Mapping Mangrove Damage: Super Typhoon Odette
The Project
By the end of this module, viewers should be able to
- understand the importance of mangrove habitat
- understand how large storms can damage mangrove habitat
- access the Google Earth Engine app to analyze the mangrove damage from Typhoon Odette
Storms can damage every part of a mangrove forest - high winds strip the trees of their leaves and branches, and coastal flooding can make the soil too salty for the trees to survive.
This is what on-the-ground damage in the Calamianes Islands looked like after Typhoon Yolanda in 2013.
This project is part of the USAID Fish Right Program. Fish Right is a partnership between the governments of the United States and the Philippines, with the goal of promoting environmentally and economically sustainable fisheries.
The Importance of Mangroves
Mangroves provide a variety of services for both their human and animal communities. They act as a stabilizing structure in areas that experience rapid change, responding to events as small as tides and as large as typhoons.
Forests act as a buffer for coastal flooding, trees can pull greenhouse gases out of the atmosphere to store in the soil, and roots provide shelter for fish of all kinds.
Super Typhoon Odette
Typhoon Rai, locally called Typhoon Odette, made landfall in Siargao Island on December 16, 1:30 pm and then quickly progressed westward. You can trace the storm's path through the Philippines and its nine separate landfalls on the map below.
Super Typhoon Odette was one of the strongest typhoons to ever hit the Philippines, and the damage was widespread -- 7 million people across 11 regions in the Philippines were affected. The damage from the storm was severe, with over 1.4 million homes destroyed or damaged. The ecological impacts are still being measured, and may have long-lasting effects for local communities that rely on healthy coasts for their livelihood ( UN OCHA Report ).
Damaged houses in Surigao City / Aerial imagery of displaced ships in Cebu City ©2021 Maxar/ Damaged forest at Puerto Princesa.
Explaining the Process
To demonstrate how Odette has impacted mangrove forest health, we examine Cebu City, one of the hardest hit areas in the storm.
This is a satellite image from November 2021.
Notice the dark green, healthy mangrove forests along the coast line.
Normalized Difference Vegetation Index (NDVI) is used to measure how "green" a forest is, as a proxy for forest health.
Essentially, the more infared light the leaves reflect, the healthier the tree. After a large storm like Odette, trees lose their leaves, and lose their greenness.
This is a screenshot from the mangrove damage mapping tool that was developed by the USAID Fish Right Program. The area shown is a portion of Cebu City where impacts were significant (e.g., displaced ships).
The majority of the Cebu City mangroves in this area were mapped as "high damage" based on NDVI(greenness) from satellite imagery.
A comparison of high-resolution satellite images from before and after the event (see below) provide support for this interpretation.
How accurate are the damage maps?
Below is high resolution satellite imagery from before and after Super Typhoon Odette covering a portion of Cebu City. Use the swipe tool below to see the storm impacts, including many ships displaced by the storm, direct damage to mangroves (e.g., by moved ships) and overall decline in greenness of the mangroves related to defoliation and other storm stress.
The Mapping Tool
The mangrove damage map is hosted through Google Earth Engine, and can be opened and explored in any web browser. Development of the mapping tool was conducted by USAID Fish Right partner Dr. David Lagomasino, from East Carolina University (ECU).
