Application of groundwater modeling to predict drought impacts on groundwater resources in the Garbaygan plain, Iran

Abstract

This study investigates the application of groundwater modeling for the understanding how meteorological droughts propagate through the groundwater system and how the latter responds in terms of storage and water levels. The study region is the Garbaygan plain, located in the southeastern area of Iran, where the farmlands are strongly dependent on irrigation by groundwater. Four meteorological drought scenarios, as defined by the standard Z-score index, the latter being computed based on precipitation data between 1993 and 2008, are considered, namely, a very wet situation, a normal, a moderate and a severe drought.  Afterwards, a numerical groundwater model is set up, calibrated and validated on observed groundwater heads during that time period to estimate the groundwater storage and levels, wherefore the unknown aquifer recharge has then been one of the calibration targets. The latter is then used to set up a linear regression model between precipitation and recharge. The results indicate that even under very wet and normal years, as defined by the corresponding annual Z-scores, the groundwater budget will still be negative (Over draft), which means that other factors, such as the increasing - and not well-known - groundwater over-exploitation may also be the origin of a groundwater drought. Finally, groundwater budgets and levels for the “future” year 2009 have been predicted for the four drought scenarios, using corresponding Z-score- estimated annual rainfall in the regression equation to compute firstly the recharge and then using the latter to drive the groundwater flow model.