オセアニアの南北貿易風帯には数多くの環礁が点在する。砂礫の州島にしみ込んだ雨水が不被圧地下水レンズを形成し、島の陸上生態系を支える厳しい環境である。天水田でのサトイモ科根茎類栽培はこの淡水資源を利用する農耕であり、その可否は環礁の人間居住を左右する。それゆえ、安定した降水量が期待できる環礁では、永続的な居住が可能となる。ポリネシアの中央に位置する北部クック諸島プカプカ島はそうした環礁の1つで、タロイモやミズズイキ類の天水田が数多く分布する。地面を掘り窪めた田面と周りに積み上げられた砂礫の廃土堤が織りなす起伏の連なりは、自然の営力と人間の営為の絡み合いが生み出した環礁の典型的な文化景観である。しかし、それは安定した静的な景観ではない。記録が残る1914年以降でさえ、プカプカは12回の熱帯サイクロンに襲われ、越波や大雨による冠水で天水田がしばしば壊滅的な打撃を受けてきた。直近では2005年2月27日早朝にカテゴリー４に発達したサイクロン・パーシーがプカプカの南40kmに最接近し、終日吹きすさんだ強風で多くの家屋から屋根が吹き飛び、ココヤシが数多くなぎ倒された。4mを超える高波が押し寄せ、ラグーン側海岸線から越波した海水が天水田を冠水させた。海水が入ってしまった天水田の復興は容易ではなかったと考えられる。本研究では、地元紙Cook Islands Newsの記事や各種文書資料と、３時期に撮影された高精細衛星画像の比較分析を組み合わせ、主島ワレ(Wale）の天水田の動態に着目しながら、サイクロン・パーシーによる被害を俯瞰した。その結果、以下の3点が明らかとなった。（１）国内外からの支援物資によって3か月後には生活が回復してきたが、塩害を受けた天水田の復興には数年を要した。（２）環礁社会の生活を支える天水田でのタロイモ栽培が１年以上にわたって滞るなかで、島内人口が急減し、10年を過ぎても人口の回復は60％台にとどまった。（３）人口が減少した状況で、労働集約しやすい島会議や村会が管理・運営する天水田から復興が進んできた可能性がある。
The north-south trade winds of Oceania are dotted with numerous atolls. The rainwater permeating into sand and gravel of the islets forms a groundwater lens, only which supports the terrestrial ecosystem of harsh environment. Cultivation of aroid tubers is farming in agricultural pits which utilizes this freshwater resource, and its success affects the human settlement of the atoll. Therefore, permanent habitation is possible in atolls where stable rainfall can be expected. Pukapuka Island, the Northern Cook Islands, located in the center of Polynesia, is one of such atolls, and many pits of Colocasia and Cyrtosperma are distributed. The series of undulations woven by the planting beds and the spoil banks of gravel piled up around pits is a typical cultural landscape of atoll societies, which can be seen as a historical product generated by entanglement of two agencies, nature and human. But it is not a static landscape. Even since the record-breaking 1914, Pukapuka has been hit by twelve tropical cyclones, and agricultural pits were often devastated by floods of sea water and heavy rains. Most recently, Cyclone Percy, which developed into Category 4 in the early morning of February 27, 2005, came closest to 40km south of Pukapuka, and the strong winds blew off the roofs of many houses and knocked down many coconut trees. High waves over 4m rushed in, and seawater overflowing from the lagoon side coastline into large agricultural pits. The reconstruction of pits once filled with seawater should not have been easy. This research combined articles of the local newspaper and various documents with comparative analysis of high-definition satellite images taken at three times as to scrutinize the damage of agricultural pits in Wale, the main islet of Pukapuka. As a result, the following three points were clarified: (1) while the daily life of people was somewhat restored three months later due to domestic and overseas relief supplies, it took several years to recover the salt-damaged agricultural pits; (2) as the cultivation of taro has been delayed for more than a year, the population has declined sharply, and it recovered only about 60% of the previous area even after 10 years; (3) the reconstruction would have progressed from some large pits managed by the island council and the village council, because these are labor-intensive pits.
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