Cyclone Idai

Floods after Cyclone Idai

Flood Extent with Sentinel 1 SAR images

Exceptional rainfall connected with cyclone Idai caused heavy flooding in the Beira region and entire villages and towns have been completely flooded in the wake of last Thursday's high-end Category 2 storm. As many as "300 to 400" bodies line the banks of a road out of the city of Beira in Mozambique, according to an eyewitness account, and flood waters have formed an inland ocean that is visible from outer space. The theory tells us that the backscatter intensity received by a radar satellite drops over flooded soil because the emitted electromagnetic waves are specularly reflected off the water surface and thus does not return to the antenna. In forest areas the opposite happens because reflections from the water surface will hit the trunks and canopy and thus enhance backscatter. I used a simple demonstration script provided by the Google Earth Engine team to see if flooded areas can be mapped using Sentinel-1 data. The algorithm takes two Sentinel-1 images that were pre-processed to backscatter coefficient in decibels after thermal noise removal, radiometric calibration and terrain correction.

Cyclone Idai developed in the Mozambique channel between Mozambique and Madagascar. Often, storms that develop there don’t strengthen as much as those that form north and east of Madagascar, but Cyclone Idai was fed by warm water temperatures.Tropical Cyclone Kenneth formed north of Madagascar and the Mozambique Channel. Fed by warm ocean temperatures, it strengthened from a Category 1 to a Category 4 storm in the 24 hours ahead of making landfall on April 25.
Starting on the evening of March 14, Cyclone Idai made landfall in Beira, Mozambique, a coastal city of half a million people. The fierce storm pummeled Mozambique, Malawi, and Zimbabwe with strong winds and rains. Cyclone Kenneth made landfall near Pemba, Mozambique, in the late afternoon of April 25, 2019, with sustained winds clocked at 140 mph. The greatest force of Kenneth was expended in a sparsely populated area, so the storm caused fewer deaths and less destruction than Cyclone Idai.
Cyclone Idai wiped out roads, bridges, and dams as it swept through Southeast Africa. The United Nations estimated that Cyclone Idai and subsequent flooding destroyed more than $773 million in buildings, infrastructure, and crops. More than 100,000 homes were damaged or destroyed.Cyclone Kenneth is estimated to have destroyed about $100 million worth of homes, crops, and infrastructure, including boats and equipment belonging to coastal fishing villages.