2010年嚴重乾旱 讓亞馬遜雨林由綠轉褐
環境資訊中心 更新日期:"2011/04/14 10:21" 洪美惠
2010年亞馬遜流域乾旱常態化差值植生指標(normalized difference vegetation index)。圖片來自:波士頓大學。

週四, 2011-04-14 10:21 — 洪美惠 摘譯自2011年3月31日ENS 美國麻州,波士頓報導;張昕瑜編譯;蔡麗伶審校

依據美國太空總署衛星資料所作的ㄧ個新的測量研究顯示,去年亞馬遜流域破紀錄的乾旱,讓將近百萬平方英里的綠地轉變為褐色。

研究的主要作者徐亮(Liang Xu音譯)表示,用來測量亞馬遜植被健康的綠覆蓋度,面積已急速銳減。減少的面積比3.5個的德州還大。

波徐亮為波士頓大學地理環境學系氣候及植被研究小組成員,他提到:「甚至一直到2010年10月下旬乾季結束之後,綠覆蓋度還是沒有恢復。」

籌備這個綜合研究的是由各國科學家組成的研究團隊。他們使用來自美國太空總署中尺度影像光譜儀(MODIS)和熱帶降雨觀測衛星(Tropical Rainfall Measuring Mission),超過十年的衛星數據進行分析。

透過這些數據的分析,製作出2010年乾旱詳細的植被綠化衰減地圖。而這個研究也被美國地球物理聯盟所發行的期刊--地球物理研究通訊接受且出版。

巴西維科薩聯邦大學的共同作者柯斯塔(Marcos Costa)表示:「根據黑河流域瑪瑙斯港的水位資料來看,去年是109年有紀錄以來最乾的一年。」他繼續提到:「相較之下,被稱為世紀最低水位的2005年乾旱,在最低水位中僅排在第八位。」

在水位紀錄中可以看出,2010年的嚴重乾旱遍布整個亞馬遜流域。就連降雨量超過整個西亞馬遜的黑河流域,也包含在其中。

水量由2010年8月開始下降,到10月下旬時降至最低。而冬季降雨又開始提高水位。

從紀錄報告中可以看出,嚴重的乾旱始於去年夏天,研究者也於此時開始近乎同步地處理大量的衛星資料。

研究團隊透過NEX將資料及模型彙整,並計算資源。NEX位在加州莫福特的艾默斯研究中心,是爲太空總署先端超級電腦而設的。

因為有了NEX,研究人員可獲得亞馬遜雨林受到乾旱影響的大量資料。而他們也因而能在短時間內,也就是於2011年1月前完成分析。

類似的2005年乾旱影響報告,也在和乾旱發生兩年後出版。報告中推斷,亞馬遜雨林在2005年的乾旱中不會復原。

任職於艾默斯研究中心的共同研究者黎曼尼(Ramakrishna Nemani)表示,:「透過衛星即時監控地球植被的狀況是相當重要的。而就像這個研究中所展現的,NEX可以有效的傳送即時資訊。」

美國地球物理學會週報EOS,在本週議題專欄中刊登了有關NEX計畫的文章。

藉由NEX,研究者將低於平均降雨量的界線作為指引,首次發展出乾旱影響區域地圖。

研究者並利用兩種不同的綠化指標,來鑑定植被受影響的狀況。一為綠葉面積,而另一指標則為生理作用。

從這個地圖中可以看出,亞馬遜植被因2010年乾旱減少了965,000平方英里。而這個面積是2005年乾旱所影響範圍的四倍多。

麻州萊星頓市大氣及環境研究所的協同研究人員Arindam Samanta提到:「由MODIS植被綠化數據所呈現的情況,可以看出亞馬遜植被受到的影響,比單由降雨量數據所推斷出的情況,範圍更廣、更嚴重且更長期。」

而另外值得擔心的一點,在暖化的氣候下,水分逆境可能導致亞馬遜雨林被草原所取代。

在這樣的情況下,雨林中所儲存的大約1000億噸的碳,將可能被釋放到大氣中,更加速了全球暖化。

聯合國跨政府氣候變化委員會已經發出警告,未來類似去年及2005年的乾旱,可能在亞馬遜區域更為頻繁地發生。

Amazon Rainforest Brown After Severe 2010 Drought 2010

Last year's record-breaking drought across the Amazon Basin has turned nearly a million square miles of green rainforest to brown, finds a new mapping study based on NASA satellite data.

"The greenness levels of Amazonian vegetation, a measure of its health, decreased dramatically over an area more than three and one-half times the size of Texas," said Liang Xu, the study's lead author.

"It did not recover to normal levels, even after the drought ended in late October 2010," said Xu, who is with Boston University's Climate and Vegetation Research Group in the Department of Geography and Environment.

The comprehensive study was prepared by an international team of scientists using more than a decade's worth of satellite data from NASA's Moderate Resolution Imaging Spectroradiometer, MODIS, and Tropical Rainfall Measuring Mission.

Analysis of these data produced detailed maps of vegetation greenness declines from the 2010 drought. The study has been accepted for publication in "Geophysical Research Letters," a journal of the American Geophysical Union.

"Last year was the driest year on record based on 109 years of Rio Negro water level data at the Manaus harbor," said Marcos Costa, co-author from the Federal University in Vicosa, Brazil. "For comparison, the lowest level during the so-called once-in-a-century drought in 2005 was only eighth lowest."

The severity of the 2010 drought was seen in records of water levels in rivers across the Amazon Basin, including the Rio Negro which represents rainfall levels over the entire western Amazon.

Water levels started to fall in August 2010, reaching record low levels in late October and began to rise with the arrival of the winter rains.

As anecdotal reports of a severe drought began to appear last summer, the authors started near-real time processing of massive amounts of satellite data.

They used a new capability, the NASA Earth Exchange, NEX, a collaborative supercomputing environment that brings together data, models and computing resources. NEX was built for the NASA Advanced Supercomputer facility at the agency's Ames Research Center in Moffett Field, California.

With NEX, the study's authors obtained a large-scale view of the impact of the drought on the Amazon forests and were able to complete the analysis by January 2011, in record time.

Similar reports about the impact of the 2005 drought were published about two years after the fact. They concluded that Amazon forests did not green up during the 2005 drought.

"Timely monitoring of our planet's vegetation with satellites is critical, and with NEX it can be done efficiently to deliver near-real time information, as this study demonstrates," said study co-author Ramakrishna Nemani, a research scientist at Ames.

An article about the NEX project appears in this week's issue of "Eos," the weekly newspaper of the American Geophysical Union.

Using NEX, the researchers first developed maps of drought-affected areas using thresholds of below-average rainfall as a guide.

Then they identified affected vegetation using two different greenness indexes - one for green leaf area and the other for physiological functioning.

The maps show the 2010 drought reduced the greenness of some 965,000 square miles of vegetation in the Amazon - more than four times the area affected by the last severe drought in 2005.

"The MODIS vegetation greenness data suggest a more widespread, severe and long-lasting impact to Amazonian vegetation than what can be inferred based solely on rainfall data," said Arindam Samanta, a co-lead author from Atmospheric and Environmental Research Inc. in Lexington, Massachusetts.

There is concern that in a warming climate the moisture stress could result in Amazon rainforests being replaced by grassy savannas.

In that case, the large reserves of carbon stored in these forests, about 100 billion tons, could be released to the atmosphere, which would accelerate global warming.

The UN's Intergovernmental Panel on Climate Change has warned droughts similar to the one last year and another in 2005 could be more frequent in the Amazon region in the future.

全文及圖片詳見:ENS報導

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