FLOOD EXTENT MAPPING USING GEOSPATIAL TOOLS

Floods have caused tremendous destruction of lives and properties in communities along different rivers in Chikwawa district. This paper is an application of Remote Sensing and Geographic Information System in mapping the extent of floods using Sentinel-1 satellite imagery provided by European Space Agency (ESA). The central focus of this project revolves around production of flood extent map, calculation of flood inundation area, and production of an exposure map for the January 2022 flood event that was caused by cyclone Ana. Sentinel Application Platform (SNAP) and ArcGIS 10.8 were the image processing and GIS applications used. The procedure consisted of collection of two sentinel-1 datasets, one for pre-flood event (21 October, 2021) and the other during the flood event (26 January, 2022). Pre-processing steps, which consisted of calibration, speckle filtering, terrain correction and stacking were applied to the images in SNAP software. The results revealed that most of the areas lying close to the Shire River are highly exposed to the floods and the floodwater covered a significant amount of area. Sentinel-1 SAR earth observation data has a tremendous potential for creating flood information with high accuracy and high spatial resolution due to the prevalence of severe weather conditions during flooding season. Improvements in flood mapping can be a vital tool mitigating disasters.

This paper is an application of Remote Sensing and Geographic Information System in mapping the extent of floods using Sentinel-1 satellite imagery provided by European Space Agency (ESA). The central focus of this project revolves around production of flood extent map, calculation of flood inundation area, and production of an exposure map for the January 2022 flood event that was caused by cyclone Ana. The results revealed that most of the areas lying close to the Shire River are highly exposed to the floods and the floodwater covered a significant amount of area. Sentinel-1 SAR earth observation data has a tremendous potential for creating flood information with high accuracy and high spatial resolution due to the prevalence of severe weather conditions during flooding season.

Chikwawa District is situated in Malawi’s southern region. With Mwanza District to the North, Blantyre to the North East, Thyolo to the East, Nsanje to the South and Mozambique international boundary to the West. The District Headquarters is approximately 54 km away from Blantyre City. Its coordinates for geographical location are 16°10'0" S and 34°45'0" E in DMS (Degrees Minutes Seconds) or -16.1667 and 34.75 (in decimal degrees). The district has a 4,892 km2 (489,165.769 ha) total land area (figure 1). Chikwawa has a growth rate of 25% with a total population of 551,538 of which 270,464 are males and 281,074 are females (NSO,2018). It is the second largest district in southern region and fifth in Malawi.

District: Chikwawa

Coordinates: -16.2153, 34.6804