A Comparative Study on the Irrigation Suitability of Kerala's Rivers Using Fuzzy AHP and Conventional Methods

ABSTRACT Food security in Kerala depends on effective irrigation, but poor‐quality irrigation water poses threats such as salinity, sodicity and reduced soil productivity. Although past assessments have been localised, this study presents the first comprehensive, statewide evaluation of irrigation water suitability across 44 major rivers in Kerala. It integrates the fuzzy analytical hierarchy process (FAHP) with the Indian Standard IS 11624:2019, creating a robust, adaptive framework that combines expert‐driven weighting with national water quality benchmarks. Water quality data from March 2017 to August 2024 were analysed via key parameters, including pH, electrical conductivity, sodium adsorption ratio, residual sodium carbonate, chloride, Mg 2+ /Ca 2+ , fluoride and boron. A novel FAHP‐based irrigation water quality index (FIWQI) and an entropy‐derived disorder index (DI) were developed to assess seasonal and spatial variability. The results revealed high suitability during the monsoon and postmonsoon seasons due to dilution, whereas the suitability during the premonsoon period significantly decreased. Rivers such as Kuttiyadi, Neyyar and Meenachil consistently presented high FIWQI scores, whereas Kallai and Mogral experienced seasonal declines. Piper diagrams confirmed hydrochemical shifts with rainfall. This study provides a replicable approach for monsoon‐driven regions, offering actionable insights for region‐specific irrigation planning, precision agriculture and sustainable watershed management.