Effect of Data Length, Study Span and Number of Stations on Amount of Rainfall Erosivity Factor Variability in Different Time Scales in Iran

Rainfall erosivity factor plays an undeniable role in beginning of water erosion. Study of different aspects of rainfall erosivity is also important to optimal soil and water resources management. On the other hand, the erosivity factor is being used in many soil erosion estimation models to achieve soil and water conservation goals. However, very limited studies have been conducted to study temporal variation of rainfall erosivity factor and also effect of data length, study span and number of stations on variability of rainfall erosivity factor countrywide. The present study therefore aimed to investigate the temporal variation of Wischmeier and Smith’s rainfall erosivity factor at different time scales and also, the role of data length, study span and number of stations on rainfall erosivity factor. Towards this attempt, the results of the present study with 70 stations, 20 years of data span and different study periods were compared with those obtained for another study with 18 stations and 23 years of data span. So that, the rainfall erosivity factor was calculated over 12,000 storm events for the present study and mean values for different time scales were compared using t-Test. The results showed that the maximum and the minimum values of monthly rainfall erosivity factor in the country were different from each other. Besides that, the results of t-Test showed significant difference between the calculated values of rainfall erosivity factor in some of months (p