Alan F. Hamlet, Nathalie Voisin, Dennis P. Lettenmaier, David W. Pierce, Tim Barnett Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington Scripps Institute of Oceanography California Energy Commission April, 2005 The Role of Climate Forecasts in Western U.S. Power Planning

Background

Effects of the PDO and ENSO on Columbia River Summer Streamflows Cool Warm PDO Red=warm ENSO Green=ENSO neutral Blue=cool ENSO

Value of Long-Range Streamflow Forecasts for PNW Hydro Marketing ~ $150 million/yr This value is created in part by marketing additional energy in late summer (when energy is more valuable) in expected wet years. Hamlet, A.F., Huppert, D., Lettenmaier, D.P., 2002, Economic Value of Long-Lead Streamflow Forecasts for Columbia River Hydropower, ASCE J. of Water Res. Planning and Mgmt, 128 (2), pp

nsf&v=17EA&e=us&m=100A&c=C1256D71001E0037C1256B E41 ~8000 MW Intertie Capacity In normal or above normal water years in the PNW, net transfers are typically from PNW to CA In below normal water years in the PNW, transfers from CA to PNW can occur in winter and transfers from PNW to CA in spring and summer may be reduced or suspended.

Research Questions: How do hydropower resources in the PNW and CA vary with climate and how predictable are these variations? How does electrical demand vary with climate in the PNW and CA and how predictable are these variations? Are extreme loads predictable? How do supply and demand co-vary in time? How predictable are energy surpluses and deficits in each region? How can we best use this information to maximize the benefits of the PNW - CA electrical intertie?

Tools and Methods

Snow Model Schematic of VIC Hydrologic Model and Energy Balance Snow Model PNW CA CR B GB

Evaluation of VIC Streamflow Simulations

Schematic Overview of CVMod and ColSim Reservoir Models CVMod ColSim Irrigation Dominates Flood Control Winter Hydro Dominate

Evaluation of Daily Time Step Energy Demand Model Demand vs Tmax Model Validation

Daily Peak Demand Models PNW (Nov-March) CA (May-Sept)

Met Data VIC Overview of Simulation and Analysis CVMod ColSim PNW Hydro Sacramento San Joaquin Hydro Statistical Demand Models PNW Demand CA Demand Population Weighted Temperature Time Series Urban Population Data Observed Demand Data

Results

Relationship Between Annual Discharge at The Dalles and Annual Hydropower Production in the PNW

Covariation of Normalized PNW and CA Hydropower Production California hydropower is less than 10% of total CA demand, but may play a significant role in energy trading on short time scales. Transferable energy from the PNW is also about 10%. R 2 =0.541

Predictability of Seasonal Demand in the PNW and CA Winter demand in the PNW is predictable with long lead times via ENSO forecasts: Warm ENSO = lower winter electrical demand Cool ENSO = higher winter electrical load Load is in phase with water availability. Summer demand in CA has been recently demonstrated to be predictable with several months lead time using the NPO (PDO) index in spring (Alfaro et al. 2005). B.Normal NPO (MAM) = B. Normal CDD in S. CA. (JJA) A.Normal NPO (MAM) = A. Normal CDD in S. CA. (JJA) Load is out of phase with PNW water availability.

Nino3.4 Anomaly vs Avg NDJF Peak Electrical Demand

MAM-PDO Index Explains about 20% of the Variance in monthly average TMAX in CA.

Relationship Between MAM avg PDO and CA Daily Peak Load Approximate Threshold of Capacity Problems

Surplus Energy in Spring the PNW is Predictable with Long Lead Times Above normal surplus hydro from the PNW is more likely in cool PDO and cool ENSO years, less likely in warm PDO and warm ENSO years.

Probability of Exceedance for Spring Surplus Energy Resources in the PNW

Simple Monthly Energy Transfer Model AprilMayJuneJulyAugust CA Natural Gas electricity$/MWh59.52 PNW hydropower sale (HHL + load variance) $/MWh (PNW transmission)$/MWh3.39 (PNW high load hour sale (HHL), PNW benefit) $/MWh If surplus energy is available (i.e. system-wide supply > PNW load) then energy can be shipped from the PNW to CA subject to the following constraints. Transferred energy does not exceed the intertie capacity during daylight hours ( instant intertie cap*10 hr*days per month) Transferred energy does not exceed the hydro production at John Day and The Dalles hydro plants Transfer is economically feasible (less cost than gas turbine generation in CA) April Benefits: CA = $36.98/ MW-hr PNW = $18.05/ MW-hr

Apr-July Surplus System Wide Energy Available for Transfer (value is constrained by intertie capacity and the capacity of John Day and The Dalles hydro plants)

Extra Benefits and Costs over April-May-June-July in millions $ CA BENEFIT PNW BENEFIT WARM ENSO13277 PDO13578 ENSO/PDO12069 COLDENSO PDO ENSO/PDO AVG Estimate of Economic Benefits of Current Energy Transfers

Why is transferable energy so much higher in the most recent decades?

Effects of the PDO and ENSO on Columbia River Summer Streamflows Cool Warm PDO Red=warm ENSO Green=ENSO neutral Blue=cool ENSO

Reservoir Storage “Resets” Sys. Storage 80% Sys. Storage 90% Reservoir system storage in the most recent decades has been relatively high, which increases efficiency.

A Forecast Timeline Jun Aug Jun On ~June 1 we have: Current Reservoir Contents ( PNW and CA ) Current Summer Streamflow Forecast (PNW and CA) ENSO forecast PDO forecast CA Demand Surplus PNW Energy for Coming Spring PNW Winter Demand Jan Forecasts:

Two Primary Energy Planning Applications: 1) Predicting Natural Gas Consumption in CA CA hydro and transferable surplus hydro in spring from the PNW to CA represents gas that will not be burned in CA to produce peaking energy in spring and summer. The probability distribution of this number is known with about 12-months lead time. Because CA and PNW hydro are typically in phase the effect is typically amplified. 2) Changes in Water Management in the PNW Releases of water in late summer are at a premium in the PNW. Using streamflow forecasts, an available energy pool can be estimated that will not jeopardize reservoir refill in spring. Power from this pool could then be sold to spot market customers in CA depending on their needs. This effective transfer of energy from the coming spring to the current summer would benefit the PNW in terms of achieving more reliable fish flows in late summer and higher power revenues on average. Such actions would not reduce drought risks to fish (no energy to ship to CA). CA would almost always produce a marginal economic benefit by buying power from the PNW, but since the net $ benefit to CA is higher in spring than summer, CA would not necessarily want to trade spring energy for summer energy.