Drought monitoring in Iran using the perpendicular drought indices

This paper aims at finding, evaluating and refining an appropriate drought estimation method for semi-arid regions, e.g., Iran using remote sensing. Recently developed methods, the Perpendicular Drought Index (PDI) and Modified Perpendicular Drought Index (MPDI), are selected as satellite based drought indices in this study. Time series of the Moderate Resolution Imaging Spectroradiometer (MODIS) images are collected over the region spanning the time interval from February 2000 to December 2005, and the PDI and MPDI are calculated. Then, these indices are evaluated against meteorological drought indices including Z-score (Z), China-Z Index (CZI) and Modified China-Z Index (MCZI) over 180 meteorological observing stations in Iran. The results show that there is a statistically significant correlation between the PDI and MPDI and regional surface dryness and drought conditions. It is further confirmed that the PDI is performing well for bare soil applications or early stages of vegetation growth, while the MPDI is best for vegetated surfaces yet effective for bare soils. Since Iran is characterized by semi-arid or arid climatic conditions, the perpendicular drought indices could be used as simple remote sensing-based drought indices in Iran and in other developing countries with similar climatic conditions.