Research Abstracts 1995-1996: Report No. 96-03

Barbour, P.L. and S.N. Walker, "Climatic Influence on energy Demand and Supply of Renewable Energy Sources," WRC 96-03, 101 pp., $25.00.

Variations in weather and climate have a strong influence on the demand for energy.  What makes the Pacific Northwest (PNW) somewhat unique is that the primary energy resource (hydroelectric power) is also highly dependent on these variations.  An understanding of how these variations influence both the demand and availability of energy is important to effective management of the region's energy resources.  This work focusses primarily on the winter relationships because the entire region experiences a peak in energy demand during the winter months.  An additional summer peak also occurs in many eastern areas.  Energy demand in the region comes from several sources including residential, commercial, industrial and agricultural customers.  the residential and commercial sectors are most dependent on climatic conditions (primarily temperature) and are the only two considered in this work.

Mean patterns of temperature, precipitation, heating degree days, streamflow and snow accumulation are examined and how these patterns vary over time. Spatial patterns of variability show that snow accumulation and temperature variations are more homogeneous than precipitation variation and variations during the cool season appear to be greater for both temperature and precipitation. The cool season is the most critical period for most utilities so this has added consequences. Climate records also indicate the presence of decadal scale “regime shifts” during which climatic conditions change from one set of mean conditions to another. These shifts are observed in most climate and environmental parameters and have important implications to both the demand for electric energy and the supply of renewable energy. For wind energy, most resource estimates have been made using wind data collected after 1976. This is a period of lower storm activity and lower winter winds. These estimates are believed to underestimate the region’s long-term wind resource potential by as much as 10%. These shifts also appear to affect streamflow and the fraction of streamflow available between April through July. The fractional streamflow appears to be as much as 6% lower for the period between 1977 and 1988 than for the period between 1945 and 1976.

Relationships between variables representing energy demand and the availability of resources were investigated. First, lag correlations are examined for individual variables at each climate division throughout the PNW (such as temperature from one season to the next). These show that little or no relationship exists between individual variables during one season and the same season during the previous year (cool season temperature from one year to the next). This suggests that each year can be considered independent. Some correlation exists from one season to the next, especially for temperature. This indicated that temperature during any particular season is partly associated with the temperature that occurred during the previous season. Streamflow during the warm season is also partly associated with the streamflow during the previous cool season. One river, the Salmon River in Idaho showed some unique and high correlations for all seasons.

Second, correlations were computed for cool season streamflow and other quantities over time to assess the contribution of each quantity. Limited association between the cool season streamflow and temperature was found with only a few streams showing significant correlations. High correlations were observed between the cool season streamflow and the precipitation during the simultaneous cool season and with the April 1st snow water equivalent (SWE).Third, correlations for the warm season streamflow showed strong correlation to temperature, precipitation and April 1st SWE during the preceding warm season. This indicates that the warm season streamflow should be much easier to estimate in advance with knowledge of these other quantities.

The seasonal standardized anomalies of temperature, precipitation, streamflow and snow accumulation are examined for periods in which a high demand for energy was observed. Strong negative temperature anomalies are observed during these periods which is expected since the high demand periods were determined partially based on temperature. No special relationships were found in this analysis for precipitation, streamflow or snow accumulation. This reflects the low correlations between temperature and precipitation quantities and illustrates that wet conditions can occur during either below or above normal temperature conditions. Of particular interest are the low correlations with snow accumulations in British Columbia, important because a large portion of the streamflow along the Columbia River can be attributed to sources in British Columbia.

The role of wind energy during years with high energy demand is also examined as well as the availability of wind energy during peak winter cold periods. Results show that wind energy provides little benefit beyond what would normally be expected, however, the two sites in the vicinity of the Columbia River Gorge (Goodnoe Hills (GU) and Kennewick (KN) ) did show positive departures for the months between April and September following years with a high demand during the cool season (October to March). The second element of this work involved an examination of the availability of wind power during critical peak demand times. For peak cold periods, Browning Depot (BD) provides the best overall availability of the sites used. 

Finally, a discussion of climate indices, particularly the Southern Oscillation Index (SOI), and their potential use is presented. An examination of the climatic elements in the PNW associated with extreme phases of the SOI confirms that during the negative phase of the SOI (called El Niño or Warm events) conditions in the PNW are generally found to be dryer and warmer than normal with slightly lower streamflows and less snow accumulation during the cool season. During the opposite phase (La Niña or cold events) the conditions are reversed and the PNW experiences somewhat cooler, wetter conditions with higher streamflow and more snow accumulation. Changes in synoptic weather patterns between these two periods is also discussed.