**2. Shortcomings in conventional frameworks**

#### **2.1 Hazard component related**

Flood hazard is conventionally described by its probability of occurrence and severity (magnitude, duration, and extent of flooding). However, evidence has been mounting that the timing of a flood really matters. On July 7, 2018, Mabi town in Okayama Prefecture, Japan, near the confluence of the Takahashi River and the Odagawa River, was inundated due to levee breaches in the two rivers. As shown in **Figure 1**, the highest water level in the Takahashi River near the river junction occurred at 3:00 AM and exceeded the historical records. In this disaster, more than 50 people perished with 90% of the victims aged from 66 to 91. These elders lived either alone or with a senior spouse. For elders, evacuation during the night is difficult both physically and mentally. Besides, there were media reports and our own interviews heard the same story from people who suffered from inundation in various places in recent years that flood waters entering their homes rose so quickly that they had difficulty to escape. Therefore, inundation is not just a matter of

**5**

**Figure 2.**

*Intensity dependency of flood water level rising rate.*

*New Frontiers in Flood Risk Management DOI: http://dx.doi.org/10.5772/intechopen.81925*

also question deserving in-depth study.

already at capacity.

developed.

ment plans.

depth but also the rate of rising. The rate of inundation depth increase may depend on many factors such as local topography, the presence of structures, and urban drainage systems as well. So far, there is little information on the variation patterns of inundation depth with time during flood disasters. How fast the inundation depth would increase should be given serious consideration in flood risk manage-

**Figure 2** shows the comparison of rising limb of hydrography at the Sakazu

On July 30 2011, the Ikarashi River in Niigata Prefecture, Japan, breached around 5:00 AM. In addition to the timing of inundation, other characteristics of this flood can be described as having two consecutive floods or a two-peak hydrological event. For the first peak, a dam in the upstream of the river regulated the peak, but for the even larger second peak, the dam failed to function since it was

These pieces of evidence serve to demonstrate that hazard identification should include flood peak timing and the possibility of multipeaks in addition to probability and magnitude. However, methodology to consider these factors has not been

hydrological station between the largest-ever flood of the Takahashi River occurred in 2018, the second largest flood in 2011, and a small flood in 2015. It is clearly seen that the rate of water level increase depended on the intensity of a flood. The larger the intensity, the fast the water level increased. The current flood warning system in Japan is based on four water levels: (1) stand-by level, (2) flood watch level, (3) flood alert level, and (4) flood danger level. Such a warning system is essential for emergency evacuation. However, a problem with this system is that information on how fast the water level may rise from one level to another in an unprecedented flood is not available because it is intensity dependent as shown in **Figure 2**. How to provide real-time forecast on water level rising speed and incorporate it into the warning system is a technical issue to be explored. Besides, a related question is: is there a link between the rate of water level increase in channel and the temporal variation pattern of inundation depth in flooded area? It is

**Figure 1.** *Hydrograph of the Takahashi River, Japan, on July 7, 2018, that peaked at 3:00 AM.*

#### *New Frontiers in Flood Risk Management DOI: http://dx.doi.org/10.5772/intechopen.81925*

*Recent Advances in Flood Risk Management*

them.

work for vulnerability.

**2.1 Hazard component related**

that make it susceptible to the damaging effects of a hazard. Thus, the choice of definition may depend on its suitability for a particular vulnerability study and its interpretation for policy or action. The fact that it can be approached in manifold

Villagran de Leon proposed a different framework of risk, which consists of hazard, vulnerability, and deficiencies in preparedness [3]. Exposure was treated as a component of the hazard. The term "deficiencies in preparedness" was used to emphasize the lack of coping capacities of a society at risk. The pressure and release model [4] considers disaster as a product of two major forces: natural hazard and vulnerability. It was intended to stress the importance of vulnerability assessment. No matter what framework one employs to deal with vulnerability and risk, the assessment should go beyond the identification of vulnerability and risk. It should probe into underlying driving forces and root causes in order to reduce or minimize

The objective of the present study is to highlight a number of shortcomings in conventional frameworks for flood risk management. A focal point is the frame-

Flood hazard is conventionally described by its probability of occurrence and severity (magnitude, duration, and extent of flooding). However, evidence has been mounting that the timing of a flood really matters. On July 7, 2018, Mabi town in Okayama Prefecture, Japan, near the confluence of the Takahashi River and the Odagawa River, was inundated due to levee breaches in the two rivers. As shown in **Figure 1**, the highest water level in the Takahashi River near the river junction occurred at 3:00 AM and exceeded the historical records. In this disaster, more than 50 people perished with 90% of the victims aged from 66 to 91. These elders lived either alone or with a senior spouse. For elders, evacuation during the night is difficult both physically and mentally. Besides, there were media reports and our own interviews heard the same story from people who suffered from inundation in various places in recent years that flood waters entering their homes rose so quickly that they had difficulty to escape. Therefore, inundation is not just a matter of

ways offers both flexibility and difficulty to use and interpret.

**2. Shortcomings in conventional frameworks**

*Hydrograph of the Takahashi River, Japan, on July 7, 2018, that peaked at 3:00 AM.*

**4**

**Figure 1.**

depth but also the rate of rising. The rate of inundation depth increase may depend on many factors such as local topography, the presence of structures, and urban drainage systems as well. So far, there is little information on the variation patterns of inundation depth with time during flood disasters. How fast the inundation depth would increase should be given serious consideration in flood risk management plans.

**Figure 2** shows the comparison of rising limb of hydrography at the Sakazu hydrological station between the largest-ever flood of the Takahashi River occurred in 2018, the second largest flood in 2011, and a small flood in 2015. It is clearly seen that the rate of water level increase depended on the intensity of a flood. The larger the intensity, the fast the water level increased. The current flood warning system in Japan is based on four water levels: (1) stand-by level, (2) flood watch level, (3) flood alert level, and (4) flood danger level. Such a warning system is essential for emergency evacuation. However, a problem with this system is that information on how fast the water level may rise from one level to another in an unprecedented flood is not available because it is intensity dependent as shown in **Figure 2**. How to provide real-time forecast on water level rising speed and incorporate it into the warning system is a technical issue to be explored. Besides, a related question is: is there a link between the rate of water level increase in channel and the temporal variation pattern of inundation depth in flooded area? It is also question deserving in-depth study.

On July 30 2011, the Ikarashi River in Niigata Prefecture, Japan, breached around 5:00 AM. In addition to the timing of inundation, other characteristics of this flood can be described as having two consecutive floods or a two-peak hydrological event. For the first peak, a dam in the upstream of the river regulated the peak, but for the even larger second peak, the dam failed to function since it was already at capacity.

These pieces of evidence serve to demonstrate that hazard identification should include flood peak timing and the possibility of multipeaks in addition to probability and magnitude. However, methodology to consider these factors has not been developed.

**Figure 2.** *Intensity dependency of flood water level rising rate.*

#### **2.2 Vulnerability component related**

Vulnerability can be defined as follows:

$$\text{Valnerability} = \text{Exposure to risk} \star \text{Inability to scope} \tag{2}$$

However, if the framework for risk (1) is used, the definition of vulnerability should simply be inability to cope with hazard since exposure is treated separately. Füssel [5] reviewed the range of definitions of vulnerability and argued that continued plurality would become a hindrance in interdisciplinary research. A common definition of vulnerability is much needed to advance the understanding of vulnerability, yet reaching consensus is challenging. As a matter of fact, some scholars have argued that previous attempts to develop a shared vulnerability framework were superficial [6, 7].

O'Brien et al. [8] presented two dominant interpretations of vulnerability, which they refer to as outcome vulnerability and contextual vulnerability. Outcome vulnerability is considered as the residual exposure to impacts of climatic changes after adaptation responses have been factored in. Studies following this interpretation often take a sectoral view, looking at which/where is likely to be worst affected. Contextual vulnerability deals dynamically with the institutional, biophysical, socioeconomic, and technological conditions that affect the extent of exposure to climate changes and the ways in which those exposed can respond. Studies following this interpretation often take a more multidimensional view in a local setting, looking at how and why groups are affected differently in the context of other changes happening simultaneously. It is, therefore, more suitable to interdisciplinary and transdisciplinary studies. The present study attempts to combine outcome vulnerability and context vulnerability for the purpose of developing a more comprehensive and structured framework.

It is a two-layer structure consisting of system vulnerability (contextual vulnerability) and component vulnerability (outcome vulnerability) as shown in **Figure 3**. Factors affecting system vulnerability can be classified into four categories. (1) The social-economic-demographic category includes factors such as general risk perception, disaster insurance, medical care, GDP, and population distribution. (2) The institutional category includes planning capability, legal system and management capability, such as evacuation operations. (3) The biophysical category includes landform and land use, river basin scale, and river dynamics. Steep river channels often generate flash floods that are difficult to predict. On the other hand, mild waterways may generate much larger floods that could be more destructive if overflow occurred. (4) The engineering category includes flood defense and warning systems.

System vulnerability can be regulated by various structural measures such as levee and retarding basin construction and nonstructural measures such as flood hazard mapping and land use regulation. The interaction of various factors results in residual system vulnerability that is then passed on to component vulnerability (or outcome vulnerability). Component vulnerability is determined by awareness, self-preparedness, community strength, and even local culture. For example, a type of old Japanese house-Mizuka as shown in **Figure 4** is a measure of self-defense. It is a two-house compound, in which one is for everyday living and another is used as shelter in case of emergency. Living in such a house reduced component vulnerability. Nevertheless, the number of such houses in Japan has been largely reduced due to various reasons, especially changes in life style and a lowering of risk awareness.

**7**

**Figure 3.**

**Figure 4.**

*A two-layer framework for vulnerability.*

*A self-prepared traditional house in Japan-Mizuka.*

System vulnerability acts at city, regional, or river basin scale, while component vulnerability acts at individual or community scale. The degree of passage from system to component vulnerability is termed as vulnerability conductivity hereafter. It depends upon risk communication and public participation. Risk communication is the exchange of information and opinions, and establishment of an effective dialog,

*New Frontiers in Flood Risk Management DOI: http://dx.doi.org/10.5772/intechopen.81925* *Recent Advances in Flood Risk Management*

**2.2 Vulnerability component related**

were superficial [6, 7].

Vulnerability can be defined as follows:

comprehensive and structured framework.

includes flood defense and warning systems.

Vulnerability = Exposure to risk + Inability to cope (2)

However, if the framework for risk (1) is used, the definition of vulnerability should simply be inability to cope with hazard since exposure is treated separately. Füssel [5] reviewed the range of definitions of vulnerability and argued that continued plurality would become a hindrance in interdisciplinary research. A common definition of vulnerability is much needed to advance the understanding of vulnerability, yet reaching consensus is challenging. As a matter of fact, some scholars have argued that previous attempts to develop a shared vulnerability framework

O'Brien et al. [8] presented two dominant interpretations of vulnerability, which they refer to as outcome vulnerability and contextual vulnerability. Outcome vulnerability is considered as the residual exposure to impacts of climatic changes after adaptation responses have been factored in. Studies following this interpretation often take a sectoral view, looking at which/where is likely to be worst affected. Contextual vulnerability deals dynamically with the institutional, biophysical, socioeconomic, and technological conditions that affect the extent of exposure to climate changes and the ways in which those exposed can respond. Studies following this interpretation often take a more multidimensional view in a local setting, looking at how and why groups are affected differently in the context of other changes happening simultaneously. It is, therefore, more suitable to interdisciplinary and transdisciplinary studies. The present study attempts to combine outcome vulnerability and context vulnerability for the purpose of developing a more

It is a two-layer structure consisting of system vulnerability (contextual vulnerability) and component vulnerability (outcome vulnerability) as shown in **Figure 3**. Factors affecting system vulnerability can be classified into four categories. (1) The social-economic-demographic category includes factors such as general risk perception, disaster insurance, medical care, GDP, and population distribution. (2) The institutional category includes planning capability, legal system and management capability, such as evacuation operations. (3) The biophysical category includes landform and land use, river basin scale, and river dynamics. Steep river channels often generate flash floods that are difficult to predict. On the other hand, mild waterways may generate much larger floods that could be more destructive if overflow occurred. (4) The engineering category

System vulnerability can be regulated by various structural measures such as levee and retarding basin construction and nonstructural measures such as flood hazard mapping and land use regulation. The interaction of various factors results in residual system vulnerability that is then passed on to component vulnerability (or outcome vulnerability). Component vulnerability is determined by awareness, self-preparedness, community strength, and even local culture. For example, a type of old Japanese house-Mizuka as shown in **Figure 4** is a measure of self-defense. It is a two-house compound, in which one is for everyday living and another is used as shelter in case of emergency. Living in such a house reduced component vulnerability. Nevertheless, the number of such houses in Japan has been largely reduced due to various reasons, especially changes in life style and a

**6**

lowering of risk awareness.

#### **Figure 3.**

*A two-layer framework for vulnerability.*

#### **Figure 4.**

*A self-prepared traditional house in Japan-Mizuka.*

System vulnerability acts at city, regional, or river basin scale, while component vulnerability acts at individual or community scale. The degree of passage from system to component vulnerability is termed as vulnerability conductivity hereafter. It depends upon risk communication and public participation. Risk communication is the exchange of information and opinions, and establishment of an effective dialog, among those responsible for assessing, minimizing, and regulating risks and those who may be affected by the outcomes of those risks. This is the first attempt to incorporate risk communication into a vulnerability framework and to place one of its roles in the linkage between contextual and outcomes vulnerability.

Flood disasters may cause extensive loss of life and property damage, which is essentially an anthropogenic phenomenon with social roots. However, the dimension of loss and damage has been less focused on vulnerability framing so far. A conventional framework to address loss and damage is the C × L framework as below:

$$\text{Risk} = \text{Consequence} \times \text{Likelihood} \tag{3}$$

where (i) likelihood is the probability of occurrence of an impact that affects the environment and (ii) consequence is the social and environmental impact if an event occurs.

This framework combines the scores from the qualitative or semiquantitative ratings of consequence and the likelihood that a specific consequence will occur to generate a risk score and risk rating. Although this risk framework takes into consideration the consequence of an event, it is not suitable for conducting integrated risk and vulnerability analyses. To incorporate loss and damage into the framework (1), vulnerability should be redefined as:

Vulnerability = Inability to cope × Potential consequence (loss and damage) (4)

The logic to include loss and damage in vulnerability is justifiable. If the level of impact upon an individual or community is low, then this individual or community is not truly vulnerable although they may not able to prevent certain consequences from happening. Accordingly, the two-layer framework includes loss and damage as already depicted in **Figure 2**.

Following this vulnerability framework, a policy that is different from the conventional can be proposed as below.

Conventional flood countermeasures have focused on preventing flood waters from reaching populated areas such that blocking may be considered a keyword to describe the concept of conventional flood countermeasures. However, such a zero-risk approach has been shown to be in vain, especially in urban areas. In urban areas, in addition to the problems of asset concentration and surface imperviousness, complex urban structures may affect the behavior of flood waters in the case of inundation. Either intentionally or by chance, roads, railroads, and buildings may function as barriers to keep flood waters from spreading to a wider area [9]. Consequently, urban flooding may be characterized as being confined and deep. It is well documented that the degree of fatality and direct economic cost of flooding is proportional to inundation depth [10]. Therefore, redesigning urban form to transform confined and deep flooding to wide and shallow flooding is a way to reduce vulnerability if the prevention of inundation is not totally avoidable. The concept can be rephrased as "managing flood waters up to your knees". Policy supporting such a concept can be termed flood sharing. How it can be implemented is a question to be answered.

An important driver of vulnerability reduction is better planning. Poorly planned and managed urbanization leads to growing flood hazard due to unsuitable land use change and increasing flood vulnerability due to development in flood-prone areas and overpopulation of such areas. As shown in **Figure 5**, river flood management planning in Japan starts with setting up a planning scale, which is the level of

**9**

**Figure 5.**

*underline).*

area larger than 1000 m2

*New Frontiers in Flood Risk Management DOI: http://dx.doi.org/10.5772/intechopen.81925*

safety against flood disasters to be provided in the area of concern. The next step is to select a number of target rainfalls for the planning site based on rainfall and historical flood records. Then, by performing rainfall-runoff simulations, a flood hydrograph can be determined as the management target, which is termed as either design flood without regulation or maximum probable flood. Once the maximum probable flood is estimated, allocation of flood water by dam, retarding basin, and river channel will be determined to safely convey flood water to its destination. In this planning procedure, however, the increase of maximum probable flood due to future urbanization is not directly considered. The increase in the total volume of the direct runoff is also not taken into consideration in dam and retarding basin planning. In addition, urban development planners often neglect, or are not aware of, the possibility that development may partially invalidate the river flood management design in operation in the absence of sound development planning. The fact that the maximum probable flood would vary with significant changes in land use, resulting in an increase in peak flow in a river channel, has been given less attention by urban planners in planning development of housing projects along waterways. What is often observed is that countermeasures were being taken to reduce urbanizationinduced flood risk years or decades after large-scale urban development, especially after experiencing serious flood disasters. Wording differently, approaches so far have often been reactive, not proactive. Therefore, a key principle of Low Impact Development or of a Sponge City should be that no significant increase in maximum probable flood results from the process of urban development. In Japan, the Act on Countermeasures against Flood Damage of Specified Rivers Running across Cities was put into effect in 2005. According to this law, any urban development with an

*Procedure of flood management planning in Japan and a proposed modification (marked with red color and* 

should not cause any increase in surface runoff. If any

increase is likely, permission from the competent authority is required. This law was first applied to the Tsurumi River basin since 2006 and currently implemented in seven river basins across Japan. However, monitoring studies on change of surface runoff in the seven targeted river basins are limited. The overall effectiveness of this regulation has not been validated. **Figure 6** shows where waterlogging occurred

*New Frontiers in Flood Risk Management DOI: http://dx.doi.org/10.5772/intechopen.81925*

#### **Figure 5.**

*Recent Advances in Flood Risk Management*

(1), vulnerability should be redefined as:

already depicted in **Figure 2**.

question to be answered.

conventional can be proposed as below.

below:

event occurs.

among those responsible for assessing, minimizing, and regulating risks and those who may be affected by the outcomes of those risks. This is the first attempt to incorporate risk communication into a vulnerability framework and to place one of

Flood disasters may cause extensive loss of life and property damage, which is essentially an anthropogenic phenomenon with social roots. However, the dimension of loss and damage has been less focused on vulnerability framing so far. A conventional framework to address loss and damage is the C × L framework as

Risk = Consequence × Likelihood (3)

where (i) likelihood is the probability of occurrence of an impact that affects the environment and (ii) consequence is the social and environmental impact if an

This framework combines the scores from the qualitative or semiquantitative ratings of consequence and the likelihood that a specific consequence will occur to generate a risk score and risk rating. Although this risk framework takes into consideration the consequence of an event, it is not suitable for conducting integrated risk and vulnerability analyses. To incorporate loss and damage into the framework

Vulnerability = Inability to cope × Potential consequence (loss and damage) (4)

The logic to include loss and damage in vulnerability is justifiable. If the level of impact upon an individual or community is low, then this individual or community is not truly vulnerable although they may not able to prevent certain consequences from happening. Accordingly, the two-layer framework includes loss and damage as

Following this vulnerability framework, a policy that is different from the

Conventional flood countermeasures have focused on preventing flood waters from reaching populated areas such that blocking may be considered a keyword to describe the concept of conventional flood countermeasures. However, such a zero-risk approach has been shown to be in vain, especially in urban areas. In urban areas, in addition to the problems of asset concentration and surface imperviousness, complex urban structures may affect the behavior of flood waters in the case of inundation. Either intentionally or by chance, roads, railroads, and buildings may function as barriers to keep flood waters from spreading to a wider area [9]. Consequently, urban flooding may be characterized as being confined and deep. It is well documented that the degree of fatality and direct economic cost of flooding is proportional to inundation depth [10]. Therefore, redesigning urban form to transform confined and deep flooding to wide and shallow flooding is a way to reduce vulnerability if the prevention of inundation is not totally avoidable. The concept can be rephrased as "managing flood waters up to your knees". Policy supporting such a concept can be termed flood sharing. How it can be implemented is a

An important driver of vulnerability reduction is better planning. Poorly planned

and managed urbanization leads to growing flood hazard due to unsuitable land use change and increasing flood vulnerability due to development in flood-prone areas and overpopulation of such areas. As shown in **Figure 5**, river flood management planning in Japan starts with setting up a planning scale, which is the level of

its roles in the linkage between contextual and outcomes vulnerability.

**8**

*Procedure of flood management planning in Japan and a proposed modification (marked with red color and underline).*

safety against flood disasters to be provided in the area of concern. The next step is to select a number of target rainfalls for the planning site based on rainfall and historical flood records. Then, by performing rainfall-runoff simulations, a flood hydrograph can be determined as the management target, which is termed as either design flood without regulation or maximum probable flood. Once the maximum probable flood is estimated, allocation of flood water by dam, retarding basin, and river channel will be determined to safely convey flood water to its destination. In this planning procedure, however, the increase of maximum probable flood due to future urbanization is not directly considered. The increase in the total volume of the direct runoff is also not taken into consideration in dam and retarding basin planning. In addition, urban development planners often neglect, or are not aware of, the possibility that development may partially invalidate the river flood management design in operation in the absence of sound development planning. The fact that the maximum probable flood would vary with significant changes in land use, resulting in an increase in peak flow in a river channel, has been given less attention by urban planners in planning development of housing projects along waterways. What is often observed is that countermeasures were being taken to reduce urbanizationinduced flood risk years or decades after large-scale urban development, especially after experiencing serious flood disasters. Wording differently, approaches so far have often been reactive, not proactive. Therefore, a key principle of Low Impact Development or of a Sponge City should be that no significant increase in maximum probable flood results from the process of urban development. In Japan, the Act on Countermeasures against Flood Damage of Specified Rivers Running across Cities was put into effect in 2005. According to this law, any urban development with an area larger than 1000 m2 should not cause any increase in surface runoff. If any increase is likely, permission from the competent authority is required. This law was first applied to the Tsurumi River basin since 2006 and currently implemented in seven river basins across Japan. However, monitoring studies on change of surface runoff in the seven targeted river basins are limited. The overall effectiveness of this regulation has not been validated. **Figure 6** shows where waterlogging occurred

#### **Figure 6.**

*Locations of waterlogging (red dot) occurred in Kawasaki City during the period of 2008–2017 (source: Kawasaki City).*

during the period of 2008–2017 in Kawasaki City, which is part of the Tsurumi River basin. **Figure 7** shows where waterlogging occurred during the period of 2006–2010 in Machida City, which is also part of the Tsurumi River basin. Although 3300 storage facilities have been installed in the river basin, inundation is still a frequent visitor to the region. Besides, the waterlogging locations in Kawasaki City are more or less uniformly distributed, while the waterlogging in Machida City mainly occurred along its administrative boundary on the west side. Such a difference in distribution of vulnerable locations may be viewed as one aspect of system vulnerability.

A fundamental issue in implementing this law is that it has not been directly linked to the river flood management planning procedure. To strike a good balance between flood risk reduction and economic development, the present study proposes a new planning scheme as shown in **Figure 5** with red color and underline. For new or redevelopment, the possibility of increasing maximum probable flood should be examined. If it is not possible to deal with the increase in maximum probable flood, the Act on Countermeasures against Flood Damage of Specified Rivers Running across Cities must be strictly implemented. If additional amounts of flood waters can be handled through reallocation such as constructing new or expanding the capacities of existing storage facilities, or by in-channel engineering works such as excavation, then the law can be executed to control the total amount of increase of surface runoff while having a priority setting to give permissions to economically important development projects.

### **2.3 Exposure component related**

In cities like Tokyo, flood waters stay on streets for a few hours or a few days at most if inundation occurs. In other places such as Bangkok, however, flood waters

**11**

**3. Eco-DRR in Japan**

**Figure 7.**

*Machida City).*

*New Frontiers in Flood Risk Management DOI: http://dx.doi.org/10.5772/intechopen.81925*

may stay on streets for more than 2 months due to the city's topography and insufficient drainage capacity. In Thailand, the flood damage to Bangkok and five adjoining provinces in 1983 was estimated by the National Statistical Office to be billions of Bath with the bulk of the damage shouldered by the private sector. A study by Tang et al. indicated that flood depth and flood duration were significant factors

*Locations of waterlogging (blue dot) occurred in Machida City during the period of 2006–2010 (source:* 

In view of such a difference in flood water residence time, the duration of inundation should be factored into exposure component, the longer the duration, the higher the level of exposure. Adding such a temporal factor to vulnerability framework will certainly lead to better planning for vulnerability reduction and smooth emergency response. It is also related to disaster insurance. To protect buildings that are constructed in flood-prone hazard areas from damage caused by flood forces, the National Flood Insurance Program (NFIP) in the United States requires that all construction below the base flood elevation must consist of flood damage-resistant building materials [12, 13]. What constitutes flood damage-resistant building materials is indeed duration dependent. The impact of duration is a much less explored

Ecosystem-based disaster risk reduction (Eco-DRR) is a relatively new concept to reduce the risk of being exposed to natural hazards by avoiding development in disaster-prone areas or by using natural systems as a way to buffer the worst impacts of natural hazards, maintain the resilience of natural ecosystems and their ecosystem services, and help people and communities adapt to changing conditions [14, 15]. The core thinking of Eco-DRR is based on the realization that disasters cause massive damage to the environment, while degraded environments exacerbate disaster impacts and responding to disasters often leads to additional environmental impacts. Well-managed ecosystems, such as wetlands, forests, and

explaining flood damage in the residential and industrial areas [11].

research area and is envisioned to gain more attention in the near future.

*Recent Advances in Flood Risk Management*

during the period of 2008–2017 in Kawasaki City, which is part of the Tsurumi River basin. **Figure 7** shows where waterlogging occurred during the period of 2006–2010 in Machida City, which is also part of the Tsurumi River basin. Although 3300 storage facilities have been installed in the river basin, inundation is still a frequent visitor to the region. Besides, the waterlogging locations in Kawasaki City are more or less uniformly distributed, while the waterlogging in Machida City mainly occurred along its administrative boundary on the west side. Such a difference in distribution of vulnerable locations may be viewed as one aspect of system

*Locations of waterlogging (red dot) occurred in Kawasaki City during the period of 2008–2017 (source:* 

A fundamental issue in implementing this law is that it has not been directly linked to the river flood management planning procedure. To strike a good balance between flood risk reduction and economic development, the present study proposes a new planning scheme as shown in **Figure 5** with red color and underline. For new or redevelopment, the possibility of increasing maximum probable flood should be examined. If it is not possible to deal with the increase in maximum probable flood, the Act on Countermeasures against Flood Damage of Specified Rivers Running across Cities must be strictly implemented. If additional amounts of flood waters can be handled through reallocation such as constructing new or expanding the capacities of existing storage facilities, or by in-channel engineering works such as excavation, then the law can be executed to control the total amount of increase of surface runoff while having a priority setting to give permissions to economically

In cities like Tokyo, flood waters stay on streets for a few hours or a few days at most if inundation occurs. In other places such as Bangkok, however, flood waters

**10**

vulnerability.

**Figure 6.**

*Kawasaki City).*

important development projects.

**2.3 Exposure component related**

*Locations of waterlogging (blue dot) occurred in Machida City during the period of 2006–2010 (source: Machida City).*

may stay on streets for more than 2 months due to the city's topography and insufficient drainage capacity. In Thailand, the flood damage to Bangkok and five adjoining provinces in 1983 was estimated by the National Statistical Office to be billions of Bath with the bulk of the damage shouldered by the private sector. A study by Tang et al. indicated that flood depth and flood duration were significant factors explaining flood damage in the residential and industrial areas [11].

In view of such a difference in flood water residence time, the duration of inundation should be factored into exposure component, the longer the duration, the higher the level of exposure. Adding such a temporal factor to vulnerability framework will certainly lead to better planning for vulnerability reduction and smooth emergency response. It is also related to disaster insurance. To protect buildings that are constructed in flood-prone hazard areas from damage caused by flood forces, the National Flood Insurance Program (NFIP) in the United States requires that all construction below the base flood elevation must consist of flood damage-resistant building materials [12, 13]. What constitutes flood damage-resistant building materials is indeed duration dependent. The impact of duration is a much less explored research area and is envisioned to gain more attention in the near future.
