Combining climate information and remote sensing in the integrated drought index, for zoning of drought the Yazd-Ardakan plain

Drought is a widespread phenomenon that its intensity varies in time and place. Drought monitoring using meteorological data alone, is not accurate due to small number and inadequate distribution of meteorological stations. Therefore, the use of remote sensing technique and vegetation indices is important as a useful integrated solution for the study of drought. The present study was conducted for Drought zoning in Yazd-Ardakan plain by combining meteorological and remote sensing data. In this research, data of meteorological stations of Yazd, Meybod and Mehriz between 2002 and 2015 have been used. First, the Standard Precipitation Index (SPI) was calculated in monthly scale for all three stations. The mean values of monthly SPI computed and mapped. Using Landsat images, the SAVI index was calculated and its map was prepared in 16 different times. Due to the role of the temperature in the occurrence of drought, the IDI (Integrated Drought Index) was calculated using temperature and precipitation and SAVI index. Zoning of mean SPI values showed that the lowest SPI values are in the middle, north and southeast and the highest values are related to the western heights of the plain. SAVI zoning showed that the rangelands of Meybod and Yazd regions have the lowest density. The correlation coefficient of SPI and SAVI values varies between 0.5 to 0.65, and larger values belong to Mehriz region. IDI values are lower in higher rangelands, meaning that these areas have been less affected by drought. The mean values of IDI in Mehriz, Yazd and Meybod regions reach a maximum of 5, 100 and 160. Temporal changes in drought indices showed that when rainfall increased, the IDI index decreased. The possibility of lag time between precipitation and changes in IDI was also observed. Comparison of monthly IDI values and rainfall showed that the time effect of rainfall on IDI index is about three months.