Hydrological trends and agricultural water footprint in the Pennaiyar basin, Tamil Nadu

India is currently facing one of its biggest challenges - the world’s worst water crisis. With only 2.5 % of India’s water resources, Tamil Nadu's water demand is rising due to increasing population, rapid urbanisation, variability in rainfall patterns and climate change, apart from agricultural water demand. In this context, the present study aims to assess the hydrological behavior of the Pennaiyar river basin located in the eastern part of Tamil Nadu, India. The assessment includes spatial and temporal analysis of rainfall and evapotranspiration (ET), dynamic evaluation of groundwater status and estimation of crop water footprint (WFP) for major crops in the basin. Results revealed that the average annual rainfall in the Pennaiyar river basin is approximately 927 mm. Seasonal rainfall distribution was 15 % in summer, 43 % during the southwest monsoon, 34 % during the northeast monsoon and 8 % in winter. Using the Hargreaves-Samani model, reference evapotranspiration (ET0) was found to range from 3.5 mm/day to 6.4 mm/day. The green WFP for paddy, maize, groundnut and sugarcane was 534 m³/t, 318 m³/t, 980 m³/t and 41 m³/t respectively. Similarly, the blue WFP for these crops was 500 m³/t, 177 m³/t, 592 m³/t and 54 m³/t respectively. The categorization of groundwater firkas (unit of Taluk) (2020, 2022 and 2023) in the Pennaiyar basin was done as over-exploited, critical, semi-critical and safe. In 2023, it was observed that there were 110 over-exploited firkas, 22 critical firkas, 61 semi-critical firkas and 63 safe firkas. The study emphasizes sustainable water management strategies for the Pennaiyar basin.