چكيده انگليسي :
Many plains in central Iran have been affected by numerous droughts and suffer from a lack of rainfall. On the other hand, many uses in this area are dependent on underground water resources. In Najaf-Abad aquifer, underground water resources are used in an unconventional way, the main consequences of which can be mentioned the quantitative and qualitative decline of underground water resources and unmanaged consumption by basin users. Therefore, examining the trend of temporal and spatial changes of underground water quality parameters along with the trend of climatic variables is very important in this region. In this research, the data of 56 wells in three different decades (2001, 2011 and 2021) were used to investigate the spatial changes of the quality parameters of underground water (TH, EC, TDS, SAR andSO_4^(2-)). To prepare zoning maps from different interpolation methods, including the inverse distance method with powers of 1, 2, 3 and 4 and simple and normal kriging methods with semi-exponential models, circles E, spherical and Gaussian were used. In order to investigate the temporal changes of the qualitative parameters of underground water in Najafabad plain, the data of 15 wells during the statistical years 1997 to 2018 were used. The monthly statistics of 30 wells during a statistical period of 19 years (2003-2022) have been used to investigate the time trend of underground water level changes. In order to determine the consistency in the changing process of climatic parameters and underground water quality, the average monthly rainfall and temperature data were used during a statistical period of 19 years (2003-2022). For this purpose, Mann-Kendall test and Shib--Sen method were used to investigate the time trend of changes in water quality parameters, groundwater level, precipitation and temperature elements. The results of zoning maps showed that the quality of underground water has decreased from 2001 to 2021, in fact the quality of underground water resources in Najaf Abad plain has decreased in 2021 compared to 2011 and 2001, so the results indicate The decline in the quality of underground water resources with the passage of time in the region. According to the Mann-Kendall and Shib-Sen test results, the most significant upward changes are related to the electrical conductivity parameter and total dissolved solids. The results of the changes in the underground water level show that the underground water level of Najaf-Abad plain has decreased between 1.18 meters to a maximum of 3.31 meters in each decade. The most downward and upward changes in precipitation in the Najaf-Abad plain are related to the months of April and July respectively, only in the 3 months of April, July and January, the trend of precipitation changes in the Najaf-Abad plain was significant, which in In the months of April and December, its significant trend was downward, and in July, its significant trend was upward. The most trend of upward changes and the least trend of upward temperature changes in Najaf-Abad plain are related to the months of Khordad, Shahrivar, and August, respectively, only in the 4 months of Aribehesht, Khordad, Shahrivar, and December, the trend of temperature changes in Najafabad plain was significant, and its significant trend was upward in these 4 months. In general, the results of the zoning maps of some water quality parameters in different decades indicate a decrease in the quality of underground water. The results of the time trend of water quality changes in the statistical period of 21 years indicate a decrease in water quality. Also, the trend of underground water level changes in some wells of Najaf Abad plain is decreasing. The trend of monthly and annual precipitation changes in the Najaf-Abad plain is also downward, and the trend of monthly and annual temperature changes is also upward. Therefore, with these interpretations, the changes in climatic parameters and temporal and spatial changes in groundwater quality parameters are consistent with each other. In other words, it can be concluded that the decrease in rainfall and increase in temperature in the study area can be one of the effective factors in reducing the quantity and quality of underground water, along with the management parameter of underground water resources.
