Climate change and non-stationary flood risk for the Upper Truckee River Basin
Abstract. Future flood frequency for the Upper Truckee River Basin (UTRB) is assessed using non-stationary extreme value models and design life risk methodology. Historical floods are simulated at two UTRB gauge locations, Farad and Reno using the Variable Infiltration Capacity (VIC) model and non-stationary Generalized Extreme Value (GEV) models. The non-stationary GEV models are fit to the cool season (November–April) monthly maximum flows using historical monthly precipitation totals and average temperature. Future cool season flood distributions are subsequently calculated using downscaled projections of precipitation and temperature from the Coupled Model Intercomparison Project Phase-5 (CMIP-5) archive. The resulting exceedance probabilities are combined into a single risk metric using recent developments in design life risk methodologies. This paper provides the first end-to-end analysis using non-stationary GEV methods coupled with contemporary downscaled climate projections to demonstrate how the risk profile of existing infrastructure evolves with time over its design life. Results show that flood risk increases significantly over the analysis period (from 1950 through 2099). This highlights the potential to underestimate flood risk using traditional methodologies that do not account for time varying risk. Although model parameters, for the non-stationary method are sensitive to small changes in input parameters, analysis shows that the changes in risk over time are robust. Overall, flood risk at both locations (Farad and Reno) is projected to increase 10–20% between the historical period 1950–1999 and the future period 2000–2050 and 30–50% between the same historical period and 2050–2099.