11:15 〜 11:30
[AHW24-09] Assessing Regional Variability in Suitable Drought Descriptions for Wildfires in Japan
キーワード：日本、林野火災、干ばつ
Wildfires impact ecosystems, biodiversity, and public health, while directly causing economic losses and fatalities. Research suggests that climate change may intensify wildfire risks in humid regions. Wildfires are complex phenomena influenced by factors such as climate, weather, terrain, vegetation characteristics, and human activities (Grillakis et al., 2022). In humid temperate regions, fuel resources are abundant and spatially continuous, but their flammability tends to be low. In these regions, wildfires are typically driven by drought, as drought conditions reduce fuel moisture, thereby affecting fuel flammability and controlling wildfire activity. Most areas of Japan have a temperate climate. However, significant latitudinal differences result in considerable climate variation between northern and southern regions. Therefore, this study defines atmospheric drought and soil drought based on hydrological processes that influence fuel moisture content. The fire reports, managed by the Fire and Disaster Management Agency (FDMA) since 1995, were used in this study. Wildfires in humid areas are generally small in Japan (Touge, et al., 2024), this study utilized 45,070 wildfire cases in Japan during 1995–2012, with a total burned area of 241.06 km². As discussed in Sun et al. (2024), this study aimed to clarify the seasonal and spatial patterns of the relationships between soil drought and atmospheric drought with wildfires in Japan, while also identifying the dominant drought type influencing wildfires in different regions during the wildfire season. Atmospheric drought refers to the reduction of fuel moisture driven by high temperatures and low humidity, which enhance vapor exchange. On the other hand, soil drought results from low soil moisture, restricting capillary action and evaporation, and ultimately drying the fuels. Effective humidity (EH) is a key indicator for wildfire alerts across Japan. Despite diverse and humid climate in Japan, EH is widely applied in fire weather reports across prefectures to assess and issue warnings on wildfire risk. Therefore, EH is analyzed as an atmospheric drought indicator in this study, while soil moisture (SM) from the Simple Biosphere including Urban Canopy (SiBUC) model is used as an indicator of soil drought.
This study investigates the primary drought drivers of wildfires across Japan’s prefectures during the wildfire season. The first results are based on the calculated annual EH and SM distributions for each day during the wildfire season in every prefecture. These distributions reveal that EH is relatively low in the southern Kanto and Chubu regions, generally below 60%, whereas Hokkaido, Tohoku and Okinawa exhibit higher EH levels. Additionally, SM is particularly low in the southern Chugoku and northern Shikoku regions, mostly below 0.7, while it remains relatively high in Tohoku, particularly along its Japan Sea coastal areas. Pearson correlation coefficients were used to examine the relationship between monthly drought indices (SM and EH) and wildfire activity, represented by the monthly total number of wildfires (NO) and the logarithm of the monthly total burned area (BA). The correlation analysis reveals distinct regional differences in the influence of EH and SM on wildfire activity. EH is more strongly associated with wildfire occurrence in northern Japan, particularly along the Sea of Japan coast, while SM plays a dominant role along the Pacific coast, where wildfires are more frequent and severe. In 11 prefectures, mainly in northern Japan, EH shows a stronger correlation with NO, whereas SM is the primary driver in the remaining 36 prefectures. A similar pattern is observed for burned area, with EH having a greater influence in 12 prefectures and SM in the other 33. Despite EH’s stronger statistical association with wildfire activity in northern regions, these areas experience fewer and smaller wildfires compared to the Pacific coast, where SM-driven drought conditions contribute to larger burned areas.
Reference:
Grillakis, M., et al. (2022). Climate drivers of global wildfire burned area. Environmental Research Letters, 17(4), 045021.
Fire and Disaster Management Agency. Fire reports (1995–2012).
Touge, Y., Shi, K., Nishino, T., Sun, C., & Sekizawa, A. (2024). Spatial-temporal characteristics of more than 50,000 wildfires in Japan from 1995 to 2020. Fire Safety Journal, 142, 104025.
Sun, C., Touge, Y., Shi, K., et al. (2024). Assessment of the suitability of drought descriptions for wildfires under various humid temperate climates in Japan. Scientific Reports, 14(1), 23759.
This study investigates the primary drought drivers of wildfires across Japan’s prefectures during the wildfire season. The first results are based on the calculated annual EH and SM distributions for each day during the wildfire season in every prefecture. These distributions reveal that EH is relatively low in the southern Kanto and Chubu regions, generally below 60%, whereas Hokkaido, Tohoku and Okinawa exhibit higher EH levels. Additionally, SM is particularly low in the southern Chugoku and northern Shikoku regions, mostly below 0.7, while it remains relatively high in Tohoku, particularly along its Japan Sea coastal areas. Pearson correlation coefficients were used to examine the relationship between monthly drought indices (SM and EH) and wildfire activity, represented by the monthly total number of wildfires (NO) and the logarithm of the monthly total burned area (BA). The correlation analysis reveals distinct regional differences in the influence of EH and SM on wildfire activity. EH is more strongly associated with wildfire occurrence in northern Japan, particularly along the Sea of Japan coast, while SM plays a dominant role along the Pacific coast, where wildfires are more frequent and severe. In 11 prefectures, mainly in northern Japan, EH shows a stronger correlation with NO, whereas SM is the primary driver in the remaining 36 prefectures. A similar pattern is observed for burned area, with EH having a greater influence in 12 prefectures and SM in the other 33. Despite EH’s stronger statistical association with wildfire activity in northern regions, these areas experience fewer and smaller wildfires compared to the Pacific coast, where SM-driven drought conditions contribute to larger burned areas.
Reference:
Grillakis, M., et al. (2022). Climate drivers of global wildfire burned area. Environmental Research Letters, 17(4), 045021.
Fire and Disaster Management Agency. Fire reports (1995–2012).
Touge, Y., Shi, K., Nishino, T., Sun, C., & Sekizawa, A. (2024). Spatial-temporal characteristics of more than 50,000 wildfires in Japan from 1995 to 2020. Fire Safety Journal, 142, 104025.
Sun, C., Touge, Y., Shi, K., et al. (2024). Assessment of the suitability of drought descriptions for wildfires under various humid temperate climates in Japan. Scientific Reports, 14(1), 23759.