Background and Objectives: The health of alluvial aquifers is one of the most important issues that have been considered by researchers and policymakers in the watersheds around the world; among them, water resources salinity is very important. Population growth and agricultural demand have increased the extraction of groundwater resources in arid and semi-arid regions. The quality of these resources is particularly affected by pollution from fertilizers and agricultural chemicals, the intensity of which has a direct relationship with the amount of these substances. Meanwhile, electrical conductivity of water is considered a key indicator for monitoring and determining qualitative changes in groundwater.

Materials and Methods: In this study, the salinity of 55 water sources in Sirjan plain aquifer was investigated. Then, geostatistical methods such as ordinary kriging (OK), inverse distance weight (IDW) and normal distance weight (NDW) were used for zoning of water salinity in Sirjan plain. To evaluate the performance of prediction and estimation models, performance indicators of coefficient of determination (R²), root mean square error (RMSE), mean square error (MSE), mean absolute error (MAE), correlation coefficient (R) and Nash-Sutcliff (NS) coefficient are used. After selecting the best method of interpolation, spatial zoning maps related to water salinity were prepared in Arc GIS and GS⁺ softwares.
Results: Results showed that minimum salinity of water is 440 µ mhos/cm that is related to the water source of Deh Ghazi aqueduct and maximum salinity level is 19700 µ mhos/cm that is related to the Mollahaji water source. In general, average salinity of studied water sources in Sirjan plain alluvial aquifer is 2323.7273 µ mhos/cm. The ordinary kriging (OK) method showed the most appropriate amount in terms of MSE (5797901), RMSE of 2407.883, R² of 0.856806, R of 1 and NS of 0.580792, compared to IDW and NDW.
Conclusion: Water salinity is an important factor in determining the chemical properties of natural waters and its biological processes. So, it is highly regarded by researchers as well as water policymakers. Obtaining an appropriate database in relation to salinity of water resources in different regions, especially in desert provinces, is of particular importance. Results of this research showed that in the west and north-west of this region, because of proximity of Sirjan salt crust, water salinity is higher and in the southeastern part due to the proximity to the Chahghale and accumulation of sediments and high evaporation, the salinity is increasing compared to other regions. It is recommended that water resources of different aquifers of Iran be studied in a highly specialized and scientific manner along with different methods of determining water salinity in order to obtain a suitable database of water resources of different aquifers throughout the country and be used in hydro-soil projects.