Passive microwave remote sensing of soil moisture for flood prediction: A case study of Derna, Libya

Monitoring environmental factors such as soil moisture and precipitation on a frequent basis plays a vital role in identifying early signs of flooding, particularly in regions prone to extreme weather. Passive microwave remote sensing stands out in this context due to its ability to collect data regardless of weather conditions, along with its regular daily coverage. In this study, changes in the Polarisation Index (PI) were examined before and after the severe flooding that struck Derna, Libya, on 11 September 2023. The data used were obtained from the AMSR2 sensor operating at X-band (10 GHz) aboard Japan’s GCOM-W1 satellite. Notably, a sharp rise in PI was recorded one day ahead of the flood, aligning with increased soil moisture linked to intense rainfall in the area. Following the event, PI values remained elevated, indicating continued ground saturation. These findings point to the potential of PI as an early warning indicator for heavy rainfall and flood risk. With appropriate selection of observation points, this method could support the development of flood forecasting systems in other high-risk regions around the world.