歐洲太空總署監測 2019巴西亞馬遜大火面積與長期平均相去不遠

環境資訊中心外電；姜唯翻譯；林大利審校；稿源：ENS

去年亞馬遜地區發生了數千起森林大火，引發國際媒體關注。但是，科學家詳細分析歐洲太空總署（European Space Agency, ESA）氣候變遷倡議（Climate Change Initiative）的資料發現，巴西2019年的火災數與2018年相比的確略有增加，與過去18年每年平均火災數比卻相去不遠。

亞馬遜經常發生森林火災，但每年因氣候變遷、森林砍伐和森林劣化狀況的不同，火災數量也變化很大。

去年，國際社會密切關注世界各地的森林火災發展，呼籲透過即時火災資訊因應林火，尤其針對巴西。然而，這些數字從未與亞馬遜地區長期以來的火災次數相比較。

從國際太空站拍攝的亞馬遜森林大火。照片來源：歐洲太空總署

最近發表在《遙測》期刊上的一篇論文使用歐洲太空總署的資料，詳細分析南美洲2018年和2019年均森林火災面積，並和2001至2018年平均值比較。

研究作者來自西班牙阿爾卡拉大學，地質地理與環境系的環境遙測研究小組。他們發現，與2018年同期相比，2019年南美洲燃燒總面積增加了約70%，但僅略高於過去17年的年平均值。

與長期平均相比，巴西2019年的燃燒面積僅多了1.7%。玻利維亞的數字就很可觀了，與年平均相比，該國2019年的燃燒面積增加了51.4%。

主持火災CCI專案的科學家、研究作者之一Emilio Chuvieco說：「此類研究對於量化和監控亞馬遜等地的火災活動很重要，但也凸顯長期資料的重要性，並且必須使用更高解析度的感測器，如Copernicus Sentinel-2多光譜儀器，來進行研究，以偵測火災。」

觀察地球的衛星可用來監測易起火地區的火災。燃燒面積的估計值來自ESA的「火災氣候變遷倡議」專案，屬於ESA氣候變遷倡議的一部分，可從衛星取得燃燒面積的長期資料集。

這些資料提供穩定的燃燒區域時間序列，對於長期燃燒規律、火災管理和排放分析以及氣候變遷的研究者來說非常有用。

從國際太空站拍攝的亞馬遜森林大火。照片來源：照片來源：歐洲太空總署

過去的幾十年間，亞馬遜地區的人為壓力一直在增加，主要與農業擴張有關。研究顯示，該地區火災不斷增加與森林砍伐和森林劣化密切相關。

ESA地球觀測計畫主任Josef Aschbacher說：「觀測結果顯示，地球和森林中的動態過程不斷在變化，這是我們的挑戰。2019年火災活動的異常增加顯示，衛星資料對於取得清晰、獨立的影像並了解長期趨勢來說非常重要。」

熱帶森林占世界生物多樣性近一半，是地球生態系統的基本要素。目前進行中的氣候研究都不能缺少森林火災的量化資料，因為火災產生大量碳排放，影響全球溫室氣體預算。」

科學家得出結論：「大致上來說，南美洲的森林火災政治爭議，焦點應是玻利維亞和委內瑞拉而非巴西，因為巴西2019年的燃燒面積雖比前一年大，長期看來仍在平均水準附近……」

「但是，亞馬遜地區2019年的火災大多發生在以前很少或不曾發生過火災的地區，包括巴西、玻利維亞、巴拉圭、委內瑞拉和秘魯，是值得深入探討的問題。」科學家指出，「許多研究發現，農業擴張是這些地區發生火災的原因，但還需要進行更詳細的研究才能確認火源。」

Amazon's 2019 Burned Area Trends Parallel Past 18 Years ALCALA de HENARES, Spain, March 6, 2020 (ENS)

Thousands of fires broke out in the Amazon last year, sparking international media alarm. But a detailed analysis, using data from the European Space Agency's Climate Change Initiative, shows that while there was a small increase of fires in 2019 compared to 2018, the number of fires in Brazil was similar to the average annual number of fires detected over the past 18 years.

While forest fires are common in the Amazon, they vary considerably from year-to-year driven by changes in climate, as well as variations in deforestation and forest degradation.

The attention on fires last year, which created great international concern crossing the limits of national policies, prompted an international demand for up-to-date information on active fires, particularly in Brazil.

Yet these numbers were never compared to the number of fires in the Amazon over a longer period of time.

Detailed in a recent paper published in the journal "Remote Sensing," scientists using data from the European Space Agency's Fire CCI project <, analyzed burned areas in South America in both 2018 and 2019 and compared the data to the 2001-18 yearly average.

The authors are affiliated with the Environmental Remote Sensing Research Group in the Department of Geology, Geography and the Environment at the Universidad de Alcalá in Spain.

They found that the total burned area in South America was around 70 percent more in 2019 compared to the same period of 2018, however only slightly more than the yearly average over the past 17 years.

Brazil experienced just a 1.7 percent increase of burned area in 2019 compared to the long-term average.

Bolivia, on the other hand, saw a 51.4 percent increase of burned areas in 2019, compared to the yearly average.

Emilio Chuvieco, science leader of the Fire CCI project and one of the paper's three authors, said, "Studies such as these are important to quantify and monitor fire activities in places such as the Amazon. However, they indicate the importance of long-term data series and studies using higher resolution sensors, such as the Copernicus Sentinel-2 multispectral instrument, to detect fires."

Earth-observing satellites can be used to detect and monitor fires over frequently affected areas. These burned area estimates are from ESA's Fire Climate Change Initiative project, which produces long-term datasets of burned area information from satellites, as part of the ESA Climate Change Initiative.

The data is useful for those interested in historical burned patterns, fire management and emissions analysis and climate change research, by providing a consistent burned area time series.

In the last decades, the anthropogenic pressure over the Amazon region has been continuously increasing, mostly linked to agricultural expansion. The increasing fire activity in the region is strongly linked to deforestation and forest degradation, the study shows.

Josef Aschbacher, ESA's Director of Earth Observation Programmes, said, "These observations show the challenge we are facing – the processes on Earth and in the forests are very dynamic. The unusual increase of fire activity in 2019 demonstrates that satellite data is essential to get a clear and independent picture in order to also understand long-term trends."

Tropical forests shelter around half of the world's biodiversity, and are considered a fundamental part of Earth's ecosystem. Quantifying fires in forests is important for the ongoing study of climate, as they have a significant impact on atmospheric emissions, with biomass burning contributing to the global budgets of greenhouse gases.

"As a general summary," the scientists conclude, "the high political controversy about new fires in the region should be more clearly applicable to Bolivia and Venezuela than to Brazil, which in 2019 had higher BAs [burned areas] than the previous year, but still around the average of the full-time series…"

"However, it is a major concern to identify areas in the Amazon region that were widely affected by fires in 2019 and had previously little or no fire occurrence, including regions in Brazil, Bolivia, Paraguay, Venezuela and Peru," the scientists write in their study. "Agricultural expansion has been identified by several studies as being behind the introduction of fire in these regions, but more detailed studies need to be carried out to detect the local drivers of fire."

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