Abstract- Human life throughout history and around the world has always been exposed to a variety of natural hazards. Some of these risks arise from geological processes such as the earthquake and some others that are more abundant and widespread, are caused by climate processes. Among them, the importance and extent of drought is significant. In this paper, Fourier and wavelet spectral analysis have been used to study the behavior of the recorded precipitation time series related to Iran's main catchments. Due to expected hydrological characteristics of each catchment and based on the coordinates of I.R.OF IRAN Meteorological Organization's synoptic stations, monthly averaged precipitation time series have been produced from 1960 to 2010 for each catchment and the extracted signals have been analyzed using Fourier and wavelet transforms, separately and together, and the results are compared with corresponding modeled Total Water Storage time series analysis outcomes. The results, introducing certain frequencies of each catchment, their common frequencies and time durations, are in good agreements with the similar previous research findings and the reported droughts in Iran.