Assessing the Effects of Recent Droughts on Changes in Groundwater Level in the Sarvestan Plain of Fars Province

In recent years, severe droughts have occurred in most regions of Iran that can be attributed to reduced atmospheric precipitation. The consequence has been a steep fall in the phreatic zone of ground water aquifer. In this study, Standardized Precipitation Index (SPI) at different time scales and Groundwater Resource Index (GRI) were used in order to investigate the state of the recent droughts and their effects on groundwater resources. First, the monthly rainfall data of 6 meteorological stations and the water level of 24 wells in Sarvestan plain of Fars province were collected during the 1991-2012 period. After performing homogeneity tests on the data and eliminating statistical deficiencies by differentiation and ratios, the indicators mentioned were calculated in annual and 3, 6, 9, 12, 18, 24 and 48 months periods. The results of this study showed that during the studied period, the meteorological drought and the groundwater of the plain had an increasing trend and the groundwater table level decreased by as much as 10.9 meters. Correlations between SPI index at different time scales with and without time delay and the average level of groundwater table and GRI index were investigated. Statistical analysis showed that the correlations between SPI index calculated on a 48-month time scale without applying time delay and the mean groundwater level and GRI index were significant at 0.01 level indicating the effect of drought on the underground water of Sarvestan plain. Regression analysis between average height of groundwater level and the SPI showed that 56% of the variance in the mean saturation level was affected by 48-month SPI and 44% were affected by other factors, especially the extra exploitation of groundwater.