Study of Spatial and Temporal Variations in Groundwater of Kerman Province to Use in Drip Irrigation of Pistachio

Kerman is one of the most arid regions of Iran, and its agriculture particularly pistachio cultivation depends on groundwater resources. In recent decades, natural factors (drought and high evaporation) and human activity (non-systematic exploitation of groundwater) caused a sharp decline in the quality and quantity of groundwater in this province. The spatial and temporal variations in groundwater salinity (EC) were evaluated using geostatistical methods and ArcGIS software. To this end, the electrical conductivity data of 2000 wells and aqueducts that are scattered in Kerman province in the years since 2002 to 2011 were used. After eliminating outstanding data and data normalization in each year, collected data were analyzed, and then choosing the best model of semivariogram, interpolating, cross-validation and mapping were done using geostatistical tools in ArcGIS software. In the study, ordinary kriging and indicator kriging were used to prepare zoning and probabilistic maps, respectively. The results of spatial structure of salinity study showed a moderate spatial structure in the studied years. Results of cross-validation indicated a good accuracy of both methods of interpolation (i.e., ordinary kriging and indicator kriging). Zoning and probabilistic maps showed an increase of more than 8 dS/m from 2002 to 2011 in the area of groundwater salinity. It was also found that groundwater of Sirjan, Shahrbabak, Rafsanjan, and Zarand cities has a very bad condition in terms of salinity, using it for pistachio orchards irrigation can seriously reduce the yield of this plant, and its cultivation in the province will be questionable. Findings showed that in 2003, 13.3% of the total of the province faced a serious risk of high salinity of 8 dS/m in which this rate was approximately constant until 2006, but in 2007 this amount rose to 8.9% and had a decreasing trend until 2011, which finally decreased to 8.4% in 2011. So as to avoid lowering the quality of groundwater resources in the province, appropriate management measures are necessary.