Tomohiro Tanaka

Kyoto University | Kyodai · Disaster Prevention Research Institute

Rice is a major agricultural crop in Thailand, while paddy fields near river lines are exposed to high flood risk. This study assesses rice exposure and economic flood risk under future climate in the Lower Chao Phraya River Basin, Thailand. To encompass various flood events, this study estimates the frequency of rice economic damage by employing a...

Integrated flood risk management based on urban policies remains challenging compared with infrastructure due to the unclear risk‐reduction effects over time. To consider heterogeneity in social responses to urban planning measures, a previous study developed an agent‐based household relocation model under flood risk (AHR‐FLOOD) by combining flood‐...

We applied the bivariate extreme value theory to extreme river discharge data calculated from d4PDF historical climate experiment in 5, 886 pairs of class-A rivers in Japan and analyzed their tail dependence and joint flood probability. The results found various pairs having joint floods at return period less than 500 years over Japan, especially in...

Fluvial floods have been considered a lower risk to society in Taiwan since the implementation of well-protection works. However, given the impact of climate change on water-related disasters, it is necessary to re-evaluate the capability of existing facilities in Taiwan to adapt to a changing climate. By utilizing the d4PDF dataset in the rainfall...

Local inertial equations (LIEs) proposed around 2010 have been implemented in many flood simulation models. The authors have studied, using both mathematical and numerical approaches, why LIEs present higher numerical stability over earlier flood simulation models and what explains their numerical stability. This article presents reviews of several...

The present and future compound coastal flooding risk by storm surges and river floods at the river mouth of Japan’s three major bays was diagnostically evaluated based on the d4PDF climate projection. The number of extreme cases in which large storm surges and large river discharges occur by the same typhoon tends to increase slightly in the futur...

Environmental flow is the minimum threshold value of streamflow discharge to guarantee the sustainable development of river environments. In this study, we propose an optimization approach to establish a balance between the water resource supply and environmental conservation based on the mixed moving average (MMA) process as a superposition of inf...

Two methods exist to address the degree to which past extreme events and associated disasters will be intensified due to climate change (CC): storyline approaches and risk-based approaches. However, the risk-based approach applied to weather similar to the target event (typhoons, a stationary weather front,…etc.) becomes theoretically similar to th...

Toward steady adaptation to a changing climate, this study analyzed the potential of a single run of the 150-year seamless experiment by the Meteorological Research Institute (hereinafter, 150-year experiment) with non-stationary frequency analysis for projecting temporal changes in 100-year basin rainfall in all the class-A river systems in Japan....

We propose a linear-quadratic (LQ) control problem of streamflow discharge by optimizing an infinite-dimensional jump-driven stochastic differential equation (SDE). Our SDE is a superposition of Ornstein–Uhlenbeck processes (supOU process), generating a sub-exponential autocorrelation function observed in actual data. The integral operator Riccati...

We investigated a cost-constrained static ergodic control problem of the variance of measure-valued affine processes and its application in streamflow management. The controlled system is a jump-driven mixed moving average process that generates realistic subexponential autocorrelation functions, and the “static” nature of the control originates fr...

In this study, we investigated a cost-constrained static ergodic control problem of the variance of measure-valued affine processes and its application in streamflow management. The controlled system is a jump-driven mixed moving average process that generates subexponential autocorrelation functions, and the static nature of the control originates...

This study constructed a rainfall runoff model corresponding to the characteristics of the Chao Phraya River basin, Thailand and projected future changes of the extreme river discharge in the Chao Phraya River basin with bias-corrected d4PDF rainfall data. As a result, the constructed model well reproduced past several severe flood events; thereby,...

Study region Chao Phraya River Basin (CPRB), the predominant basin located in Thailand. Study focus This study aims to ascertain the difference between spatial bias heterogeneity of streamflow in large river basins such as CPRB for a robust analysis. The upstream major dams and the outlet of the basin were examined with two-step bias correction an...

This chapter describes the hydrodynamic characteristics of Tonle Sap Lake (TSL), primarily based on the 2D-LIE model presented in the previous chapter. This approach allows us to evaluate the inundation area, water volume, and depth distribution of the whole lake at every 500 m at a daily or longer time step. The minimum inundation area and water v...

The effects of external and internal processes of phosphorus on eutrophication in Tonle Sap Lake (TSL) were assessed in this chapter using the phosphorus dynamics model described in Chap. 25. Spatial sensitivity analyses revealed that the total phosphorus (TP) concentration in TSL is more sensitive to the settling rate and the internal and atmosphe...

This book has elucidated the updated knowledge on Tonle Sap Lake (TSL) and identified relevant knowledge gaps. In this final chapter, we carefully selected and concisely summarized the important remaining knowledge gaps and directions for lake environmental management. For most of the lake components, we stress the importance of continuous and comp...

This chapter describes phosphorus dynamics in Tonle Sap Lake (TSL) based on a two-dimensional phosphorus dynamics model, including the major processes of horizontal advection–dispersion, internal loading, sedimentation, and the input from atmosphere, villages on the water, and tributary rivers of the lake. The calibrated model estimated that the to...

We propose a linear-quadratic (LQ) control problem of streamflow discharge by optimizing an infinite-dimensional jump-driven stochastic differential equation (SDE). Our SDE is a superposition of Ornstein-Uhlenbeck processes (supOU process), generating a sub-exponential autocorrelation function observed in actual data. The integral operator Riccati...

The 2-dimensional local inertial equations (20 LIE), a computationally efficient approximation of the shallow water equations, has been applied to surface water flow simulation in Tonle Sap Lake (TSL), Cambodia. Focusing on the unique characteristic that the lake flow is dominated by the mainstream of the Mekong River, this study examined the predi...

Many urban areas at higher flood risk owing to climate change, and mitigating these risks requires a combination of structural and nonstructural adaptation measures. Previous studies assessing adaptation measures are limited in quantifying the effects of climatic and social changes. As an interdisciplinary approach, this study developed an agent‐ba...

In recent years, maintenance and management of irrigation ponds have become important social issues because of the frequent occurrence of natural disasters and the decrease in the number of agricultural workers. This paper presents a proposed integrated evaluation indicator that contributes to irrigation pond maintenance and management, considering...

The development of a multidimensional phosphorus dynamic model for lake floodplain systems is still limited due to its complex hydrodynamics and environmental processes, which constrains our understanding and environmental management on eutrophication. Therefore, we developed a horizontal two-dimensional hydrodynamics-based phosphorus model and app...

The two-dimensional local inertial equation (2D LIE) is a system of nonlinear hyperbolic partial differential equations describing shallow surface water flows. It is a central tool for modeling and analysis in hydraulics and hydrology and has been applied to a variety of numerical simulations of surface water flows. In this chapter, we review the p...

The two-dimensional local inertial equation (2D LIE), a simpler and computationally efficient approximation of the shallow water equations, was applied to Tonle Sap Lake (TSL), and the daily water level and flood area from 1998 to 2003 were then successfully reproduced. This implementation was realized by combining 2D LIE with the distributed hydro...

We applied the bivariate extreme value theory to d4PDF 4-degree rise experiment in the Kanto and Kyushu regions and the metropolitan areas and analyzed the future change of cooccurrence probability of floods over the design level (extreme floods). Its return period in the 4-degree rise scenario was estimated as 800 years in Kanto and 473 years in Kyu...

Taiwan has been devastated by water-related disasters during the wet season and will face more challenges under climate change. The uncertainty of future projections of extreme rainfall events is primarily derived from the internal climate variability. The d4PDF, especially at a 20-km resolution, has the potential to assess the impact of climate ch...

Simulating streamflow under both high-and low-flows is required for versatile eco-hydrological modeling. Typical streamflow simulators require hydrological data such as river geometry and observed river discharge/water level as upstream/downstream boundary conditions. However, these are not always available in data-sparse regions. Furthermore, beca...

This study investigated simultaneous flood risk among all the 109 class-A river basins over Japan using the big data of (over 1000 years) annual maximum hourly flow simulated from a large ensemble climate simulation database for policy decision making for future climate change, and proposed a novel approach in its geospatial analysis by applying tw...

Climate change due to global warming is expected to have major impacts on phenomena such as tropical cyclones (TCs), Baiu, precipitation, and seasonal storms. Many natural disasters in East Asia are driven by TC (typhoon) activity in particular and their associated hazards are sensitive to local-scale characteristics. As such, it is critically impo...

This is a call for application to a column page "Eggs of ideas" handled by young editorial members, for sharing "eggs" of research ideas and/or any thoughts in our research life. It also includes the self-introduction of the four editorial members.

Future changes of flood control effect (FCE) by major existing dams were analyzed for 59 river systems all over Japan using d4PDF rainfall data and the rainfall-runoff model 1K-DHM. The rate of flood peak discharge with/without dams increased for floods over a particular magnitude (FCE was reduced) for some river systems near the Pacific Ocean and not...

Recently, large scale inundation has occurred frequently. In addition, in the study of flood in consideration of climate change, the occurrence of extremely large floods has also been calculated. If large flood and large scale urban inundation occur, the flood water flows to the lower part of the urban area. Then amount of flood water may flow into...

A reduced-order model for flood simulation was developed by using the proper orthogonal decomposition (POD) and the discrete empirical interpolation method (DEIM). The primitive reduced-order equations were first derived by substiting linear combinations of the POD basis vectors for the state variables into the original model equations. The DEIM wa...

Toward assessing climate change impact on extreme meteorological events, database for policy decision making for future climate change (d4PDF) was developed and 3000-year climate reproduction data is provided for the present climate. This accelerated impact assessment studies on floods, initiating multi-basin simultaneous flood risk. However, there...

Typhoon Hagibis caused serious damage to large area of Japan. This study estimated the future changes in frequency of flood peak discharge and multi-basin flooding probability by the typhoon using bias-corrected d4PDF and a rainfall-runoff model constructed for all the class-A rivers in northeastern Japan (Tohoku, Kanto, and Koshinetsu regions). As t...

This study estimated future changes in extreme river discharge in all the class-A rivers in Japan using d4PDF. A distributed rainfall-runoff model was constructed for all the rivers accounting flood control of major dams. A novel bias correction method was developed and applied to the annual maxima of basin rainfall in d4PDF with thousand-year data...

Future changes in annual maximum river discharge in the Southeast Asia region were estimated using “database for Policy Decision making for Future climate change (d4PDF)” taking the Red River basin, Vietnam as a case study. A distributed Hydrologic Model 1K-DHM, based on a kinematic wave approximation, was used for rainfall-runoff simulation. In ad...

This study proposes a generalized framework for the assessment of flood risk and potential strategies to mitigate flood under various vulnerability and adaptation scenarios. The possible causes of hazard, exposure and vulnerability in flood disaster were clearly identified by using a climate risk template. Then, levels of exposure and vulnerability...

Simulating flow dynamics in large-scale lakes is often time-consuming. For river flood simulation, the automatic domain updating (ADU), which can effectively control the simulation domain only in and around the flooded areas, has recently been developed. It is easily implementable without any computational errors for river flood simulation; however...

d4PDF runoff data was applied to river discharge simulation in the Chao Phraya River basin. The simulated discharge underestimated and overestimated observed one in the upstream Bhumibol and Sirikit dams and downstream Nakhon Sawan station, respectively. These different biases were corrected separately through 1) bias correction of wet and dry seaso...

To derive flood risk curves considering spatiotemporal rainfall variability, frequency analysis of basin rainfall has been combined with thousands of normalized profiles of historical rainfall considering dependence of rainfall on duration. This study proposed to consider their further dependence on spatial concentration of profiles for deriving tr...

Hydrological-hydraulic modeling is a core technique in assessing surface water dynamics of rivers, lakes, and floodplains. The local inertial model (LIM) as a physically simplified model of the shallow water equations is essential for efficient numerical simulator of surface water dynamics. In this paper, we point out that the conventional semi-imp...

This research group held a workshop to discuss river basin research efforts with emphasis on future interdisciplinary studies of the sustainable utilization and management of river basin systems. This report describes the workshop activities and their related information, which was held during 18–19 July, 2018 in Takayama city, Gifu.

Flood-inundation modelling is essential for understanding flood dynamics and implementing flood risk management. Despite its increasing demands, it remains computationally expensive to perform 2-D flood-inundation simulations at large scales or fine spatial resolutions. This study presents a simple and novel algorithm for 2-D flood-inundation model...

This study examined the reproducibility of d4PDF extreme rainfall data on all the 109 class-A rivers in Japan. Annual maximum basin-averaged rainfall of d4PDF present climate experiment was compared with one of radar-AMeDAS composite precipitation (1988-2016) on each basin. The two-samples Kolmogorov-Smirnov test indicated that d4PDF shows high per...

A flood risk curve is the relation between annual maximum economic damage due to floods and its exceedance probability, which provides useful information for quantitative flood risk assessment. This study proposed to examine the applicability of d4PDF, a large ensemble climate projection dataset, to develop a probabilistic flood risk curve for the...

Twelve young researchers in the Japan Society of Hydrology and Water Resources review histories and future perspectives in the field of hydrology and water resources research. This review intends to describe its state-of-the-art and to record ongoing research activities by early-career researchers. This review article covers the broad field in hydr...

The local inertial equation (LIE) is a simple shallow water model for simulating surface water dynamics. Recently, the model has been widely applied to flood simulation worldwide. Keys in numerical implementation of the LIE are the staggered spatio-temporal discretization and the stable treatment of the friction slope terms. The latter is critical...

An integrated hydrological-hydraulic model employing the 2-D local inertial equation as the core is established for effective numerical simulation of surface water flows in a great lake and its floodplain. The model is a cascade of validated hydrological and hydraulic sub-models. The model was applied to simulating the surface water flows of the To...

Integrated flood risk management is essential to reduce damage due to floods over the design level. For this, a fluvial flood risk curve, which indicates the exceedance probability of the annual maximum flood damage, has been developed. A flood risk curve is helpful for assessing the current risk and the effect of various measures in the whole targ...

Future changes of probability distributions of extreme rainfall and flood are analyzed using “Database for Policy Decision-Making for Future Climate Change, d4PDF” having 60-years climate simulations with 50 ensemble members for the historical experiment and 90 members for the future experiment. The magnitude of a largest-class flood equivalent to...

This article presents a review of characteristics and challenges of numerical techniques used for surface water flow analysis from an interdisciplinary view related to hydrology and water resources. The article provides a comprehensive perspective of numerical analysis to promote collaborative studies of surface water flow. Each chapter explains ch...

The discussion in the WACCA meeting 06 is reported. The topics in the meeting was issues and breakthroughs in the field of water related researches. Based on the presentations about issues and breakthroughs in each research target, our next challenges to work on were discussed.

The local inertial equations, which drop the nonlinear acceleration term from the Saint-Venant equations, are effective and efficient for fast flood computation thanks to its hyperbolic nature and semi-implicit discretization of the friction term. However, mechanisms that the semi-implicit discretization works successfully has not been clarified, w...

In previous studies, reanalysis data has been used instead of observational data for bias correction of GCM outputs in observation data scarce basin. However, reanalysis data does not match the real weather characteristics (e.g. precipitation, temperature) in a local scale since it is targeted at a global scale. Therefore, this study aims to develo...

Design flood, river discharge with a particular return period, is fundamental to determine the scale of flood control facilities. In addition, considering a changing climate, not only frequencies of river discharge at design level but those of devastating flooding are also crucial. Characteristics of river discharge during extreme floods largely di...

In flood risk curve estimation under various scenarios, inundation simulations with various spatio-temporal rainfall distributions are required since a rainfall pattern has a large impact on estimating economic flood damage; however, inundation simulation takes longer time than rainfall-runoff simulations due to its high computational costs. If a h...

To design integrated flood risk management, flood risk assessment based on the economic damage is essential. In previous studies, the authors have developed a method to estimate a flood risk curve considering spatio-temporal distribution of rainfall by applying the Synthesis Probability Method (SPM) that estimates probability function of annual max...

A largest-class flood caused by a typhoon under a climate change condition at the Yodo River basin is examined by using rainfall data developed by a physically-based course ensemble typhoon experiment for the Isewan Typhoon in 1959 and a distributed rainfall-runoff model including flood regulation with dam reservoir operation. Simulated flood disch...

A new formulation of the St. Venant momentum equation, the local inertial equation, was developed recently at the University of Bristol for stable and fast flood inundation modelling. The local inertial term of the momentum equation, which is neglected in the diffusive wave approximation, is additionally considered in the local inertial equation. H...

The synthesis probability method, which estimates T-year annual maximum flood peak discharge considering spatio-temporal distribution of rainfall, has the assumption of independency between total precipitation and its spatio-temporal distribution. This research improved the method to consider a relation between the two by using conditional probabil...

To manage flood disaster with an exceeding designed level, flood risk control based on appropriate risk assessment is essential. To make an integrated economic risk assessment by flood disaster, a flood risk curve, which is a relation between flood inundation damage and its exceedance probability, plays an important role. This research purposes a m...

Steep mountainous areas account for 70% of all river catchments in Japan. To predict river discharge for the mountainous catchments, many studies have applied DHM-KWSS (Distributed Hydrologic Models based on a Kinematic Wave approximation with Surface and Subsurface flow components). These models well reproduce observed river discharge of catchment...

An impact assessment of a risk of water-related disaster under a changing climate has been highly concerned recently. For the assessment, it is important to examine a change of the magnitude of inundation disasters as well as that of flow regime under various climate conditions. To make an ensemble assessment of the magnitude of inundation disaster...