An approach to assess sediment disaster risk using soil moisture deficit: A case study about sediment disasters occurred during 2010–2011 in Niigata prefecture, Japan

Abstract

Most sediment disasters are caused by surface failures, mostly induced by rainfall, and many of them cause extensive damages. Assessment of the risk of such disasters is crucial for the safety and security of society. This is becoming increasingly important in the era of global warming when torrential rains and localized heavy rains are on the increase. Instead of the index such as accumulated rainfall amount, we attempted to make a risk assessment using the soil moisture deficit, i.e., the remained capacity of the soil column to accept rainwater. First, a numerical model was developed to calculate soil moisture deficit in any or all tertiary meshes with existing routine data. The model was then applied to 446 tertiary meshes in Niigata Prefecture within which failures occurred during a period from 2010 to 2011. The model showed that the soil moisture deficit near the failure occurrence became smaller, i.e., the soil column was closer to complete saturation. This suggests that soil moisture deficit could be a good indicator of the risk. Furthermore, a probability distribution model was constructed from the minimum soil moisture deficit data near the failure occurrence. With this probability model, the threshold of soil moisture deficit to put an area on alert, corresponding to the disaster coverage ratio, can be easily calculated. The possibility of early warning is also demonstrated by combining the soil moisture deficit at a certain time with a short-time rainfall forecast for several hours in the future.