Assessment the Effect of Drought on Vegetation in Desert Area using Landsat Data

Drought phenomenon is one kind of a disaster that can significantly affect the density of vegetation in any area especially dry regions. This study tries to express the effect of drought on vegetation cover in Yazd-Ardakan plain, central Iran. At first, annual average for SPI index was calculated from 1996 to 2015, and then NDVI was calculated for May in 1998, 2000, 2009, 2010, 2011 and 2015. Afterwards, NDVI maps were classified into three groups including no vegetation, poor vegetation (pastures), and dense vegetation (farmlands and gardens). Based on the results the worst value of drought was −1.92 in year 1999. Besides, the annual SPI of 1996 with value of 2.4 was considered as the wettest year during study period (1996-2015). The highest percentage of dense vegetation and poor vegetation were related to 2010 and 1998 respectively, and the lowest percentage for both classes was related to 2000. There was correlation among the area of poor vegetation class in middle of spring and previous annual SPI at the significant level of 95%. In contract, no correlation was found between dense vegetation class areas in middle spring and previous amount of annual SPI. The study of the correlation between the SPI average and the percentage of vegetation classes indicated that pastures were highly sensitive to SPI changes; however, farming lands showed less sensitivity in short term due to using deep wells.