Expected impacts of climate change on rainfall erosivity of farmlands in Japan

• We assessed impacts of a climate change scenario on rainfall erosivity of farmlands.
• Erosivity was obtained based on the regional climate model RCM20.
• Future erosivity is expected to increase by more than 20%.
• Relative changes in future erosivity are expected to vary seasonally and spatially.

In this article we have assessed the expected impacts of future climate changes on rainfall erosivity, a rainfall factor associated with soil erosion, of farmlands in Japan. The assessment compared values of R-factors for two future periods with values for a near past period. The R-factor is defined as the mean annual sum of individual storm erosion index values EI30, where E is the total energy for a storm and I30 is the maximum 30-min intensity. The R-values at 1036 meteorological stations for three periods (1981–2000, 2031–2050 and 2081–2100) were calculated with a model that estimates monthly EI30 values based on daily precipitation data. Subsequently, R-values for farmland areas were obtained. The daily precipitation data were provided from the regional climate model RCM20, which simulates climate change based on the SRES A2 scenario. The model to estimate monthly EI30 values performed well with a coefficient of determination in excess of 0.5 for 97% of the 1036 stations when parameters of the model were optimized. Therefore, the rainfall erosivity model can be used to accurately estimate the R-factors. Calculations of relative changes in R-values for the two future periods compared to the near past period indicated that rainfall erosivity will increase in most farmland areas due to climate change. The R-values of farmland areas for the two future periods are expected to increase an average of more than 20% when compared to the near past. Additionally, changes in rainfall erosivity during each of the future periods are expected to vary with different seasonal and spatial patterns. The changes in erosivity appear to be attributed mainly to changes in precipitation intensity as well as amount of precipitation. Therefore, these results suggest the scenario of climate changes occurring in the future up to 2100 will increase soil erosion of farmlands in Japan at an average rate of increase greater than 20% based on just the effects of the rainfall erosivity factor.