2024-08-04 20:02:00
2024/08/05 05:02 Weather News
“Climate change has a negative impact on human society through water,” explained Daiki Oki, a professor at the Graduate School of Engineering at the University of Tokyo.
Professor Oki, who studies the water cycle and climate change and is the author of The Future of Water: Global Risks and Japan (Iwanami Shoten), tells us about the impact of climate change on everything from weather to rivers and oceans. of lakes to oceans and groundwater.
What’s happening across Japan
For example, Oishinto in Lake Suwa (Nagano Prefecture). This is a phenomenon in which the entire lake freezes over during cold winters. Due to the cold night, the ice shrinks and expands during the day, causing the ice to break up and rise like a mountain range. . It was noted that the frequency has declined in recent years.
Lake Suwa, where the sacred ferry has not appeared for six consecutive seasons (Photo/Suwa Tourism Association)
In Tokyo Bay, green mussels, native to Southeast Asia, have been shown to survive the winter, while the southern fish butterflyfish is active even after autumn.
The winter circulation cycle of Lake Biwa (Shiga Prefecture) is delayed and has not been confirmed for the second consecutive year in 2019-2020. Full-layer circulation is a phenomenon in which the surface water temperature decreases from autumn to winter, melting snow flows in, circulates to the deep layers, and distributes oxygen. However, abnormalities can lead to deterioration of water quality and affect the ecosystem.
What happened to Japan’s lakes, oceans and rivers?
Extreme weather causes landslides and floods
Heavy rain and thunderstorms appear to be increasing not just in the summer but year-round, but has the pattern of rainfall changed?
Why is Japan’s weather becoming more and more extreme?
The world’s average temperature continues to rise and fluctuate repeatedly. Between 1898 and 2019, Japan’s temperature increased at a rate of 1.24 degrees Celsius per 100 years.
It is said that this is the reason for the frequent heavy rains in recent years.
The trend of extreme rainfall is expected to continue in the future. The risk of landslides and flooding, especially urban flooding, will increase. If infrastructure such as roads, railways, water supply facilities, communication facilities, and energy facilities are interrupted due to heavy rain, the impact will be serious.
In late July this year, Yamagata Prefecture, Akita Prefecture and other areas encountered heavy rains.
“Heavy rains that were rare in the past are becoming more likely to occur because of climate changes caused by global warming.
In my impression, Kyushu, Shikoku, and even Honshu, Niigata, and Fukushima are the main areas where heavy rains in the rainy season cause major disasters. The recent heavy rains in Akita, Yamagata, and even Hokkaido during the rainy season are likely a reflection of changes in the water cycle caused by climate change.
Although heavy rains continue to increase, droughts occur every summer, causing problems such as restrictions on water access and damage to agriculture.
“Water is a circulating thing, but the question is whether it is available when and where you want to use it.
Japan’s annual precipitation and seasonal precipitation have shown a slight long-term downward trend, but have not changed much. However, as the average rainfall intensity increases, the frequency of rainfall decreases and the time between rainfalls becomes longer, which brings difficulties to the operation of dams and reservoirs.
Additionally, as rainfall intensity increases, more water flows down rivers rather than seeping into groundwater or forest soils, so the amount of water available is significantly reduced even with the same amount of rainfall.
Heavy rains can also cause water quality to deteriorate due to sediment runoff. The sediments carried by rivers also contain nutrient salts such as phosphorus and nitrogen. When they enter reservoirs and oceans, eutrophication will occur, causing algae such as blue-green algae to bloom.
When sediment builds up in dams and reservoirs, their water storage capacity decreases. These factors result in a reduction in the amount of water that can be stably used.
The pattern of snowfall can also affect post-spring water.
The impact of changes in snow on water resources cannot be ignored. Japan is one of the snowiest countries in the world. In winter, the monsoon carries a large amount of water vapor from the Sea of Japan, causing it to fall as snow on the Sea of Japan side.
“In addition to the negative impact on ski area management, there are concerns that early spring snowmelt will reduce water supplies. Snow is a valuable water resource, compared to forests, which are often called green dams, known as white dams.
In snowy areas such as Northeast China, a large amount of snowmelt water flows into rivers in spring and is used as irrigation water during the period when rice cultivation requires most water. Because snow melts slowly, it seeps into the soil and is often stored as groundwater.
If global warming causes snow to turn to rain or snow to melt prematurely, seasonal water supplies will change. Dam management will become difficult and hydropower supply will be affected.
In the ocean, water temperatures and sea levels are rising
The average sea surface temperature in the waters surrounding Japan is rising, with a 100-year rate of increase as of 2019 of +1.14°C/100 years.
“Although average sea surface temperatures around the world have been rising over the long term (+0.55°C/100 years), the rate of increase in waters near Japan is more than twice the world average.
Changes in Japanese squid and amberjack along the Sea of Japan coast and green mussels and butterfly fish in Tokyo Bay are thought to be partly due to persistently high water temperatures.
“Mean sea levels are expected to continue to rise along Japan’s coast, and rising sea levels will lead to risks of storm surges and tsunamis, loss of beaches and coastal erosion, and saltwater intrusion into rivers.
Saltwater intrusion into groundwater is also a problem.In Japan, an estimated 11.8 billion cubic meters of groundwater is produced annually
For domestic, industrial and agricultural purposes.
Especially on islands, where groundwater is often an important water source, the impacts can be severe. Groundwater on small islands is known as a freshwater lens. Freshwater floats in a thin lens on top of salt water due to differences in density, but rising sea levels may reduce the thickness of freshwater lenses.
As ocean temperatures and sea levels rise, acidification changes the quality of the ocean. As the concentration of carbon dioxide in the atmosphere increases, the amount dissolved in seawater also increases, causing acidification. While areas along the Sea of Japan vary, on average acidification is progressing and there are concerns about the impact on corals and shellfish.
Box 9
Recently, the phrase “once in a hundred years” has become commonplace in the news. Major meteorological disasters also occur every year.
“Some areas in Japan and around the world are at risk of increased frequency of floods and droughts.
If there were 100 rivers, a 100-year flood would occur at some point each year on average, but in the 21st century the rare extreme event that occurs once every 100 years by 20th century standards becomes more common due to climate change, with the frequency expected to Increase to once every 50 years or once every 30 years.
Will Japan’s long-established ecosystems, lifestyles and infrastructure based on Japan’s rain, snow and water cycles continue to be forced to change?
At Weather News, we study global warming countermeasures from the perspective of a weather information company, explain various information in a simple and easy-to-understand way, and think about the future of the earth with everyone. Let us start by understanding climate change and work together to combat it.
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References
Ministry of Education, Culture, Sports, Science and Technology and the Meteorological Agency “Climate Change in Japan 2020 – Atmosphere, Land, and Ocean Observation Forecast and Assessment Report”, Ministry of the Environment “Climate Change Observation Forecast and Impact Assessment Comprehensive Report 2018 ~ Climate Change and Its Impact in Japan ~”, Ministry of Land, Infrastructure, Transport and Tourism’s “The Current Situation of Water Resources in Japan 2020 Edition” Reference Materials, etc.
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