[env-trinity] SF Chronicle- Why water levels remain low at one major California reservoir, even after rain

[Tom Stokely]

While I'm sure some of the factors that the quoted people in this article
talk about are true, they fail to recognize that Trinity Lake is twice the
size of the average annual runoff, so refill is slow.

TS

https://www.sfchronicle.com/climate/article/california-drought-water-level-17872187.php
Why water levels remain low at one major California
reservoir, even after rain
Claire Hao
Updated: April 1, 2023 9 p.m.


After an extraordinarily wet winter, most reservoirs in California are at,
over or
near their historical average capacity.
But there’s a major exception: Trinity Lake, in far northern California,
the third largest
reservoir in California behind Shasta and Oroville reservoirs. Trinity is
only at 51% of its historical average capacity — and 37% of capacity
overall — as
of April 1, according to data from the Department of Water Resources.
Lewiston Dam is on the Trinity River, which has received less rainfall than
other parts of the state.

Trinity may be filling slower than other reservoirs because the northernmost
part of the state has received less rainfall relative to other parts of the
state,
according to Jeffrey Mount, senior fellow with the Public Policy Institute
of
California Water Policy Center.
Additionally, Trinity “is heavily dependent on snowpack; versus Shasta,
which is
mostly dependent on rainfall to fill,” Mary Lee Knecht, Bureau of
Reclamation
Region 10 public affairs officer, wrote in an email to the Chronicle. Much
of the
snowfall may not melt and flow into the reservoir until late spring or
summer,
according to the Trinity River Restoration Program.
According to a closely watched map from the U.S. Drought Monitor, the
northernmost parts of the state continue to remain in “moderate drought” in
counties such as Siskiyou, Modoc, Lassen, Shasta and Trinity, with interior
parts
of Northern California also remaining “abnormally dry.”
Gov. Gavin Newsom rolled back some drought restrictions last week but said
he
didn’t revoke his drought emergency proclamation because of persistent
dryness
in certain parts of the state.
“It is incumbent upon us to recognize that the conditions have radically
changed
throughout the state, but not enough in places like Klamath and around the
Colorado River Basin to call for the end of the drought in California,”
Newsom
said at a news conference last month.
The parts of the state that remain dry are also usually arid areas: The
northeast
corner of California is known to be a rain shadow, whereas the southeast —
where drought also persists — is desert, Mount said. The southeast corner of
California also gets much of its precipitation from summertime monsoon rains
instead of winter storms, Mount said.
Inyo, San Bernardino, Imperial and Riverside counties remain in “moderate
drought,” with parts of Inyo and San Bernardino counties in “severe
drought,”
according to the U.S. Drought Monitor.
Most of the atmospheric rivers that hit California since December have been
concentrated in the Bay Area and Central Coast, with some also hitting the
Los
Angeles region, Mount said, referring to a map of atmospheric rivers from
the
UC San Diego Institution of Oceanography.
Few, however, have been directed at the Klamath Basin, with many landing
just
north or south of the region or brushing against it, Mount said. Trinity
Lake is
part of the Klamath Basin, with Trinity River being the largest tributary
of the
Klamath River.
“For what you might call the luck of the draw, just enough of those
atmospheric
rivers shifted a couple hundred miles to the south this year rather than
plowing
into their normal location, which would be in the Trinity, Klamath watershed
and Shasta and upper Sacramento. So we’ve got one of those years where we
turned our normal gradient of precipitation — dry in the south, wet in the
north
— and flipped it so that our far north was not particularly wet,” Mount
said.
But even areas of California that on paper are out of drought will still
feel the
effects of long-term water supply problems. The Drought Monitor can be
“notoriously unreliable” for California because it doesn’t take into account
groundwater conditions — which have been slow to recover despite winter’s
deluges — and the fact that California transports water across the state to
meet
local needs, according to Mount.

Even if “the drought is largely over, water scarcity is enduring,” said Jay
Lund,
vice director of the UC Davis Center for Watershed Sciences. That remains
true
in the San Joaquin and Sacramento valleys, where it may take years for
groundwater to recover from the overpumping during drought years.
It also remains true in the Klamath Basin, where contentious debates about
water use between agriculture and ecosystem preservation, which the drought
exacerbated, won’t be alleviated soon, Lund said.
“Tribes want to see lots of releases of water for salmon. Farmers are
really seeing
very little water from the projects because … of tremendous changes that are
going to be occurring with the removal of some of the hydropower dams. It’s
just
a lively place for water conflicts,” Lund said.
Why water levels remain low at one major California reservoir
https://www.sfchronicle.com/climate/article/california-drought-water-le...

To the south, in San Bernardino County, Heather Dyer, CEO of the San
Bernardino Valley Municipal Water District, is not ready to declare the end
of the
drought either. The water district’s service area has received 56.9 inches
this wet
season, above the historical average of 31.1 inches, she said.
Still, when looking at the pattern of rainfall over the past 20 years, this
year’s
above-average total hasn’t made up for the cumulative loss of precipitation
the
region has suffered since 1997, Dyer said. The district’s cumulative
departure
from the mean since then has trended downward, with wet years like this only
marginally shifting the marker upward, she said.
“To me, being in a drought is basically the cumulative amount of rain over
time,
and what that means to our ecosystems and our water systems,” Dyer said.
“It’s
going to take more than one wet year to get out of that hole.”
In anticipation of future dry years, the San Bernardino Valley Municipal
Water
District is starting construction on a new stormwater capture project in
April,
which Dyer estimates will take 18 months to complete.
“I wish we had that in place. I wish that many water agencies had those
types of
systems in place,” she said. “I feel like this has given me a new sense of
urgency
that we need to be building infrastructure for the future, and this year is
exactly
why we need to do that.”
Reach Claire Hao: claire.hao at sfchronicle.com; Twitter: @clairehao_
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