4:30 PM - 4:45 PM
[ACG43-11] Climate change impact assessment in Shikoku with the ensemble climate prediction database d4PDF
Keywords:climate change adaptation, d4DPF, river management
In the presentation of last year, we evaluated the impact in the Yoshino River basin climate change prediction model output CMIP 5 with statistical downscaling, but some problems were clarified.It is important to apply dynamical downscaling including a large number of outputs for appropriate impact assessment.
We used the ensemble climate prediction database d4PDF to evaluate the impact of climate change in the Yoshino River Basin in this study. We made a comparison with the grid near Sameura Dam in the Shikoku mountain area, Tokushima and Kochi. In the Shikoku mountains, the observation rainfall amount are close to members with a lot of rain ,and in Tokushima it was close to members with little rainfall. In Kochi, the model output can not reproduce heavy rainfall caused by typhoon or special factors that occurred in the past. As a result, it is clear that it can be utilized without bias correction for the risk assessment if the scale and rainfall characteristics of the Yoshino river basin area, but it can not be used as it is in smaller rivers and rivers with localized rainfall.
In Sameura Dam, a renewal project to expand the drainage channel is planned. This project makes it possible to release dam water more quickly and increase flood control capacity. At the same time, dam operator are planning to revise the operation rules and increase the ability to respond to large floods.
In order to develop climate change adaptation measures utilizing Sameura Dam, which is a key to flood control and water use in the basin, we should optimize the dam operational rule according to not only flood flow rate but also the trend of the dam reservoir volume of the long term. In order to estimate the dam water level at the time of large scale flooding, we compared the relationship between the discharge rate into the dam and the amount of monthly rain in April to June. GCM greatly differed from non-global warming experiments in each GCM, GCM increased the occurrence of floods from low rain, and GCM tended to have more precipitation in the year when flooding occurred. Compared with the non-global warming experiment, the trend greatly differs in each GCMs. A GCM has the trend increasing the occurrence of floods in drought condition, and other GCM tended to have more precipitation in the year when flooding occurred. For this reason, it is difficult to fixedly change the operational rules of the dam, and it is considered that an "adaptive" approach is required according to changes in rainfall characteristics due to climate change.
In addition, as a result of interviews with local government in the downstream section, it became clear that they are concerned about the risk of complex disasters of flooding in and out of water. Due to heavy rain caused by typhoons and the like, inundation flooding occurred, there is a possibility that evacuation routes in urban areas will be disrupted. In addition, the rainfall in the upstream generated flood and it reaches the downstream section after several hours, and is exposed to the risk of flooding the outside. For this reason, the flood flow rate in the downstream section and the time difference from the rainfall occurrence to the flood arrival were analyzed. The time from heavy rain to flood reached fluctuated stronger than the current reproduction. As a result, it became clear that diversification of complex disaster scenario is necessary.