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Volume 41, Issue 1 (2026)
GeoRes 2026, 41(1): 30-40 |
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Received: 2025/12/19 | Accepted: 2026/01/21 | Published: 2026/02/15
Received: 2025/12/19 | Accepted: 2026/01/21 | Published: 2026/02/15
How to cite this article
Ebadi L, Baghani A. Forty-Year (1986-2025) Monitoring of Gorgan Bay Surface Area and Its Relationship with Caspian Sea Level Fluctuations. GeoRes 2026; 41 (1) :30-40
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1- “Department of Surveying Engineering, Faculty of Engineering” and “Environmental Hazard Institute”, Golestan University, Gorgan, Iran
Abstract (595 Views)
Aims: In light of the alarming desiccation trend of Gorgan Bay, the primary objective of this research is to conduct long-term monitoring of the bay's water surface area changes over a 40-year period (1986-2025) and to investigate the determining roles of Caspian Sea level (CSL) oscillations and precipitation in the Qarasu watershed on these morphological variations.
Methodology: This study utilized a time series of 36 Landsat satellite images. For precise water body extraction, the Modified Normalized Difference Water Index was applied. To evaluate the accuracy of the area results, a classification map was generated from a Sentinel-2 image using the Support Vector Machine method, followed by error matrix calculations. Water level data were retrieved and harmonized by integrating Baku station records with the DAHITI database. Additionally, precipitation data for the Qarasu basin were obtained from the CHIRPS database. Statistical analyses were performed using the Pearson correlation coefficient.
Findings: The area of Gorgan Bay decreased from a maximum of 565.48km2 in 1995 to a minimum of 275.12km2 in 2023, indicating a loss of more than 50% of its peak area. The area of Gorgan Bay was significantly positively correlated with the level of the Caspian Sea (p<0.001; r=0.9419), but not with the rainfall of the basin (p=0.2142; r=0.2121).
Conclusion: As a semi-closed ecosystem, Gorgan Bay is subject to the hydrodynamic regime of the Caspian Sea and, due to the gentle slope of the bed, acts as a sensitive indicator of sea level changes. Local precipitation in the catchment area cannot compensate for the coastline's retreat caused by a fall in the Caspian Sea level.
Methodology: This study utilized a time series of 36 Landsat satellite images. For precise water body extraction, the Modified Normalized Difference Water Index was applied. To evaluate the accuracy of the area results, a classification map was generated from a Sentinel-2 image using the Support Vector Machine method, followed by error matrix calculations. Water level data were retrieved and harmonized by integrating Baku station records with the DAHITI database. Additionally, precipitation data for the Qarasu basin were obtained from the CHIRPS database. Statistical analyses were performed using the Pearson correlation coefficient.
Findings: The area of Gorgan Bay decreased from a maximum of 565.48km2 in 1995 to a minimum of 275.12km2 in 2023, indicating a loss of more than 50% of its peak area. The area of Gorgan Bay was significantly positively correlated with the level of the Caspian Sea (p<0.001; r=0.9419), but not with the rainfall of the basin (p=0.2142; r=0.2121).
Conclusion: As a semi-closed ecosystem, Gorgan Bay is subject to the hydrodynamic regime of the Caspian Sea and, due to the gentle slope of the bed, acts as a sensitive indicator of sea level changes. Local precipitation in the catchment area cannot compensate for the coastline's retreat caused by a fall in the Caspian Sea level.