Evaluating and monitoring of moisture variations in Meyghan wetland using the remote sensing technique and the relation to the meteorological drought indices

Wetlands are one of the most important natural ecosystems that due to climate changes and recent droughts, their moisture levels have been reduced. The purpose of this study was to investigate the relationship between the Standardized precipitation, drought index  (SPI) and Standardized precipitation-evapotranspiration index (SPEI) with mean values of Modified normalized difference water index (MNDWI)in Meyghan wetland. For this purpose, Landsat multitemporal images and climatic data related to the Arak synoptic station were used for the period of 28-year (1990-2017). After applying the necessary preprocessing on satellite images, MNDWI and its average values were computed for each year. In order to investigate the relationship between drought indices and mean values of MNDWI, the scatter diagram between them was delineated and the coefficient of determination obtained from the bivariate regression model was calculated. The results showed that the drying trend in Meyghan wetland during the study period was growing so that the average surface moisture of the wetland decreased from 0.36 in the initial years to -0.04 in the final years the coefficient of determination obtained from the fitting of the regression model between the SPI and MNDWI and between SPEI and MNDWI was estimated 0.34 and 0.51, respectively. These results indicate that 34% and 51% of the moisture changes in Meyghan wetland are explained by the SPI and SPEI, respectively.