How soil moisture impacts water availability
in the Klamath Basin
Klamath Basin’s snowpack is at 85% of what it would be
normally this time of year, there’s already more water
stored in the mountains than last year. So why are Basin
hydrologists projecting another exceptionally dry summer for
Upper Klamath Lake? The answer lies beneath the snowpack—in
a soil scientist with the Natural Resources Conservation
Service, said the amount of moisture present in the Basin’s
soils at the beginning of a water year has a big effect on
how much of that winter’s snowpack becomes available as
“If the soil is
moist already, it’s like a jumpstart,” Gebauer said.
Think of the
soil as a sponge: When it’s dry, it absorbs more water
released from the snowpack in the spring, but when it’s wet,
it allows more water to pass through or over itself. Water
not absorbed by the soil then runs off into streams and
reservoirs or percolates into subsurface aquifers to
Basin soils were parched following an extremely hot, dry
summer, so Gebauer said we can expect them to retain a
significant portion of this winter’s accumulated snowpack
once it melts.
getting soaked up, you’ll have less water getting into the
drainage systems,” Gebauer said.
Dry soils also
take longer to absorb water, so if the snow melts quickly in
the spring, most of it will run off and potentially cause
erosion, and less of it will percolate into aquifers.
Hydrologists are still evaluating how much of the Basin’s
water comes from surface runoff versus springs, but a dry
soil profile isn’t good news either way.
snow survey supervisory hydrologist for NRCS, said the
optimal situation following a dry summer is to have fall
rains that wet the soil enough to saturate it before
snowpack begins accumulating.
“That way, when
springtime comes, we’re holding that water in the soil plus
the available snowpack,” he said.
As a warming
climate makes both summers and winters hotter and drier,
soil moisture has become a major limiting factor for water
availability in the Basin. Over the last several decades,
dry falls have sent the Basin into winter with existing
moisture ‘debt’ it’ll have to pay back in the spring. Oviatt
said some years, like this one, have also seen abnormally
warm soil temperatures to the point where the ground is
above freezing during the winter. That allows the soil to
soak up some melting snow or rain before spring even
It’s a vicious
cycle exacerbated by a warming climate: There wasn’t enough
precipitation last year to saturate soils, and a minimal
snowpack meant that plants in the Basin had to suck up all
the moisture they could from the soil, leaving it bone-dry
at the end of the summer.
with below average precipitation couldn’t replenish those
soils without reducing surface water availability in the
basin, setting it up for yet another dry summer. If fall
rains remain elusive this year, we can expect a similar
situation for Water Year 2022. Dry years beget future dry
multiple years to build drought scenarios, and it takes
multiple years to get out of them,” Oviatt said. “You can’t
just flip a switch.”
sites do record soil temperature and moisture content at
varying depths, Oviatt said that data isn’t being
incorporated into streamflow forecast models yet. That means
there’s no magic number to achieve regarding soil saturation
that will keep the snowpack from being absorbed, and, by
extension, streams flowing at normal rates.
conditions still play a qualitative role in modeling by
informing previous years’ conditions used to predict future
streamflows: Dry (or not wet enough) years that follow dry
years tend to exhibit lower streamflows because they
accumulated moisture on top of dry soils.
look at that based on previous years with similar
conditions,” Oviatt said.
Oviatt said the
Klamath Basin has seen about 75% of normal precipitation
since the water year began in October. The moisture deficit
accumulated by the dry soils mean that even 100% of normal
precipitation will still result in drought conditions,
because a portion of that precipitation won’t make it to
streams or springs.
At this point,
Oviatt said a best-case scenario would be an abnormally
large late-winter snowpack accumulation, or a cool and wet
spring that restores normal streamflows through rains. With
climatologists predicting only slightly above average
precipitation and slightly below average temperatures for
the next few months, it’s not out of the question, but
Oviatt isn’t banking on it.
dream. It’s an unlikely dream,” Oviatt said.
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