Monitoring surface water dynamics of Chembarambakkam tank during major crop seasons using Sentinel-1 SAR data

Water availability in irrigation reservoirs plays an important role in agriculture productivity all over the world, especially in monsoon dependent regions like Tamil Nadu, India. Chembarambakkam tank is a prominent water reservoir situated in Kancheepuram district that serves as an important source of irrigation and drinking water for the areas surrounding it, including the Chennai city. Temporal variation in the tank's surface area affects cropping patterns and irrigation directly. Estimation and exploration of the spatiotemporal pattern of water spread area of Chembarambakkam tank during the 3 major crop seasons of kharif (June–September), rabi (October–January) and summer (February–May) using multi-temporal Sentinel-1 Synthetic Aperture Radar (SAR) images is the focus of this study. Sentinel-1 SAR data were processed to obtain waterbodies using backscatter thresholding technique for VV polarisation. Monthly and seasonal comparisons were conducted to evaluate the fluctuations by computing water spread areas. It was noted that there was a substantial reduction in water spread area by 1752.24 ha from June to September, which indicates a substantial reduction during the kharif season. Minimum water extent was realised in October at the onset of the rabi season (1740.08 ha) and maximum spread was released in January, which indicates recovery of water due to the northeast monsoon. In the summer season, additional reduction in water spread was realised, with the estimated reduction being 1915.68 ha by May. The findings highlight significant variations in surface water availability, which has direct influence on irrigation planning, crop selection and agricultural sustainability in the region. The study demonstrates the potential of Sentinel-1 SAR imagery for near real-time tracking of surface water bodies under evolving climatic conditions and indicates the importance of including remote sensing-based water estimation in regional water resource and agricultural planning.