Cropping Pattern Dynamics, Climatic Trends and Rice Water Use in Thiruvarur District, Tamil Nadu, India: An Economic Analysis

Rice-based agriculture in the lower Cauvery Delta is subject to climatic variability and water-management pressures. This study integrates district crop-area indices for 2013–2014 to 2023–2024, annual meteorological trend statistics, contextual vulnerability indicators, two seasonal rice-water scenarios and stochastic-frontier estimates for 120 rice farms in Thiruvarur district. The composite entropy index decreased from 0.409 to 0.118, with fluctuations and a pronounced decline in 2023–2024. A 10-state Markov matrix implies conditional stationary shares of 0.246 for cotton and 0.105 for rice, rather than observed crop substitutions. The minimum-temperature Sen slope was +0.0216 °C/year (nominal p = 0.0257), and the wind-speed slope was −0.0082 m/s/year (nominal p = 0.0020); after Holm adjustment for five tests, only wind speed remained significant at 0.05. Exposure, sensitivity and adaptive-capacity indicator means were 0.650, 0.750 and 0.475, but inconsistent score direction and absent validation preclude a district vulnerability classification. Using stated seasonal water depths, yields and nitrogen assumptions, green, blue-evapotranspiration and grey footprints were approximately 570, 593 and 205 m³/t for Kuruvai rice and 697, 558 and 212 m³/t for Samba rice. Their composite unweighted seasonal mean was 1,417 m³/t, not a measured district-wide footprint. The frontier's reported inefficiency variance fraction was 0.0031, although insufficient information is available for causal attribution. The illustrative gross-output-to-irrigation ratio was ₹10.19/m³. The findings characterise crop-area variability and conditional water-use indicators; independent validation of underlying time series and fitted models is still necessary.