Spatio-temporal variability of dust aerosols over the Sistan region in Iran based on satellite observations

Satellite remote sensing provides important observational constraints for monitoring dust life cycle and improving the understanding of its effects on local to global scales. The present work analyzes the dust aerosol patterns over the arid environment of the Sistan region in southeastern Iran, by means of multiple satellite platforms aiming to reveal the spatio-temporal distribution and trends. The dataset includes records of Aerosol Index (AI) from Total Ozone Mapping Spectrometer (TOMS) (1978-2001) and 6-year AI records from the Ozone Monitoring Instrument (OMI) aboard Aura. Moreover, the aerosol optical depth is analyzed through 11-year records from Multi-angle Imaging Spectroradiometer (MISR) aboard Terra (2000-2010) and from Moderate-resolution Imaging Spectroradiometer (MODIS) onboard Terra (2000-2007) and Aqua (2002-2011). The main focus is to determine the similarities and differences in dust variability over southwest Asia, in general, and the Sistan region, in particular. The results show a marked seasonal cycle with high aerosol loading during summer and lower in winter, while MISR, MODIS, and TOMS/OMI observations agree in both terms of monthly and seasonally mean spatial and temporal patterns. The higher aerosol concentrations during summer are interpreted as a result of the combined effect of the seasonal drying of the Hamoun lakes and the strong northerly Levar winds favoring dust erosion from the alluvial deposits in Sistan. After prolonged drought period, the dust aerosol load over the area has increased in the beginning of the 2000 s and decreased after 2004, thereby leading to an overall declining trend during the last decade. Such a trend is absent during the winter period when dust emission over the region is minimal.