Background and Objectives: The Caspian Sea, as the largest enclosed inland body of water in the world, plays a critical role in regulating the water levels of its surrounding coastal areas and wetlands. The water level of the Caspian Sea is influenced by various climatic factors, with evaporation being one of the most significant contributors. Due to the lack of a natural outlet for the world's oceans, evaporation represents the primary mechanism for water loss from this lake. Variations in evaporation rates can lead to significant impacts on the water level of the lake, and by extension, on the delicate coastal ecosystems, including bays and wetlands. Gorgan Bay, the largest bay of the Caspian Sea, is particularly sensitive to fluctuations in water levels, making it of considerable environmental and economic importance. This study aims to assess the impact of different evaporation scenarios in the Caspian Sea on the water level and salinity of Gorgan Bay using hydrodynamic modeling techniques.
Methods: In this study, a hydrodynamic model was employed to simulate the effects of evaporation changes on the water level and salinity of the Caspian Sea and Gorgan Bay. The model considers parameters such as temperature, evaporation, wind, and water level fluctuations, analyzing their interactions across various spatial and temporal scales to provide accurate predictions of ecological changes and water resources. Three different evaporation scenarios (10%, 20%, and 30% increase) were applied over the period from 2020 to 2040, and their impacts on the water level and salinity of the region were assessed.
Findings: The results of this study demonstrate that increased evaporation leads to a significant reduction in the water level of the Caspian Sea and Gorgan Bay. In the scenario with a 10% increase in evaporation, the water level drops to -28.3 meters, causing the Chapoghli Channel to dry up, which reduces the area of the bay to 230 km². In the 20% evaporation increase scenario, the water level decreases to -28.7 meters, and in addition to the Chapoghli Channel, the Ashuradeh Channel also dries up, further reducing the bay’s area to 200 km². In the scenario with a 30% increase in evaporation, the water level reaches -29.1 meters. From 2032 onwards, the water connection between the bay and the Caspian Sea is completely severed, with the bay’s area shrinking to 175 km². The salinity modeling results also indicate an increasing trend in salinity in Gorgan Bay across all three scenarios. In the 30% evaporation increase scenario, the salinity in the center of the bay reaches 23.6 ppt, marking a substantial rise compared to the current level.
Conclusion: Based on the results obtained, the management of water resources in Gorgan Bay and the monitoring of its hydrological changes appear to be essential. To prevent the bay from drying up under the predicted critical conditions, it is recommended to dredge the connecting channels with minimal damage to the wetlands and bird habitats. Given that the sedimentation rate in the Chapoghli Channel is lower than in other channels, this channel could be the primary candidate for dredging. Additionally, transferring water from the Caspian Sea to Gorgan Bay via a secure pipeline or channel in the central region of the Miankaleh Peninsula, due to its more favorable morphological conditions, is proposed as a cost-effective solution. These measures could play a crucial role in mitigating the negative effects of increased evaporation on the ecosystem and water resources of Gorgan Bay. |
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