Research press release





今回、Jean-Francois Pekelの研究チームは、1984~2015年に地球観測衛星ランドサットによって撮影された300万点以上の画像を解析し、30メートルの分解能で表層水の月々の変化を定量化した。Pekelたちは、それぞれ30メートル四方の地上部分を土地または開水面(淡水面と塩水面の両方を含むが海洋を除く)に分類するアルゴリズムを用いて、過去32年間に約90,000 km2の地域(スペリオル湖の面積にほぼ匹敵する)から永久表層水が消滅し、その70%が中東と中央アジアで起こったことを明らかにした。その一方でPekelたちは、新たな永久表層水が別の地域に出現し、その面積が、永久表層水が消滅した面積のほぼ2倍(184,000 km2)であり、ほぼ全ての大陸地域で永久水が正味で増加し、オセアニアでは正味で1%減少したことを明らかにした。


Changes in global surface water distribution over the past 30 years are mapped at high-resolution in a paper published online in Nature this week. The study suggests that drought, reservoir creation (such as dam building) and water extraction seem to drive most of the changes.

Previous studies have mapped the global distribution of surface water and tracked local and regional changes in surface water over time. However, a global and methodologically consistent quantification of changes in surface water over time did not exist, until now.

Jean-Francois Pekel and colleagues analysed over three million Landsat images, taken between 1984 and 2015, to quantify month-to-month changes in surface water at a resolution of 30 metres. They use an algorithm to classify each 30 m × 30 m square as either land or open water (including both fresh and saltwater, but excluding the oceans). The authors show that over the past 32 years permanent surface water has disappeared from an area of almost 90,000 km2, roughly equivalent to that of Lake Superior, with 70% of that loss occurring in the Middle East and Central Asia. However, they also show that new permanent surface water has formed elsewhere, covering an area about double that from which water was lost (184,000 km2), and that all continental regions show a net increase in permanent water except Oceania, which experienced a 1% net loss.

The authors conclude that their new data set provides an additional resource on the impact of climate change and climate oscillation on surface water distribution, while also capturing the effects that humans have on surface water resource distribution.

doi: 10.1038/nature20584

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