Abstract
Abstract. The objective of this study was to estimate the potential sediment yield distribution in Japan attributed to extreme-rainfall-induced slope failures in the future. For this purpose, a regression relationship between the slope failure probability and the subsequent sediment yield was developed by using sediment yield observations from 59 dams throughout Japan. The slope failure probability accounts for the effects of topography (as relief energy), geology and hydro-climate variations (hydraulic gradient changes due to extreme rainfall variations) and determines the potential slope failure occurrence with a 1-km resolution. The applicability of the developed relationship was then validated by comparing the simulated and observed sediment yields in another 43 dams. To incorporate the effects of a changing climate, extreme rainfall variations were estimated by using two climate change scenarios (the MRI-RCM20 Ver.2 model A2 scenario and the MIROC A1B scenario) for the future and by accounting for the slope failure probability through the effect of extreme rainfall on the hydraulic gradient. Finally, the developed slope failure hazard-sediment yield relationship was employed to estimate the potential sediment yield distribution under a changing climate in Japan. Time series analyses of annual sediment yields covering 15–20 years in 59 dams reveal that extreme sedimentation events have a high probability of occurring on average every 5–7 years. Therefore, the extreme-rainfall-induced slope failure probability with a five-year return period has a statistically robust relationship with specific sediment yield observations (with r2 = 0.65). The verification demonstrated that the model is effective for use in simulating specific sediment yields with r2 = 0.74. The results of the GCM scenarios suggest that the sediment yield issue will be critical in Japan in the future. When the spatially averaged sediment yield for all of Japan is considered, both scenarios produced an approximately 17–18% increase around the first half of the 21st century as compared to the present climate. For the second half of the century, the MIROC and MRI-RCM20 scenarios predict increased sediment yields of 22% and 14%, respectively, as compared to present climate estimations. On a regional scale, both scenarios identified several common areas prone to increased sediment yields in the future. Substantially higher specific sediment yield changes (over 1000 m3/km2/year) were estimated for the Hokuriku, Kinki and Shikoku regions. Out of 105 river basins in Japan, 96 will have an increasing trend of sediment yield under a changing climate, according to the predictions. Among them, five river basins will experience an increase of more than 90% of the present sediment yield in the future. This study is therefore expected to guide decision-makers in identifying the basins that are prone to sedimentation hazard under a changing climate in order to prepare and implement appropriate mitigation measures to cope with the impacts.
Highlights
The latest report from the Intergovernmental Panel on Climate Change (IPCC AR4 by Parry et al, 2007) along with many other studies predicts increases in the frequency and intensity of heavy rainfall in high-latitude areas under enhanced greenhouse conditions (Jones and Reid, 2001; Palmer and Raisanen, 2002; Fowler et al, 2005)
They can be used to predict the susceptibility of the impact, which enables us to link the model with climate change studies
We developed a relationship between the annual average specific sediment yield and the average probability of slope failure in the representative catchment
Summary
The latest report from the Intergovernmental Panel on Climate Change (IPCC AR4 by Parry et al, 2007) along with many other studies predicts increases in the frequency and intensity of heavy rainfall in high-latitude areas under enhanced greenhouse conditions (Jones and Reid, 2001; Palmer and Raisanen, 2002; Fowler et al, 2005). The rapid buildup of pore water pressure beyond hydrological thresholds following extreme rainfall events can induce substantial increases in sediment yields through slope failure, resulting in enormous economical and environmental damage. Extreme rainfall events bringing large quantities of sediment can push many structures, including hydro-power plants, sabo dams, urban drainage facilities, flood barriers, and other infrastructure facilities, to failure (Kunkel et al, 1999; IADB, 2000). High sediment concentrations added to rivers and streams can degrade the drinking water quality, increasing the cost of water treatment, and are harmful to certain species of fish and aquatic organisms (Waters, 1995)
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