Mapping the impacts of cyclone Idai in Mozambique using Sentinel-2 and OBIA approach

Cyclones are some of the most devastating natural disasters that cause major losses of life and property. A few months after Cyclone Idai swept through Beira, Mozambique between 4 and 20 March 2019. An analysis is presented on the impacts of this disaster by assessing the extent of the floods. This study employed Sentinel-2 imagery and remote sensing techniques including a threshold analysis and an object‑based image analysis (OBIA) approach. Water and non-water land covers were established by using a Modified Normalized Difference Water Index (MNDWI), while the classification approach assessed three land covers. These assessments were done on four dates: (1) 31 January (before), (2) 25 February 20 (before), (3) 12 March (during) and (4) 16 April (after). Accuracies ranging from 74% to 90% were attained. The OBIA approach showed that 61% of the study area was affected by floods, while the threshold approach showed that 55% of the area was flooded. Areas with low elevation and close to the coast were more effected by the floods. After the cyclone, the area under water reduced by more than 20%. The results here could be useful for developing early warning systems, risk assessment, establishing damage and developing natural hazard policies.