Earthshots: Satellite Images of Environmental Change

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» Ayeyarwady Delta, Myanmar

The Ayeyarwady Delta—also called the Irrawaddy Delta—is a vast alluvial floodplain. The delta spans over 35,000 km2 (13,500 mi2) and was once home to an extensive tract of mangrove forests, but deforestation has changed the landscape. One scientific study estimated that the delta lost 1,685 km2 (651 mi2) from 1978 to 2011. This 45-year sequence of Landsat images shows the relatively rapid loss of mangrove forest.

Map of the featured area.

Mangroves are sturdy species. They can recover from storm disturbances relatively quickly. They can tolerate salt water, saturated soil, high wind, and storms. But they are a threatened ecosystem because of overexploitation of its resources.

Mangrove forests appear bright green in the Landsat images. Their degradation is evident in the reduction of the green color throughout the series. One island remains bright green amid the deforestation. That’s the Meinmahla Kyun Wildlife Sanctuary, which was established in 1986.

Mangroves offer a multitude of benefits, both for the environment and for people. As guardians of the shoreline, mangroves reduce the impacts from storms and tsunamis. Their dense and partially submerged root system protects inland areas from erosion and flooding.

Food security is closely linked to a healthy mangrove ecosystem. A mangrove delta is a nursing ground for aquatic species, which provide food for local communities. Besides providing fuel wood and building material for people, mangroves also purify the water.

Mangrove ecosystems have a global benefit, too. Worldwide, mangroves sequester an estimated 22.8 to 25.5 million metric tons of carbon each year. A mangrove region as extensive as the Ayeyarwady Delta is well worth monitoring.

Scientists have been tracking the distribution of the mangrove forests in the Ayeyarwady Delta using satellite observations dating back to the 1970s. The change map shows when and where mangrove loss occurred. Green indicates current mangrove forest as of 2005. However, red dominates the map, which means that much of the mangrove loss occurred during the 1990s.


Legend for mangrove change map of the Ayeyarwady Delta, Myanmar (Giri and others, 2008).

People are drawn to delta and coastal regions, and about 7.7 million people live on the Ayeyarwady Delta. Deltas can be productive agricultural areas because the soil is rich and the flat terrain and water provide easy access to water-based transportation. The Ayeyarwady Delta produces 35% of Myanmar’s rice. Cutting wood for fuel also contributes to mangrove loss, but most of the deforestation in this delta has been for rice fields.

A more close-up look at the eastern portion of the delta shows this degradation in more detail. As the sequence of images progresses, the bright green of healthy mangrove changes into a mottled green of degraded mangrove.

This mangrove loss could have implications for protecting people on the delta. The delta’s low elevation and flat landscape make it vulnerable to flooding from storm surges, as with Cyclone Nargis in May 2008. The mangrove forests provide a buffer for storm surge.

Mangroves in the Ayeyarwady Delta are also being replaced by aquaculture. In the southwestern part of the delta, brackish shrimp pond development is expanding. The dark blue shapes in the images represent the shrimp ponds. Not as much land is being taken up by aquaculture, but this industry is growing.

While some mangroves have been restored on the delta, the aquaculture, agriculture, and cutting activities need to be monitored so that the benefits of mangroves can be maintained. Researchers continue to use Landsat and other remote sensing information to monitor this region.


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