ORIGINAL PAPER Trend analysis of the rainfall erosivity index at different time scales in Iran Seyed Hamid Reza Sadeghi • Zeinab Hazbavi Received: 4 December 2012 / Accepted: 3 January 2015 Ó Springer Science+Business Media Dordrecht 2015 Abstract The minute study of the magnitude of changeability and the trend of the rainfall erosivity index has not been taken carried out yet in Iran. The present research therefore aimed to analyze the trends of the rainfall erosivity index as an initial step in the study of the consequences of climatic change on soil environments. The trend analyses were done at three time scales, viz., monthly, seasonal and annual, by the Mann–Kendall (M–K) nonparametric statistical test. The study was conducted for 18 synoptic stations distributed throughout Iran with a 23-year (1970–1992) common data period. The results of the application of the M–K test considering the weighted area on a monthly basis showed that all months except August and December had decreasing trends in the rainfall erosivity index for the study period, while only June (p value = 0.06) and November (p value = 0.01) had a signiﬁcant decreasing trend in the rainfall erosivity index at a conﬁdence level beyond 94 %. According to the results, there was also a small general decreasing trend in the seasonal rainfall erosivity index in all time series, but not all were statistically signiﬁcant. The result of the M–K test ultimately veriﬁed a signiﬁcant trend in the annual rainfall erosivity index for the entire country with respective p, Kendall’s statistic and Kendall’s tau values of 0.042, -73 and -0.316. Keywords Erosivity index  R factor  Soil conservation  Soil erosion  Time scales  USLE 1 Introduction During the 4 last decades, the natural resources of Iran have faced some serious degra- dation problems such as land use changes, soil degradation and erosion, overgrazing in the rangelands and groundwater overexploitation (Soltani et al. 2012). Increasing land S. H. R. Sadeghi (&)  Z. Hazbavi Department of Watershed Management Engineering, Faculty of Natural Resources, Tarbiat Modares University, 46417-76489 Noor, Mazandaran, Islamic Republic of Iran e-mail: sadeghi@modares.ac.ir 123 Nat Hazards DOI 10.1007/s11069-015-1607-z