Evaluation of indices for characterizing the distribution and concentration of precipitation: A case for the region of Southeastern Anatolia Project, Turkey

There is a need to understand and analyze rainfall variability, since it is most variable in time and space, for assessing the erosive potential of rainfall and its impacts on soil erosion and conservation measures. In order to have a spatially realistic surface of the modified fournier index (MFI) and a statistically valid method, two different procedures of calculating the MFI were performed using the daily rainfall amounts recorded for 29 years in the region of Southeastern Anatolia Project (GAP), Turkey and efficiently integrating elevation and GIS. The method that calculated the MFI surface from the monthly rainfall amounts of each individual year and averaged over a number of years ðMFIj Þ was compared with the method that calculated the MFI surface from the averages of ith monthly rainfall amounts and averaged over a number of years ðMFIÞ. Results indicated that the MFI led to the lower-risk MFI classes than the MFIj. This was attributed to the fact that the MFI was statistically unable to account for the year-to-year variability in the rainfall data. An analysis with the relationship between the MFI and the coefficient of variation (CV) also suggested the total variability in the data set be better represented to have dependable MFI surfaces because of integration of elevation. Further calculations for surfaces of the precipitation concentration index (PCI) similar to the calculations made for the MFI surfaces conclusively indicated that the MFIj was valuable in determining the potential of the rains for causing soil erosion by providing information on a long-term total variability in the rainfall amount received.