Investigation of Drought effect on Groundwater in Gareh Baygan Plain and management plan using MODFLOW model

Groundwater drought is a natural hazard that develops when groundwater systems are affected by climatical drought, when climatical drought occurs, first groundwater recharge, later groundwater levels and groundwater discharge decrease. The origin of drought is a deficit in precipitation and that takes place in all the elements that comprise the hydrological cycle (flow in the rivers, soil moisture and groundwater). The frequency and severity of hydrological droughts are often defined on a watershed or river basin scale. Although all droughts originate with a deficiency of precipitation, hydrological droughts are usually out of phase with or lag the occurrence of meteorological and agricultural droughts. It takes longer for precipitation deficiencies to show up in components of the hydrological system such as soil moisture, streamflow, and groundwater. In fact, the present research has focused on forecasting the effects of drought on water budget and groundwater table using MODFLOW mathematical model in Garbaygan plain, located in the southeastern of Iran. In this study four scenarios including wet year, normal, moderate and severe drought have been considered. It means in which the rate of precipitation by solving of SPI index under four mentioned scenarios has been predicted. Then using an agreement with relationship between precipitation and recharge (natural and artificial) in transient calibration, the best estimators have been fitted for forecasting of recharge. The results showed that firstly, the hydrograph of aquifer was changing as the water budget was positive until 1996, while in 1993, the storage of aquifer increased more than 6 Mm3 but from 1997 it has decreased and in 2006 the maximum of aquifers' shortage about -2/27 Mm3 observe. In addition, the forecasting of water budget illustrates that under different precipitation conditions (from wet year to severe drought) it will be negative as it varies from -1/7 to -2/27 respectively. Moreover, groundwater level will fluctuate in different conditions and it will decline more in the locations with high densities of farming wells.