4:00 PM - 4:15 PM
[AHW29-03] A comprehensive analysis for compound of rainfall runoff and storm surge by using a regional distributed hydrological model forced large ensemble climate dataset
Keywords:Compound of rainfall runoff and storm surge, Regional distributed hydrological model, d4PDF 5km, RRI model
Rainfall runoff and storm surges are both natural phenomena that cause river water levels to rise in coastal areas, and when they occur simultaneously, they have the potential to cause more significant flood damage than when they occur independently. Many cities are located in coastal areas, and because there are many exposed populations and assets, it is important to consider the compound effects of rainfall runoff and storm surges in flood risk management. In order to gain a bird's-eye view of the compound events, an analysis using a global model has been attempted to analyze the simultaneous occurrence of rainfall runoff and storm surges in large rivers with a basin area over 1000 km^2. However, attempts to gain a bird's-eye view of the compound events under conditions with finer spatiotemporal resolution have not been sufficiently advanced due to limitations in the calculation cost and the data.
In this study, we conducted a comprehensive analysis of the compound events in Japan, including small and medium-sized rivers, using the JRRI model, which covers the whole of Japan with a spatial resolution of 150 m, and the d4PDF-5km large-scale ensemble climate data set. the aim was to detect watersheds with a high risk of compound events and to analyze their characteristics in more detail.
Using the JRRI model, we analyzed compound events in watersheds with a catchment area of 5 km^2 or more in the Kanto, Chubu, Kinki, Chugoku, Shikoku and Kyushu regions. The data consisted of 776 typhoon events extracted from the d4PDF-5km current climate scenario, and rainfall was used as the input for the JRRI model. For storm surges, the output of the ADvanced CIRCulation model is used as boundary conditions in JRRI model.
The compound effect of the rise in water levels was analyzed by comparing the results of the following three cases. ① Rainfall runoff case ② Storm surge case ③ Compound case. We analyzed how much the water levels in each basin would rise in the compound case, to compare cases 1 and 2 as independent cases.
Since some typhoon events do not bring rainfall in some areas, we classified the watersheds by focusing on the top 144 events (with a return period of 5 years or more) in each watershed for the compound case. We defined a compound event as one in which the difference between the compound case and the single case was 0.05 or more (a rise in water level over 5% of the river depth occurred due to the combined case). We then extracted the basins in which more than 10% of the top 144 events were compound events as those with a high probability of compound events occurring. Furthermore, we compared the water levels of the rainfall runoff and storm surge in each of the top 144 events to determine which was greater, and classified the basins in which rainfall runoff or storm surge was dominant in more than 75% of the 144 events as Type R and Type S, and the others as Type RS.
There were 150 basins (total 1421) where the probability of a compound event occurring was high. Of these, 65 were classified as Type RS, 68 as Type R, and 17 as Type S. In Type RS, compound events consist of a combination of high rainfall runoff and high storm surge. On the other hand, in Type R, the compound events consist of a combination of high storm surge and low rainfall runoff. However, since Type R is a basin where rainfall runoff is dominant, it is possible that large-scale events for rainfall runoff alone will cause high water level than compound events.
It was found that the areas where compound of rainfall runoff and storm surge are likely to occur are located mainly in the Ise Bay and the northern part of the Seto Inland Sea. These watersheds tend to face south, and it is possible that the timing of the preceding rainfall runoff and the following storm surge is more likely to match for typhoons moving north.
In this study, we conducted a comprehensive analysis of the compound events in Japan, including small and medium-sized rivers, using the JRRI model, which covers the whole of Japan with a spatial resolution of 150 m, and the d4PDF-5km large-scale ensemble climate data set. the aim was to detect watersheds with a high risk of compound events and to analyze their characteristics in more detail.
Using the JRRI model, we analyzed compound events in watersheds with a catchment area of 5 km^2 or more in the Kanto, Chubu, Kinki, Chugoku, Shikoku and Kyushu regions. The data consisted of 776 typhoon events extracted from the d4PDF-5km current climate scenario, and rainfall was used as the input for the JRRI model. For storm surges, the output of the ADvanced CIRCulation model is used as boundary conditions in JRRI model.
The compound effect of the rise in water levels was analyzed by comparing the results of the following three cases. ① Rainfall runoff case ② Storm surge case ③ Compound case. We analyzed how much the water levels in each basin would rise in the compound case, to compare cases 1 and 2 as independent cases.
Since some typhoon events do not bring rainfall in some areas, we classified the watersheds by focusing on the top 144 events (with a return period of 5 years or more) in each watershed for the compound case. We defined a compound event as one in which the difference between the compound case and the single case was 0.05 or more (a rise in water level over 5% of the river depth occurred due to the combined case). We then extracted the basins in which more than 10% of the top 144 events were compound events as those with a high probability of compound events occurring. Furthermore, we compared the water levels of the rainfall runoff and storm surge in each of the top 144 events to determine which was greater, and classified the basins in which rainfall runoff or storm surge was dominant in more than 75% of the 144 events as Type R and Type S, and the others as Type RS.
There were 150 basins (total 1421) where the probability of a compound event occurring was high. Of these, 65 were classified as Type RS, 68 as Type R, and 17 as Type S. In Type RS, compound events consist of a combination of high rainfall runoff and high storm surge. On the other hand, in Type R, the compound events consist of a combination of high storm surge and low rainfall runoff. However, since Type R is a basin where rainfall runoff is dominant, it is possible that large-scale events for rainfall runoff alone will cause high water level than compound events.
It was found that the areas where compound of rainfall runoff and storm surge are likely to occur are located mainly in the Ise Bay and the northern part of the Seto Inland Sea. These watersheds tend to face south, and it is possible that the timing of the preceding rainfall runoff and the following storm surge is more likely to match for typhoons moving north.