Time series analysis of the subsidence of Esfarayen plain using radar interferometric method

This research combines analytical techniques and field surveys as its primary methodological components.Ground data, including piezometric wells and groundwater level decline, were analyzed using Inverse Distance Weighting (IDW) interpolation.Additionally, radar data from Sentinel-1 images were processed using SNAP software to calculate the subsidence rate during the first eight months of 2023.The results were subsequently validated through field surveys to ensure accuracy and reliability. Results and DiscussionUsing piezometric data from the periods 2018-2019, 2019-2020, 2020-2021, 2021-2022, 2022-2023, and 2018-2023, the groundwater level and its decline were evaluated using the Inverse Distance Weighting (IDW) method.The resulting maps indicate that the piezometric wells of Shorb 4 Borj, south of Zarqabad, Kalateh Shur, East Izi, northwest of Stin, and East Toy, as well as the wells of Sorkh Tapeh, Kalateh Karbalai Hossein, and south of Qamiteh, exhibit the lowest groundwater levels.This suggests that the groundwater level is significantly higher in the northern, central, and southeastern parts of the basin.The presence of karst limestone formations, permeable sandstones in the Binalud zone, and alluvial, fan, and Quaternary foothill deposits, along with numerous faults in the northern region, contribute to the enrichment of the groundwater table.However, excessive extraction in these areas has led to a decline in water levels.Similarly, the central and southeastern parts of the basin, characterized by loose, porous, and permeable sediments, show high groundwater level anomalies.To further analyze groundwater loss, the Change Detection tool in ArcGIS Pro software was used to calculate and map the decline in groundwater levels for the years 2017-2018, 2018-2019, 2019-2020, 2020-2021, 2021-2022, 2022-2023, and the cumulative period of 2018-2023.The results reveal a consistent decline in groundwater levels over these years.The piezometric wells south of Arg, south of Khorasha, south of Gazan, north of Abbas Abad, and the exploratory wells of Qasem Abad experienced the highest groundwater declines during 2018-2023, with values of -3.5, -3.2, -3.07, -2.985, and -2.65 meters, respectively.These significant declines are likely contributing to land subsidence in the region.Subsidence rates were estimated using SNAP software.The analysis focused on the first four months and the subsequent four months of 2023, followed by calculating the overall subsidence growth rate over the eight-month period.This was achieved by summing the two outputs (from the first and second four-month periods) and then multiplying by 8 to derive the final subsidence growth rate and its spatial distribution. ConclusionThis study determined that the subsidence rate in the Esfarayen plain ranged from 1 to 12 mm over an eight-month period, as calculated using SNAP software.Subsidence zoning revealed that 26.45% of the basin falls within the "high critical" zone (5 to 12 mm), and when combined with the "medium critical" areas, a total of 75.2% of the basin is classified as critical.This indicates that the Esfarayen Plain is in a critical state regarding land subsidence.The highest levels of groundwater extraction were observed in the southern regions of Sankhasat, Khorasha, Arg, Gazan, Jafarabad Kharaba, and Mehdiabad Kal Beko, all of which are located in the "very critical" zone.Wells in the "medium critical" zone include