Simulating Potential Impacts of Climate Change on Sediment Production and Shallow Landslide in Western Japan

Abstract

本研究では気候変動が西日本の地域レベルでの土砂生産及び斜面不安定性に与える潜在的な影響をシミュレーションにより評価する．気象研究所の気候モデル（MRI-AGCM20)により計算された20km解像度の降雨データを地質水文モデルに入力し，時間解像度1時間，空間解像度1kmでこの影響評価を実施する．結果として，将来気候下での降雨変化が，河川流域における土砂生産と斜面不安定性に影響を及ぼすことがわかった．将来気候下では，6月と7月の総降水量が減少するが，8月の総降水量は増加する．西日本の各地域で8月に5-75%総降雨が増加し，これにより河川流量が1-20%増加，土砂生産は1-30％の増加，浅層崩壊は1-50%増加することわかった．特に変化が顕著な地域は時期と位置により異なる。

This study uses a continuous simulation model to assess the potential implications of climate changes on soil production and slope instability at regional scale in the western part of Japan. Using the product of a very high-resolution atmospheric global climate model having 20-km spatial resolution (MRI-AGCM20) as the climate forcing data, a calibrated geohydrologic model was implemented with hourly output and 1-km grid resolution. The results suggest that the river basins hydrological responses to precipitation changes under the future climate is going to have direct impact on soil productions and slope instability. In the future climate condition, peak time and magnitude of gross precipitation in June and July decreases, while it is going to be shifted to and increase in August. The study found a 5-75% increase in August precipitation to be associated with up to an approximate 1% to 20% of change in streamflow discharge, 1% to 30% of increase in soil production and 1% to 50% of increase in shallow landslide probability. Hotspots of significant changes differ according to the time and location.