Analysis of relationship between drought and NDVI variations in different vegetation types (Case study: Southern rangelands of Yazd Province)

Abstract

Drought can be caused by reducing rainfall and/or increasing temperature. Drought has negative impact on water resources and vegetation, accelerates the desertification. In order to investigate the relationship between annual droughts and vegetation changes in southern part of the Yazd province, meteorological drought indices and remote sensing technology were employed. Firstly, annual drought intensities were determined using SPI and RDI indices. Five interpolation methods have been investigated and compared for drought zoning. In the next step, mean annual and seasonal NDVI were calculated using time series of MODIS images of 2000 to 2014 years. Then, relationship between drought indices and NDVI in 16 vegetation types were determined. According to the results, the drought intensity of the study area during time span of 1999-2000 and 2007-2008 were moderate and very high, respectively. Analyzing of correlation between NDVI and drought indices in different vegetation types indicates a significant correlation between annual, spring, and summer NDVI in most of the vegetation types (P<0.01). Coefficient of determination (R2) between annual variations of NDVI and annual SPI was obtained in Artemisia sieberi-Ebenus stellata, Zygophyllum eurypterum-Artemisia sieberi, Artemisia sieberi - Amygdalus scoparia and Amygdalus scoparia-Acer cineracens-Pistasia atlantica vegetation type with R2 = 0.75, 0,68, 0.65 and 0.63, respectively. So, in these plant types, 75, 68, 65 and 63 percent of variations of the annual NDVI index are in order subject to changes in the SPI drought index. Moreover, depending on ecological condition, species type, life forms, and accompany species; effect of drought on vegetation types is different.