For the past five years, California has been devastated by an extraordinary drought. The state’s historic drought reached its peak during the summer of 2014, when 58 percent of California was in an exceptional drought. There were high expectations for last year’s ‘Super El Niño’ to bring much needed rainfall statewide, but it failed to alleviate the exceptionally dry conditions in southern California and the Central Valley.
SOURCE: MIMIC-TPW2 product: Real-time Product View: Atmospheric River event from January 7 to January 11, 2017.
These conditions persisted through September 2016, which was one of the driest months on record for northern California and the Central Coast. By this month, the statewide precipitation deficit reached just over 26 inches. However, a major pattern change emerged in early October, resulting in drought improvement for portions of northern California. There was also a noticeable uptick in atmospheric river activity that surged through the month, resulting in the wettest October in California since 1962. Several prominent atmospheric river events since then have delivered anomalous precipitation to northern California, including the most recent supplying the southern Cascades and Sierra Nevada with anomalously high snow totals. Record precipitation levels caused major flooding and pushed hydroelectric generation to levels last seen in January 2011.
Meteorological Setup
The overall atmospheric flow through October 2016 displayed a strong correlation with a typical La Niña pattern, where the subtropical jet stream extends from northern California into the northwestern U.S. The combination of a weak La Niña, positive West Pacific Oscillation (WPO), positive North Atlantic Oscillation (NAO), and negative Arctic Oscillation (AO) made for one of the wettest Octobers on record in northern California. The resulting pattern enhanced low pressure systems off the northwestern coast and above-average precipitation over northern California.
November 2016 saw a pattern change with the WPO emerging as the main driver of warmer and drier conditions across California relative to October. The positive phase of the WPO produced strong ridging across the interior U.S., and produced far-fewer atmospheric river events than the previous month.
A great deal of volatility in temperature and precipitation occurred in December 2016, as well as an uptick in atmospheric river event frequency. The Pacific-North America (PNA) pattern trended negative through most of the month, which allowed troughing to extend into California. Several atmospheric river events resulted in as much as nine inches of liquid precipitation falling in the northern Sierra Nevada.
The wet weather continued through early January 2017 with four strong atmospheric river events as of January 23. The event on January 8 to 9 packed a powerful punch and was followed by another atmospheric river event on January 11 to 13, where as much as 12 inches of liquid precipitation fell over 72 hours in parts of northern California. Soil across most of northern California was saturated by late December and exorbitant rainfall led to increased flooding. Between January 3 and 10, exceptional drought had been reduced by 16 percent. Additionally, on January 13, snow at the summit of Mammoth Mountain reached over 19 feet.
January Deluge: A Lot of Dam Potential
Anomalous precipitation since the beginning of January 2017 has had a profound impact on hydroelectric generation in California. Between January 4 and 13, 16.8 inches of liquid precipitation fell at Huntington Lake, one of the primary reservoirs that comprise the Big Creek Hydroelectric Project. Genscape generation monitors at Big Creek, which supplies roughly 90 percent of Southern California Edison's (SCE) total hydro power, showed a surge in output January 5, rising steadily through January 8 and reaching nearly 700 MW (70 percent of capacity). Strong generation persisted through January 17.
As California’s water supply has been steadily increasing, forward NP and SP prices have been decreasing. With much healthier storage in reservoirs, coupled with above average snowpack in the southern Cascades and northern Sierra Nevada, there will be ample runoff for hydroelectric generation in the coming months. This will not only displace thermal generation for baseload power, but it will also increase the ramping capabilities of the supply stack in California before we see peak runoff.
When the spring season approaches from April to June, hydro runoff is likely to be powerful throughout the entire day, hindering its flexibility to ramp up to higher levels during the morning and evening peaks. This will have a negative effect on CAISO’s ramping problems as hydro generation displaces flexible thermal units, while not being able to significantly alter the shape of their output. Then after the peak runoff season, hydro generation will be able to ramp down to lower levels in the middle of the day again, becoming an overall benefit to CAISO’s ramping. This results in there being greater price volatility during the spring runoff period. Additionally, Genscape’s NatGas Basis Commentary Report published on January 17, 2017, discussed the bearish impact of increased hydropower on western natural gas prices.
Above average precipitation since October has the potential to make the 2017 Water Year (WY) the new benchmark for strong monthly hydroelectric generation. There are noticeable similarities between WY2011 and WY2017, where both water years began with some of the wettest Octobers on record. WY2017 surpassed the WY2011 monthly average by only a tenth of an inch. While November of WY2011 received slightly more precipitation, December was the wettest since 1955 receiving more than nine inches of liquid precipitation.
The anomalous precipitation so far this month is expected to result in ranking as one of the top five wettest Januarys on record. Despite above-average freezing levels, snow-water equivalent currently averages roughly 170 percent of normal in the Sierra Nevada and has surpassed levels seen in 2011. While February is expected to trend warmer, runoff from a substantial snowpack will aid in propelling above-average generation. Going forward, February 2017 average hourly generation in California is forecast to surpass February 2011 levels.
Precipitation returns to California in February and increases through March, will set March 2017 average hourly generation closely in line with March 2011. Temperatures through the spring will have a large impact on the generation peak, and there is slight downside risk to summer hydro generation if warmer temperatures lead to an early runoff season. Should our expectations for seasonal precipitation through spring verify, there is a high probability that WY2017 becomes the new benchmark.
Drought conditions and heavy rainfall can have a direct impact on power and transmission generation. As California has been hit with record precipitation levels during January 2017, being able to understand and track the rainfall can assist market participants with trading or business decisions. Click here to learn more about Genscape’s Power Market Services.