Rainfall Variability and Monsoonal Extremes in Thanjavur District, Tamil Nadu, India: A Four-Decade Hydro-Climatic Assessment for Climate-Resilient Planning

This study presents a comprehensive hydro-climatic assessment of Thanjavur District, Tamil Nadu, over 40 years (1984–2024) to evaluate rainfall variability and monsoonal extremes for climate-resilient water resource planning. Using high-resolution daily, monthly, and seasonal rainfall data from NASA POWER, IMD, and TNSDMA, statistical analyses including time-series decomposition, trend estimation, and graphical visualization were performed. Results reveal a distinct seasonal skew, with the Northeast Monsoon (October–December) contributing 52–55% of the annual rainfall, followed by the Southwest Monsoon (30–32%). November consistently emerged as the wettest month. The district exhibits significant inter-annual variability, with extreme wet years (1993, 2005, 2015) exceeding 1500 mm and drought years (2002, 2012, 2016) falling below 750 mm. These fluctuations have a critical impact on tank-fed irrigation systems, groundwater recharge, and crop productivity. The study highlights the increasing frequency of high-intensity rainfall events and prolonged dry spells, reflecting the regional influence of climate change. Recommendations include enhanced rainwater harvesting, tank rehabilitation, dynamic reservoir operations, and adoption of climate-resilient agricultural practices. This long-term rainfall analysis provides a scientific basis for adaptive water resource management, drought mitigation, and sustainable agricultural planning in the Cauvery Delta region.