Chapter 1: Introduction

Vietnam is one of the five countries in the world that would be most affected by the climate change. It has the coastal line of more than 3,260 kilometers in total length and high-population density with over 23% of the 84 million Vietnamese populations residing in the costal areas. Most of the people in coastal areas are engaged in farming and fisheries, and, hence, will be vulnerable to the immense and direct impacts of climate change and subsequent changes in hydrology.

In this chapter, I review the literature on climate change impacts in Vietnam. The Vietnamese government established the National Target Programs and policies coping with climate change. They assumed some scenarios under climate changes through to the end of the 21st century, and derived actions against the changes top-down from the scenarios, while neglecting the local people's reactions to the climatic and societal changes. There is a contrasting approach, however, that starts with the local peoples' perception of changes in climate as well as other natural and societal conditions. It seeks the information on local concerns on climate and other natural and societal conditions, and focuses on the people's reactions to the perceived changes.

I take this 'bottom-up' approach in my thesis hoping that the top-down policies against the climate change impacts can be adjusted or even designed on the basis of the bottom-up understandings of the local peoples' strategies for sustainable livelihood against the changes in climate and other socio-economic determinants in the near future. I explored sustainable farming systems in adaptation to changing climate on the basis of case studies at two locations in the North and South of coastal Vietnam.

Chapter 2. Methodologies

Two coastal districts in Vietnam were chosen for this study. The first case study was done in Nga Son district of Thanh Hoa province, which is located in the North and neighboring the Red River Delta, the second largest delta in Vietnam. The district has been the largest and most famous producer of sedge (Cyperus spp.), an industrial crop used to make mats and handicrafts, for more than 500 years. The second case study was conducted in Cai Nuoc district of Ca Mau province located in the Mekong River Delta that is the largest delta of Vietnam. Two surveys were conducted in March 2008 and 2009.

The primary data were collected by participatory methods including key-informants interview, key-informant discussion, focus group discussion, field observation, transect walks, and semi-structured interviews, in which 200 (Case study #1) and 100 (Case study #2) households were visited with questionnaires.

Chapter 3. Case study #1: Sedge growers in Nga Son district of Thanh Hoa province

In this chapter, I investigated the farmers' perception of climate change, their responses to the changes in climate and hydrology as well as the determinants of their adaptive capacity.

With respect to the farmers' perception of climatic changes, 96 out of 200 interviewees (48%) reported higher temperature than 20 years ago, and 83 interviewees (42%) mentioned a delay in the end of rainy season. The sedge harvest had to be delayed in response to the later end of rainy season as reported by 115 (58%) interviewees.

Farmers also reacted to the decrease of sedge productivity and salinity intrusion in recent years. The reaction included changes in cropping calendar and pattern, diversification of income sources by finding non-agriculture jobs, developing animal husbandry and aquaculture as well as setting up private businesses.

The farmers' adaptive capacity depends on the economic and topographic conditions. The study compared one group located inland (the rich group) and the other located closer to the coast (the poor group). The two groups were significantly different in options to develop aquaculture and to start private businesses. These options give them a high cash income, but they require more initial investments than the poor can afford.

Chapter 4: Case study #2: Shrimp farmers in Cai Nuoc district of Ca Mau province

With the same purpose as chapter 3, I investigated farmers' perception of climatic changes, their adaptive responses to the changes, and the determinants of their adaptive capacity in Cai Nuoc district. In this district, the rice paddies had been converted dramatically to shrimp ponds due to the salinity intrusion since 2000.

Among the 100 interviewees, 49 reported that temperature had risen since 20 years ago, 42 mentioned later commencement of the rainy season, and 41 reported a higher frequency of tropical storms than in the past.

The study revealed that the rich farmers increased intensive shrimp and selected better seeds of shrimp, and that the poor opted for other income sources, e.g. growing fruits, vegetables and other crops to reduce their daily expenditure. Increase in rice cropping area was opted for by many farmers irrespective of the economic conditions. However, the farmers' adoption of this option of increasing rice cropping varied by topography. Switching from direct-seeding to transplanting and selecting more salt-tolerant varieties were common responses for the farmers to the increasing salinity.

Chapter 5: General discussion

The findings in Chapters 3 and 4 were synthesized in this chapter. In the Case study in Cai Nuoc district, government had implemented policies to cope with the increased salinity since 1994. Under the policies, they installed engineering adaptations such as the construction of sluice gates and canals to protect rice paddies from salinity intrusion in some areas, and the conversion of rice paddies to shrimp ponds in the other areas. These two types of adaptations were not really successful, however. The sluice gates have altered local hydrological regimes, and resulted in severe conflict between the people over fresh water supply. Conversion from rice to shrimp also negatively affected the environmental and social aspects. One of the reasons for the problems was the lack of information and experiences at local scales. These experiences from the second case study could be transferred to the first study site in the North, where the policies on land use change are yet to be established to cope with the salinity intrusion due to the sea level rise and damages due to extreme weather events.

The top-down and bottom-up approaches shall complement each other in achieving sustainable farming systems in the coastal areas, where the vulnerability to climate changes should be reduced for the future.

Chapter 6: Conclusions and implications

This chapter summarizes the findings in the preceding chapters. The findings have shown that the farmers have some capabilities to adapt themselves to the changes in climate and hydrology, but that they also need institutional assistances at scales larger than the villages such as policy makers, land planners and agricultural extension officers. Incorporating local knowledge into policy making process would facilitate sustainable agricultural developments in coastal Vietnam in adaptation to the climate changes in the near future.

背景

ヴェトナムは,気候変化の影響を世界でも最も顕著に受ける国の一つに数えられる.特に世界有数の巨大デルタ(紅河デルタとメコンデルタ)を有する沿岸域は,同国の主要農業生産地帯であるが,低平な地形のために,海面上昇など気候変動に対してきわめて脆弱であると想定されており,その対応が国家的課題となっている.海面上昇への対策として,ダムや堤防の設置がしばしば想定されるが,そうした工学的対応は膨大なコストがかかるだけでなく,それ自体が水文環境を変化させて,水質汚染の激化や水域生態系の破壊を招くことが多い.むしろ「気候変化とともに生きる」可能性を探ることが,コスト的にもまた生態系保全のためにも有効なのではないか.そうした考えを背景に,本研究は,紅河およびメコンデルタの塩水遡上地域において,農家の塩水遡上などの環境変化をどう捉え,どのように対応しているかを,実態調査によって解明しようとしたものである.

ヴェトナム北部の紅河デルタ南部沿岸域におけるシチトウイ栽培農家の塩水遡上への適応

紅河デルタの南に位置するThanh Hoa 省Nga Son地区にて,塩水遡上へのシチトウイ(Cyperus spp.)栽培農家の対応を,訪問調査などによって調べた.その結果,農家は20年前に比べて,気温は上昇し,雨季の終わりが遅くなっていると感じていることが分かった.農家はまた,近年塩水の遡上が激化し,シチトウイの収量が低下していると感じていた.こうした農家の「感じ」は,気象記録の解析結果と部分的には一致していた.調査対象地区を,海岸に面した村々とより内陸側の村々とに分け,塩水遡上への農家の対応のしかたを比べた.農外収入の確保や家畜の飼養は共通した対応であったが,水産養殖への転換や小売店経営の開始などは,内陸側の農民たちのほうが明らかに多かった.水産養殖は,むしろ沿岸側で容易であることを考えると奇妙な結果であるが,養殖池の設置には大きな初期投資が必要で,農業収入の少ない沿岸側の農家にとっては,内陸側の農民に比べて,初期資金がより高いハードルとなっていることが判明した.

ヴェトナム南部のメコンデルタで水稲栽培からエビ養殖に転換した農家の塩水遡上への適応

メコンデルタの最南部に位置するCa Mau省 Cai Nuoc 地区にて,塩水遡上対策として水稲栽培から汽水エビ養殖へ転換した農民を対象に,環境変化への適応を訪問調査などによって調べた.農民は,20年前に比べて気温は上昇し,雨季の始まりが遅くなり,また台風が増えたと感じていた.これらの農民が感じた環境変化は,気象観測記録によって部分的にではあるが確かめられた.彼らが水稲からエビに転換した背景には塩水遡上の激化があるが, 2000年に実施された土地利用制限の緩和がより直接的なきっかけとなった.エビ養殖への転換後数年して,病害多発や水質汚染などの問題が生じてきた.また,エビ養殖池自体が周囲の塩水濃度を高める結果にもなった.調査対象農家を,年収によって富裕層,中間層,貧困層の3つに分けて,エビの生産性の低下や環境変化に対する農家の対応を調べたところ,富裕層は管理強度を高めた集約的エビ養殖に向かったのに対して,貧困層は他の農作物の栽培を取り入れて,自家用食料の確保と家計支出節約に努めたことが分かった.自家食料の確保は,どの農家も共通して重視しており,いったん中止した水稲栽培を再開して自家飯米を確保する動きが広く見られた.その際,塩水の影響を軽減するために,直播から移植栽培への転換や塩水耐性の高い品種を選ぶ対応がなされていた.水稲栽培の再開は,灌漑用水が確保できる地域に限られ,河川から遠い地域の農家は不可能であった.

Cai Nuoc地区の調査対象農家を,集約的エビ専作,粗放的エビ専作,そして水稲-エビ輪作の3類型に分けて,グループディスカッションによって,水稲からエビへの転換を彼ら自身がどうとらえているかを調べた.農民は,エビ養殖に伴う環境負荷の問題を把握しており,また貧富の拡大や銀行からの借金の増大など社会的な問題の拡大も認識していた.多くの農民が,エビ専作と比べた際の水稲-エビ輪作の利点を理解しており,例えば,主食が自家で確保できること,水稲栽培の残渣を後作のエビ養殖で利用できることなどが挙げられた.Cai Nuoc地区では水稲の栽培面積が増えつつあり,農家の意見が裏打ちされた.

気候変動への適応に関するボトム・アップ アプローチの意義

気候変動への適応策として,工学的対策がしばしば想定される.例えば,海面上昇や降水パターンの変化には,堤防や水門の建設によって塩水遡上や水位の変化を防止する対策が考えられる.しかしそうした工学的対策は水文環境を変化させ,しばしば農業や水産業に大きな影響を及ぼす.いっぽう,土地利用政策を変えることによって,環境変化に適応することも考えられる.こうした,いわばトップ・ダウンの適応対策に対して,農家が現実の環境変動にどう対応しているかを調べることから始めるボトム・アップの適応策が,本研究のアプローチである.本研究は,ヴェトナム沿岸部の農家が環境変動を的確に把握し,様々な適応行動をとっていることを明らかにした.また,適応行動を制約する要因として,局所的な水文環境に加えて各農家の経済状態の重要性が示された.有利な環境条件にある農家は,水文環境の変化に対して有効に適応できるが,環境的,経済的に不利な条件にある農家は,適応の幅が限られてしまう.塩水遡上に対して水稲作から水産養殖への転換は有効な適応策と考えられるが,急激な変化は多くの課題を生じることが分かった.今後は,本研究のようなボトム・アップ的に得られる知見を,工学的・政策的なトップダウン的な適応策の立案にフィードバックすることが必要と考えられる.

以上のように,本論文が,ヴェトナムの沿岸部における塩水遡上への農家の対応と対応策の選択にかかわる要因を,気候変化への適応という視点から解明したことは,学術上,応用上貢献するところが大きく,よって審査委員一同は本論文が博士(農学)の学位論文として価値あるものと認めた.