Determination of Natural Groundwater Drought by Using New Developed NGDI Index

In addition to the over extraction of groundwater resources, one of the problems with sustainable use of groundwater, especially in the arid areas, is the occurrence of successive droughts. Therefore, an important challenge in managing groundwater resources, is to consider the effects of drought in the hydrological system. In this study, due to the necessity of separating human activities from natural droughts, a new groundwater drought index was developed and its capability evaluated in the Najaf Abad plain. In the new index, first, the effects of human activities, such as groundwater extraction or land use changes, were separated by HARTT model, and then the natural drought values are determined, by fitting the best probabilistic distribution function and standardizing that. The results of the evaluation of NGDI index in the Najafabad plain showed that, natural drought conditions prevailed over the groundwater resources in the plain between 1992 and 2000. According to the obtained results, the NGDI index provides the ability to determine the natural drought in the groundwater and distinguish the human effects from it and predict drought from several months or even more than a year before it occurs. This index can be used as an appropriate tool for managers to better control and manage groundwater resources. Therefore, the use of this index is recommended in management strategies for prediction and drought warning systems.