Cluster landslides and associated damage in the Dima Hasao district of Assam, India due to heavy rainfall in May 2022

During 11–18 May 2022, the Dima Hasao district of Assam state in India received heavy rainfall. The rainfall triggered floods and landslides across the district, resulting in the death of three people and damage to property (mainly road and rail network) worth few hundred crores of Indian rupees. Platforms of the New Haflong railway station were completely buried by multiple debris flows, and several coaches of a train were overtoppled. We hereby investigate the cause of the landslide disaster by analyzing temporal rainfall data and also assess damages in the region using high-resolution optical satellite imagery from Resourcesat-2A (5.8 m), Sentinel-2 (10 m), and Cartosat-3 (1.1 m) satellites. It is seen from the satellite-based precipitation measurement that the region around Haflong town received maximum 24 h rainfall (156 mm) on 11 May 2022 and the heavy rainfall continued till 18 May 2022. This resulted in the occurrence of 5178 landslides, which are mapped using multi-temporal cloud free optical satellite data. Rainfall data analysis shows that 4 days antecedent rainfall of ~ 200 mm has mainly triggered landslides in this area. The initial heavy rainfall has saturated the soil and increased the pore pressure, which caused slope failure due to subsequent spell of rains. Small-sized landslides are seen to damage buildings in the Haflong town and neighboring villages. Various roads, including the Lumding-Silchar highway, were damaged at multiple places by landslides. Landslides were triggered mainly within Renji and Bokabil Rock Formations on moderate to high slopes. Results are further substantiated by debris flow simulations which showed that ~ 4 m height of debris may have been accumulated in the New Haflong railway station, thus burying the railway track and platforms.