Abstract
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 to calculate the probability of a flood of a given magnitude occurring over a specific time period (referred to as flood risk) 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 the evolution of a flood risk profile over typical design life periods of existing infrastructure that are vulnerable to flooding (e.g., dams, levees, bridges and sewers). 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 to 1999 and the future period 2000 to 2050 and 30–50% between the same historical period and a future period of 2050 to 2099.
Highlights
This section provides background on the study area (Sect. 2.1), streamflow data and simulations (Sect. 2.2) and climate data and models (Sect. 2.3).2.1 Upper Truckee River basinThe Truckee River originates in the northern Sierra Nevada in California and flows northeast to Nevada, where it ends in the Pyramid Lake (Fig. 1)
While the methodology used for this analysis is previously established, this paper provides the first end-to-end demonstration of non-stationary Generalized Extreme Value (GEV) analysis coupled with contemporary downscaled climate projections to quantify how the flood risk profiles may evolve in the upper Truckee River basin over the 21st century
We observed no clear trend in flood risk based on the different representative concentration pathways (RCPs). This indicates that, for this flood statistic in this basin, the variability between global circulation model (GCM) model form and initial conditions likely overwhelms the influence of greenhouse gas emissions when comparing between scenarios. We caution that this is not a general finding, for this application we show that the variability between projections within any RCP scenario is larger than the difference between RCP scenarios
Summary
We provide background on the study area (Sect. 2.1), streamflow data and simulations (Sect. 2.2) and climate data and models (Sect. 2.3).2.1 Upper Truckee River basinThe Truckee River originates in the northern Sierra Nevada in California (above Lake Tahoe) and flows northeast to Nevada, where it ends in the Pyramid Lake (Fig. 1). The total basin area is roughly 7900 km; the area upstream of Reno (2763 km2), referred to as the upper Truckee River, provides the majority of the basin’s precipitation through snowpack. The focus of this analysis is on the Farad and Reno gauge locations shown, referred to as Farad and Reno. The Farad gauge is located roughly 1.5 km downstream of the Farad hydropower plant and provides a cumulative measure of all of the upper basin tributaries (Stokes, 2002). The intervening area between the Farad and Reno gauges is small, roughly 350 km2 [km], and there are only two small tributaries that enter the main stem between Farad and Reno
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