The use of the Universal Soil Loss Equation to predict erosion losses and for conservation planning requires an evaluation of index values of local rainfall erosivity. As a contribution to knowledge on these indexes in the coastal zone of Ceará State, the objectives of this study were: (a) to determine the R factor and the annual EI30 index values, its monthly distribution, probability of occurrence and return periods in Fortaleza, Ceará State, Brazil for the period of 1962 to 1981, and (b) to create a data bank that allows, by a subsequent analysis, the assessment of correlation between the EI30 index and monthly rainfall amounts in order to simplify the index calculation and to update its values for the years 1982 to 2000. Total rainfall kinetic energy, uniform intensities, maximum 30 minutes intensity and the EI30 index for individual rainstorms were determined on 7,300 daily rain gauge charts from 1962 to 1981, available at the Meteorological Station of the Federal University of Ceará, in Fortaleza. The distribution frequency for the maximum individual and annual EI30 values and their return periods were calculated and plotted on curves of occurrence probability of these values. Over the 20 years period, the R factor found in Fortaleza was 6,774 in a range from 2,237 to 12,881 MJ mm (ha h y)-1 and this average annual value is expected to occur, or to be exceeded, at least once in 2.2 years with an occurrence probability of 46 %. Maximum individual EI30 values estimated for return periods of 2, 5, 20, 50 and 100 years were 1,363, 2,415, 3,783, 5,950 and 8,000 MJ mm (ha h)-1, respectively. Distribution of the local erosivity showed that 97 % of the annual EI30 occurs in the first semester of the year. Highest soil and water losses are to be expected during the months of February to May, since 70 % of the annual erosivity index value occurs in this quarter of the year, when conventional tillage is used for seedbed preparation and the canopy is incipient.
R factor; conservation planning; EI30 index; Universal Soil Loss Equation
