An improved Victorian erosivity map

The impact of raindrops on the soil surface and surface water runoff are two of the agents of soil detachment and sediment transport. The magnitude of these erosion processes is a function of the erosive potential, or erosivity of a rainstorm. The erosivity of rainfall is commonly quantified using the R factor developed for the universal soil loss equation. R is the average of the annual sum of the individual storm erosivity values and can be estimated from published relationships between the storm energy and the rainfall intensity. Currently the most likely source of R-values in Victoria is a hand-drawn contour map produced more than 20 years ago by an expert panel and published in an out-of-print handbook. A new R-value contour map for Victoria is presented, developed from current empirical relationships between rainfall intensity-frequency-duration and R. The R contours vary in value across the state by about a factor of 4, from <800 MJ.mm/ha.h.year in the north-west, to >2700 MJ.mm/ha.h.year in the eastern ranges. The new map improves the resolution and accuracy of erosivity values for Victoria, especially in steeper, forested areas, and will assist in the prediction and modelling of erosion and water quality.