Abstract
Abstract. Rainfall erosivity, considering rainfall amount and intensity, is an important parameter for soil erosion risk assessment under future land use and climate change. Despite its importance, rainfall erosivity is usually implemented in models with a low spatial and temporal resolution. The purpose of this study is to assess the temporal- and spatial distribution of rainfall erosivity in form of the (Revised) Universal Soil Loss Equation R-factor for Switzerland. Time series of 22 yr for rainfall (10 min resolution) and temperature (1 h resolution) data were analysed for 71 automatic gauging stations distributed throughout Switzerland. Regression-kriging was used to interpolate the rainfall erosivity values of single stations and to generate a map for Switzerland. Latitude, longitude, average annual precipitation, biogeographic units (Jura, Midland, etc.), aspect and elevation were used as covariates, of which average annual precipitation, elevation and the biographic unit (Western Central Alps) were significant (p<0.01) predictors. The mean value of long-term rainfall erosivity is 1330 MJ mm ha−1 h−1 yr−1 with a range of lowest values of 124 MJ mm ha−1 h−1 yr−1 at an elevated station in Grisons to highest values of 5611 MJ mm ha−1 h−1 yr−1 in Ticino. All stations have highest erosivity values from July to August and lowest values in the winter months. Swiss-wide the month May to October show significantly increasing trends of rainfall erosivity for the observed period (p<0.005). Only in February a significantly decreasing trend of rainfall erosivity is found (p<0.01). The increasing trends of rainfall erosivity in May, September and October when vegetation cover is scarce are likely to enhance soil erosion risk for certain agricultural crops and alpine grasslands in Switzerland.
Highlights
Soil erosion by water in Switzerland is a major environmental threat because Switzerland is one of the countries where strongest effects of climate change are expected (Beniston, 2006; IPCC, 2007)
As field measurements of the kinetic energy of rainfall are scarce both in space and time, numerous works have assessed the relationship between conventional rainfall characteristics and soil detachment e.g. Hudson (1971) for the USA and some regions in Africa, Lal (1976) for Nigeria and Arnoldus (1977) for Morocco
This study aims to evaluate the temporal as well as the spatial distribution of rainfall erosivity and to produce a map of average annual rainfall erosivity for Switzerland
Summary
Soil erosion by water in Switzerland is a major environmental threat because Switzerland is one of the countries where strongest effects of climate change are expected (Beniston, 2006; IPCC, 2007). Rainfall is one of the main drivers of soil erosion by water. Climate change may lead to changes in rainfall characteristics and is a major concern to soil conservation. The relation between rainfall and sediment yield is given by the rainfall erosivity, which quantifies the kinetic energy of raindrop impact and rate of associated surface runoff. As field measurements of the kinetic energy of rainfall are scarce both in space and time, numerous works have assessed the relationship between conventional rainfall characteristics and soil detachment e.g. The most prominent and widely-used for temperate zones is probably the (Revised) Universal Soil Loss Equation R-factor, which is the sum of all erosive events during a one year period (Wischmeier and Smith, 1978; Brown and Foster, 1987; Renard et al, 1997)
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