Background and Motivation

ENSO (El Niño Southern Oscillation) the water year for which the December to February Sea Surface Temperature in the NINO 3.4 region exceeds 0.5 standard deviations above its long-term ( ) mean value. ENSO is classified in three states:  Warm (El Niño)  Neutral  Cool (La Niña) A Warm ENSO year :

The effects of ENSO on PNW winter climate Warm ENSO (El Niño) : winters tend to be warmer and drier than average. Cool ENSO (La Niña) : winters tend to be cooler and wetter than average. Source: Climate Impacts Group website

Bonners Ferry Columbia Falls The Dalles The effects of ENSO on flood risk for Columbia River Basin - Warm ENSO - Neutral ENSO X - Cool ENSO

The effects of ENSO on storage deficits

Objective:  Develop ENSO conditioned Flood Control Curves by Rebalancing Flood Control and Reservoir Refill Flood Control Refill

Test Case: The Columbia River Basin Multi-objective Reservoir System  Flood Control  Hydropower  Instream Flow  Water Supply  Recreation  Navigation The Dalles Columbia Falls Bonners Ferry

Method : Optimization – Simulation Method Optimization Model Develop Optimized Flood Control Curves Simulation Model Test and Refine Proposed Rule Curves Hydrologic Model Generate Streamflow for 20 th Century

VIC Hydrologic Model  Macroscale Hydrologic Model developed by University of Washington which simulates energy and water balance at large scale at 1/8 degree (Approximately 50 mi 2 / Cell) (Variable Infiltration Capacity Hydrologic Model)

 Optimization model developed by the US Army Corps of Engineers  Penalty functions are used to constrain the Columbia River basin system operation Flood control penalties Flood control penalties Storage penalties Storage penalties HEC-PRM (Hydrologic Engineering Center’s Prescriptive Model)

ColSim  Flood control  Hydropower  Irrigation  Instream flow  Navigation  Recreation (Columbia Simulation Model)

Optimization Strategy Adjust Penalty functions Classify Water Years into Each ENSO State Select Penalty Functions for Each ENSO State Generate Optimized Flood Rule Curves for Each ENSO State Evaluate Flood and Refill Statistics using Simulation for Each ENSO state

 - Warm ENSO  - Neutral ENSO X - Cool ENSO Bonners Ferry Columbia Falls The Dalles

Bonners Ferry Columbia Falls  - Warm ENSO The Dalles

Results

Flood Frequency Analysis at Bonners Ferry - Current Flood Control Curves - HEC Flood Control Curves X - ENSO Flood Control Curves Warm ENSO Neutral ENSO Cool ENSO

Flood Frequency Analysis at Columbia Falls - Current Flood Control Curves - HEC Flood Control Curves X - ENSO Flood Control Curves Warm ENSO Neutral ENSO Cool ENSO

Flood Frequency Analysis at The Dalles Warm ENSO Neutral ENSO Cool ENSO - Current Flood Control Curves - HEC Flood Control Curves X - ENSO Flood Control Curves

Storage Deficits Warm ENSO Neutral ENSO Cool ENSO

Flood Control Curves vs. Simulated Storage (a low flow year)

Flood Control Curves vs. Simulated Storage (a high flow year)

Conclusions  ENSO conditioned FC rule curves yield lower storage deficits than Current FC without significantly increasing flood risks  ENSO FC is successfully calibrated using ENSO conditioned flood frequency curves and storage deficit statistics even though each ENSO category has relatively small sample size.

Conclusions  ENSO conditioned FC rule curves yield reduced storage deficits relative to HEC FC  There is no effect of reduced flood space on storage deficits for low flow years because flood control is not the main driver in low flow years.

Conclusions  ENSO conditioned FC rule curves yield reduced storage deficits relative to HEC FC  There is no effect of reduced flood space on storage deficits for low flow years because flood control is not the main driver in low flow years.