Flood frequency analysis for ungauged sites using a region of influence approach

Abstract A framework is presented for regional flood frequency analysis that is applicable for estimating extreme flow quantiles at ungauged catchments. The methodology uses the Region of Influence (ROI) approach to regionalization and explicitly incorporate a homogeneity test in the process of selecting the collection of stations that comprise the ‘region’ for an ungauged site. The relative merits of the methodology are demonstrated through an application to extreme flow data for sites in Newfoundland, Canada. The new approach is compared with results obtained from regression analysis and is shown to provide improved estimates of extreme quantiles at sites which are considered to be ungauged.