103/04/01 至 103/12/31
本計畫進行乾旱缺水指標之改良與整合，改良後指標可準確量化乾旱缺水事件之特性並應用於評估氣候變遷對於水資源系統之衝擊。首先，本計畫針對三個基本的單一型乾旱缺水指標(可靠度、脆弱度與回復度)進行單調性測試，測試結果指出脆弱度與回復度具有不單調特性，其結果可能為錯誤資訊。因此，本計畫提出修正脆弱度(Vuls)與修正回復度(Resw)，並測試其單調特性，測試結果指出修正脆弱度具有良好單調特性，而修正回復度仍不具單調特性，但其不單調行為有受到明顯抑制。本計畫整合可靠度、修正脆弱度與修正回復度為水短缺指標，該指標屬於複合型乾旱缺水指標可提供更多乾旱事件訊息，包含缺水延時、強度與數量等。此外，本計畫亦針對此複合型指標與另兩個常見之複合型指標(永續指標與乾旱風險指標)進行單調性測試，測試結果指出僅本計畫提出之複合型指標具有良好之單調行為，故本計畫應用水短缺指標以評估氣候變遷對於乾旱之衝擊。衝擊分析結果指出：若僅考慮氣候變遷之影響，未來18個情境案例中僅4個情境案例之缺水情況會比基期之缺水情況嚴重，其機率約為22.2% (4/18)；若同時考慮氣候變遷與水庫淤積之影響，未來18個情境案例中則有12個情境案例之缺水情況比基期之缺水情況嚴重，其機率約為66.7% (12/18)。
In this project, innovative drought indices are developed to accurately quantify the characteristics of drought events and their possible impacts to the water resources system of the Tsengwen Reservoir of Taiwan. We applied a monotonic test to three fundamental single drought indices, namely reliability, vulnerability and resilience, to demonstrate that indices showing non-monotonic behaviour can potentially give misleading information regarding the effects of drought to water resources systems. We further tested two newly proposed single drought indices, Vuls and Resw, to the study site, of which Vuls showed monotonic behaviour but Resw still behaved non-monotonically, even though in a suppressed manner. Next, we proposed and tested three composite drought indices, sustainability index (SI), drought risk index (DRI) and the water shortage index (WSI), of which only the WSI behaved monotonically. As a result, WSI was applied to investigate the potential impact of climate change to the future drought risk of the study site. On the basis of WSI values derived from runoffs simulated by the modified HBV and a reservoir operation (water balance) model driven with 18 sets of climate changes scenarios of IPCC (2007) statistically downscaled using the MarkSim GCM model, it seems that there is a 20% chance that climate change impact could lead to more severe droughts in the study site. However, under the combined impact of climate change and the effect of sedimentation to the Tsengwen Reservoir, which could decrease its storage capacity by about 12% (i.e., s = 0.88), it seems more severe drought impacts will increase to 2/3 of the 18 test cases.