In this paper, we develop a thin and thick shell theory consistent with continuum mechanics, taking an asymptotic expansion on the ratio of thickness to radius. A Lagrangian for displacement function is derived, and the first- or second-order expansion corresponds to thin or thick shell, respectively. The form of the Lagrangian is surprisingly simple because its integrand consists of four terms for the thin shell and two terms are added for the thick shell. Important features of the theory, such as the causes of the simple form Lagrangian and the sectional force equilibrium, are discussed.

 Observation of the water surface area of lakes is essential for understanding the amount of water stored in them. This study analyzed the long-term and seasonal changes in the area of natural lakes and reservoirs using a global dataset of monthly area estimates. The global area of natural lakes has been decreasing while the seasonal amplitude is increasing. Those trends are not significant in reservoirs. Seasonal variations and their interannual trends were different depending on the size of the reservoirs. The results were consistent with the results of the change in the terrestrial water storage determined by gravity observation, but some areas showed different trends. Thus, satellite observation of lake surface area provides helpful information for water resource management. In combination with water surface elevation observation, it is expected to enable a more comprehensive estimation of water storage volume.

 Under global warming, large-scale linear heavy rainfall systems can cause severe floods over a wide area. In such a case, simultaneous floodings from multiple rivers must be considered. In this study, numerical inundation simulations were implemented considering simultaneous levee breaches in the Kakehashi and Tedori rivers in Ishikawa Prefecture, Japan. Flood disaster risk was evaluated based on the simulation results. The potential window time for evacuation was estimated based on the simulated inundation depth and flood flow velocity at each simulation time. The maximum inundation depth on the right bank of the Kakehashi River was larger in the case of simultaneous levee breaches at the two rivers than that in the case of a levee breach at a single river. The window time for evacuation was shorter in the same area. In an area affected by the two rivers, the arrival times of inundation flow from the two rivers are typically different. Depending on the time lags between the floods in the two rivers, the evacuation window time must be estimated based on the time when the later flood level reaches the evacuation decision water level.

 This study evaluates the applicability of an artificial neural network (ANN)-based regression model for downscaling d4PDF daily precipitation data from a coarse spatial resolution of 20 km to a finer spatial resolution of 5 km, considering the precipitation as the sole predictor. For this purpose, two sets of d4PDF data have been utilized for downscaling: 20 km to 5 km resolution. The area covered was a square grid of 33 at 20 km resolution, and the downscaling target was the center grid of this square. The results of this study demonstrated that the performance of ANN varies across regions and seasons. While it shows better performance in capturing the long-term mean during winter, it tends to exhibit high biases in the mean, standard deviation (SD), and maximum values, particularly during the summer seasons. Generally, the ANN does not preserve the overall statistical properties of the original data.

 This study aimed to analyze the erosion risk based on time-series changes in flow rate and riverbed changes in rapidly flowing rivers under climate change. The Toyohira River, the subject of this study, is a rapidly flowing river that flows through the urban area of Sapporo and is prone to erosion due to high-speed flood flow. In this study, in order to take into account the uncertainty of climate change, runoff calculations were conducted using a large amount of ensemble rainfall data obtained from d4PDF. Next, a riverbed fluctuation calculation was conducted for each event to estimate the time-series changes in riverbed fluctuations and erosion risk. Finally, a cluster analysis of the present and future spatial distribution of rainfall was conducted to determine the spatial distribution of rainfall that is likely to cause significant flood damage. The results show that the magnitude of erosion risk varies temporally and spatially depending on the characteristics of the runoff, and suggest that erosion risk tends to increase when the rainfall is concentrated in the middle part of the Toyohira River.

 Dam break flows (DBF) can cause significant destruction due to their high kinetic energy, entraining large amounts of sediment and altering landforms in inundated areas. While the vegetation is expected to mitigate DBF energy, uncertainties exist about DBF over movable beds with vegetation. This study develops a numerical model to predict DBF over movable beds with vegetation through experimental investigations. Experiments were conducted in a horizontal rectangular flume with sand and rigid emergent vegetation. Various initial tailwater depths were set up with the constant reservoir depth, both with and without vegetation. Results showed that sediment transport by the DBF front varied with tailwater depths and decreased due to vegetation-induced energy attenuation. The quasi-3D two-phase model, based on a non-hydrostatic depth-integrated approach with a dynamic rough wall law (DWL), was developed to account for DBF–sediment–vegetation interactions, capturing key trends such as intense sediment transport and upstream sediment deposition near vegetation.

 This study aims to propose a risk map for each inundation point (local safety levels), taking into account the risk assessment of levees, in order to support local residents in recognizing the potential risks to their residential areas and to promote evacuations. In this study, flood inundation analysis was conducted for multiple scenarios of the Jinzu River and the Joganji River, which run through Toyama Prefecture, in order to calculate the risk at the site. The external forces are evaluated in multiple stages using the peak discharge of each river in the return period of each year. The results of the analysis show that the risk of inundation of the Jinzu River is particularly high. Also, it was found that there is a high probability of flooding and the need for horizontal evacuation, especially in the lower reaches of the Jinzu River and low elevation areas. It should be emphasized that the need for horizontal evacuation in the Joganji River was due to the location of the assumed levee breach points.

 Monitoring CO₂ concentration in the sea is mandatory at offshore CO₂ storage sites in Japan. This paper discusses whether anomalous partial pressure of CO₂ (pCO₂) due to CO₂ leak could be detected by observing pCO₂, based on a simulation of passive tracers in Hidaka Bay off Tomakomai. The area where anomalous pCO₂ due to CO₂ leak could be detected is much larger in summer than in winter, and the area where the probability of detection is higher than 25% is estimated to be roughly at most 0.4 km² even in summer if the observation is sporadic. This implies that approximately 90 observation points are necessary within 6 km by 6 km while 12 points were arranged in the Tomakomai CCS Demonstration project. It is suggested that CO₂ leak could be hardly detected by a sporadic observation of pCO₂ unless unrealistically dense observation points were deployed, and that few of the observed pCO₂ data that exceed the threshold would be due to CO₂ leak. If monitoring CO₂ concentration in the sea is required, it should be conducted at a few important areas such as fishing grounds and aquaculture farms around the CO₂ storage site to verify that CO₂ concentration is within the natural variability, rather than to detect CO₂ leakage.

 In hydrological frequency analysis, it is common to analyze the frequency of annual maxima of peak discharge or rainfall amount during the rainfall duration. The shape parameter of the generalized extreme value distribution used in the analysis of annual maxima is related to the thickness of the upper tail of the probability density function. The peak flow at a given point in a watershed is closely related to the average rainfall in the watershed upstream of that point. Although the quantile through extreme analysis of peak discharge and the peak value of discharge hydrograph obtained by runoff calculation with the quantile through extreme analysis of the average rainfall in the watershed for an appropriate rainfall duration are assumed to be equivalent, they are often quite different. This paper discusses the causes of this difference and points out some key considerations to keep in mind when using the return levels for flood control planning.

 Lake Shibunotsunai, located at the end of the Shibunotsunai River system, is a small brackish water lake that yields brackish water clam and smelt. Here, a training wall was constructed to prevent river mouth closure due to coastal sand drift. In this study, we investigated the water quality and sediment of the lake and the benthic community and examined the current state of the lake environment. During the survey period, the salinity of the lake was 5 psu or less and remained under 1 psu for one year or more, and the occurrence of blue-green algae was confirmed. The bottom of the lake had a mud content of 50% or more, an ignition loss of 10% or more, and a mud content of 90% or more near the inflowing river in most areas except the eastern lakeshore. The dominant species of macrobenthos are chironomid larvae and Capitellid polychaete, and the density of constituent species common to the good fishing grounds of the brackish water clam in Japan was very low. From the above results, it was suggested that the open state of the river mouth training wall strongly affects the water quality, sediment, and organisms in the lake.

 In recent years, due to the progression of population decline and aging, research on factors influencing population change has attracted much attention in regional development policies. In particular, the influence of such an important component of well-being as happiness is viewed as one of the urgent topics in urban development. In this research, the actual state of happiness in Japan considering the impact of urban aging is analyzed compared to residential satisfaction. The following results were revealed: 1) There is a correlation between happiness and population change, although happiness is less varied than residential satisfaction. 2) The distribution of happiness and residential satisfaction values in city typology considering urban aging is narrower for happiness but with more outliers. The general trend shows an increase of both indicators with the increase in population. 3) As for the influence of urban aging problems, happiness is more affected by components related to personal life, such as the number of families in a municipality. 4) There are some exceptions from the general trend of the distribution of happiness and residential satisfaction values in city typology, which the conditions of urban aging problems can explain.

 In Japan, various efforts are underway to achieve carbon neutrality by 2050. Reforestation and the use of harvested wood products are well-established and are considered to be reliable and realistic climate change mitigation measures. Therefore, using wood underground for countermeasures against soft ground is expected to provide substantial carbon storage. However, there is little academic data on the extent to which wood deteriorates under underground conditions; thus, the effect of this method of carbon storage has not been recognized internationally. In this work, log piles driven into the ground more than 84 years ago in the Tama River Lowland, Japan, near the mouth of the Tama River were excavated, and the degree of deterioration and the groundwater level were investigated. The degree of deterioration was low, and the half-life of mass loss was estimated to be about 400 years, even though the log piles had been above the groundwater level for a long period of time.

 Roads adjacent to wildlife habitats typically exhibit a heightened risk of roadkill. Within agricultural landscapes, characterized by historical forest clearing, windbreak forests function as vital local habitats for mammalian species. This ecological role suggests that windbreak forests may contribute to increased roadkill incidents. We postulated that mammalian presence would be concentrated in proximity to windbreak forests. This hypothesis was assessed by examining the spatial relationship between mammal detection locations on roads and the configuration of windbreak forests in Hokkaido, Japan. Our survey exclusively identified the red fox, Vulpes vulpes, with 57 mammals recorded. The mean distance from detected mammals to windbreak forests was 153.82 m (ranging from 0 to 851.23 m). The majority of red fox detections were situated less than 200 m from windbreak forests, a distance significantly shorter than observations from random locations. This evidence implies that windbreak forests represent a considerable roadkill hazard for red foxes within agricultural environments. To prevent red fox roadkill in these landscapes, we recommend increased driver awareness near windbreak forests and the strategic mesures such as placement of warning signs approximately 200 m from their boundaries.