Investigating the changes in the water body of Gorgan Bay and its relationship with precipitation and water level of the Caspian Sea by using remote sensing data

In the present study, long-term (during 1999 to 2019) and seasonal changes (during 2018) of the area of Gorgan Bay and its relationship with the changes in precipitation and Caspian Sea water level have been studied. The long-term water body was calculated by using the time series of Landsat8, Landsat5 and Sentinel-2 satellites imagery, and employ the MNDWI2 index. Also, data from Topix and Json satellites were used to study the changes of Caspian Sea water level and TRMM satellite data was used for precipitation changes. The results showed that the water body of Gorgan Bay has decreased significantly during the study period and this trend continues. The long term changes in the water area of Gorgan Bay have a high correlation (0.92) with the amount of fluctuations in the water level of the Caspian Sea. During this 20-year period, the changes in the water level of the Caspian Sea have been about 120 cm. But the correlation between water area and precipitation in the long period is low (0.1). This trend is quite the opposite in a short period of one year and since the changes in the water level of the Caspian Sea in a period of one year is very small (5 cm), so the water area of Gorgan Bay has a very low correlation (0.09) with it. But in the same period, there is a relatively moderate correlation between rainfall changes and the area of Gorgan Bay water body with a delay of one month.