Introduction of ecosystem-based disaster risk reduction (Eco-DRR), Gekkan Keidanren
2019 was also a year of many natural disasters, with Typhoon Faxai in September and Typhoon Hagibis making landfall in October. Typhoon No. 19 brought torrential rain even before it made landfall, with a record 24-hour rainfall of 942 mm in Hakone. This has resulted in severe flooding and sediment disasters across large areas of eastern Japan. Global warming is expected to lead to more powerful typhoons. How should we prepare for the financial strains caused by a declining population?
Natural disasters and disaster risk
Natural disasters are caused by natural events (called hazards). Hazards are constantly occurring all over the planet, and it's a universal earthly practice. Outbreaks are extremely difficult for humans to manage, and hazards are an important process in shaping natural ecosystems. If there is no damage to life or property due to the hazard in the first place, it is not called a disaster.
Since the hazards that cause disasters cannot be stopped, it is important to reduce the risk of disasters (DRR). In addition to hazards, disaster risk is determined by exposure, vulnerability and capacity. Exposure is when a person lives or property is placed in a dangerous place. Vulnerability can include a variety of things, such as living in a building that is not seismically resistant even though there is a high probability of an earthquake. Capacity is the capacity of a community, organization, etc., to be tolerant during a disaster.
Let me give you an example of the Great East Japan Earthquake regarding exposure. Figure 1 shows the changes in land use over the past 100 years and the extent of tsunami inundation in the center of Kesennuma City, which was severely damaged by the Great East Japan Earthquake and tsunami. In the past, land with a high risk of tsunamis and water damage was used for salt and rice paddies. However, the development of residential and commercial areas during the post-war period of high economic growth resulted in a higher risk of disaster.
Fig. 1. Land use change of Kesennuma City Center in 100 years and Tsunami of Tohoku Disaster in 2011 affected area
The idea of ecosystem-based disaster risk reduction
Ecosystem-based disaster risk reduction (Eco-DRR) is said that healthy ecosystems prevent disasters and act as buffer zones for the effects of disasters, reducing the risk of people and property being endangered, and such functions are collectively referred to as Eco-DRR. In other words, it is about disaster prevention and risk reduction that makes good use of ecosystems.
It was the tsunami disaster caused by the December 2004 earthquake off the coast of Sumatra that brought widespread attention to Eco-DRR. A 9.1-magnitude earthquake, the world's largest, sent a massive tsunami across the Indian Ocean coast, killing nearly 228,000 people and making it the worst natural disaster in recorded history. Although coastal cities were heavily damaged, mangrove forests were found to have mitigated the power of the tsunami. Although experts were well aware of the sediment disaster prevention and other similar functions of forest vegetation, the worst natural disaster in history made people widely aware of the benefits of natural ecosystems.
Eco-DRR is not particularly new; it has been used traditionally in Japanese history. For example, a river embankment, called a haze bank, is a discontinuous structure with breaks in it, which was designed to allow water to slowly overflow out of the river area through openings during a flood. There are many examples where openings are routinely used as wet habitats by numerous organisms. It is believed that the seawall that has been developed along the coastline provided a certain amount of tsunami attenuation after the Great East Japan Earthquake.
Eco-DRR is not a trade-off with existing infrastructure, but can be leveraged in combination with existing infrastructure. Photo 1 shows a coastal forest at the Oki Coast, Tosa Shimizu City, Kochi Prefecture, which was originally a pine forest but has now developed into a beautiful evergreen broad-leaved forest. Sand-filled embankments are present when trees begin to grow on the shore. It is thought that the dikes stabilized the sand and made it easier for plants to grow even if they were not so far from the sea. This coastal forest is seen to be approaching its natural vegetation and is far less difficult to manage than a pine forest.
I have only given examples of haze dikes and coastal forests, but there are many possibilities for Eco-DRR. However, Eco-DRR requires space and is difficult to implement in overcrowded metropolitan areas. However, in an era of declining population, the problem of vacant or unused land in Japan has been pointed out, and now is the time for disaster prevention and risk reduction measures to be utilized. Regenerating nature and reducing disaster risk will also help achieve the SDGs goals.