Research press release


Nature Climate Change

Vulnerable island populations to face increasing aridity



今回、Kristopher Karnauskasたちは、この問題を克服するため、小さな島々での可能蒸発散量を推定する方法を用いて、全世界に分布する80の諸島について乾燥度変化指数(ACI)を計算した。その結果、これらの諸島の73%以上で乾燥度が上昇する傾向が認められた。また、これらの諸島の約半数(ほとんどが熱帯海洋上の諸島)で降水量の増加が予想されているものの、ほぼ全ての諸島で可能蒸発散量が増加しており、世界の島嶼地域の淡水収支において乾燥度が上昇する傾向にあるとKarnauskasたちは結論づけている。

Climate change may subject nearly three-quarters of the world’s small islands - home to around 16 million people - to reduced fresh water availability by 2050, reports a paper published online this week in Nature Climate Change.

Changes in water balance - the difference between precipitation and evaporation - are expected in many regions as a result of climate change. However, islands smaller than the spatial resolution used in climate models, including French Polynesia, the Marshall Islands and the Lesser Antilles, have been difficult to assess. The standard method for assessing aridity is to calculate the ratio of precipitation to potential evapotranspiration (water loss by evaporation from surfaces and through plant leaves), but this does not work for small islands as global circulation models can only provide estimates of precipitation, not potential evapotranspiration.

To overcome this problem, Kristopher Karnauskas and colleagues used a method for estimating the potential evapotranspiration for small islands, to enable them to calculate an aridity change index (ACI) for 80 globally distributed island groups. They find a tendency towards increasing aridity at over 73% of the island groups. Although they find that about half of the island groups will experience increased rainfall (mostly those in the deep tropics), increases in evaporation were more consistent across the islands, resulting in a shift of global island freshwater balance towards greater aridity.

doi: 10.1038/nclimate2987


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