forecasting of groundwater table and water budget under different drought scenarios using modflow model (case study: garbaygan plain, fars province, iran)

groundwater drought is a natural hazard that develops when groundwater systems are affected by climatical drought, when climatical drought occures, 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). hydrological drought is concerned with the effects of periods of precipitation (including snowfall) shortfalls on surface or subsurface water supply (such as streamflow, reservoir and lake levels, 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. 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. also the forecasting of water budget illustrates that under different precipitation conditions (from wet year to severe drought). moreover groundwater level will fluctuate in different conditions and it will decline more in the locations with high densities of wells.