氣候變遷對台北市雨水下水道系統之衝擊影響評估

Abstract

台北市區建構有完整的雨水下水道系統，保護眾多生命與財產的安全；近年來，溫室效應造成全球氣候變遷，導致降雨異常，台灣極可能面臨暴雨雨量增幅的衝擊。本研究進行排水系統效能模擬，並且預測未來氣候變遷下的衝擊影響，使系統較有機會進行合適的改善工程與調適策略。 本研究以位於台北市中央區內之古亭排水系統與松山排水系統為研究區域，收集並建構模擬所需水文、地文、排水系統之相關資料，以SWMM雨水下水道模式與二維地表漫地流模式為工具進行數值模擬。全球環流模式能夠推估氣候變遷情境24小時降雨量，然而在推估氣候變遷情境90分鐘雨量的過程中會遭遇時間方面的降尺度問題。本研究利用Horner公式連接24小時與90分鐘降雨量的關係，並推估氣候變遷情境對應之Horner公式，然後得到氣候變遷情境的90分鐘降雨量。 本研究發現降雨量的變化對雨水下水道系統之總溢流體積與地表淹水面積有明顯的影響；若利用總溢流體積與地表淹水面積進行忍受度分析，分析結果皆可觀察到三個階段的忍受度趨勢變化。本研究採取保守觀點選擇降雨增幅最嚴重的HADCM3模式A2情境預估未來氣候變遷，並計算列出短期、中期、長期境況相應之衝擊影響。模擬結果顯示HADCM3模式A2情境對雨水下水道系統人孔溢流與地表淹水的災情有明顯衝擊影響。

Taipei city is well protected by complete storm sewer systems. Recently, global warning has caused climate change, then higher extreme rainfalls and more inundation disasters are expected in the future. As necessary, simulations of storm sewer system and predictions of impact of climate change shall be conducive to improvement of storm sewer systems. In the present study, simulation area is set to be Guting and Songshan storm sewer systems, located in Taipei central area. Hydrologic data, geographic data, and sewer system data are collected for numerical simulation. Tools for numerical simulation are the storm water management model (SWMM) and 2-Dimensional overland flow model. GCMs can produce 24-hour duration precipitation with climate change, but it will have problems of time-scale downscaling when 90-minute duration precipitation with climate change is needed. In order to solve this problem, Horner formula is used to build the relationship between 24-hour duration precipitation and 90-minute duration precipitation, after that Horner formula for climate change situation is estimated, then 90-minute duration precipitation with climate change can be calculated. It is observed that the effect of increasing precipitation on total overflow volume and inundation area is significant. In addition to tolerance analysis, we can find three different phases of tolerance. It shows that the system tolerance would also change with precipitation amount. Because of taking conservative decision, A2 scenario in HADCM3 model is selected to perform climate change analysis. Impact of climate change in 2010 to 2039, 2040 to 2069, and 2070 to 2099 are all calculated and listed. Simulation results show that impact of climate change on storm sewer system is significant on total overflow volume and inundation area.