Comparison of Annual Moisture Flux Variability during Dry and Wet Years over Iran

The main objective of this study is to investigate the relationship between the variability of the atmospheric moisture flux and precipitation during wet and dry years over Iran. For this purpose, the ERA-Interim data including precipitation, specific humidity and eastward-northward wind components were extracted from European Centre for Medium-Range Weather Forecasts database with a spatial resolution of 1° × 1°. Then, wet and dry years were determined by standardized z -index during the 1981–2011 period. The vertically integrated moisture flux was calculated for the troposphere layer from 1000 to 300 hPa. Results revealed that moisture flux into the troposphere in wet years has been 16.54% more than in dry years. However, moisture changes in the lower layers of the troposphere directly affect precipitation variability over the country ( r = 0.6). The atmospheric circulation patterns have transported the most moisture from the south direction toward Iran. Transported moisture from Arabian Sea in a wet year (1999–2000) has been higher than a dry year (2007–2008) by 62.9%. However, this Sea is the main source of moisture transfer into the lower layers of troposphere in both selected dry and wet years. Hereupon, it can be concluded that annual changes in the amount of moisture transfer from the Arabian Sea can be considered as one of the main reasons for drought occurrence in Iran.