Heavy Rain Disaster NOW

Do you know the definition of heavy rain? "If it rains hard, doesn't that mean it's raining hard?"　"I see and hear it all the time, but I just kind of take it as it is..." Most people will not know the exact definition of a heavy rain. On this page, we will explain heavy rain disaster as like in a nutshell, as well as the current situation!

1.What is heavy rain?
What is the difference between heavy rain?

The JMA refers to torrential rainfall as a noticeably heavy rainfall phenomenon that has caused significant disasters.

Actually, there is no clear definition of how many millimeters or more constitutes torrential rain! The Japan Meteorological Agency defines heavy rainfall as "rain that has the potential to cause damage, Rain that causes a disaster is called heavy rain and no specific numerical difference is indicated", and until the Japan Meteorological Agency certifies it as heavy rain, it is often called localized heavy rain.

It's a little difficult... Even heavy rainfall caused by typhoons or rainy season fronts is considered torrential when the Japan Meteorological Agency certifies that a disaster has occurred, so the cause of the heavy rainfall has nothing to do with the certification of torrential rainfall.

In summary, the definition of torrential rain in Japan is that a rainstorm is considered torrential if it causes significant damage, and a rainstorm for which a warning is issued is considered a rainstorm with the potential to become a torrential downpour. Thus, there is a big difference between torrential rain and heavy rain.

2.Causes of torrential rain

So what is the cause of these frequent torrential rains? It is Rise in sea surface temperature due to global warming.

According to the Japan Meteorological Agency, more than 90% of the thermal energy accumulated on the entire planet during the 40 years from 1971 to 2010 has been absorbed by the oceans, which have absorbed about 30% of the carbon dioxide released by human activities.

This is considered to be the case. Global warming causes seawater temperatures to rise, which increases the amount of water vapor in the air, and warm, moist air flows into the atmosphere, making weather conditions unstable. And as the updrafts become stronger and clouds continue to grow, cumulonimbus clouds develop that can dump heavy rainfall in a short time over a narrow area, causing torrential rainfall disasters.

In particular, the average annual sea surface temperature (SST) increase in the seas around Japan over the next 100 years until 2021 is +1.19°C/100 years, which is about twice the global rate of increase of +0.56°C/100 years.

This shows that Japan has a higher level of More likely to experience more severe and heavy rainfall disasters that goes on at the scale of never you've seen.

Therefore, if a major rainstorm disaster occurs, it will be important for each individual to take evacuation action.

3.Damage caused by torrential rain

The image of 2020 torrential rain
Image By: MLIT Chugoku Regional Development Bureau

Torrential rains can cause rivers to overflow, landslides, flooding of buildings, and flooding of roads, causing damage in many directions. The damage is immeasurable, including deaths, serious injuries, and destruction of ecosystems.

In addition, the torrential rains have also had an impact on the economy. For example, the July 2008 torrential rains caused 1.158 trillion yen in damage. Total destruction and flooding of houses and damage to agricultural products accounted for most of the damage.

Why did so much damage occur?

This is believed to be due to the fact that damage occurred over a wide area, rivers flooded simultaneously, and internal flooding, mudslides, etc. occurred.

What we can do to reduce such damage will be explained in the pages that follow.

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