氣候變遷對區域水資源衝擊評估整合系統之研究

Abstract

近年來，極端氣候頻率的增加與威脅，提高了人類對於氣候變遷的重視，並促進了氣候變遷衝擊評估等相關研究，雖然研究方法漸趨成熟，但卻缺少一整合評估系統。本研究建立氣候變遷對區域水資源衝擊評估整合系統，並以臺灣南部之高屏溪流域為研究區域，分析與探討供水系統容忍缺水範圍，進一步建立供水系統承載力分析流程與工具，探討現有水資源供水系統的供水承載力與供水能力，並建立氣候分區降尺度，評估氣候變遷對高屏溪流域水資源供水系統所帶來的衝擊，並評估氣候變遷下水資源供水系統缺水之風險性。 整合評估系統包括了氣候分區降尺度、氣象資料產生器、GWLF水文模式、水資源系統動力模式、層級分析等，藉由Visual Basic建立操作介面，完整提供在氣候變遷衝擊評估流程中所需要的工具，可作為國內外相關研究之氣候變遷評估工具。其中氣候分區降尺度乃利用主成分分析法配合群集分析法，將台灣氣候分成九個氣候分區，並針對各區挑選各大氣環流模式鄰近格點資料作為氣候變遷衝擊評估的氣候變化值，修正大氣模式資料與各區測站之間的誤差，以合理評估未來可能的降雨與氣溫變化。透過氣象資料產生器，合成出水文模式所需的日降雨資料以及氣溫資料，以進一步利用GWLF模式模擬水資源供水系統內之入流量，進而代入水資源系統動力模式，評估水資源供水承載力，最後可利用層級分析工具進行調適策略之優先順序分析。 本研究利用VENSIM系統動力學軟體，就現有之水資源設施，以及供需關係，建立高屏溪與曾文溪流域水資源系統動力模式，進而評估高屏溪流域之供水承載力。供水系統之承載力是考量可容忍缺水風險下之最大可供水量，本研究採用缺水百分日指標(%-day)(Deficit Percent Day Index, 簡稱DPD)，並以DPD=1500%-day作為缺水容忍值，分析高屏溪供水承載力，並推求對應之缺水指數(Shortage Index, 簡稱SI)。 若以缺水容忍度作為供水承載力之設計標準，則必須加上缺水風險的門檻值，才能決定供水系統之供水承載力。當設計需水量為每日177.9萬立方公尺時，高屏溪供水系統能容忍DPD小於1500%-day之2年重現期距缺水事件，該設計需水量即為符合該缺水容忍度與風險之供水承載力。若以SI缺水指數作為供水承載力之評估指標， SI=1時，供水承載力為每日231.5萬立方公尺，而SI=0.5時，供水承載力為每日190.6萬立方公尺；SI=0.1所對應的供水承載力為每日143.5萬立方公尺。目前需水量為180萬立方公尺，SI為0.39。未來工業與生活需求成長下，原本高屏溪供水系統之SI逐漸增加，到民國120年時，SI到達1.03。以目前水資源設施而言，現況缺水風險52%，到民國120年時，將提高為74.1%。 未來高屏溪流域供水系統將面臨氣候變遷及需水量成長之雙重壓力，利用整合評估系統進行模擬，多數結果顯示氣候變遷與需水量增加的影響將使供水承載力下降，缺水風險將提高。針對未來供水系統之供水能力，除了考慮需水量的成長之外，對於氣候變遷造成供水能力下降與應該加以考慮，才能應付未來之供水。

In recent years, the threat and increasing frequency of extreme weather rised up human attention on climate change, and advanced the study on climate change impact. The research method is developed, but yet needs an integrated assessment system. This study established an integrated climate change impact assessment system on reginoal water resources. The study area of this study is the Gaoping river basin which is located in south area in Taiwan. The carrying capacity of the water supply system restricted by shortage tolerance was analyzed and approached. The process and simulation tools on analyzing carrying capacity of water supply system were built. The approach of downscaling with climate region classification was established to estimate the effect of climate change. The risk of water shortage was also adopted for climatic change conditions. The integrated assessment system includes downscaling with climate region classification, weather generator, GWLF model, water resources system dynamics model and Analytic Hierarchy Process(AHP) tool, and was built with Visual Basic computer program. It provides the tools in the process of climate change impact assessment, and could be applied for the related research on climate change. The downscaling with climate region classification used principal component analysis with cluster analysis to classify Taiwan into 9 climate regions. The changing value of each general circulation model in the nearest point to each climate region was adopted and corrected bias to evaluate future precipitation and temperature reasonably. Using weather generator to generate daily precipitation and temperature data for hydrological model simulation, the inflow was simulated by GWLF model and put in water resources system dynamics model to estimate the carrying capacity of water supply system in water resources. Then the AHP tool can help to find the prior plan for the decision maker. This study used System Dynamics software- VENSIM to build the water resources system dynamics model of Goaping and Zenwun river basin with considering the water resources structures and water demands, and evaluate the carrying capacity of water supply system in Gaoping river basin. The carrying capacity of water supply system is the most available water supply under the tolerance of water shortage. The Deficit Percent Day Index (DPD Index) was used and the tolerance of water shortage,DPD=1500%-day, was adopted to analyze the carrying capacity of water supply system and related water shortage index of Gaoping river basin in this study. The carrying capacity of water supply system was adopted for different return period of DPD. The carrying capacity is 1.78 million CMD referring to return period of 2 years of water shortage risk which was defined as the probability of water shortage over the tolerance, DPD=1500%-day. The carrying capacity also adopted for different SI. It is 1.43 million CMD, 1.91 million CMD, and 2.32 million CMD for SI=0.1, SI=0.5 and SI=1, respectively. The SI is 0.39 for present which the domestic and industrial water demand is 1.8 million CMD, and the SI will rise up to 1.03 in year 2031 due to expanded water demand. The risk of water shortage will rise up from 52% to 74.1%. The water supply system in Gaoping river basin is under two threats in the future. One is the expanded water demand, and another is climatic change. Using integrated assessment system to simulate, most results indicated that under threast of climate change and expanding water demand, the carrying capacity will decrease down and the water shortage will rise up. To the capacity of water supply system for the future, the consideration is not only growing water demand but also the impact of climate change.