Investigating the role of meteorological drought and geodetic factors on land subsidence vulnerability using fuzzy overlay

Land subsidence has caused severe environmental hazards in most plains of Iran due to unbalanced extraction between groundwater and rainfall and the geodetic factors. In this regard, three basins of Kohpaye Segzi, Isfahan Borkhar, and Najafabad in Isfahan province were selected to study the areas with land subsidence vulnerability. Changes in aquifer water volume influenced by geodetic factors and meteorological drought were studied. The maps of the Standardized Water Level Index (SWI) and isodeep were provided in ArcGIS 10.7 software using the statistical data of piezometric wells (2002-2018). The time series analysis of 6, 12, 18, and 24-month were performed by DIP software for September as the driest month of the year. the time series with the highest correlation was zoned to show the number of SPI changes. In the last step, the weight of all indices including groundwater loss, meteorological drought, slope, and altitude was equated to evaluate land subsidence vulnerability. Land subsidence vulnerability map was prepared by overlaying the fuzzy maps of indices with strategic points. The relationship between meteorological drought and groundwater level; and correlation analysis of these two parameters with the Pearson statistical method showed a positive correlation only in 18-months time series. The results also showed that 4202 km2of the region has located in high to very high drop class, and the groundwater table has decreased 9.05 m from 2002 to 2018. In general, with a negative trend of precipitation, a positive trend was observed in the standard water level index, which increases the effective stress and was the main reason for land subsidence. According to the vulnerability map, 49 and 12.5 percent of the study area were categorized into high and very high classes of landslide vulnerability, respectively. The results showed that the probability of land subsidence will increase in the next few years because of reduction in precipitation due to climate fluctuation, slope effects, altitude, over-harvesting of groundwater potential in all parts of the basin, especially in the northern areas, and increasing density and loading especially in recent years.