Flood risk zone mapping and future projections for the Thamirabarani river basin, Southern India: insights from decadal rainfall trends and GIS-based analytical hierarchy process technique

The Thamirabarani river basin (TRB) in Tamil Nadu, India, is increasingly vulnerable to flooding, especially during the northeast monsoon. The present study identifies flood risk zones in the TRB using decadal average rainfall (2000–2023), annual average rainfall for 2023, and rainfall trends at 5 cm and 10 cm levels above the 2023 average. A GIS-based analytical hierarchy process was applied to multiple geo-environmental parameters, including slope, elevation, land use, soil texture, rainfall, and proximity to streams and settlements. Results indicate that 43% of the TRB is in a severe flood risk zone, 34% in moderate risk, and 23% in low-risk areas, primarily in uplands and pediplains. Predicted future flood zones based on increasing rainfall trends show severe risk areas expanding to 45–46%, especially in suburban and cropland regions near water bodies. The study highlights the impact of increased heavy rainfall events from 2000 to 2023, exacerbating flood risks in poorly drained, low-lying areas. Cross-validation using the area under the curve method with Sentinel-1A SAR data from December 2023 showed an accuracy of 0.899. Multi-criteria decision making was also used to identify optimal locations for flood shelters and relief camps. The study emphasizes the need for continuous monitoring, sustainable urban planning, and community-based disaster risk reduction to enhance flood preparedness. These findings are critical for policymakers to develop effective strategies to mitigate future flood impacts and improve resilience in the TRB.