So Kazama

Regionalization of lumped water balance model parameters based on multiple regression

This study establishes a method for evaluating the coefficients of tank model. First, the model coefficients were optimized using the Standardized Powell Method at 12 watersheds. Then 16 characteristics were derived from geographical information on topography, soil type, geology, and land-use of the basins. Finally, a multiple linear regression model was applied to the relationship between the model coefficients and the basin characteristics. Trial application of the regression equations worked successfully at two different watersheds, suggesting that the coefficients of the tank model could be evaluated based solely on the geographical characteristics of the basin.

Evaluating the cost of flood damage based on changes in extreme rainfall in Japan

The fourth report of the Intergovernmental Panel on Climate Change (IPCC) provoked a significant amount of controversy, as experts have sought to apply it to climate change in Japan. In particular, the Ministry of Land, Infrastructure, Transportation, and Tourism (MLIT) organized a committee of experts responsible for implementing flood control policies (MLIT 2008). Japan is particularly vulnerable to flooding because of its steep geography and humid climate characterized by typhoons. Consequently, Japan has been coping with the problem of flood control for a long time (Takahasi and Uitto 2004). The number of floods, and, hence, the damage due to flooding, has increased since 2004. Even though these flood events may not be caused directly by climate change, many researchers are interested in the various problems of climate change and its broader implications for economic development.

A comparison of historical land-use change patterns and recommendations for flood plain developments in three delta regions in Southeast Asia

Historical land-cover changes in three delta regions in Southeast Asia are assessed by using selected Landsat images from 1990 to 2005. Potential inundation areas of the delta regions for different return periods are estimated by using digital elevation model data and extreme-value distribution of annual maximum river discharges. The results indicate significant changes of natural land cover within the potential inundation areas due to agricultural exploitation and industrialization. Implications for flood-mitigation policies are discussed. There is a clear need for sustainable land-use management strategies in all three areas.

STUDY ON THE 2000 FLOOD IN THE LOWER MEKONG BY FIELD SURVEY AND NUMERICAL SIMULATION

The Japan Society of Civil Engineers (JSCE) seconded a survey team for the 2000 flood in the lower Mekong River to understand the processes, phenomenon and the damage. The team made interviews to some related ministries, organizations and agencies, and made field survey in Cambodia and Vietnam. Interviews for resident people and water level data at some observing stations are helpful for understanding of physical phenomenon on inundation. There were many child casualties because they approached to water intake with high velocity to catch fishes and they fallen to water from stilt houses during night. Inundated water body generated long fetches for wind generating high wave. The flood made not only economic and infrastructure damages but also some benefits such as fishery, irrigation and ground water storage. Especially, fishing in flooded area is a good chance for rural people to obtain cash. In Vietnam, flood changed from uncultivated field with acid soil to cultivable field. Canal network and dike system were very effective for flood life. Numerical simulation provides us good information of physical processes. Expansion process and the distribution of water depth by numerical simulation results are helpful for discussion and consideration comparing with field survey.

Assessment of water conflict in Mae Chaem River Basin, Northern Thailand

For this study, we conducted a quantitative water resources assessment of the Mae Chaem River Basin, Thailand, an area with dry season water scarcity and water use conflicts between upstream and downstream inhabitants. The block-wise TOPMODEL with the Muskingum–Cunge flow routing method (BTOPMC) was used to predict run-off in 21 sub-basins and Geographic Information System (GIS) was employed to collect information for crop water demand evaluation. Four sub-basins exhibited critical water conditions in 2000. The conversion of forestlands into agricultural lands during the past decade has engendered water scarcity in the dry season and flooding in the wet season.

Assessment of rainfall-induced shallow landslides in Phetchabun and Krabi provinces, Thailand

Shallow landslides are a common type of rainfall-induced landslide, and various methods are currently used to predict their occurrence on a regional scale. Physically based models, such as the shallow landslide instability prediction (SLIP) model, have many advantages because these models can assess the hazards of shallow landslides dynamically, based on physical stability equations that consider rainfall as a triggering factor. The main objective of this research is to test the SLIP model’s potential to predict shallow landslide hazards in Thailand. To achieve this goal, the SLIP model was applied to two massive landslide events in Thailand. The results predicted by the SLIP model for the two study areas are outlined, and the model prediction capabilities were evaluated using the receiver operating characteristic plot. The Phetchabun results showed that the western part of the catchment had the lowest factor of safety (FS) value, whereas the Krabi results showed that the slopes surrounding the peak of Khao Panom Mountain had the lowest FS value, explaining the highest potentials for shallow landslides in each area. The SLIP model showed good performance: The global accuracies were 0.828 for the Phetchabun area and 0.824 for the Krabi area. The SLIP model predicted the daily time-varying percentage of unstable areas over the analyzed periods. The SLIP model simulated a negligible percentage of unstable areas over all considered periods, except for expected dates, suggesting that the prediction capability is reasonably accurate.

The potential role of urban green areas for controlling ground surface and subsurface warming

Subsurface warming in urban areas is higher in magnitude than increases in surface air temperatures. However, little evidence exists on the effects of urbanization on subsurface environments, and there are few quantitative estimates of the effectiveness of adaptation measures. We analyzed the relationship between ground surface warming and the extent of landscape change using subsurface temperature anomalies as an indicator of surface warming in five urban areas in Japan. To interpret these results for urban planning, we presented the percentages of green areas that would be needed to achieve certain reductions in ground surface temperatures for areas with different urbanization levels. Accordingly, a 0.5 °C reduction in average ground surface temperatures can be achieved by an increased Normalized Difference Vegetation Index (NDVI) value of 0.035, which accounts for approximately a 17% increase in natural green areas in an area with 75% urbanization. This study provides quantitative estimates to cope with urban warming at the local scale in the face of climate change.

Catchment-Scale Modeling of Riverine Species Diversity Using Hydrological Simulation: Application to Tests of Species-Genetic Diversity Correlation

Species distribution models were developed to predict the spatial patterns of the species diversity and the genetic diversity of stream organisms using a distributed hydrological model. We derived annual metrics of water depth and flow velocity in rivers using a hydrological model covering an entire catchment in northeastern Japan. We acquired geospatial data throughout the catchment and the presence records of six taxa within the part of the catchment. Subsequently we derived habitat suitability indices (HSIs) for these taxa using a frequency analysis or the maximum-entropy approach (MaxEnt) to predict three metrics of species diversity. The Shannon-Wieners diversity index based on MaxEnt (Shannon_MaxE) most effectively represented empirical taxon richness. Subsequently, by comparing Shannon_MaxE and empirical genetic diversity for the four species of stream insects, we evaluated species-genetic diversity correlations (SGDCs). Of the four species, only one caddisfly species (Hydropsyche orientalis) displayed significant positive SGDCs. The result reflects the broad habitat range of this taxon throughout the catchment and its poor dispersal ability, whereas the other three species lacked SGDCs and displayed either a strong dispersal potential (Stenopsyche marmorata and Ephemera japonica) or a narrower habitat range within upstream domains (Hydropsyche albicephala). Finally, we estimated the spatial distribution of genetic diversity of H. orientalis populations based on the calculated Shannon_MaxE using the positive SGDC. This framework is promising for projecting future biodiversity in the context of anthropogenic perturbations such as climate change.

Opportunities and constraints in adapting to flood and drought conditions in the Upper Chao Phraya River basin in Thailand

ABSTRACT To assess alterations of the rice-growing season as a sustainable option to overcome temporary groundwater storage shortages resulting from flood and drought conditions in the Upper Chao Phraya River basin in Thailand, rice was planted in May (1.5 months earlier) to harvest before seasonal flooding occurred (normally in October). The assessment showed that a cropping intensity (CI) of approximately 1.4 (100% and 40% of the total agricultural area for the wet and dry seasons, respectively) could be supported by the total available water (surface runoff and renewable groundwater storage). Shifting the growing season did not have a negative impact in terms of rice production area, but it did ensure that the area of rice cultivation avoided flooding or surface water shortage conditions. Expanding the rice production area was also assessed; however, this required the implementation of artificial groundwater recharge (AGR). For example, 1.0 km3 of AGR annually was enough to support CI equal to 1.5 without experiencing groundwater depletion.

An ecological assessment of a dammed pool formed by a slit check dam

This study surveyed physical, chemical, and biological parameters in a dammed pool in comparison to those of the adjacent main stream. Because the dammed pool in this study was a unique zone formed by a slit check dam, the properties of the pool and the main stream could be considered representative of the conditions with and without a slit check dam, respectively. Data were collected in the dammed pool and in the reach of the main stream above the slit check dam in the Wasada Stream, Miyagi Prefecture, Japan. The dammed pool exhibited a lower velocity and finer substrate than those of the main stream. In addition, the water temperature in the dammed pool was slightly higher than in the main stream. Dissolved Oxygen and Chemical Oxygen Demand in the pool were lower than the allowable standards for water pollution. The pool exhibited worse biological indices of water quality than the main stream. Out of a total of 18 taxa found in the stream, only 5 taxa were found in the dammed pool. Most individuals in the dammed pool belonged to the genus Chironomus, which tends to colonize heavily polluted sites. According to these various indicators, the water quality of the dammed pool was lower than that of the main stream. The longest durations of the presence of the dammed pool mainly occurred during snowmelt and during the rainy season. The average duration of the presence of the dammed pool was calculated as 14 days. The dammed pool exhibited a short-duration cycle of formation and extinction according to seasonal variations in water discharge. This cycle reduces the negative effects of the pool on water quality. Therefore, the dammed pool has a minimal negative effect on restoration of the entire reach of the Wasada Stream.