Risk Analysis for Agriculture Drought

台灣水資源雖然豐沛，但因季節豐枯明顯，各標的用水競爭激烈，故仍常有缺水事件發生。現行乾旱管理方式，皆以調度農業用水或公告休耕之短期因應措施為主，而長期乾旱規劃重點仍著重於供水面之風險評估，需求面之乾旱風險規劃卻少有。故本研究擬針對需求面之乾旱風險規劃，找出農業乾旱發生之頻率、程度以及位置分佈以建立農業乾旱潛勢，並由於不同之乾旱管理方式皆會影響乾旱風險之分佈，因此研究以農田休耕手段為乾旱調配模式，探討現行水利會灌溉計畫下農業乾旱分佈之情況，建立農業乾旱潛勢分佈，以作為後續農業灌區乾旱風險評估與管理之基礎。 本研究主要彙整嘉南地區民生、工業與農業用水資訊以評估各標的用水需求，考慮農業灌區用水特性與公平性分配建立乾旱調配原則以建構農業乾旱調配模式。透過模擬各種調配原則，評估各原則下之休耕區域與範圍對農業用水管理的衝擊，並配合序率優勢方法決定出最佳調配原則。最後透過此最佳調配原則，即可建立並分析農業乾旱缺水潛勢。 透過對調配原則之評估結果發現，以用水效率分配與管理處灌溉管理單元公平分配作為模式調配原則之長期缺水率與休耕衝擊最小，而以此調配原則分析曾文-烏山頭灌區乾旱潛勢分佈狀況，以休耕機率而言一期作缺水風險較二期作高。另由休耕面積配合單位面積產量與產值計算之局部休耕影響指標顯示一期作乾旱發生多以雙期作田(水稻)為主之地區，二期作則分佈於部分區域之單期作田與三年兩作田乾旱潛勢較高，但大致而言皆較一期作不嚴重。若能加強改善與調整該區之用水與耕作制度，應可有效降低區域性農業灌區乾旱風險。Although with abundant water resources, Taiwan suffers from frequent drought due to uneven distribution of precipitation and stream flows in temporal and spatial aspects and the keen competitions among water use sectors. Fallow strategies are the mostly used measure for short term drought relief so that agricultural water supplies are reallocated to other sectors as domestic and industrial during drought period. Not much attention was paid to the demand sides even in the long term water resource planning. Special attention was directed to the demand sides for drought risk planning in this thesis research to identify the agricultural drought risk for its frequency, severity, and spatial distribution. Because regional drought risk patterns will be changed by different water resource management schemes, different drought allocation schemes were evaluated in this research for better adoption to the drought. The drought potential maps can be used for drought risk assessment and management. Chia-Nan Region in southern Taiwan was chosen as the study area. The water demand and supply information for this region was compiled into the Linear Programming model for water managements and drought allocations. Three different drought allocation strategies as water use efficiencies and equities for water shortage in different spatial units were studied. These strategies were evaluated by the drought impact indices that take into account of the scale and spatial distribution of the water shortages. The agricultural drought potential maps were then created using the best performed drought allocation scheme. The drought allocation scheme base on the water use efficiency and considering the water shortage equity among larger spatial units is found to be one of best performance. The drought potential maps derived under this drought allocation scheme show the first crop of paddy has higher drought risk than that of the second crop. Most of areas with high drought risk potential are located in paddy farming area. The regional drought risk may be attenuated through the adjustment of the cropping patterns.謝誌..............................................................................................................................Ⅰ 中文摘要......................................................................................................................Ⅱ 英文摘要......................................................................................................................Ⅲ 目錄..............................................................................................................................Ⅳ 圖目錄..........................................................................................................................Ⅵ 表目錄..........................................................................................................................Ⅷ 第一章 緒論..................................................................................................................1 第二章 文獻回顧..........................................................................................................4 2-1 水資源系統分析.............................................................................................4 2-2 區域水資源調配模式.....................................................................................4 2-3 乾旱定義與評估方式.....................................................................................6 2-4 短期乾旱應變...............................................................................................10 2-5 長期乾旱規劃...............................................................................................12 第三章 研究區域概述................................................................................................14 3-1 地理位置.......................................................................................................14 3-2 自然環境.......................................................................................................15 3-3 水庫蓄水設施...............................................................................................17 3-4 各標的用水現況...........................................................................................21 3-4-1 自來水供水系統...............................................................................21 3-4-2 農業灌溉系統...................................................................................27 第四章 農業乾旱調配模式........................................................................................30 4-1 供需系統整合...............................................................................................30 4-2 供水資料.......................................................................................................32 4-2-1 河川與水庫入流量資料...................................................................32 4-2-2 地下水補注量...................................................................................33 4-2-3 水庫蒸發量資料...............................................................................33 4-2-4 水庫最大與最小蓄水量資料...........................................................35 4-3 標的需水資料...............................................................................................35 4-3-1 民生與工業用水推估.......................................................................35 4-3-2 農業用水推估...................................................................................45 4-4 目標函數式...................................................................................................53 4-4-1 用水效率分配原則...........................................................................54 4-5 限制式...........................................................................................................58 4-5-1 供水限制式.......................................................................................58 4-5-2 標的基準配水量限制.......................................................................59 4-5-3 休耕門檻限制...................................................................................60 4-5-4 公平性分配原則...............................................................................61 第五章 農業乾旱調配原則評估方法........................................................................64 5-1 乾旱調配原則...............................................................................................64 5-2 綜合休耕影響指標.......................................................................................65 5-3 序率優勢分析...............................................................................................68 第六章 調配原則評估結果與農業乾旱潛勢分析....................................................71 6-1 休耕衝擊評估...............................................................................................71 6-2 農業乾旱潛勢分析.......................................................................................85 第七章 結論與建議....................................................................................................99 7-1 結論...............................................................................................................99 7-2 建議.............................................................................................................101 參考文獻....................................................................................................................10