3D small scale model experiments were conducted to determine the design values of turbine and diffuser of tidal and ocean current power generator in the Tsugaru Strait that enable the device to generate efficiency on field . For a diffuser, the flange length, the internal tilt angle, and the length and for a turbine, the installation position, the blade tilt angle, the blade thickness, and the number of blades were verified, and the optimal those values are make clearly so as to rotate the turbine efficiently. Furthermore, a power generation model combining the optimized turbine and diffuser was fabricated and used in experiments. As the results, the converted electric power generation per unit on the field were calculated to be approximately 15 to 180 W. It was also found that the electric power generation at the basic flow velocity at the field increased quadruple approximately compared to the model before optimization.

 Accurate and rapid prediction of typhoons is required to protect our society from typhoon disasters. Deep learning can be an effective way to reduce computational costs significantly. However, it is difficult to prepare enough training data when focusing on extreme and infrequent weather events such as typhoons. In this study, we constructed CNN-LSTM deep learning networks for typhoon track prediction based on 45000 typhoon events extracted from a large ensemble climate dataset d4PDF. The abundance of training data improved prediction accuracy by approximately 10% to 50%. On the other hand, the prediction errors remained about 5 times larger than those in numerical weather prediction. Additionally, the prediction accuracy tended to decline when typhoons moved on land at low and high latitudes, and when their tracks were complex.

 There is concern that global warming will increase the risk of storm surge damage in coastal areas. However, climate change is influenced by a variety of factors and is highly uncertain. Yasuda et al. (2024) applied real options analysis to the planning of coastal protection facilities as a method to cope with this uncertainty and demonstrated its effectiveness, but comparative studies with cost-benefit analysis and phased maintenance plans have not been sufficiently conducted. This study evaluates the usefulness of real options analysis, cost-benefit analysis, and phased maintenance plan by comparing the three analyses. As a novelty from the study by Yasuda et al., this study also examines the impact of the social discount rate (4.0% and 2.0%) on the calculation of damages by taking into account future changes in assets in light of economic growth. The results of the analysis indicated that real option analysis is an effective analytical method for reducing total social costs in both scenarios. Furthermore, comparing the real options analysis and the phased maintenance plan in terms of the number of construction projects, the scenario with an increase in the number of construction projects is significantly reduced in the real options analysis when the social discount rate based on the latest social conditions is 2.0%, compared to when the social discount rate is 4.0%.

 To clarify climate change impacts on the nitrogen cycle in the Ariake Sea and the Yatsushiro Sea, we conducted numerical simulations under the present and the RCP2.6/8.5 future climate conditions using an integrated river basin – coastal environment assessment model. The simulated net flows of seawater and TN indicated that they flowed from the open ocean into the Ariake Sea through Tachibana Bay, and then flowed out to the open ocean through the Yatsushiro Sea with the southward flow from the bay head area of the Ariake Sea. The predominant source of TN in the Ariake Sea was the inflow from the land, but in the case of DIN, the inflow from the open ocean comparable to that from the land. The impact of climate change was particularly strong on the DIN flow; the flow was predicted to change in the direction that the outflow from the Ariake Sea and the Yatsushiro Sea to the open ocean as a whole was enhanced. As a result, the net DIN flow in the bay head area of the Ariake Sea in the present climate condition was the inflow from the central bay, while it turned into the outflow in the future scenarios of RCP2.6 and 8.5. Therefore in the future climates, during the season of nori cultivation, from November to March, the amount of DIN in the seawater was predicted to decrease compared to the present.

 Granulated coal ash can probably contribute to sediment improvement and carbon dioxide fixation through shell formation of clams owing to its high calcium release rate. In this study, blackish water clam Corbicula japonica was exposed to silt/clay sediment mixed with granulated coal ash (0%, 30%, 90%) to investigate the growth and antioxidant responses of the clam. Although the rate of calcium release from the granulated coal ash exceeded the calcifying rate of the clam, significant increase in the calcification of the clam was not identified during the 30-day experimental period. In granulated coal ash 0%, superoxide dismutase, catalase, oxygen radical absorbance capacity, and lipid peroxidation (LPO) were higher than those in the control. In granulated coal ash 30%, LPO was significantly improved (p<0.05). However, there was still oxidative damage in granulated coal ash 90%. The results concluded that an appropriate mixture of granulated coal ash was important from the viewpoints of the growth and antioxidant system of the clam.

 Many studies have been conducted on the impacts of global warming on oxygen dynamics in estuaries like Osaka Bay. Although they focused on water temperature and changes in heavy rain, studies on future summer drought impact are rare. In this study, we performed numerical simulations to assess the impact of future changes in summer drought on the oxygen cycle in Osaka Bay. We used database for Policy Decision making for Future climate change (d4PDF) and prepared 21 samples based on the rainfall pattern before the drought season, as the input for a 3-D hydrodynamic and water quality model to predict the extent of hypoxia during present and future drought conditions. The results suggest that the combined impacts of temperature rise and discharge decrease during summer drought expand the volume of hypoxia, while the discharge decrease during summer drought itself may slightly reduce the volume of hypoxia. The decrease in discharge leads to less oxygen consumption due to less organic matter decomposition and increases dissolved oxygen in the middle layer of the inner bay. Meanwhile, the temperature rise decreases oxygen solubility, resulting in a decrease in dissolved oxygen throughout the coastal area. The impact of the decrease in discharge during summer drought on the oxygen cycle is smaller than the impact of the temperature rise.

 Achieving Eco-DDR—disaster risk reduction coupled with minimal environmental impact—is a critical challenge for resilient infrastructure. Although recent efforts have explored using mangrove forests for coastal disaster mitigation in tropical and subtropical regions, most studies focus on wave attenuation, leaving beach stability and morphological change underexamined.

 In this study, we conducted continuous RTK-GNSS surveys, water-level monitoring, and time-lapse photography across a ~200 m × 75 m mangrove zone and adjacent revetment in Nagura Bay, Ishigaki Island, to characterize shoreline dynamics inside and outside the forest. We then performed XBeach simulations using field-derived vegetation parameters to reproduce sediment deposition behind the mangroves and to evaluate how the combined presence of mangrove stands and a breakwater influences hydrodynamics and sediment transport.

 This study focuses on oxygen supersaturation in subtropical coastal ecosystems, using high-resolution (10-minute interval) monitoring of dissolved oxygen (DO) across adjacent mangrove, seagrass, and coral reef habitats in Ishigaki Island, Japan, over a 27-day period in summer. Supersaturation occurred most frequently and persistently in the seagrass bed, while DO in the mangrove estuary exhibited wide tidal variability, ranging from hypoxia to supersaturation (20–146%). Coral reef and seagrass sites displayed distinct diel oscillations, with DO fluctuations ranging from 66% to 162% at the seagrass bed and from 62% to 172% at the coral reef.

 Spectral analysis revealed that DO dynamics in the coral reef and seagrass habitats were dominated by a 24-hour periodicity, indicating a strong diel (photosynthesis-respiration) cycle. Minor peaks were also detected at 12 h and 22.34 h. In contrast, the mangrove estuary exhibited a primary spectral peak at 12.5 h, corresponding to the semidiurnal tidal cycle, followed by a secondary peak at 24 h, suggesting a stronger influence of tidal forcing. These findings highlight contrasting physical and biological drivers of DO variability across ecosystems: diel production-respiration cycles dominate in coral reef and seagrass systems, while tidal exchange governs DO fluctuations in the mangrove estuary.

 PCA and GLM analyses identified water temperature as a primary driver of supersaturation events. Our results underscore the importance of cross-ecosystem connectivity in buffering hypoxia in mangrove-dominated systems and provide new insights into the temporal dynamics and drivers of oxygen variability in subtropical coastal environments.

 The tsunami caused by the 2011 off the Pacific coast of Tohoku Earthquake resulted in the driftwood formation of coastal trees, especially those with shallow root systems. Currently, reconstructed forests are being created on embankments to promote the development of long tap roots and improve resistance to falling over. On the other hand, the development of thick and long tap roots may cause increased scouring around the root system, which could lead to a loss of support. Horizontal roots are expected to prevent scouring and strengthen support, but it is unclear to what extent horizontal roots affect resistance to falling over. In this study, we conducted hydrodynamic model experiments focusing on the effects of tap root length, shape (distribution of tap roots and horizontal roots), and rootstock volume on resistance to falling over in standing trees with different breast heights (three types). The results confirmed that, in addition to pendulous root length, chest height diameter, root shape, and changes in support capacity due to surrounding erosion are important factors contributing to falling over of coastal trees by tsunami flow.

 An empirical typhoon model frequently used for storm surge estimations includes input parameters such as maximum wind speed radius and shape parameters, which are difficult to observe directly. In this study, we propose an enhanced Myers equation, which constitutes the empirical typhoon model, to allow the surface pressure at an infinite radius to vary freely. We then combine this enhanced Myers equation with variational data assimilation to estimate parameters for multiple typhoon cases. Additionally, we applied the variational data assimilation method to a storm surge estimation and verified its accuracy. By incorporating surface pressure observations from various locations away from the typhoon center into the variational data assimilation, we demonstrated that it is possible to estimate parameters that fit the observations well. Furthermore, we clarified that the proposed data assimilation method improves the accuracy of storm surge estimation.

 Generally, in storm surge inundation assessment, the maximum inundation depth is calculated deterministically by storm surge inundation analysis based on the historical largest typhoon. On the other hand, not only deterministic but also probabilistic evaluation of inundation depth is useful in BCP. In this study, multiple typhoon data were generated by a stochastic typhoon model created using an autoregressive model (AR model) with historical typhoons, and storm surge inundation analysis was conducted for a virtual landfill site in Osaka Bay. The inundation depths were probabilistically evaluated by statistically analyzing the inundation depths obtained from the inundation analysis for multiple typhoons. Additionally, the storm surge anomaly was calculated by the JMA's storm surge anomaly formula based on typhoon information, and inundation analysis was conducted targeting the probability typhoons selected based on the statistical analysis of the results. By comparing these results, the relationship between storm surge anomaly and probabilistically evaluated inundation depth was investigated.

 In this study, a field survey was conducted on tsunami deposits that were formed on land and preserved within the strata of the island areas of Matsushima Bay, Miyagi Prefecture, as a result of the tsunami triggered by the 2011 off the Pacific coast of Tohoku Earthquake. As a result, the distribution patterns, preservation conditions, and relationships with topography of the tsunami deposits on the coast of Fukuura island in Matsushima Town were clarified. The factors determining the thickness and distribution patterns of the tsunami deposits are diverse, including the sources and grain sizes of the deposits on land, transport pathways, and the surrounding microtopography. However, the processes of formation and preservation of tsunami deposits on the coastal areas of the island－which are believed to have served as natural seawalls mitigating tsunami inundation in the inner part of Matsushima Bay－as well as methods for estimating tsunami magnitude in such contexts, have not yet been established. Based on the findings of this study, it is expected that examining the details of tsunami deposits on island coastal areas where inundation depths are unknown will contribute to the advancement of tsunami assessment methods based on tsunami deposits.