氣候變遷引起的土壤變化會讓侵蝕加劇以及更多暴洪發生

原文網址：https://news.ucr.edu/articles/2018/09/12/climate-induced-soil-changes-may-cause-more-erosion-and-flash-flooding

氣候變遷引起的土壤變化會讓侵蝕加劇以及更多暴洪發生

水循環的加速對生物多樣性、人體健康和水源與糧食的安全都有影響

Sarah Nightingale

當我們考慮氣候變遷帶來的影響時，通常第一個不會想到我們腳下踩的土地。然而，加州大學河濱分校領導的研究團隊預估氣候變遷會讓土壤中的大型孔隙減少，這可能造成21世紀末的水循環速度加快，並讓暴洪(flash flooding)頻率增加以及土壤侵蝕加劇。

由於氣候變遷造成土壤的大孔隙減少，未來可能會讓農地淹水更常發生。圖片來源：USDA

在9月5日發表於《自然》(Nature)的論文中，這群科學家研究氣候變遷如何影響大孔隙率(macroporosity)――也就是土壤中的大型孔隙含量。大孔隙(Macropore)是土壤中直徑大於0.08釐米的孔洞，其中含有的水分可以輕易地被周遭土壤吸收，進而讓植物利用、運輸養分，最後回到地下含水層當中。

「預估大孔隙率因為氣候變遷而產生的變化相當重要，因為大孔隙是水循環的其中一段，所以它的變化最終會影響到水資源短缺、食物安全、人體健康以及生物多樣性減少等現象。」研究主要作者，該大學環境科學系的副教授Daniel Hirmas表示。

研究人員利用的資料庫彙整了美國各處50多年來關於土壤的大量資料。結合氣象站網絡蒐集到的大氣數據，他們檢視了在不同雨量、溫度、濕度的變化梯度下，大孔隙率會產生什麼變化。結果發現土壤在乾燥氣候中形成的大孔隙比濕潤氣候多；此外，大孔隙率因為氣候而產生的變化比過往認為得還要更快發生。

研究人員接著利用預測中21世紀末的氣候，得出到了2080至2100年，濕度增加會讓美國大部份地區的土壤大孔隙率降低。(除了包括阿拉巴馬州和路易斯安那州在內的南部海岸平原之外。)

這項結果代表未來的水分更難滲入到土壤當中，造成地表逕流和土壤侵蝕增加，以及更多暴洪發生。

「這是首次有研究顯示氣候可以在短時間內影響土壤大孔隙的形成。同時，這項結果也更加鞏固氣候變遷可能會使水循環速度加快的理論。」Hirmas表示。「我們的研究結果代表全球氣候模型必須要納入土壤大孔隙率的影響，如此才能更加了解水循環，進而預期未來變化並加以準備。」

這篇論文的題目為「氣候引起的土壤大孔隙率變化規模擴及整個大陸，而且可能會加快水循環。」除了Hirmas之外，作者還包括美國羅格斯大學的Daniel Giménez、挪威生物經濟研究所(NIBIO)的Attila Nemes、美國楊百翰大學的Ruth Kerry、美國堪薩斯大學的Nathaniel A. Brunsell和 Cassandra J. Wilson。研究經費來自於美國農業部的農業與食品研究計畫以及NIBIO。

Climate-induced soil changes may cause more erosion and flash flooding

More intensive water cycle could have impact on biodiversity, human health, and water and food security

The earth beneath our feet isn’t usually the first thing that comes to mind when people think about the impacts of climate change. However, a study by a UC Riverside-led team of researchers predicts a climate-induced reduction in large soil pores, which may intensify the water cycle and contribute to more flash flooding and soil erosion by the end of the 21st century.

In a paper published Sept. 5 in Nature, the scientists studied the impact of climate change on macroporosity—the amount of large pores in the soil. Macropores, which are greater than 0.08 mm in diameter, allow water to be absorbed easily into the surrounding soil, where it can be used by plants, transport nutrients, and eventually make its way back into underground aquifers.

“It is important to predict the response of macroporosity to climate change because of its role in the water cycle, and ultimately in water scarcity, food security, human health and loss of biodiversity,” said Daniel Hirmas, an associate professor in the Department of Environmental Sciences and lead author on the study.

Using a large database of soils collected over 50 years from across the continental U.S. combined with atmospheric data from a network of weather stations, the researchers examined changes in macroporosity across a rainfall, temperature, and humidity gradient. They found macropores were more likely to develop in drier climates than humid climates, and that climate-related changes in macroporosity occur over shorter timescales than previously thought.

The researchers then used climate projections for the end of the 21st Century to predict that increasing humidity by 2080-2100 will reduce soil macroporosity in most regions of the U.S. (with the exception of the southern coastal plain, which comprises Alabama and Louisiana).

The consequences could be less infiltration of water into the ground, more surface runoff and erosion, and more flash flooding.

“This is the first study to show that the development of macropores is influenced by climate at short timescales and it reinforces the hypothesis that climate change will probably intensify the water cycle,” Hirmas said. “Our results suggest that macroporosity should be incorporated into global climate models to better understand the water cycle, anticipate changes, and prepare for the future.”

The title of the paper is “Climate-induced changes in continental-scale soil macroporosity may intensify water cycle.” In addition to Hirmas, authors include Daniel Giménez from Rutgers University; Attila Nemes from the Norwegian Institute of Bioeconomy Research (NIBIO); Ruth Kerry from Brigham Young University; and Nathaniel A. Brunsell and Cassandra J. Wilson from the University of Kansas. The work was funded by the United States Department of Agriculture’s Agriculture and Food Research Initiative (USDA-AFRI) and NIBIO.

原始論文：Daniel R. Hirmas, Daniel Giménez, Attila Nemes, Ruth Kerry, Nathaniel A. Brunsell, Cassandra J. Wilson. Climate-induced changes in continental-scale soil macroporosity may intensify water cycle. Nature, 2018; 561 (7721): 100 DOI: 10.1038/s41586-018-0463-x

引用自：University of California - Riverside. "Climate-induced soil changes may cause more erosion and flash flooding.”