Estimate the Coastal Flood Prone Zone From the Past Events in Tamilnadu and Kerala

Tamil Nadu and Kerala achieve the coastal flood disaster that leads to the maximum social and economic loss for India. The coastal flood prone methods used Sentinel 1A, Tropical Rainfall Measuring Mission (TRMM), and Gravity Recovery and Climate Experiment with Terrestrial Water Storage Anomaly (GRACE‐TWSA) product in the Tamil Nadu and Ernakulam flood events. These data estimate the change detection of pre‐flood and post‐flood events, flood inundation mapping, and Reager’s Flood Potential Index (RFPI). Sentinel 1A was overlaid for four consecutive days to determine the portion of flood inundation mapping. Using GRACE‐TWSA and TRMM data, the Flood Potential Index (FPI) used the RFPI method at a monthly scale. Then, RFPI, GRACE‐TWSA, and TRMM data were compared for four cities of the flooded year in Chennai, Tamil Nadu, and Ernakulam, Kerala. Finally, flood inundation determined the 90‐sq·km of the 2015 Chennai flood and 25‐sq·km of the 2018 Ernakulam flood with the limited remote sensing data. Maximum RFPI between the postflood and preflood period (12 months) achieves the maximum, approximately 80% from the monsoon rainfall with approximately 20% of the total water storage to attain 100% at RFPI at both flooded years. The RFPI results monitor the prone locations from these extreme past floods on the south coast of India. The research insight shares the surplus water resources by the downpour from northeast monsoon in Tamil Nadu and southwest monsoon in Kerala. Downpour naturally disputes the water resources to sustain the socioeconomic reforms between interstates. The study also supports the policy of sustainable development goals in 11, 13, 14, and 15 in the future.