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Sea level rise will pose a significant challenge to coastal settlements throughout the planet and is likely to disproportionately affect poorer communities, which are usually located in particularly vulnerable areas. Coastal areas in Jakarta have been experiencing rapid subsidence in recent years, and could serve to illustrate the likely challenges that future sea level rise could have on such communities. To ascertain the level of awareness about the threats facing them questionnaire surveys were conducted amongst one relatively poor community that is situated below sea level, protected from the sea by a thin concrete dyke. The results show that while local inhabitants appear to be aware about the hazards they face, many seem to underestimate their severity, possibly due to a high frequency of exposure in the recent past. The situation in the area appears to be worsening with each passing year, and it is imperative that remedial actions to halt ground subsidence are carried out and/or important remedial actions to adapt to the ground subsidence are implemented. Failure to do so could eventually result in a significant loss of life in the area.

The present work projects the extent of coastal floods by the year 2050 in Jakarta, one of the fastest growing megacities in the world, using a coastal hydrodynamic model that considers abnormal high tides, sea-level rise, and land subsidence. The tidal constituents were adjusted in a manner to reproduce the observed tidal record during the extensive coastal floods that took place on November 2007, when it is likely that a La Niña event, the 18.6 year lunar nodal high-tide cycle, and other abnormal tide mechanisms took place simultaneously. The simulations demonstrate that by the middle of this century extensive floods could potentially reach several kilometers inland in Jakarta. Land subsidence is clearly one of the major challenges facing the city, as considering only the influence of sea-level rise indicates that such floods may be limited to within a few hundred meters of the coastline. From 2000 to 2050 the potential flood extent is estimated to increase by 110.5 km2. Land subsidence is responsible for 88% of this increase. The results also indicate that the rate of flood area expansion in the 2025–2050 period would be 3.4 times faster than during the 2000–2025 period, demonstrating a non-linear increase in flood risk with the passage of time. Keywords Jakarta; Coastal flood; Land subsidence; Sea-level rise; Oceanic tide; Urbanization; Abnormal high tides; ENSO; 18.6-year lunar nodal cycle Highlights •Future coastal flooding in Jakarta was projected through a coastal hydrodynamic model. •The model took into account land subsidence, SLR, and abnormal high tide. •From 2000 to 2050 the potential flood extent is estimated to increase by 110.5 km2. •Land subsidence is responsible for 88% of this increase. •The extent of flood areas will exponentially increase with the passage of time.

In recent years, many tsunami disasters have taken place in small remote islands, which can be considered to be particularly vulnerable against coastal disasters. In this chapter the authors discuss how to prepare for future tsunami threats in remote islands based on the results of their own field surveys conducted after two recent tsunami events. First, the results of the surveys on the 2009 Samoan and 2010 Mentawai islands tsunamis are summarized, providing the measured tsunami heights at a variety of locations. Then, the lessons learnt from the Samoan and Mentawai islands cases are described from two points of view: triggers for evacuation actions and evacuation routes and areas. Ground shaking due to an earthquake, information through a tsunami warning system, and unusual behavior of the sea are typical triggers for tsunami evacuation actions and it is important to increase the number and types of triggers. Preparing evacuation routes and signs, which can help people evacuate to higher ground quickly, are also important countermeasures against tsunamis in remote islands.

The combined effect of an increase in typhoon intensity and sea level rise could pose significant challenges to coastal defences around Tokyo Bay. In the present chapter the authors determined the storm surge that could result from an increase in typhoon intensity around Tokyo Bay around the turn of the twenty-first century. This was then combined with a variety of sea level rise scenarios to obtain potential water levels for a 1 in 100 year design storm in the year 2100. The results show that the various settlements around Tokyo Bay, and particularly those along the low-lying areas in the Koto delta in Tokyo, are at considerable risk of storm surges and sea level rise in the future. If these defences are breached the potential direct economic consequences would be significant, potentially in excess of 100 trillion yen (around 0.92 trillion USD or 0.72 trillion euros, or 20% of the current GDP of Japan), with the indirect costs likely to be even greater. As a result it is likely that sea defences will have to be strengthened around Tokyo Bay in the future, which could cost in the order of 370 bn yen to defend against a 1 in 100 year storm by the year 2100. Alternatively, a storm surge barrier could be built, which would cost in the range of 700-800 bn yen, though such a structure could raise the protection level and cope with a 1 in 500 year storm, amongst other benefits.

Coastal dikes, breakwaters, and seawalls are generally used to control floods, debris flows, erosion, and even massive catastrophic events such as tsunamis. However, these structures will only perform well if they are firmly constructed in terms of strength and stability of slopes and toes and can resist the dynamic forces imposed by the incident wave energy. During a Level 2 tsunami such as the 2011 Tohoku Earthquake Tsunami many concrete coastal defenses in the NE of the country could not withstand the forces imposed by the tsunami overflowing water and as a result failed either partially or completely. The authors carried out detailed field surveys in Miyagi and Fukushima prefectures during the period from 2011 to 2013 in order to explore the failure modes and mechanisms of coastal structures due to the 2011 Tohoku Earthquake Tsunami. Eight locations which were severely affected by this event were considered in the analysis. Subsequently, six major failure modes could be identified from the collected field data, namely: (i) leeward toe scour failure, (ii) crown armor failure, (iii) leeward slope armor failure, (iv) seaward toe scour and armor failure, (v) overturning failure, and (vi) parapet wall failure. At most surveyed locations the critical failure mode was identified as the scour initiated at the leeward toe. The present chapter discusses all six failure mechanisms, highlighting how the lessons learnt from them can help to improve the design of coastal structures under tsunami attack.

Despite the regularity with which tsunami waves attack a variety of countries around the world, comparatively little attention has been paid in the past to the design of tsunami-resilient breakwaters. This chapter will highlight some of the problems related to the failure mechanisms of caisson and armored caisson breakwaters against tsunami attack, focusing mainly on two modes: bearing capacity failure at the heel of the caisson and the stability of primary armor units. A methodology for the design of such armor will be provided for the case of overtopping waves, based on real life analysis of the failure of such armor. This method takes into account not only the tsunami level and height, but also the function of the structure (in terms of the importance of what it has been designed to protect), highlighting the need for an approach that can minimize the cost of such countermeasures.

On October 29, 2012, Hurricane Sandy made landfall along the eastern coast of the United States, generating a storm surge that caused serious damage to New York City and its vicinity. The authors carried out a post storm surge field survey in New York City, including Manhattan and Staten Island, to clarify the distribution of storm surge heights and the damage to infrastructures along urban waterfront areas. The inundation heights were 2.5 to 3 m along the southern coast of Manhattan and around 4 m along the southern coast of Staten Island. In the south part of Manhattan many types of infrastructure, such as the subway system, tunnels under the river, and an electric substation, were damaged due to flooding of their underground facilities. Prior to the hurricane’s landfall, the city prepared reasonably well against the storm surge (a mandatory evacuation order was issued and a suspension of the rapid transit system was carried out) and these measures contributed to reducing damage, though it appears to still be necessary to increase residents’ awareness of such disasters. Preparation efforts for the storm arrival contrast markedly to the poor state of preparedness of the city’s infrastructure, which were clearly not designed to cope with a storm surge and which should be significantly improved.

Vietnam, with 3260 km coastline and two vast low-lying deltas (the Red River Delta and Mekong Delta), could be considered one of the most vulnerable countries against coastal disasters and climate change. However, it appears that people outside Vietnam do not notice the vulnerability of this country's coasts against disasters, and even the vast majority of Vietnamese people may not be aware of the extent of the perils faced by their neighboring coastal communities, even though they suffer from frequent coastal floods. The challenges faced by this country in the future will have important regional and global repercussions. This chapter briefly examines threats such as tropical cyclones, sea-level rise, flooding, and coastal erosion in Vietnam. The authors wish this chapter to be an important source of information for all those who are looking at the challenges posed by impending coastal problems in Vietnam as well as other developing countries.

The 2004 Indian Ocean tsunami was the first significant transoceanic tsunami in the digital age, allowing the population of the entire world to witness the destructive power of such phenomena. Despite the fact that such events form part of the culture of countries such as Chile and Japan, many other places had virtually not heard about them before 2004. However, subsequent events in the past 10 years have led to the emergence of a heightened stage of tsunami awareness not only in countries affected recently by these events, but also in other countries which have not experienced them for a long time, such as Vietnam. The present chapter will analyze tsunami awareness in 3 countries—Chile, Indonesia, and Japan—that recently experienced a tsunami and contrast them to the case of Vietnam. The analysis will include observations on whether a multi-layer-countermeasure system existed in each area, together with interviews conducted with local residents to understand their awareness about such events. It is clear that awareness in all countries has greatly increased, though further efforts are required to increase resilience so that the inhabitants of coastal areas are adequately protected.

The present chapter describes the characteristics of the massive storm surge generated by the 2013 Typhoon Yolanda (Haiyan), which made landfall on the coast of the Philippines on November 2013. The authors conducted a series of field surveys and numerical analysis in Leyte and Samar Islands in the aftermath of the disaster in order to understand the characteristics of what constituted an almost unprecedented event in the modern era. As a result it was revealed that Yolanda struck Leyte Island at near peak strength, with maximum sustained wind speeds of 160 knots, the strongest in the recorded history of the Western North Pacific. The weather system approached land very quickly, with a forward speed of 41 km/hr as it reached Leyte, which was also one of the fastest among typhoons in the past 6 decades. As a result, Yolanda caused the largest storm surge in the recorded history of Philippines. Storm surge field surveys conducted by the authors recorded a maximum inundation height of 7 m at Tacloban, located at the northern end of Leyte Gulf. Through their interviews with local population and officials, the authors also found that water levels at some locations first lowered and then rapidly began to increase, which is in good agreement with the results of the numerical simulations carried out.

On the 11th of March 2011 an earthquake offshore the northeast coast of Japan generated a huge tsunami which overwhelmed coastal defences and inundated extensive areas of the Tohoku coastline. Japan was considered to be well prepared against such disasters but nevertheless casualties were high, though death rates were not homogeneous within the affected regions. In the present paper the authors investigate the relationship between human damage, maximum tsunami wave height and arrival time during the 2011 Tohoku Earthquake Tsunami. Generally speaking, the results indicate a positive correlation between the casualty rates inside inundated coastal settlements and tsunami height and a negative one regarding the arrival time (i.e. longer arrival times allowed residents more time to successfully evacuate). Based on these results a new tsunami category is introduced to clarify the potential threat that various earthquake scenarios pose to coastal communities in the Kanto area in Japan. These results contain useful insights for managing risks and prioritizing the investment in tsunami countermeasures to reduce future human suffering due to these disasters.

The Vietnamese coast faces the East Sea, which has been recognized as having the potential to generate devastating tsunamis, thus requiring a careful consideration of tsunami risk. In this chapter, tsunami risk and vulnerability are analyzed based on the numerical simulation of tsunami propagation and the social and geographical background of Vietnam. The numerical simulation of a potentially hazardous earthquake scenario in the Manila Trench shows the distributions of the maximum tsunami amplitude and arrival time along the Vietnamese coast. When discussing the vulnerability of the coastline, particular attention is given to three main elements affecting this type of potential disaster in Vietnam: the extensive area of low-lying ground, namely large deltas; a lack of past experience regarding tsunami events; and underdeveloped tsunami mitigation measures. Tsunami mitigation measures implemented recently in coastal communities in Vietnam, such as tsunami warning stations and tsunami drills, are also mentioned.