The Sistan Basin lies on the Iran-Afghanistan border. Melted snow from the Hindu Kush Mountains of Afghanistan nourishes this dry basin. The Helmand River carries the snowmelt across the Margo Desert and into the Sistan Basin, where the water pools into Lake Hamoun. Sometimes anyway. Lake Hamoun is seasonal, and water is generally only present during the spring melt season.
Surrounded by hundreds of kilometers of arid plains, the Sistan Basin is in one of the driest regions of the world, so the three shallow lakes that make up Hamoun naturally expand and contract in the wet to dry seasons. These lakes and wetlands once supported great plant and animal diversity. But the combination of drought and water diversion for irrigation has caused Lake Hamoun to nearly disappear, along with the local bird and fish populations.
The Lake Hamoun area is classified as freshwater wetlands. Because Hamoun is a closed basin, it’s more of an inland delta. About 60,000 hectares of the wetlands in the Hamoun region in Iran are protected under the Ramsar Convention. The Hamoun region on the Afghanistan side is not protected under the Ramsar Convention even though it represents more area that is permanently inundated and vegetated.
The Hamoun wetlands have a normal wet and dry cycle. The water level typically rises in the spring and falls from April to January. Large areas dry up regularly. But during prolonged dry periods, birds migrate elsewhere, and fishing is not possible.
The annual precipitation in this extremely dry basin is only about 50 millimeters. The average depth of the lake, even at its highest water level, is only 3 meters. That means the area is vulnerable to major changes in water level that happen naturally. When in addition people alter the water flow, the changes are more pronounced. Irrigation expansion has made the lakes more vulnerable to drought. The once thriving wetlands are now mostly lifeless salt flats.
Water from the Helmand River is used upstream for agriculture. The river turns west and flows across the border into Iran and drains into the Lake Hamoun wetlands.
Lake Gowd-e-Zareh, at the southern end of the Sistan basin, is the lowest level of the basin and only receives runoff when the river overflows, every 10 years on average. It has no outlet—water is lost only via evaporation, so it is a hypersaline lake. Temporary vegetation grows along the lake’s shore (shown as red in the 1998 and 2000 images) where the water from Lake Hamoun overspill is less salty.
The lakes visible in these close-up images are the Chah-Nimeh reservoirs. These natural cavities in the southern Sistan plain are near Zabol, Iran, which is seen in the upper left of these images. The water in these reservoirs provides drinking water for Zabol, whose 2013 population was about 122,000. Canals connecting the reservoirs can be seen along with a canal that that branches off the Helmand River, on the right.
A field study conducted in December 2009 and January 2010 found a low level of water flow in the Helmand River, which failed to reach Lake Hamoun. Instead, the water was diverted to the Chah-Nimeh reservoirs.
Even with these reservoirs, dry lakebeds surrounding Zabol are problematic. A “120-day wind” blows in this region. These persistent spring and summer winds can cause dust storms in and around Zabol.
Zabol reports dozens of dust storms every year. Clouds of dust from the lakebed cause breathing problems and can spread respiratory diseases. Many villages in the region have been abandoned.
The August 2000 image shows an extensive dust storm blowing sediment off the dry lakebed toward the south. The dust plumes obscure most land features and reach to Lake Gowd-e Zareh and beyond.