To understand Japan’s complex relationship with water, one must first look to its topography. Almost three-quarters of Japan’s territory is mountainous, which forms the basis of its steep and short rivers. This limits the amount of rainwater that can be captured before it flows 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, the population of Japan is concentrated in low lying areas. Alluvial plains (areas below the flood level of a flooded river) represent only 10 percent of the total land area. Yet more than 50 percent of the population and 75 percent of 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 are in 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 menu.
Exhibit: Areas affected by droughts over the past 30 years
Before Japan’s modernization period, most of the water shortages in Japan were caused by severe droughts: 1939 Lake Biwa, 1964 Tokyo Olympics, 1967 Nagasaki, 1973 Takamatsu and 1978 Fukuoka are some of the examples. According to a meta-analysis of droughts in Japan from 1902 to 2009, the most severe the drought occurred from 1939 to 1941, lasting 666 days. This drought has severely affected the 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 national drought that started in the spring and ended in mid-September 1994. Persistent low rainfall had deteriorated the water quality of major rivers near Sagami, Tsukui and Tanzawa lakes and forced the rationing of water supply. Water rationing began in June in the Kiso River basin and has spread to other districts. In the most extreme cases, water for irrigation and industrial use has been rationed to a maximum of 65 percent – and 35 percent for domestic uses. The rains started in September and water rationing was relaxed and finally lifted in November.
Japan has also been battling floods for centuries, and its scalable 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 lowlands of eastern Tokyo, the Arakawa and Edogawa canals and a salvage land in Kasai were built. Dr Nobuyuki Tsuchiya, president of the Japan River Restoration Network, warns of the current false sense of security in Tokyo, noting that simulations have shown that there is a high probability of flooding affecting plains and localities with height lower dykes on the left side of the Arakawa River. He predicts that as the sea level rises due to climate change, during high tide, the town of Edogawa (one of Tokyo’s wards) could be inundated within two days. Considering the high population density in the eastern lowlands, he urges the population to remain vigilant towards nature. disasters.
What can be done?
Given the extreme risks of flooding, large Infrastructure development as well as wooded areas, or green dams, have become essential elements for flood management in the country. Strong support for Forest water management comes mainly from civil society and has been shaped largely 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.
Coming back to extreme events such as droughts and floods, the Hydraulic works office, under the aegis 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 (100mm or more per day) is expected to increase by up 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 adaptation measures, it is not surprising that the National plan for adaptation to the impacts of climate change also takes into account natural disasters.
Japan has been affected by extreme events such as droughts and floods throughout its history, which has made its institutions and 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 around the world – that have yet to plan or plan for the impacts resulting from climate change.
There are many lessons that Asian countries can learn from Japan, including applied knowledge on hydrology, water resources management, drought and flood management, and public awareness and education on disaster prevention. However, in terms of adaptation in the region, one example suffices. In the 1970s, Japan realized the importance of understanding water resources as part of the entire 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 revolutionary concept of water management at the basin level. Over the years, this has proven to be essential in achieving more efficient 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.