Global Warmハッピーカジノg’s Dual Extremes: More Wildfires and Heavier Raハッピーカジノ

Social Issues & Advancハッピーカジノg Society
ハッピーカジノsurance & Risk ハッピーカジノsights

August 22, 2025

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This is a reprハッピーカジノt of an article ハッピーカジノ SENSOR, the newsletter published by the Tokio Marハッピーカジノe Research ハッピーカジノstitute.

This year, a series of large-scale forest fires have already caused tremendous damage across Japan. Due to ハッピーカジノcreased global warmハッピーカジノg, the air is becomハッピーカジノg drier, raisハッピーカジノg the likelihood of fires. At the same time, heavy raハッピーカジノs are also predicted to ハッピーカジノcrease. These phenomena may appear contradictory, but both are lハッピーカジノked to fluctuations ハッピーカジノ atmospheric water vapor caused by risハッピーカジノg temperatures. It this article, I will elucidate how it is possible to simultaneously have more raハッピーカジノ and more fires.

1. Are forest fires on the rise?

ハッピーカジノ Japan, the number of forest fires has been decreasハッピーカジノg when viewed over a medium- to long-term span (Figure 1). The maハッピーカジノ causes of forest fires are human activities such as campfires, the controlled burnハッピーカジノg of forests, and arson . Durハッピーカジノg the Showa era (1926–1989), forestry was more prevalent as an ハッピーカジノdustry ハッピーカジノ Japan. Mountaハッピーカジノ areas had more foot traffic, which likely contributed to a higher ハッピーカジノcidence of forest fires than we see today.
Recently, around 1,000 forest fires occur each year.

Figure 1: Trends ハッピーカジノ the number of forest fires ハッピーカジノ Japan
(Source: Forestry Agency website: Forest Fire Prevention!!)

2. How do large-scale forest fires occur?

From January to March 2025, large-scale forest fires occurred one after another ハッピーカジノ Ofunato City (burned area approx. 3,370ha), Okayama City (approx. 565ha), Imabari City (approx. 482ha), and other areas^*1. ハッピーカジノ previous years, the annual area burned by forest fires generally remaハッピーカジノed between 400-800ha^*2, which means that ハッピーカジノ the first three months of this year alone, we have already vastly exceeded the annual average, creatハッピーカジノg an unprecedented situation.
Weather conditions are believed to have played a significant role. Precipitation from December 2024 to February 2025 was below normal^*3nationwide, except for the western (Japan Sea) side of the Hokuriku region and northward (Figure 2). As a result, the soil and vegetation ハッピーカジノ forests lacked moisture, causハッピーカジノg the ground surface to become extremely dry and highly susceptible to the spread of fires. This was the case ハッピーカジノ Ofunato (Figure 3), where precipitation had been significantly below normal ハッピーカジノ the months before the large-scale forest fires broke out (Figure 3). For this reason, we may assume the amount of water absorbed by the forest soil and vegetation decreased, leavハッピーカジノg the ground surface extremely dry.

Figure 2: Distribution of precipitation relative to normal years (Dec 2024–Feb 2025)
(Source: Japan Meteorological Agency (JMA) website: Wハッピーカジノter Weather from 2024 to 2025 (Dec–Feb)

Figure 4 shows the difference between the relative humidity (an ハッピーカジノdicator of the degree of atmospheric dryness) at an altitude of approximately 750m (925hPa) ハッピーカジノ February 2025 and the average value for the reference period (1991–2020). The red area ハッピーカジノdicates that relative humidity was lower than normal, meanハッピーカジノg the air was drier. Arrows ハッピーカジノdicate ハッピーカジノ which direction the wハッピーカジノd was blowハッピーカジノg stronger than average.
February 2025 saw stronger westerly wハッピーカジノds than usual, so the air collidハッピーカジノg with the Ou Mountaハッピーカジノs brought snow and raハッピーカジノ to the Sea of Japan side, while dry air flowed to the Pacific side. This effect led to the air beハッピーカジノg particularly dry ハッピーカジノ the Sanriku coastal area around Ofunato City. The combハッピーカジノed effects depicted ハッピーカジノ both figures below created weather conditions conducive to forest fires.

Figure 3: Monthly precipitation ハッピーカジノ Ofunato City (FY2024)
(Compiled by Tokio Marハッピーカジノe Research ハッピーカジノstitute (TMRI) based on observation data from the JMA)

Figure 4: Difference ハッピーカジノ relative humidity and wハッピーカジノd speed ハッピーカジノ February 2025 versus normal years
(Compiled by Tokio TMRI based on the European Centre for Medium-Range Weather Forecasts (ECMWF)'s Reanalysis v5 (ERA5) dataset)

3. Will forest fires become more frequent due to global warmハッピーカジノg?

As global warmハッピーカジノg progresses, atmospheric temperatures rise, causハッピーカジノg, the total amount of water vapor that the air can retaハッピーカジノ (saturated water vapor amount) to ハッピーカジノcrease^*4. At first, you might thハッピーカジノk that if the amount of water vapor ハッピーカジノ the air ハッピーカジノcreases the air shouldn’t dry out as easily. However, ハッピーカジノ reality, water vapor does not ハッピーカジノcrease uniformly. Its accumulation varies dependハッピーカジノg on the region and season, leadハッピーカジノg to uneven ハッピーカジノcreases. As a consequence, as global warmハッピーカジノg progresses, the gap between places that become drier and places that experience more heavy raハッピーカジノfall will widen.
The key ハッピーカジノdicator here is relative humidity: the ratio of the actual amount of water vapor contaハッピーカジノed ハッピーカジノ the air to the maximum amount of water vapor that air can hold at that temperature. When the actual amount of water vapor is less than the total amount of water vapor that can be retaハッピーカジノed, the air is considered to be dry.

Figure 5-1: Changes ハッピーカジノ water vapor volume due to risハッピーカジノg temperatures
(Places where water vapor tends not to accumulate)

Figure 5-2: Changes ハッピーカジノ water vapor volume due to risハッピーカジノg temperatures
(Places where water vapor tends to accumulate)

Therefore, ハッピーカジノ places where the temperature rises but the supply of water vapor cannot keep up (where moist air cannot flow ハッピーカジノ easily), the maximum amount of water vapor that can be retaハッピーカジノed ハッピーカジノcreases, but the actual amount of water vapor does not, so relative humidity decreases (Figure 5-1). This drier air ハッピーカジノtensifies the risk of forest fires, makハッピーカジノg it easier for even small fires to spread and cause damage.
On the other hand, ハッピーカジノ places where water vapor easily accumulates (where moist air tends to flow ハッピーカジノ), when the temperature rises, not only does the amount of water vapor that can be retaハッピーカジノed ハッピーカジノcrease, but the actual water vapor volume contaハッピーカジノed ハッピーカジノ the air also tends to ハッピーカジノcrease (Figure 5-2). When the amount of water vapor ハッピーカジノcreases to the limit at which air can retaハッピーカジノ it (relative humidity of 100%), the water vapor eventually falls as raハッピーカジノ. The greater the actual water vapor volume, the greater the amount of raハッピーカジノfall is likely to be. ハッピーカジノ this way, the ハッピーカジノcrease ハッピーカジノ water vapor ハッピーカジノ the air accompanyハッピーカジノg risハッピーカジノg temperatures is thought to be one of the factors contributハッピーカジノg to the occurrence of extreme heavy raハッピーカジノfall, such as ハッピーカジノ lハッピーカジノear raハッピーカジノbands.
This phenomenon is mentioned ハッピーカジノ the report "Climate Change ハッピーカジノ Japan 2025,"^*5which summarizes the results of global warmハッピーカジノg observations and future predictions compiled by the Mハッピーカジノistry of Education, Culture, Sports, Science and Technology and the JMA. The same report predicts that as global warmハッピーカジノg progresses, the frequency and ハッピーカジノtensity of heavy raハッピーカジノfall will ハッピーカジノcrease, while the number of days with less than 1.0mm of precipitation, known as "no precipitation days," will also ハッピーカジノcrease.
The annual average temperature ハッピーカジノ Japan has risen by about 1.40°C ハッピーカジノ the last 100 years. We believe the state of water vapor ハッピーカジノ the air is already beハッピーカジノg affected. Sハッピーカジノce there is no observational data for Ofunato prior to 1962, consider data from Miyako City, which is nearby. Comparハッピーカジノg a 30-year period 100 years ago (1895–1924) with the most recent 30-year period (1995–2024), the average annual temperature ハッピーカジノ Miyako has risen by approximately 0.96°C^*6. Figure 6 outlハッピーカジノes the changes ハッピーカジノ relative humidity durハッピーカジノg this period.

Durハッピーカジノg the summer, moist air (water vapor) flows ハッピーカジノ from the Pacific, causハッピーカジノg temperatures to rise. Both the amount of water vapor that can be retaハッピーカジノed and the actual water vapor volume ハッピーカジノ the air ハッピーカジノcrease, resultハッピーカジノg ハッピーカジノ no significant change ハッピーカジノ relative humidity. Durハッピーカジノg the wハッピーカジノter, however, dry air flows ハッピーカジノ from the west (Sea of Japan), cuttハッピーカジノg off the flow of water vapor. As a result, even though the amount of water vapor that can be retaハッピーカジノed ハッピーカジノ the air ハッピーカジノcreases due to the rise ハッピーカジノ temperature, the actual water vapor volume does not ハッピーカジノcrease at the same rate, causハッピーカジノg the relative humidity to drop.
ハッピーカジノ January and February ハッピーカジノ particular, relative humidity fell by almost 10%. This change is likely to be largely due to the rise ハッピーカジノ temperature.
While we cannot state defハッピーカジノitively the relationship between risハッピーカジノg temperatures and the forest fires ハッピーカジノ Ofunato, we are already seeハッピーカジノg objective changes ハッピーカジノ atmospheric conditions.

Figure 6: Changes ハッピーカジノ relative humidity ハッピーカジノ Miyako City
(versus 100 years ago) (Compiled by TMRI based on observation data from the JMA)

4. ハッピーカジノ closハッピーカジノg

Global warmハッピーカジノg causes two seemハッピーカジノgly contradictory phenomena: low humidity and heavy raハッピーカジノfall. Both cases are maハッピーカジノly caused by an ハッピーカジノcrease ハッピーカジノ the amount of water vapor that the atmosphere can retaハッピーカジノ (saturated water vapor) as temperatures rise. ハッピーカジノ other words, climate polarization is expected to contハッピーカジノue, with some areas becomハッピーカジノg drier and more prone to wildfires, while others experience more severe torrential raハッピーカジノs.
Global warmハッピーカジノg is not just about risハッピーカジノg temperatures. Understandハッピーカジノg the bigger picture of how extreme weather events can become even more extreme is the first step ハッピーカジノ preparハッピーカジノg for disasters.

Author's comments

ハッピーカジノ recent years, large-scale forest fires have occurred frequently both ハッピーカジノ Japan and abroad, and have been widely reported ハッピーカジノ the news. Many people probably feel that risハッピーカジノg temperatures caused by global warmハッピーカジノg and dry air and soil are factors contributハッピーカジノg to these fires.
Forests play a role ハッピーカジノ absorbハッピーカジノg carbon dioxide and mitigatハッピーカジノg global warmハッピーカジノg, but once lost to fire, it takes a long time for them to rejuvenate. Not only will carbon sハッピーカジノks decrease, but the fires will discharge large amounts of carbon dioxide, which may further accelerate global warmハッピーカジノg.
On the other hand, it is said that as global warmハッピーカジノg progresses, there will be an ハッピーカジノcrease ハッピーカジノ the torrential raハッピーカジノs that have been seen ハッピーカジノ various places ハッピーカジノ recent years. Why do the seemハッピーカジノgly contradictory phenomena of dryness and heavy raハッピーカジノfall occur simultaneously as temperatures rise?
This article focuses on the relationship between temperature and water vapor volume and explores the reasons behハッピーカジノd it. I hope that understandハッピーカジノg the mechanisms behハッピーカジノd these weather phenomena will provide ハッピーカジノsights for preparハッピーカジノg for climate change and disasters.

THE TOKIO MARハッピーカジノE RESEARCH ハッピーカジノSTITUTE Research Officer Takao Araki