The Impact of the Delta Change Approach on the Severity of Ice-jam Flooding Under Future Climate Scenarios

Abstract Projection of the impact of future climate on ice-jam flood intensity is an essential component of a flood mitigation strategy for many northern communities. General Circulation Model (GCM) outputs are used to derive hydrological conditions under future climate scenarios. Although GCMs are often downscaled to a point of interest, there can still be significant differences between modelled climate scenarios and historically observed climate scenarios. Therefore, the model-indicated changes between baseline and future values of climatic scenarios are applied to observed baseline values to estimate projected future values. This can be carried out by using the delta change method which is an approach for adjusting GCM output. This study evaluates the impact of the delta change method on the frequency and severity of ice-jam flooding under a future climate scenario. The Athabasca River at Fort McMurray is presented as the test site. Streamflow conditions were derived from a physically-based hydrological model, Modélisation Environnementale communautaire-Surface Hydrology (MESH), by forcing the Canadian Regional Climate Model (CRCM) driven by the Third Generation Coupled Climate Model (CGCM3) for both baseline (1971–2000) and future (2041–2070) periods. Streamflow under future climatic conditions was developed based on the delta change method for both absolute and relative changes. The adjusting streamflow was then used in a fully dynamic river ice hydraulic model, RIVICE, to project future ice-jam scenarios using a stochastic modelling framework. Finally, the impact of the delta changes on the frequency and severity of simulated ice-jam flooding was assessed by producing ice-jam stage-frequency distributions (SFDs) under future climatic conditions. The results indicate that there is a notable difference in the projected frequency and severity of ice-jam flooding between absolute and relative change approaches.