11:00 AM - 11:15 AM
[ACG43-07] Development of a coupled sea-land model for coastal ocean simulation - an attempt to reproduce stormy current -
★Invited Papers
Keywords:Kyucho, FVCOM, RRI, MSM, Wakasa bay
Various phenomena that occur in coastal waters are related to multiple factors on different spatiotemporal scales, such as freshwater inflow from land, changes in meteorological condition, and interactions with outer ocean. In order to reproduce and predict such phenomena in the coastal ocean, we apply the UCHI (Unstructured Coastal model with High resolution Information) model using high-resolution coastal ocean model FVCOM (Finite Volume Community Ocean Model, Chen et al. 2006) as a base model, with Japan Meteorological Agency MSM/GPV data, the sea state prediction model DREAMS (Hirose et al. 2005) for the outer ocean conditions, and the Rainfall Runoff Inundation model (RRI, Sayama et al. 2014) for freshwater inflow assessment. In this presentation, we report an example of its application to stormy currents in Wakasa Bay.
Wakasa Bay is an open ria-type bay that straddles Kyoto and Fukui Prefecture, and has a very complex coastal and submarine topography. Set-net fishing is popular, and its catch accounts for approximately 80% of total catch in Kyoto Prefecture. A problem that troubles set-net fishermen is damage to fishing gear caused by stormy currents with a velocity of 0.5 m/s or faster, so-called Kyucho. In order to reduce the damage, it is necessary to remove part of the set-net and evacuate it to land before the Kyucho occurrence. Since it is generally hard work and cannot expect to catch any fish. it is desirable to keep the frequency of taking such measures to minimum.
Previous research has shown that the Kyucho in Wakasa Bay were caused by the Tsushima Current flowing offshore, inertial-frequency oscillation caused by the Coriolis force due to the earth's rotation, continuous strong winds due to typhoons or extratropical cyclones, and fresh water inflows from large rivers. Therefore, numerical models for the Kyucho reproduction are required to reproduce the complex coast and seafloor topography of the bay, appropriately incorporate the effects of the outer ocean and meteorological fields and accurately evaluate the freshwater inflow process. Currently, attempts are being made to predict the Kyucho occurrence using DREAMS, but its recall rate remains at around 10%.
Calculation domain of the UCHI model was set as wide as possible in order to reproduce the Kyucho in Wakasa Bay. The resolution of the horizontal grid was 1500 m at the open boundary and a minimum of 70 m at the inner part of the bay. Vertical grid uses general σ coordinates with 20 layers. Tide level, current, water potential temperature, and salinity were introduced from DREAMS_Cp for the open boundary conditions. The Japan Meteorological Agency MSM/GPV was used for the weather conditions. The amount of freshwater inflow into the UCHI domain was calculated using the RRI model. HydroSHEDS (https://www.hydrosheds.org/) was used for the land topography, and land use data provided by the Ministry of Land, Infrastructure, Transport and Tourism was used. Rainfall data input to RRI model was from MSM/GPV. Hindcast simulations were conducted for years 2021 and 2022, and the reproducibility of the Kyucho was examined through comparison with field observations.
The UCHI model reproduced the Kyucho that occurred in the northern to western part of the Tango Peninsula and entered into Wakasa Bay. This behavior was in good agreement with previous reports. As the Kyucho entered the bay, a well-developed clockwise flow was also reproduced. We evaluated the recall rate of the UCHI model for strong currents with a top 5% (mean value + 2 standard deviations or faster) of current velocities observed at stations near the shore around Wakasa Bay. As a result, the recall rate using UCHI was approximately 40%, which was higher than the current model (DREAMS). In particular, we confirmed an even higher recall rate at Sta. Araizaki and Sta. Ine, which are areas with high frequency of the Kyucho. This result shows the effectiveness of the UCHI model in reproducing the Kyucho.
Wakasa Bay is an open ria-type bay that straddles Kyoto and Fukui Prefecture, and has a very complex coastal and submarine topography. Set-net fishing is popular, and its catch accounts for approximately 80% of total catch in Kyoto Prefecture. A problem that troubles set-net fishermen is damage to fishing gear caused by stormy currents with a velocity of 0.5 m/s or faster, so-called Kyucho. In order to reduce the damage, it is necessary to remove part of the set-net and evacuate it to land before the Kyucho occurrence. Since it is generally hard work and cannot expect to catch any fish. it is desirable to keep the frequency of taking such measures to minimum.
Previous research has shown that the Kyucho in Wakasa Bay were caused by the Tsushima Current flowing offshore, inertial-frequency oscillation caused by the Coriolis force due to the earth's rotation, continuous strong winds due to typhoons or extratropical cyclones, and fresh water inflows from large rivers. Therefore, numerical models for the Kyucho reproduction are required to reproduce the complex coast and seafloor topography of the bay, appropriately incorporate the effects of the outer ocean and meteorological fields and accurately evaluate the freshwater inflow process. Currently, attempts are being made to predict the Kyucho occurrence using DREAMS, but its recall rate remains at around 10%.
Calculation domain of the UCHI model was set as wide as possible in order to reproduce the Kyucho in Wakasa Bay. The resolution of the horizontal grid was 1500 m at the open boundary and a minimum of 70 m at the inner part of the bay. Vertical grid uses general σ coordinates with 20 layers. Tide level, current, water potential temperature, and salinity were introduced from DREAMS_Cp for the open boundary conditions. The Japan Meteorological Agency MSM/GPV was used for the weather conditions. The amount of freshwater inflow into the UCHI domain was calculated using the RRI model. HydroSHEDS (https://www.hydrosheds.org/) was used for the land topography, and land use data provided by the Ministry of Land, Infrastructure, Transport and Tourism was used. Rainfall data input to RRI model was from MSM/GPV. Hindcast simulations were conducted for years 2021 and 2022, and the reproducibility of the Kyucho was examined through comparison with field observations.
The UCHI model reproduced the Kyucho that occurred in the northern to western part of the Tango Peninsula and entered into Wakasa Bay. This behavior was in good agreement with previous reports. As the Kyucho entered the bay, a well-developed clockwise flow was also reproduced. We evaluated the recall rate of the UCHI model for strong currents with a top 5% (mean value + 2 standard deviations or faster) of current velocities observed at stations near the shore around Wakasa Bay. As a result, the recall rate using UCHI was approximately 40%, which was higher than the current model (DREAMS). In particular, we confirmed an even higher recall rate at Sta. Araizaki and Sta. Ine, which are areas with high frequency of the Kyucho. This result shows the effectiveness of the UCHI model in reproducing the Kyucho.