Evaluation of the relationship between forest drought and drought using statistical models in Ilam province

In this study, the relationship between dieback of Persian oak trees and drought in Ilam province has been investigated. The main purpose of the research is to introduce a suitable model of relationship between oak dieback and drought. So from SPI and NDVI indicators and Moran index and statistical regression statistics and satellite images of Modis and Landsat have used to analyze the relationship between dieback of Ilam forests and happened drought in the region. The precipitation data of 93 rain gauge stations were analyzed during the statistical period and according to the dry coefficients of SPI index, drought zoning layers of Ilam province were prepared for two time series of 2000 to 2009 and 2010 to 2019. Greenery's raster layers were prepared from Modis satellite imagery for the mentioned time series. The results of analysis of Moran's statistical showed a significant correlation between the SPI index and the NDVI index in spatial dimensions. By a simple random method, 143 points of oak dieback with dimension of 30 m2, which each point was equivalent to a pixel-size, were recorded with a GPS device, and by simulating in satellite imagery, the droplet layer of oak dieback was extracted. Although linear regression between extracted oak dieback points with SPI and Moran statistical indicators was significant, but the relationship between NDVI index and Moran statistic has the effect of independent variable of drought trend in spatial and temporal dimensions on the dependent variable process of oak drought with spatial analysis. And nonlinear regression has a more appropriate and accurate statistical significance and explanation. So this method as desirable method has been introduced for analyzing of drought and oak dieback.