Forecasting 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 is developed when groundwater systems are affected by drought. When meteorological drought occurs, first groundwater recharge decreases, then groundwater level and groundwater discharge from aquifer decrease. The origin of drought is a deficit in precipitation that takes place in all hydrological cycle elements (flow in 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 stream flow, 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 from a deficiency in precipitation, hydrological droughts usually occur with a lag comparing to meteorological and agricultural droughts. It takes longer for precipitation deficiencies to show up in components of the hydrological system such as soil moisture, stream flow, and groundwater. 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 southeast of Iran. In this study four scenarios including wet year, normal, moderate and severe drought have been considered. Then, using the obtained relationship between precipitation and recharge (natural and artificial) in transient calibration stage, the best estimators have been fit to forecast the recharge. In addition, forecasting water budget illustrated that under different precipitation conditions (from wet year to severe drought), groundwater level will fluctuate so that a larger loss will occur in locations with high densities of wells.