大規模な山火事は、さらなる火災を助長する天候を作り出す(Large wildfires create weather that favors more fire)

ad

2024-06-18 カリフォルニア大学リバーサイド校(UCR)

カリフォルニア州の大規模な山火事から出る煤(すす)は、太陽光を吸収し、日中の気温を上げ、湿度を下げることが新しいUCリバーサイドの研究で明らかになりました。研究は、山火事が気候にどのような影響を与えるかを調査しました。山火事の多い北カリフォルニアでは、火事の際に気温が約1度上昇し、乾燥することが確認されました。これは、煤が太陽光を吸収し、湿度を減らすためです。研究は、山火事が自身の火事天候を作り出し、さらに火事を引き起こしやすくすることを示しています。煤は吸光性エアロゾルであり、雲の形成を妨げるため、降水量も減少します。CO2排出の削減と適切な土地管理が、山火事の頻度を減らす鍵となります。

<関連情報>

カリフォルニアの山火事の煙が、米国西部の大気温度偏差をプラスにした California wildfire smoke contributes to a positive atmospheric temperature anomaly over the western United States

James L. Gomez, Robert J. Allen, and King-Fai Li
Atmospheric Chemistry and Physics  Published:14 Jun 2024
DOI:https://doi.org/10.5194/acp-24-6937-2024

大規模な山火事は、さらなる火災を助長する天候を作り出す(Large wildfires create weather that favors more fire)

Abstract

Wildfires in the southwestern United States, particularly in northern California (nCA), have grown in size and severity in the past decade. As they have grown larger, they have been associated with large emissions of absorbing aerosols and heat into the troposphere. Utilizing satellite observations from MODIS, CERES, and AIRS as well as reanalysis from MERRA-2, the meteorology associated with fires during the wildfire season (June–October) was discerned over the nCA-NV (northern California and Nevada) region during the period 2003–2022. Wildfires in the region have a higher probability of occurring on days of positive temperature (T) anomalies and negative relative humidity (RH) anomalies, making it difficult to discern the radiative effects of aerosols that are concurrent with fires. To attempt to better isolate the effects of large fire emissions on meteorological variables, such as clouds and precipitation, variable anomalies on high fire emission days (90th percentile) were compared with low fire emission days (10th percentile) and were further stratified based on whether surface relative humidity (RHs) was anomalously high (75th percentile) or low (25th percentile) compared with typical fire season conditions. Comparing the simultaneously high fire emission and high RHs data with the simultaneously low fire emission and high RHs data, positive tropospheric T anomalies were found to be concurrent with positive AOD anomalies. Further investigation found that due to shortwave absorption, the aerosols heat the atmosphere at a rate of 0.041 ± 0.016 to 0.093 ± 0.019 K d−1, depending on whether RH conditions are anomalously positive or negative. The positive T anomalies were associated with significant negative 850–300 hPa RH anomalies during both 75th percentile RHs conditions. Furthermore, high fire emission days under high RHs conditions are associated with negative CF anomalies that are concurrent with the negative RH anomalies. This negative CF anomaly is associated with a significantly negative regional precipitation anomaly and a positive net top-of-atmosphere radiative flux anomaly (a warming effect) in certain areas. The T, RH, and CF anomalies under the simultaneously high fire emission and high RHs conditions compared with the simultaneously low fire emission and high RHs conditions have a significant spatial correlation with AOD anomalies. Additionally, the vertical profile of these variables under the same stratification is consistent with positive black carbon mass mixing ratio anomalies from MERRA-2. However, causality is difficult to discern, and further study is warranted to determine to what extent the aerosols are contributing to these anomalies.

1702地球物理及び地球化学
ad
ad
Follow
ad
タイトルとURLをコピーしました