Earthshots: Satellite Images of Environmental Change

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» Lake Urmia, Iran

Lake Urmia in Iran is another closed basin lake that has been shrinking. Continuous declines in water flowing into the lake have caused a general decline in its surface area since 1995.

Water only enters Lake Urmia via rainfall and runoff from rivers flowing into it. As a closed basin lake, its water levels fluctuate with changes in rainfall. Once water reaches the lake, it only leaves via evaporation. When the water that flows into the lake is diverted for human uses, those dynamics are prone to big changes.

The lake’s southern basin is shallower than its northern basin, so recent images show the water disappearing from the southern basin first. These Landsat images use the shortwave-infrared, near-infrared, and green wavelengths of light. Because water absorbs infrared light, water (dark blue to black) contrasts with the surrounding land areas. As the water becomes shallower, light is reflected off of the lakebed in shades of light blue. Lighter blue and bright areas immediately surrounding the lake are where the receding shoreline has exposed the lake bottom.

Data from the USDA Foreign Agricultural Service shows a downward trend since the mid-1990s. However, a fresh pulse of water from rains during fall 2018 and spring 2019, along with seasonal snowmelt, increased lake levels. This increase isn’t only evident in the graph data. The 2019 Landsat image shows a rebound in water levels over 2018.

Map of the featured area.

About 76 million people live within 500 kilometers (310 miles) of Lake Urmia. Residents of the region fear that what has happened to the Aral Sea is happening to Lake Urmia. The almost complete loss of the Aral Sea has had serious economic and environmental consequences. The population near Lake Urmia is denser, so more people are at risk.

The city of Urmia is the gray patch in the lower left of these images. Agricultural fields spread out to the north and east of the city. The oval shape on the east side of the lake is an extinct volcano. This feature was an island as recently as 1998. A causeway and bridge completed in 2008 connects the oval and the western shore. Construction of the causeway began in 1979, was abandoned, and then started again in the early 2000s.

Lake Urmia is a hypersaline lake. Rivers carry sediments and minerals to the lake, and as the lake water evaporates, the minerals remain. As a result, the salts in the lake become more concentrated and the water becomes increasingly more saline.

As the lake’s water recedes, the salty lakebed is exposed. Light blue or pale shades fringe the lake’s shoreline in these images. These salt flats do not support agriculture, and this salty desert could cause windblown salt to damage nearby fields. A similar phenomenon is happening in the vicinity of the Aral Sea.

Crops are grown near rivers that flow into Lake Urmia. Green fields mark these river deltas, such as the ones shown southeast of the lake. With little precipitation in this region, farming depends on irrigation from the rivers. An increasing population is putting more pressure on water resources. Much of the streamflow from these rivers no longer reaches the lake.

The diversion of water from the rivers for agricultural use is probably the most significant cause of Lake Urmia’s decline. Several dams have also been built on rivers that flow into the lake. Since 1996, droughts have further contributed to the lower lake levels.

The lake level is back up because of rainfall in 2018–2019. That may not be a permanent restoration of the lake, so the Iranian government is planning to build dikes to keep remaining water in smaller areas to prevent the rapid evaporation of water from shallow pools.

No single fix can help the lake recover. But the continual monitoring from Landsat helps decision makers plan for the best solutions.


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