Affectability of runoff threshold and coefficient from rainfall intensity and antecedent soil moisture content in laboratorial erosion plots

Rainfall intensity, antecedent soil moisture condition and slope steepness are among the main important physico-climatic factors whose individual or interactive effects determine the hydrological response of a watershed to a rainfall event. The present research was conducted to study the individual and interactive effects of rainfall intensity and antecedent soil moisture contents on runoff threshold and coefficient under laboratory conditions in four rainfall intensities of 30, 50, 70 and 90 mm h-1 and five antecedent soil moisture contents of 12, 19, 29, 36 and 44 volumetric percent in sandy-loam soils taken from a summer rangeland in the Alborz Mountains, Northern Iran. The results showed the significant correlation (p<0.01) between rainfall intensity and antecedent soil moisture, and runoff threshold with correlation coefficients of -0.709 and -0.628 and runoff coefficient of 0.517 and 0.804, respectively. The significant antagonistic interaction between rainfall intensity and antecedent soil moisture content on runoff threshold was confirmed. Separation of treatment levels also confirmed the existence of significant turning points in runoff threshold and coefficient at the rainfall intensities about 40 and 60 mm h-1, respectively, and in the runoff threshold at the antecedent soil moisture content between 12 and 19 volumetric percent.