Investigating quantity and salinity trend of groundwater in Shiraz basin and its affecting factors using in situ and remote sensing data

Declining water table and its consequences due to overexploitation of groundwater resources will be one of the challenges in the coming years in arid and semi-arid areas. Therefore, in this study, the groundwater level and its salinity in Shiraz basin for 27 years (1993-2020) was investigated. The trend of the water table time series was analyzed using Mann-Kendall test. Result shows a significantly decreasing trend; So that the negative trend of water table after the change point in June 2002 has increased to 2.8 times of the previous period. The possibility of using Gravity Recovery and Climate Experiment (GRACE) satellite data to monitor the groundwater level was also investigated. The results show very good accuracy (NRMSE <10%) of different versions of data. Examination of groundwater salinity using electrical conductivity (EC) data showed an increasing salinity trend in the basin. Factors affecting decreasing trend of quantity and quality in the basin were also analyzed. Results showed no significant trend in rainfall time-series. However, the increasing trend of the population and vegetation in the basin and the lack of surface water resources have led to a significant increase in groundwater abstraction. Thus, when planning, the land sustainability should be seriously considered by managers.