Investigation of the effect of different rainfall patterns on runoff and soil loss in Tokat region

In this research, rainfall pattern distributions and some characteristics of natural rainfall of Tokat region are identified. Rainfall duration, amount, intensity, energy, 10, 15 and 30 minutes maximum intensity values, soil losses and runoff relationships of the grouped rainfall patterns are compared. For this purpose, a total of 361 erosive individual rainfalls recorded between 1978 and 1995 in Tokat province are evaluated. Nine of these rainfalls were uniform, 96 of them advanced, 159 of them intermediate, 41 of them delayed and 56 of them were of mixed rainfall patterns that did not comply with the classification. The rainfall characteristics, runoff and soil loss values evaluated for each precipitation pattern are compared statistically using the Mann-Whitney u non-parametric test. The rainfall duration for different rainfall patterns increased as Uniform, Delayed, Advanced, Mixed and Intermediate pattern, respectively. Uniform pattern rainfall duration differentiated from other rainfall patterns and showed a statistically significant difference. The amount of precipitation increased to present a Delayed, Uniform, Intermediate and Advanced rainfall pattern, respectively. The Delayed pattern which has the lowest rainfall amount was in the same group with the Uniform rainfall pattern, statistically, however showed a significant difference from other rainfall patterns. Precipitation intensities increased as Mixed, Delayed, Moderate, Advanced and Uniform rainfall pattern, respectively. The difference between the intensity values of the Uniform and Mixed rainfall pattern was found to be statistically significant. The maximum intensity values of 10 and 15 minutes rainfalls were statistically significant between Uniform and Moderate, Uniform and Delayed, Uniform and Mixed, Advanced and Medium, Advanced and Delayed, and Advanced and Mixed pattern rains. Considering the 30-minutes maximum intensity of precipitation, the difference between Uniform and Medium, Uniform and Mixed, Delayed and Mixed patterns were found to be significant. No statistical relationship was found between the rainfall with different rainfall patterns and the runoff and soil losses occurring in the model plot. On the other hand, the amount of soil loss and runoff values in the model plot were compared with the precipitation patterns depending on night, daylight and mix times rainfall periods. According to this assessment, the highest total soil loss occurred as 39.27 ton ha-1 in the advanced pattern night rainfalls. The highest total runoff occurred as 43.08 mm in moderate precipitation with mixed rainfall durations. Keywords: Erosive Rainfall, Natural Rainfall, Rainfall Pattern, Runoff, Soil Loss, Tokat