2023-09-25 カリフォルニア大学校アーバイン校(UCI)
◆カリフォルニア大学アーバイン校の地球システム科学者らは、カリフォルニアのシエラネバダ山脈での山火事の主要な燃料の1つが、数十年前の大木の残骸であることを報告しています。この発見は、大径の燃料が火災の激しさに強く寄与していることを示し、カリフォルニアの山火事をより効果的に管理するための洞察を提供しています。
◆しかし、森林床から木を取り除くことは簡単な解決策ではなく、野生生物の生息地としての機能も考慮する必要があります。
＜関連情報＞
- https://news.uci.edu/2023/09/25/uc-irvine-scientists-reveal-what-fuels-wildfires-in-sierra-nevada-mountains/
- https://iopscience.iop.org/article/10.1088/1748-9326/aced17
カリフォルニア州の大規模山火事における数十年にわたる燃料蓄積を煙の放射性炭素測定から証明 Evidence for multi-decadal fuel buildup in a large California wildfire from smoke radiocarbon measurements
A Odwuor, C C Yañez, Y Chen, F M Hopkins, A Moreno, X Xu, C I Czimczik and J T Randerson
Environmental Research Letters Published 24 August 2023
DOI:10.1088/1748-9326/aced17
Abstract
In recent decades, there has been a significant increase in annual area burned in California’s Sierra Nevada mountains. This rise in fire activity has prompted the need to understand how historical forest management practices affect fuel composition and emissions. Here we examined the total carbon (TC) concentration and radiocarbon abundance (Δ14C) of particulate matter (PM) emitted by the KNP Complex Fire, which occurred during California’s 2021 wildfire season and affected several groves of giant sequoia trees in the southern Sierra Nevada. During a 26 h sampling period, we measured concentrations of fine airborne PM (PM2.5), as well as dry air mole fractions of carbon monoxide (CO) and methane (CH4), using a ground-based mobile laboratory. We also collected filter samples of PM2.5 for analysis of TC concentration and Δ14C. High correlation among PM2.5, CO, and CH4 time series confirmed that our PM2.5 measurements captured variability in wildfire emissions. Using a Keeling plot approach, we determined that the mean Δ14C of PM2.5 was 111.6 ± 7.7‰ (n = 12), which was considerably enriched relative to atmospheric carbon dioxide in the northern hemisphere in 2021 (−3.2 ± 1.4‰). Combining these Δ14C data with a steady-state one-box ecosystem model, we estimated that the mean age of fuels combusted in the KNP Complex Fire was 40 years, with a range of 29–57 years. These results provide evidence for emissions originating from woody biomass, larger-diameter fine fuels, and coarse woody debris that have accumulated over multiple decades. This is consistent with independent field observations that indicate high fire intensity contributed to widespread giant sequoia mortality. With the expanded use of prescribed fires planned over the next decade in California to mitigate wildfire impacts, our measurement approach has the potential to provide regionally-integrated estimates of the effectiveness of fuel treatment programs.
