Located on the border of Iran and Afghanistan, Hamun Lake is a critical source of water for communities, irrigated agriculture, and wildlife across a river basin that covers 40% of Afghanistan. Two main storage dams regulate flow and support irrigated agriculture in this river valley. The surface area of Hamun has fluctuated dramatically over the past 40 years due to climatic variability and anthropogenic withdrawals, but only completely dried up for the first time in 2003. Although seasonal floods temporarily refill Hamun Lake, it has been in a cycle of long periods of dryness and short periods of water availability ever since. This study provides a framework for quantification and assessment of the meteorological and anthropogenic conditions that led to the environmental collapse of Hamun Lake and its surrounding region. Researchers integrate multiple water and vegetation indices including Normalized Difference Water Index, Automated Water Extraction Index, and Normalized Difference Vegetation Index derived from historical Landsat remote sensing data to map monthly surface water and biannual agriculture changes in the watershed region. The proposed framework eliminates the unique shortcomings of each water index for detection of water bodies, while incorporating their robust features, including separation of shadows from water, detection of muddy waters, and detection of pixels with a mixture of water and vegetation. To this end, more than 8,000 Landsat cloud-free images were assembled between 1985 and 2019 using Google Earth Engine. Results show that Hamun Lake experienced an increased surface area in the 1990s and shrinkage that has persisted since 2001. The derived vegetation indices time series also reveal that irrigated agriculture has expanded from the early 2000s in the region upstream of the river feeding Hamun Lake. Agricultural expansion together with long-term persistent drought and the expansion of downstream artificial storage lakes (Chah-nimeh) have contributed to the drying of the lake and land use change impacts in this cross-border human-environment system. This project is a collaboration between the USGS and Boise State University.
Water surface area (ha) time series of Hamun Lake on the border of Iran and Afghanistan from Landsat data (1986–2019), using the Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (mNDWI), Automated Water Extraction Index (AWEI), and Water Index (WI).