![](media/image1.jpeg){width="1.9326388888888888in"
height="1.4479166666666667in"}**Long-Range Hydropower Forecasts for the
Columbia River, Colorado River, and Sacramento/San Joaquin Systems**

Alan F. Hamlet

Andrew Wood, Nathalie Voisin , Dennis P. Lettenmaier,

Tony Westerling, David Pierce, Tim Barnett

> *JISAO/CSES Climate Impacts Group*

*Department of Civil and Environmental Engineering*

*University of Washington*

*Scripps Institution of Oceanography*

*California Energy Commission*

**[Background]{.underline}**

**Effects of the PDO and ENSO on Columbia River Summer Streamflows**

In the Pacific Northwest, we have known for a long time that the ENSO
forecast has considerable effect on the probability distribution of the
stream flow. The following figure shows the natural streamflow at the
Columbia River in Dalles, which is down to the bottom of the basin, from
April to September.

![](media/image2.png){width="3.1972222222222224in"
height="2.509027777777778in"}

The source of the water is the snow pack in the basin. It essentially
stores winter clime variability that comes out of the basin in
summertime. We see the step changes in the long term mean that are very
well lined up with the decadal variability associated with the PDO. We
also see variations from year to year that are reflected in the ENSO
variability. If we just look at all the red dots (the warm ENSO events)
as a whole we might not see too much signal, but when you look at each
of these bins, the red dots are in the lower 2/3 of these bins pretty
much in a consistent way. So, if we count the shift of the long term
mean, ENSO does a nice job of giving you a shift of probability
distribution. It does pretty much the same for La Nina years that the
blue dots are mostly in the upper 2/3 of those bins.

**Value of Long-Range Streamflow Forecasts for Pacific Northwest (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.

Reference: 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 91-101

**Pacific NW and SW \~ 8000 MW Intertie**

![](media/image3.wmf){width="1.6347222222222222in"
height="2.076388888888889in"}**Capacity**

This is an inter-connected system that permits certain amount of energy
to be moved around.

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.

We are going to explore how the climate feeds into both active and
passive decision processes regarding how much energy moves across the
system.

**Baseline: Covariation of Normalized PNW and CA Hydropower Production**

![](media/image4.wmf){width="3.2618055555555556in"
height="1.5506944444444444in"}

The two time series co-vary pretty strongly, especially in the last
thirty years, when the precipitation across the entire the west has
become extremely synchronism which is going to very large red noise
swing. It affects the entire west as a whole.

Reference: Voisin, N., A. F. Hamlet, L. P. Graham, D. W. Pierce, T. P.
Barnett, and D. P. Lettenmaier, 2006: The role of climate forecasts in
western U.S. power planning, Journal of Applied Meteorology (in press).

**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. (having a lot of water
    associated with high energy demand)

```{=html}
<!-- -->
```
-   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). Even longer lead times may be possible.

> Below Normal NPO (MAM) = lower Cooling Degree Day (CDD) in S. CA.
> (JJA)

Above Normal NPO (MAM) = higher CDD in S. CA. (JJA)

-   Load is *out of phase* with PNW water availability.

**Probability of Exceedance for Spring Surplus Energy Resources in the
PNW**

![](media/image5.png){width="3.2465277777777777in"
height="2.495138888888889in"}

The figure shows the composite exercise for the transferable energy
resources for April to July. For example, in El Nino years of that data
time period, we can achieve 4000 AMW at only 25% of time, whereas in La
Nina years maybe at \~80% of time. That is a very big split between
those two effects. There are benefits to transfer energy across. Even in
the passive management sense this is very useful information.

Voisin, N., A. F. Hamlet, L. P. Graham, D. W. Pierce, T. P. Barnett, and
D. P. Lettenmaier, 2006: The role of climate forecasts in western U.S.
power planning, Journal of Applied Meteorology (in press).

**A Forecast Timeline -- Mitigate potential capacity problem for
California**

Integrated management idea: On \~June 1 we have:

-   Current Reservoir Contents (PNW and CA)

```{=html}
<!-- -->
```
-   Current Summer Streamflow Forecast (PNW and CA)

```{=html}
<!-- -->
```
-   ENSO forecast

-   PDO forecast

Forecasts:

![](media/image6.png){width="3.1951388888888888in"
height="1.0854166666666667in"}

**Overview of Research Objectives**

-   Validate hydropower simulation approaches using several levels of
    model complexity

-   Produce long retrospective simulations of hydropower for the three
    major western hydropower systems (PNW, CA and Colorado)

-   Produce ensemble streamflow and hydropower production hindcasts
    using methods comparable to the UW West-wide forecasting system

-   Understand the nature of both physical and water management
    constraints on energy transfers in the West

-   Understand the capability to use both "passive" and "active"
    management frameworks using climate-driven hydropower and load
    forecasts as decision support inputs

**[Tools and Methods]{.underline}**

**Overview of Forecast Approach**

![](media/image7.png){width="3.2847222222222223in"
height="2.392361111111111in"}

**UW West-Wide Seasonal Hydrologic Forecast System**

![](media/image8.png){width="3.1930555555555555in"
height="2.0680555555555555in"}

**Evaluation of VIC Streamflow Simulations**

![](media/image9.png)

![](media/image10.png){width="3.25in" height="3.5375in"}

The system does a good job simulating the stream flow. The model was
calibrated from 1950 forward. Looking backward we can see our driving
data is quite reliable.

**ColSim Reservoir Model**

![](media/image11.jpeg){width="2.8513888888888888in"
height="2.9541666666666666in"}

The model is used for interannual forecast, looking at forecasts,
reservoir storage and hydropower production on an ensemble basis. It is
fed by the west-wide system. The following is the forecast for 2005.

**All Years from 1950-2003 for which Jan Nino3.4 Anom. \>= 0.2 AND
\<=1.2**

![](media/image12.png){width="3.4472222222222224in"
height="2.283333333333333in"}

**Sources of Long-Lead Hydropower Forecast Skill (July 1 Forecast
Date)**

![](media/image13.png){width="3.1958333333333333in"
height="2.2381944444444444in"}

**Sources of Long Lead Hydropower Forecast Skill (April 1 Forecast
Date)**

*Importance of the hydrological initial condition because of the snow on
the ground*

![](media/image14.png){width="3.1958333333333333in"
height="2.2381944444444444in"}

0 : quite a bit of skill or strong effect

o: certain amount of skill or minor effect

?: not sure