Extreme events including cyclones, storm surges, heavy rainfall, and oil spills, have significant impacts on coastal water quality and marine ecosystems. Thus, assessing the spatial and temporal variability of coastal water quality induced by extreme events is crucial for effective coastal management. This study utilises high-resolution PlanetScope satellite data to assess the impact of extreme events on coastal water quality in southern India. The key water quality constituents, such as Chlorophyll ( \(\:Chl\) ), Total Suspended Solids ( \(\:TSS\) ), and Coloured Dissolved Organic Matter ( \(\:CDOM\) ), were analysed and a fuzzy-based Water Quality Index ( \(\:WQI\) ) model, was implemented to study the water quality variability caused due to extreme events, which include extreme rainfall (December 2015), Cyclone Nivar (November 2020), Cyclone Mandous (December 2022), and an oil spill (December 2023). Additionally, pre- and post-cyclone Mandous conditions were examined, revealing biological responses to cyclone-induced vertical mixing in offshore waters. Results indicate significant water quality degradation, primarily due to \(\:TSS\) influx from the Adyar and Coovum rivers during extreme events, while the oil spill caused increased \(\:CDOM\) and \(\:TSS\) values. A time-series analysis (2011–2024) using MODIS-Aqua satellite data showed a rise in \(\:Chl\) and \(\:TSS\) concentrations following cyclonic events. The analysis performed in this study will contribute to an enhanced understanding of the complex interactions between extreme events and coastal water quality and also reveal the critical role of high spatial and temporal resolution satellite observations in mitigating the adverse effects of such disasters on coastal ecosystems.
