Spatial and temporal distribution of rainfall erosivity in New Zealand

Abstract

Rainfall and its kinetic energy, expressed by rainfall erosivity, drives soil erosion processes by water. One of the most commonly used erosivity parameters is the rainfall-runoff erosivity factor R of the Revised Universal Soil Loss Equation. The goal of this study was to investigate for the first time the spatial distribution of annual rainfall erosivity in New Zealand. High-resolution data from 35 weather stations were used to calculate the R-factors. Based on these results, region-specific equations were developed and were applied by using long-term precipitation records from 597 stations. The values were interpolated with a geographic information system to generate a map showing spatial variations of rainfall erosivity. Annual R-values vary across both islands by a factor of 30, from <550 MJ mm ha–1 h–1 in parts of Central Otago to >16 000 MJ mm ha–1 h–1 in the Southern Alps. These large differences are related to climatic and topographic features. Nevertheless, the data show a high correlation to the precipitation. In most parts of New Zealand, highest erosivity values occurred in December and January, whereas the lowest values were observed in August.