigation infrastructure, including meter installation under the Rural Development Programme (RDP) 2014-20 (European Commission, 2019c), and adopting Decree-Law No. 119/2019, which implements Regulation 2020/741 for reclaimed water use (Portuguese Republic, 2019). Additional efforts focus on strengthening water-user associations, promoting precision farming, and improving data-driven irrigation management (Gonçalves et al., 2020). Modernizing irrigation systems to align with broader economic development is essential but complex, requiring coordinated efforts and investment. Effective water monitoring at the irrigation district scale is fundamental, providing critical data on water supply, demand, and quality, identifying infrastructure and operational issues, environmental risks, and guiding adaptive farm practices to address water scarcity and contamination (Gonçalves et al., 2020). According to the methodology suggested by the Food and Agricultural Organization of the United Nations (FAO), crop water requirements are estimated as the product of reference evapotranspiration (ETo) and crop coefficient (Kc), yielding maximum evapotranspiration (ETm = Kc × ETo). However, under water stress conditions, actual evapotranspiration (ETa) is reduced and calculated as ETa = Ks × Kc × ETo, where Ks is the water stress coefficient (0 < Ks