Doktorsafaei,Hamid

Assessment and Development of Integrated Groundwater Drought Index (IGDI),

A Case Study: Zayandehroud River Basin

Drought is a stochastic natural hazard that is instigated by intense and persistent shortage of precipitation. Following an initial meteorological phenomenon, subsequent impacts are realized on agriculture, hydrology and with delay, on groundwater. Among the natural hazards, droughts possess certain unique features. In addition to delayed effects, droughts vary by multiple dynamic dimensions including severity and duration, which in addition to causing a pervasive and subjective network of impacts makes them difficult to characterize. Development and assessment of drought indices for estimating the severity of drought in groundwater provides appropriate approaches and plans to deal with this destructive phenomenon.

This study has been carried out for defining an integrated index including main factors of drought and applied to the Zayandehrood river basin in the central Iran plateau as a study area. Like most areas in Iran, many other drought indices have been developed over the years, with monitoring and forecasting purposes but some of few drought indices are focused on the groundwater resources for this basin.

An integrated index includes various factors such as meteorological, hydrological, agricultural, socio - economic and environmental drought. In recent years, due to shortages of surface water resources, the study area has been faced with increasing use of groundwater and consequently a severe reduction in groundwater resources. In this study, a novel integrated groundwater drought index (IGDI) is presented as a reliable and useful tool in a multi-analysis approach for monitoring drought conditions. The long-term climate data (1374-1390) are used for assessment. In designing of integrated index, we have used combination of static and dynamic layers. Static layers including soil in three categories (surface, saturated and unsaturated), hydraulic conductivity and land use. Dynamic layers including infiltration of precipitation, groundwater levels, thickness of saturated layer, released water from upstream dam, and electrical conductivity of ground water. All static and dynamic layers representing spatial maps of different factors were prepared and compiled using Geographic Information System (Arc-GIS software). Each of static and dynamic factors has been categorized in to various sub- justify; LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt; unicode-bidi: embed; DIRECTION: ltr; mso-layout-grid-align: none" dir=ltr >Integrated index was verified by observed groundwater droughts in the Zayandehrood basin. Results show that based on values of integrated index, water year 1374-75 was very wet year and water year 1389-90 was very extremely drought year.

Keywords: Drought, Integrated Index, Zayandehrood basin, Groundwater resources, Geographic Information System (GIS).