Assessment of MODIS-Derived NDVI and EVI for Different Vegetation Types in Arid Region: A Study in Sirjan Plain Catchment of Kerman Province, Iran
Trend of vegetation in typology scale has remained uncertain especially in arid ecosystems. Therefore, we aimed to asses two vegetation indices including as the Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI). Trends and their rates of indices in vegetation types were analyzed by the Mann–Kendall test and Theil–Sen trend estimator. To this end, first we determined the typologies maps of Sirjan Plain catchment based on field operations then, Moderate Resolution Imaging Spectroradiometer (MODIS) monthly data with the spatial resolution as 250 m × 250 m from 2000 to 2019 were organized into the NDVI and EVI time series to investigate the trend. The results showed that some vegetation types which had not a distinct trend, were random and time-independent however, the Alhagi camelorum type demonstrated the EVI and NDVI annual increase by 0.0009 and 0.0011 year-1 respectively. The other types that changed dimensionally associated with stochastically, had different slopes of increase according to Theil–Sen estimate. The most increased rate of the NDVI was attributed to Artemisia sieberi- Amygdalus lycioides- Ebenus stellata type (0.0015 year-1) whereas, for the EVI Artemisia aucheri-Astragalus parrowianus, Zygophyllum eurypterum- Artemisia sieberi- Astragalus arbusculinus, Dendrostellera lessertii-Noaea minuta, Artemisia sieberi- Zygophyllum eurypterum and Cornulaca monacantha-Salsola orientalis types were increased by 0.0008 year-1. Of note, sudden NDVI and EVI changes (out of confidence level of Theil–Sen estimate) were observed for majority of types especially in 2008 and 2017. More investigations on environmental data and human activity in the mentioned years affecting as turbulator of majority of types, are recommend.