Projecting the Impact of Climate Change on Extreme Runoff in the Pacific Northwest

Mohammad Reza Najafi, Western University, Department of Civil and Environmental Engineering, London, ON, Canada and Hamid Moradkhani, The University of Alabama, Department of Civil, Construction and Environmental Engineering, Tuscaloosa, United States

Contact First Author: Mohammad Reza Najafi; mnajafi7@uwo.ca

Previously Published Material: Part of this study is recently published in the journal of Hydrologic Processes however additional assessments will be included (covering basins in Canada) which are not published or presented previously.

Abstract ID#: 35446

 

English Abstract:
Changes in snowpack and snowmelt characteristics caused by warming temperature trends and the increased probability of extreme rainfall, due to climate change, will alter the frequency and intensity of extreme runoff. Understanding these changes is necessary before taking any adaptation plan. In this study the changes in extreme runoff over the Pacific Northwest (PNW) region are assessed based on suite of regional climate model simulations provided by North American Regional Climate Change Assessment Program (NARCCAP). Considering the limited number of available extreme events (30 years of historical/future simulations) the spatial hierarchical modeling framework is used to combine data from different locations to provide a more reliable assessment compared with single point analysis. Seasonal variations are investigated to detect possible shifts in extreme events. RCM output variables including precipitation, maximum and minimum temperature and wind speed are downscaled to 1/8° resolution for the regional assessment. Hydrologic modeling is performed using the Variable Infiltration Capacity (VIC) model and the results of these assessments are then merged using the Bayesian Model Averaging approach. Overall the results show increase in the extreme runoff in the future for most seasons particularly during winter and over the high elevation areas. North of Rockies in particular experiences increase during spring. The reduction of extreme events in most dry areas in summer is also evident. Based on these results substantial shift in the seasonality of peak streamflow is expected from summer to spring in many regions of the PNW.
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