Analysis and Comparison of SPI and GRI Indices in Assessing Meteorological Drought and Groundwater, Case Study: Mehran Plain, Ilam Province

Droughts are one of the most devastating weather events, causing significant damage to both natural resources and human life. The purpose of this study is to analyze and compare meteorological drought and groundwater of Mehran plain using standardized precipitation index (SPI) and groundwater index (GRI). In order to study the meteorological drought, the monthly rainfall information of Mehran synoptic station was used and in order to study the dryness of the groundwater of Mehran plain, the changes of groundwater level of Mehran plain were analyzed based on water level data of 23 observation wells. Also, SPI index was used for meteorological drought monitoring and GRI index was used for hydrological drought monitoring of Mehran plain. The statistical period required for drought analysis of a 25-year statistical period from the water year of 75-74 to 97-96 was selected. After determining the moisture periods of the indices, monthly groundwater zoning maps were prepared. To prepare these maps, the kriging model was selected from among different models. Finally, by applying the optimal half-change model in kriging and entering groundwater data as a point layer, raster maps were prepared using Arc GIS software. The results of the study of SPI index show that during the statistical periods in question, 4 severe droughts occurred, the most severe of which was 90-91, with a value of SPI index of -1.73. Also, the results obtained from the GRI index in the region show that an 11-year drought period of groundwater occurred, ie it started from the water year 88-87 and continued until the water year 98-97, the most severe of which was 90-91 with the amount of The index is -1.11.