[Special Feature: Thinking About Disaster Prevention] Preparing for Natural Disasters in an Era of Population Decline through Ecosystem-based Disaster Risk Reduction

2018/03/01

Image: Earthquake ruins from the 2004 Indian Ocean earthquake in Banda Aceh, Sumatra

"Ecosystem-based Disaster Risk Reduction" is the Japanese translation of the term. It is often abbreviated as Eco-DRR. Hereafter, it will be referred to as "Ecosystem-based DRR." Healthy ecosystems are said to prevent disasters or function as buffers against the impacts of disasters, reducing the risk of people and property being exposed to danger; these functions are collectively called Ecosystem-based DRR.

Ecosystem-based DRR suddenly came into the spotlight following the tsunami disaster caused by the 2004 Sumatra earthquake. In the tropics, mangrove forests are often seen along coastlines. Examples were observed in various locations where these mangroves reduced the power of the tsunami and mitigated the damage. On the other hand, in areas where mangroves had disappeared due to urban development or aquaculture, devastating tsunami damage reached deep inland. Such ecosystem functions are called ecosystem services, and while they were well known among experts as one of the benefits ecosystems provide us, they became widely recognized globally starting in 2004.

Ecosystem-based DRR was already mentioned in the Hyogo Framework for Action 2005–2015, agreed upon at the Second UN World Conference on Disaster Risk Reduction held in Kobe in 2005. As you know, this world conference was held in Kobe precisely because it was the site of the 1995 Great Hanshin-Awaji Earthquake, but the contents of the framework for action agreed upon there did not receive much attention in Japan.

However, a major turning point for Japan was the Great East Japan Earthquake in March 2011. Although nearly seven years have passed, it likely remains fresh in many people's memories. The word "unforeseen" was frequently used, but we witnessed how existing infrastructure was completely unable to withstand a disaster that exceeded the assumed external forces. Following the Great East Japan Earthquake, Japan began examining how infrastructure should function to a certain extent even when assumptions are exceeded, and discussions began regarding the pros and cons of living in areas with a high risk of disaster in the first place.

In March 2015, the Third UN World Conference on Disaster Risk Reduction was held in Sendai, and based on the experience of the Great East Japan Earthquake, the Sendai Framework for Disaster Risk Reduction 2015–2030 was adopted. The new framework has various noteworthy points, but let us introduce it from the perspective of Ecosystem-based DRR. It explicitly included the formulation of policies and plans using ecosystem-based approaches, the conservation of ecosystem functions useful for disaster risk reduction, rural development planning and management in vulnerable areas, and the strengthening of sustainable use and management of ecosystems to implement integrated environmental and natural resource management approaches that incorporate disaster risk reduction.

Starting with the UN World Conference on Disaster Risk Reduction, 2015 became what could be called the inaugural year for Ecosystem-based DRR in Japan. In August, a new National Spatial Strategy (National Plan) and National Land Use Plan (National Plan) were approved by the Cabinet, followed by the Priority Plan for Social Infrastructure Development in September. These are, so to speak, the national land plans that determine the state of Japan's territory. National land planning used to be about how to distribute new development to every corner of the country, but entering the 21st century and facing an era of population decline and a super-aging society, we must think about how to manage the land while both people and budgets decrease, and that role has changed significantly.

In these three plans, it was explicitly stated that the diverse functions of the natural environment (providing habitats for organisms, forming good landscapes, suppressing temperature rises, etc.) should be actively utilized to improve regional attractiveness and living environments and to obtain various effects such as disaster prevention and mitigation. While these plans do not explicitly use the terms "Ecosystem-based DRR" or "Eco-DRR," their necessity was recognized in the national land plans that form the foundation of the country.

To conclude 2015, the Climate Change Adaptation Plan was approved by the Cabinet in late November. In this plan, Ecosystem-based DRR is mentioned frequently. For example, as one of the adaptation measures for coasts, it specifically states that research on adaptation in the coastal sector will be promoted, such as the development of quantitative evaluation methods for disaster reduction functions by ecosystems in coastal areas. This indicated that in addition to disaster prevention in conventional concrete-based infrastructure, initiatives for Ecosystem-based DRR are necessary.

The author and co-researchers analyzed the damage situation in central Kesennuma City and the transition of land use over the past approximately 100 years as part of the Environment Research and Technology Development Fund (4-1505) of the Ministry of the Environment. As a result, it was found that as of 1913, the majority of the area consisted of rice paddies, wetlands, and water bodies, with urban land use being only partial (Figure 1).

In 1952, shortly after the war, urban land use expanded slightly, but no significant changes in land use were seen. However, by 1979, after the period of high economic growth, it is clear that the majority had been converted to urban land use. Note that the population of Kesennuma City peaked around 1980 and began to decline thereafter. The population of the area corresponding to the current Kesennuma City limits was approximately 92,000 in 1980, but by 2010, it had decreased by nearly 19,000 to approximately 73,500. Despite a population decline of more than 20%, urban land use was still expanding.

As of 1913, rice paddies accounted for 56% of the area inundated by the tsunami from the Great East Japan Earthquake, while urban land use was about 7%. Over approximately 100 years, rice paddies decreased to 18% (about one-third), while urban land use expanded to 76% (about ten times). Based on estimates by the 77 Bank, we calculated the amount of damage within our research target area. As a result, the damage was calculated at 112.7 billion yen for urban land use and 69.2 million yen for agricultural land.

If the land use had been the same as in 1913, the damage to urban land use was estimated at 10.7 billion yen and 250 million yen for agricultural land, showing that the expansion of urban land use increased the damage more than tenfold. Of course, it is also true that the seafood processing industry and related industries that support Kesennuma's economy have been located in the urban land use area that expanded into this tsunami inundation zone, bringing significant economic benefits until now.

However, unlike other municipalities along the Sanriku coast, Kesennuma City has many areas where the topography is not so steep, and urban development has also taken place on high ground outside the coastal areas. Even in this tsunami, there was no damage in such locations, or if there was, it was minimal.

Tracing the history of Kesennuma City, coastal development had already begun in the Edo period. However, at that time, salt pans and rice paddies were the focus, and as the salt-making industry declined in the Taisho era, salt pans were converted to rice paddies. Urban land use in the lowlands was limited to the area around the fishing port. Such land use reduced disaster risk as a tsunami-prone area.

Kesennuma City was affected by the 1960 Chile tsunami, but the damage was not that great. This may have led to insufficient tsunami countermeasures in subsequent urban development. In reducing disaster risk, it is considered important not to use places where there is a possibility of damage from disasters and not to place things that constitute property there. While economic loss is one thing, if intensive use such as urban land use had not been carried out, many precious lives would not have been lost.

Furthermore, since the Great East Japan Earthquake, numerous natural disasters such as the Kumamoto Earthquake have occurred, and news about the disaster-stricken areas of the Great East Japan Earthquake has become significantly less frequent. However, many of the areas that suffered heavy damage are still in the process of recovery even after seven years. Land readjustment projects are still underway, with work proceeding toward a target of March 2020. Recovery from a large-scale disaster requires more than 10 years.

At the end of February 2011, just before the Great East Japan Earthquake, the interim report "Long-term Outlook for National Land" by the Long-term Outlook Committee of the National Land Council Policy Group was released. The author was also a member of this committee, and a shocking vision of Japan's future was made public, stating that about 20% of the areas where the population was distributed as of 2005 would become uninhabited by 2050. Due to the Great East Japan Earthquake, interest in population decline and the super-aging society temporarily decreased relatively, but it gained national attention again with the subsequent so-called Masuda Report.

In light of the tsunami damage from the Great East Japan Earthquake, the assumptions for the Tokai, Tonankai, and Nankai earthquakes (the so-called Nankai Trough Megathrust Earthquake) were raised to a three-region linked type with a magnitude of 9.1. Government estimates predict up to 320,000 deaths and tsunamis of over 30 meters at the highest points. Voices saying they have already given up have begun to be heard from many of the areas expected to be hit by a giant tsunami.

However, the intensity of the earthquake and the height of the tsunami are merely the largest assumed. Nankai Trough earthquakes have occurred in various patterns throughout history, and past tsunami heights estimated from geological research are said to be around 10-plus meters. In the recovery from the Great East Japan Earthquake, tsunami height levels called L1 and L2 were actively discussed to determine the height of seawalls, but those assumptions include considerable uncertainty.

On the other hand, population decline has significant positive aspects from the perspectives of disaster prevention and the natural environment. As mentioned earlier in the example of Kesennuma, intensive use of land with high disaster risk was inevitably carried out during the population growth phase. Population decline also reduces the total load on the natural environment. Immediately after a disaster, disaster prevention receives great attention, but people do not live solely to protect themselves from disasters. Now that small and medium-sized regional cities are expected to face a population decline of about 40% by 2040, the utilization of Ecosystem-based DRR is inevitable.

However, how to realize this has become a major challenge. Kochi City formulated a Location Optimization Plan in March 2017. A Location Optimization Plan is a plan to make cities more compact in response to the era of population decline. To prepare for the Nankai Trough Megathrust Earthquake, Kochi City formulated the Kochi City Resilience Plan in 2015, which is positioned as the highest-level plan, under which the Comprehensive Plan, Urban Master Plan, and Location Optimization Plan are positioned.

The Location Optimization Plan explicitly stated that the residential induction zones would be reduced by 8% compared to the current urbanization zones to account for population decline and disaster risk reduction. However, tsunami countermeasures focus on the development and expansion of infrastructure, and measures like Ecosystem-based DRR are not incorporated. The population of Kochi City is expected to decrease from the current approximately 333,000 to just over 260,000 by 2040, which corresponds to the population in the 1970s. While it is true that land in the bay area is limited, there may be a possibility of introducing Ecosystem-based DRR in the future.

In October 2017, the author and co-researchers began a study titled "Development of Ecosystem-based Disaster Risk Reduction (Eco-DRR) Methods Assuming Tsunamis from the Nankai Trough Megathrust Earthquake" with a grant from the Nippon Life Insurance Foundation. Associate Professor Seiko Oki of the Faculty of Environment and Information Studies, who appears in the roundtable discussion of this special feature, is also a member. We selected Kochi and Tokushima Prefectures as research sites, and in Kochi Prefecture, we chose Tosashimizu City, which is predicted to be hit by tsunamis of over 30 meters. Tosashimizu City is located at the southernmost tip of Kochi Prefecture and is famous for Cape Ashizuri, where many typhoons have made landfall. It is required to respond to rapid population decline and aging, but on the other hand, most of the coastline is designated as Ashizuri-Uwakai National Park and is known as a scenic spot. We are conducting several studies with cooperation from the Tosashimizu City Hall, and among them, we are focusing on the coastal forest of the Ohki Coast (Photo top).

The Ohki Coast was once an artificially planted black pine forest, similar to coastal forests throughout Japan. Even today, local people call it Ohki Matsubara. Due to the death of many black pines from pine wilt disease after the war and the fact that it was designated as a national park, it was no longer actively used by local people, and it has now transitioned into a magnificent coastal forest centered on the evergreen broad-leaved tree Machilus thunbergii (Photo middle).

In the Great East Japan Earthquake, many coastal pine forests were knocked down by the tsunami, and it was pointed out that the fallen trees that were washed away expanded the damage. Coastal pine forests are not natural but are artificial forests that have been planted and managed by humans. On the coastlines damaged by the Great East Japan Earthquake, a vast number of pines have since been planted (Photo bottom), but as the damage from pine wilt disease expands to northern Japan, the importance of restoring original natural coastal forests was pointed out early on.

However, most of Japan's sandy coastlines have been changed to pine forests, and very little natural vegetation remains. In addition, there is no accumulation of technology to restore such natural vegetation on a large scale, and in the recovery from the Great East Japan Earthquake, although there were some experimental efforts, there was no choice but to select monotonous pine planting. While it is said that the technology has not been established, at the Ohki Coast in Tosashimizu City, a magnificent coastal forest had indeed been established naturally over several decades. What factors promoted the development of a coastal forest close to nature? How much can an evergreen broad-leaved coastal forest reduce the power of a tsunami? We are working on this research, viewing it as a key case for future tsunami disaster prevention on Japan's coasts.

**Affiliations and titles are as of the time of publication.