後都市化時期，都市地區的不透水表面使建築基地原始表面之涵養水源能力盡失。維持生態、調節環境的綠色空間被取代，加以氣候驟變下之極端降雨現象，使都市區經常面臨危及生命財產之洪澇急症。在提昇既成下水道系統排水能力有其工程與經濟困難情況下，借鑒他國雨洪管理良方並評估其運用於國內之成效實屬當務之急。 本研究的主要目的為：建立建築基地運用自然排水與屋頂綠化策略時，基地逕流量之評估方式，並藉以比較策略相對於現有基地之逕流量改善。利用美國水土保持局(Soil Conservation Service，SCS)SCS Curve Number法，另外結合台灣屋頂綠化相關研究之降雨、逕流、蒸發散實驗推導值建立逕流計算方法。評估特定氣候條件下建築基地雨洪管理策略配置對逕流削減之影響。 運用屋頂綠化與自然排水策略，設計包含基地現況之四種排水配置方案，模擬方案在台北市三種建蔽率基地降雨逕流削減情形。結果顯示不論是高建蔽率或低建蔽率基地，若利用自然排水，再結合建物屋頂施作屋頂綠化作為半透水之綠化空間成效良好。其中高建蔽率基地，由於有較高比例之屋頂面積，運用屋頂綠化策略時有特別顯著的效果。低建蔽率基地含有較多綠地作為自然排水空間，運用在降低洪峰成效良好。 Green spaces have been replaced by impervious surface at urbanized areas in recent years. This change causes the construction site losing capacity of water conservation. Therefore, even small to medium precipitation events have brought about serious flood damage. However, improvement of storm water sewer system is difficult because of many reasons. In order to address urban flood issue, experience of storm water management alternative for green roof will be addressed and discussed. This study attempts to present an approach to assess runoff mitigation by using the green roof and natural drainage strategies. Parameters derived from experiments of green roof researches in rainfall-runoff are used to build up a runoff modeling methodology. This method is based on Curve Number method established by U.S. Soil Conservation Service. In this study, there are four drainage scenarios, devised by consists of green roof and natural drainage strategies, to simulate three selected building coverage ratios (BCR) with assumed construction area. The results indicate that all cases have the significant effects on reducing the rainfall runoff when green roof and natural drainage are used. Among which, in the high BCR case, green roof will have the particularly significant effects in runoff reduction.