MODIS vegetation and water indices for drought assessment in semi-arid ecosystems of Iran

Abstract

In order to evaluate how vegetation indices are affected by climatic patterns and to assess the relationships between them in semi-arid ecosystems of Iran, a six year (2000-2005) time series Moderate Resolution Image Spectrometer (MODIS) data over a six month growing season was used for retrieving Normalized Difference Vegetation Index (NDVI) and two Normalized Difference Infrared Indices (NDII6 and NDII7 using band 6 and 7 MODIS data, respectively) used as Vegetation Water Index (VWI). The study was carried out in dry farming and rangeland areas located in northwestern part of the country. Vegetation indices dynamics and relationships as well as their response to precipitation were studied. The results revealed the high dependence of temporal dynamics of MODIS vegetation indices on precipitation, promising the capability to differentiate drought and normal conditions in different land cover types. Among all indices, NDVI was found to be the best index to be used for drought detection for it had better relationship with precipitation and close relationship with the VWIs. The results of this research can be used as the basis to develop a region-specific drought index for semi-arid regions of Iran.