DEVELOPMENT OF EXTREME RAINFALL INTENSITY-DURATION-FREQUENCY RELATIONS AT UNGAGED LOCATIONS IN THE REGIONAL CLIMATE CHANGE CONTEXT

Climate change has been recognized as having a profound impact on hydrologic processes. Consequently, there is an urgent need to assess this impact on the extreme rainfalls (ERs) for hydraulic structure design. The key challenge is how to develop the linkage between global-scale climate change information and the short duration ERs at a given local site of interest. In addition, several existing approaches have been proposed to establish this linkage at "gaged" sites but very few methods are available for linking climate change projections to the ERs at an "ungaged" location where rainfall record is limited or unavailable. Therefore, the main objective of this study is to propose an innovative approach that could be used for constructing reliable IDF relations at an ungaged location in consideration of climate change projection uncertainty given by different climate models. The proposed approach consists of a regional-to-point downscaling to link daily regional rainfalls to daily extreme rainfalls at a given ungaged site and a temporal downscaling using the scale-invariance GEV model to link daily-to-sub-daily extreme rainfall distributions at the same location. Results of an illustrative application using the 25-km regional rainfall data downscaled from 21 global climate model outputs and the observed extreme rainfall data from a network of 84 raingages located in Ontario region (Canada) have indicated the feasibility and accuracy of the proposed method.