Rainfall erosivity map for south-central Chile

Abstract

The average annual rainfall-runoff erosivity factor R is a location specific index that reflects the effects of both the amount of rainfall and its intensity on erosion. The R factor is traditionally determined by calculating the average annual sum of the product of a storm’s energy E and its maximum 30-minute intensity I30, known as the EI30. High resolution precipitation data are needed to rigorously evaluate rainfall erosivity, so the original method proposed to calculate EI30 requires pluviograph records. Data with such high temporal resolution is difficult to obtain in many parts of the world, and its processing is both time-consuming and laborious. In spite of time and/or data limitations, many efforts have been carried out all over the world in order to compute R factor values. In Chile, even though there is a well distributed rain gauge network, no systematic characterization of the territory exists in terms of rainfall erosivity. This paper presents a rainfall erosivity map for most of the cultivated land in South-Central Chile, an area approximately 840 km long by 100 km wide. Rainfall erosivity estimates were based on two kind of spatial data: a) direct calculation of the erosivity based on pluviograph records and b) indirect estimation by using an empirical procedure based on annual rainfall. Point estimates generated by both methods were interpolated by using kriging to create a map. The results showed a consistent increment in the rainfall erosivities as a result of the latitude, elevation and annual rainfall rate. Although the estimates could be improved by generating additional point estimates, the erosivity map should prove to be a good tool for land-use planners in the South-Central region of Chile and other areas with similar rainfall characteristics.