Estimation of soil loss from single storm events is essential for basin planning and nonpoint source pollution control. Rainfall-runoff erosivity factors for single storm events in northern Iraq were derived from the basic theory of soil detachment and transport. The factors derived are a single parameter which includes runoff depth only and a factor which combines runoff depth and peak rate. These two erosivity factors gave satisfactory results when tested using data from natural runoff plots collected at different sites in the region. The same data were then used to test the applicability of various established erosivity factors. The two derived erosivity factors were superior to any known erosivity factor tested in the region. These include factors currently in use in Universal Soil Loss Equation (USLE) applications in different parts of the world.