Development of a New Composite Drought Index (CDI) based on Shannon's Entropy Theory for Multivariate Assessment of Drought in Shahrekord Plain

Drought is a climatic phenomenon that begins slowly and has a hidden nature. The duration of its occurrence and the resulting damage occur gradually in different sectors. Therefore, assessment and investigation of drought is very important in planning and implementation of actions to cope with drought. Droughts are divided into different types. One of the common methods of drought assessment is the use of drought indices which everyone can describes a type of droughts. In recent years, the use of Composite Drought Index (CDI) have attracted the attention of researchers. In this study, a new Composite Drought Index was developed that combined the three components, including the Groundwater Resource Drought Index (GRI), the Modified Standardized Precipitation Index (SPImod) and the potential evapotranspiration (ETP). In the next stage, the drought condition of Shahrekord plain located in Chaharmahal and Bakhtiari province was assessed in a 31-year period (1985-2015) using the Composite Drought Index (CDI). The results showed that the Shahrekord Plain was frequently experienced some wet conditions during the years 1985 to 2000, but it has suffered from consecutive severe droughts from 2008. In general it can be said that the developed CDI index is well able to describe the composite behavior of meteorological and groundwater droughts in the study area and is recommended as a new index for monitoring and assessing regional drought.