Research press release


Nature Climate Change

A damp prospect under future warming



今回、平林由希子(ひらばやし・ゆきこ)たちは、11の気候モデルから得られたデータを用いて、21世紀末の洪水リスクの全球的予測を公表した。今回の研究では、洪水の変化予測を調べて、その一貫性と広がりを評価した。平林たちは、東南アジア、インド半島、アフリカ東部とアンデス山脈北部において洪水の頻度が増加すると予測し、これとは対照的に、北欧、東欧、アナトリア、中央アジア、北米中部、南米南部の多くの地域で洪水の頻度が減少するという見方を示した。 こうした全球規模の分析に加えて、特定の河川流域の河口で、上述のモデルの分析が行われた。これらのモデルは、21世紀において、南アジア、東南アジア、オセアニア、アフリカ、北東ユーラシアの特定の河川のほぼすべてで洪水の頻度が増加することを示唆している。また、平林たちは、こうした河川の多くで、20世紀には100年に1回の頻度で起こっていた洪水事象が、21世紀には約10~50年に1回の頻度で起こると予測している。


A large increase in flood frequency in parts of Asia, Africa and South America is predicted in response to future warming conditions, reports a study in Nature Climate Change this week. In certain areas of the world, however, flood frequency is projected to decrease. These findings suggest that there is a necessity for adaptation to intensified floods and the introduction of further strategies to mitigate greenhouse gas emissions.

A recent IPCC special report on projected flooding stated that, “Overall, there is low confidence in projections of changes in fluvial floods” due to “limited evidence”. Indeed, up until now few studies have used multiple models for their projections and none has estimated flood risk in a warmer future climate.

Yukiko Hirabayashi and colleagues now present global flood risk for the end of this century based on the outputs of 11 climate models. They look at changes in flooding and evaluate its consistency and spread. The team predict an increase in flood frequency in Southeast Asia, Peninsular India, eastern Africa and the northern half of the Andes. In contrast, they suggest that flood frequency is set to decrease in many regions of northern and Eastern Europe, Anatolia, Central Asia, central North America and southern South America.

In addition to the global-scale analysis, the models were analysed at the outlets of selected river basins. The models suggest that during the twenty-first century, the frequency of floods will increase in almost all of the selected rivers in South Asia, Southeast Asia, Oceania, Africa and Northeast Eurasia. They also project that the twentieth-century 100-year flood event will occur about every 10-50 years in many of these rivers in the twenty-first century.

The authors caution that global exposure to floods would increase depending on the degree of warming, but interannual variability of the exposure may imply the necessity of adaptation before significant warming. They highlight that major attention should be paid to adaptation and mitigation strategies in lower-latitude countries where flood frequency and population are both projected to increase.

doi: 10.1038/nclimate1911

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