Atmospheric Rivers
Continued from page 29
storage levels are in the water supply pool.
WCM operating procedures call for wa-ter
to be stored during a rain event until
the storage level encroaches into the flood
control pool. At this storage condition,
the Army Corps releases water from the
reservoir as quickly as possible, consid-ering
ramping rates designed to protect
juvenile salmonids from stranding due
to rapid changes in river stage. The rule
curve provided in the water control man-ual
(shown as “storage curve” in Figure
1 is the specified elevation for an upper
volume of reservoir storage that must be
kept available for capturing storm runoff
and reducing flood risk and a lower vol-ume
of storage that may be used for water
supply) is predicated on typical historical
weather patterns as understood at the time
of its development in the late 1950s. It does
not account for the increased variation in
weather patterns the watershed may be
experiencing or reductions to in-flows.
As a result, the water supply reliability of
Lake Mendocino is affected, significantly
impacting municipal and agricultural wa-ter
users, as well as the endangered coho
salmon, threatened steelhead trout, and
Chinook salmon.
Following an atmospheric river-type
storm in December 2012, for example,
water released to create flood control
space dropped the reservoir by more
than 35 percent. The following year
was the driest on record, and the lack of
precipitation resulted in little inflow to
refill the reservoir. By December 2013,
levels were extremely low and remained
low through 2014. As a consequence,
SCWA was required to petition the
California State Water Resource
Control Board on several occasions for
Temporary Urgency Change Orders to
reduce minimum in-stream river flows
to as low as 25 cubic feet per second.
Hypothetically, accurate precipitation
forecasts could have allowed some of
the water from the December 2012 event
to have been retained as a precaution
against subsequent drought.
The three-part goal of the Lake
Mendocino joint project is to help define
the role of atmospheric rivers in recharging
Lake Mendocino, increase precipitation
predictability, develop protocols for
44 SOURCE winter 2017
Figure 1. Rationale for FIRO: In the 2012 water year, rainfall occurred at the “right” time of year, i.e., when
the storage maximum is rising. In water year 2013, significant rainfall occurred in December and had to
be released according to the designated storage maximum. However, after the December 2012 rainfall, no
additional rain fell for over one year. Courtesy Jay Jasperse.
retaining water in the reservoir without
increasing flood risk, and potentially
increase flood protection without risking
water supply. Specifically, the project will
assess the feasibility of Forecast Informed
Reservoir Operations (FIRO). A steering
committee of representatives from each of
the partnering organizations has developed
a work plan describing current technical and
scientific capabilities, outlining technical
and scientific analyses, and future efforts
that will be needed to demonstrate the
potential of FIRO for improving reservoir
management. If the approach proves to
be a successful water management tool, it
will likely be implemented incrementally
as science evolves and implementation
criteria are met.
Specifically, the FIRO work plan con-sists
of the following steps:
1. Develop evaluation criteria and
methodology.
2. Develop evaluation scenarios.
3. Identify science needs and carry out
necessary research projects.
4. Evaluate model results.
5. Evaluate preliminary FIRO viability
and assess benefits.
6. Develop implementation strategies.
A preliminary viability assessment is
scheduled for release in Spring 2017. For
more information, see scwa.ca.gov/reser-voir-
operations/ and cw3e.ucsd.edu/FIRO/.
The frequency and strength of AR
events in a given region over the course
of a typical West Coast wet season greatly
influence droughts, floods, human activ-ities,
and ecosystem health. Better cou-pling
of climate forecasts with seasonal
weather forecasts of ARs has the potential
to improve water management outcomes.
Long-term monitoring using satellite
measurements, offshore aircraft recon-naissance,
and land-based atmospheric
river observatories, combined with better
numerical modeling, scientific progress,
and the development of AR-based smart
decision aids for resource managers is be-ing
explored so as to potentially enhance
water supply reliability, enable society to
be more resilient to storms and droughts,
and safeguard critical ecosystems. S