Frequency of forest road collapses with various rainfall intensities.

Abstract

The authors estimated the expected value of the number of forest road collapses in a 1-km road segment caused by a rainfall event with various intensities. Radar/Raingauge-Analyzed Precipitation data, basic data of forest roads in private forest areas in the Toyama prefecture, and data about forest road collapses that occurred in the areas in the past 21 years were used to estimate the expected value. The estimated expected value was 10^-3 orders of magnitude with a rainfall event where the maximum rainfall per 24 hours was 100 mm or more, and less than 150 mm, while the value was 10^-1 orders of magnitude with a rainfall event of 300 mm or more, and less than 350 mm. This model enables us to predict the number of forest road collapses in a given area over a certain period, taking into account the increase in density of forest roads and the frequency of intense rainfall events due to climate change.