To understand Japan’s complex relationship with water, one must first look to its topography. Almost three-quarters of Japan’s land is mountainous, which forms the basis of its steep and short rivers. This limits the amount of rainwater that can be captured before it empties into the sea. As a nation that receives intense rainfall during specific times of the year (rainy season from June to July and typhoon season from August to September), Japan has traditionally suffered from extreme floods.
In addition, Japan’s population is concentrated in low-lying areas. Alluvial plains – areas below the water level of a flooded river – make up only 10% of the total land area. However, more than 50% of the population and 75% of the gross assets are concentrated in these plains. Tokyo, the capital of Japan, is also built on alluvial plains. In fact, 13,120 square kilometers of Tokyo’s land area falls within the “zero meter zone,” referring to land where the elevation is at or below sea level.
Droughts and floods in Japan
The high concentration of the Japanese population in small habitable areas has made Japan historically vulnerable to droughts. Water supply areas affected by drought at least once in the past 30 years are shown on the card.
Exposure: Areas affected by drought in the last 30 years
Before Japan’s modernization period, most water shortages in Japan were caused by severe droughtsExamples include Lake Biwa in 1939, Tokyo Olympics in 1964, Nagasaki in 1967, Takamatsu in 1973 and Fukuoka in 1978. According to a meta-analysis of droughts in Japan from 1902 to 2009the most severe drought occurred from 1939 to 1941, lasting 666 days. This drought has seriously affected water supply, electricity, hydroelectric production, factories, rail and maritime transport. It was even considered the reason for the nationalization of major industries.
A more recent example is the nationwide drought that began in the spring and ended in mid-September 1994. Persistent low rainfall had deteriorated the water quality of major rivers near Lakes Sagami, Tsukui and Tanzawa and forced the rationing of water supply. Water rationing began in June in the Kiso River basin and spread to other districts. In the most extreme cases, water for irrigation and industrial use was rationed at a maximum of 65%, and 35% in the case of domestic use. Rainfall began in September and water rationing was eased and finally lifted in November.
Japan has also struggled with floods for centuries, and the evolution of its flood management has been documented widely. The Tokyo we know today is a product of the engineering of the Tone River in the east and the Arakawa River in the west during the Tokugawa era (1603–1867). To avoid disasters in the eastern lowlands of Tokyo, the Arakawa Canal and the Edogawa Canal and a recovery ground in Kasai were built. Dr. Nobuyuki Tsuchiya, president of the Japan River Restoration Network, warns of the current false sense of security in Tokyo, pointing out that simulations have shown that there is a high probability of flooding affecting lowlands and localities with low rise dykes on the left side of the Arakawa River. He predicts that as sea levels rise due to climate change, during high tide, the city of Edogawa (one of Tokyo’s districts) could be flooded within two days. Given the high population density in the Eastern Lowlands, he urges people to remain vigilant of disasters.
What can be done?
Given the extreme risk of flooding, vast Infrastructure development as well as forest areas, or green dams, have become essential elements for flood management in the country. The strong support for Forest Water management comes mainly from civil society and has been largely shaped by the media rather than academia.
Forests cannot replace dams or vice versa: they complement each other. Dams continue to be built and, at the same time, policies, laws and regulations are enacted, promoting integrated forest and water management at the national level.
Going back to extreme events such as droughts and floods, the Aqueducts Office, under the auspices of the Tokyo Metropolitan Government, has planned mitigation and adaptation measures to deal with the impacts of climate change on hydraulic structures. He estimates that the number of heavy rain days (100 mm or more per day) is expected to increase to 10 days per year over the next 100 years.
Mitigation measures include the use of renewable energy, forest conservation and drainage infrastructure for leakage prevention. When it comes to accommodation, it’s no surprise that National Plan for Adaptation to the Impacts of Climate Change also takes natural disasters into account.
Japan has been affected by extreme events such as droughts and floods throughout its history, which has rendered its institutions and its company aware of the importance of preparation. With climate variability and change, these events are only expected to increase.
Can Asia learn from the Japanese experience?
The level of preparedness shown by Japan can be a lesson for many countries in the region – and the world – who have yet to plan or plan for the impacts resulting from climate change.
Asian countries can learn many lessons from Japan, including applied knowledge on hydrology, water resources management, drought and flood management, and public awareness and education for disaster prevention. However, in terms of adaptation in the region, one example is enough. In the 1970s, Japan realized the importance of understanding water resources as part of the whole hydrological system rather than trying to control them through infrastructure alone. The pioneering work of Professor Yutaka Takahasi, Japan’s most renowned hydrologist, was essential for the country to accept the then innovative concept of water management at the basin level. Over the years, this has proven essential in achieving more effective management of water resources, including for floods and droughts. More than 40 years later, this concept has still not been implemented in most developing countries.