中国の記録的な洪水、その背景とは？

【北京ＡＦＰ＝時事】中国では毎年大規模な洪水が発生しており、政府は国内各地に設置した巨大ダムのネットワークを対応策としてアピールしてきた。しかし今年もまた記録的な大洪水に見舞われ、数百人が死亡した他、家屋数千棟が浸水した。（写真は2020年8月に中国・重慶で発生した洪水）
　今回影響を受けた人は数百万人に上っている。数十万人が避難し、道路は水没、観光地も閉鎖され、巨額の経済損失が出ている。
　なぜ中国は毎年深刻な洪水被害を受けるのか、５つの疑問点をまとめた。

■ダムは機能しているのか？
　中国では以前から、水流を制御したり迂回（うかい）させたりするために、ダムやせき、堤防、貯水池に依存してきた。
　中国応急管理部によると、６月から８月初旬にかけて、アジア最長河川の長江のダムや貯水池で約３００億立方メートルの水がせき止められ、上海を含む下流域への被害を軽減している。
　だが巨大インフラをもってしても、すべての洪水は食い止められていない。国営中国中央テレビ（ＣＣＴＶ）によると、先月には●河（じょが、●はさんずいに除）流域の２つのせきの爆破を余儀なくされ、川からあふれた水を田畑に放流したという。
　また長江上流に設けられた世界最大の水力発電ダム、三峡ダムの構造上の懸念も絶えない。同ダムは、地下の断層が複雑に入り組んだ場所に位置しているからだ。

■気候変動による影響は？
　気候変動により、極端な気象現象が頻発するにつれて、中国のダムにかかる負荷がさらに増す可能性が高い。
　中国水利部によると、今夏は５３の河川で過去最高水位を記録したという。

■「スポンジシティー」の効果は？
　中国の急速な発展と都市化も、洪水被害の悪化を招いてきた。都市化に伴い、より多くの土地が不透水性のコンクリートで覆われ、豪雨の際に地面に水が急速にたまるリスクが高まった。
　政府が提示した解決策の一つが、２０１４年に始まった「海綿城市（スポンジシティー）」計画だ。
　都会の不透水性の地面を、透水性舗装材など多孔質材で置き換え、緑化を進め、排水溝や貯水池を増設することにより、地面に水がたまるのを防ぐとしている。

■洪水による最大の被害者は？
　とはいえスポンジシティーは、迂回流の通り道に位置し、洪水によってすでに家屋や作物に甚大な被害を受けてきた地方部の集落にとっては、利益は少ないとみられる。
　人口密度の高い都市への被害を防ぐため、複数の村で全体が洪水の犠牲となることも多く、そのたびに村民は避難を余儀なくされてきた。

■他に講じられる対策は？
　中国は洪水による人的被害の抑制策として、洪水の監視強化と早期避難に注目している。
　応急管理部の発表によると、今年６月から８月初旬の洪水による死者・行方不明者は２１９人で、過去５年間の年間平均に比べると半数に満たなかったという。
　その一方で、今年の洪水による経済損失は１５％増加し、１７９０億元（約２兆７０００億円）に上ったことが、当局が先週開いた記者会見で明らかになっている。
　シンガポール国立大学で水政策を研究するセシリア・トルタハーダ氏は、洪水予防は究極的には気候変動に対する世界規模の行動も必要になるとの見方を示し、「国ごとの備えは進んでも、世界全体としての備えはできていない」と指摘している。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/08/25-12:56）

China has touted its massive dam network as a remedy for its devastating annual floods, but record deluges have once again killed hundreds of people and submerged thousands of homes this year.
Millions of people have been affected this time -- with hundreds of thousands evacuated, roads submerged, tourist sites closed and soaring economic costs.
Here are five questions about why China still endures severe flooding every year.
- Do the dams work? -
China has historically relied on dams, levees and reservoirs to control and divert the flow of water.
From June to early August, around 30 billion cubic metres of floodwater were intercepted by dams and reservoirs in Asia's longest river, the Yangtze, mitigating flooding downstream in areas including Shanghai, China's emergency management ministry said.
But the country's vast infrastructure has been unable to contain all the flooding, with authorities in the eastern city of Chuizhou, Anhui province, forced to blow up two dams last month to release water from the rising Chuhe river over cropland, state broadcaster CCTV reported.
And fears re-emerge periodically over the structural integrity of the Three Gorges Dam on the upper Yangtze, the world's largest hydroelectric dam, built in an area criss-crossed by geological faultlines.
- What impact is climate change having? -
The burden on China's dams is likely to grow as climate change makes extreme weather events more common.
As the Earth's atmosphere gets warmer, it holds more moisture, making downpours more intense, Benjamin Horton, director of the Earth Observatory of Singapore, told AFP.
Water levels reached historic highs in 53 rivers this summer, according to China's ministry of water resources.
Authorities warned this week that the Three Gorges Dam is facing the largest flood peak since it began operating in 2003.
Heavy rains are set to send 74,000 cubic metres of water per second rushing into the Three Gorges reservoir, the official Xinhua news agency reported.
This summer's floods ring an alarm bell for China that climate change is here, Li Shuo, a climate analyst for Greenpeace East Asia, told AFP.
- Could 'sponge cities' help? -
The country's rapid development and breakneck urbanization has also exacerbated flooding.
Urban sprawl has covered more and more land in impermeable concrete -- increasing the risk of rapid water buildup on the surface during heavy rain.
Horton also said that some of the country's big lakes have been drastically reduced in size.
One of the solutions proposed by the government has been the sponge city programme that began in 2014.
It seeks to replace impermeable urban surfaces with porous materials like permeable pavements, more green spaces, drainage areas and reservoirs to stop water accumulating on the ground.
The objective is that stormwater goes into drains or the green areas, and affects the built areas less, Cecilia Tortajada, a researcher of water policy at the National University of Singapore, told AFP.
- Who suffers the most from flooding? -
But sponge cities will be little consolation for rural communities in the path of diverted water, which have suffered severe damage to their homes and crops.
While urban dwellers in China's megacities are largely spared from the rising water, much of the country's hinterlands along the Yangtze River were put on the frontline, Li said.
Entire villages are routinely allowed to flood, with residents evacuated, in order to spare densely populated cities.
Over the last week more than 165,000 hectares of crops were damaged in severe flooding in Sichuan, officials said.
The Mengwa Flood Diversion Area, home to four townships and nearly 200,000 people, was inundated after officials ordered the opening of 13 sluice gates on the Huaihe river in July, state media reported.
- What more can be done? -
China is also turning to increased flood surveillance and early evacuation to mitigate the human cost of flooding.
In addition to conventional weather monitoring technology, Anqing city in China's Anhui province is using virtual reality goggles linked to river-monitoring cameras that use 5G internet to transmit images to inspectors, according to Xinhua.
The number of people dead or missing as a result of flooding from June to early August this year fell to 219 -- less than half the average figure each year in the past five years, the ministry of emergency management said last week.
However, the economic costs of flooding have soared 15 percent this year, reaching 179 billion yuan ($26 billion), officials said at a press conference this week.
Tortajada said that ultimately, flood prevention will also require global action against climate change.
While countries are getting better prepared, the world as a whole is not prepared, she told AFP.