4.1.2 Lecture - Waterbudgets for Sierra Nevada catchments
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Transcript of 4.1.2 Lecture - Waterbudgets for Sierra Nevada catchments
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Water & Sierra Nevada forestsWhat do we know & what do we not
know?
1. Introduction: Montane water balances
2. Background: Forests and snow3. SSCZO
Martha Conklin,Sierra Nevada
Research Institute, UC Merced
Collaborators: R Bales, UC Merced; S. Glaser, UC Berkeley; & many others
Photo courtesy SSCZO
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1. Introduction: Montane Water Balances & Forests
Image by Jenny Parks, courtesy SSCZO
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Basic annual montane water balance
Precipitation = Evapotranspiration + Runoff
= +
(Evapotranspiration is mainly water use by vegetation)
MODIS-derived map of Sierra Nevadasnow cover, courtesy Robert Rice
Photos courtesy SSCZO
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What elevations provide the most snowmelt?
Fraction of annual snowmelt by elevation band in Merced River basin.From Rice & Bales, 2013.
9000
7000
6000
10000
5000
12000
11000
8000
feet
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Snowpack loss & water storage: 30-yr horizon for the Sierra Nevada
13.5 MAF
11 MAF
14 MAF
Likely loss of ~3.5 MAF of snowpack storage in next 1-3 decades
Sacramento Valley storage San Joaquin Valley storage
snowpack annual storage
MAF: million acre feet Storage data from CA Department of Water Resources
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2. Background: Trees & snow accumulation
Image by Jenny Parks, courtesy SSCZO
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Trees block low-angle winter sun, retarding snowmelt …
… but intercept snowfall, some of which sublimates (< 20%) …
… and emit longwave radiation that melts snow(see tree wells) …
Tree density affects snow accumulation
Photo courtesy SSCZO
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Thinned unit w/ control in backgroundStanislaus-Tuolumne Experimental Forest
Photo by Eric Knapp, USFS
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Measuring forest effects on snow accumulation
1200 measurements
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3. UC Research: Forest Evapotranspiration & Runoff
Image by Jenny Parks, courtesy SSCZO
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University of California catchment field sites
Yosemite NPSNAMP
American R & SNAMP
MODIS image
6001200180024003000Elev., m
San Joaquin Experimental
Range400 m
Shorthair Creek
2700 mCZO P301
2000 m
Soaproot Saddle1100 m
E-W transect of flux towers
CZO sitesFigure courtesy SSCZO
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SSCZO conceptual model
Figure courtesy SSCZO. Pore-to-plot and catena illustrations by Jenny Parks.
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3 headwater catchments w/ stream gauges & water-quality measurements
2 met stations60-m tall flux tower60-node wireless embedded
sensor network214 EC-TM sensors for
volumetric water content113 MPS sensors for matric
potential57 snow-depth sensorsMeadow piezometers & wellsSap-flow sensors
Providence Ck (2100 m) – instrumentation
Figure courtesy SSCZO
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Drilling, deeper wells, additional geophysics
in progressPhotos courtesy SSCZO
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Seismic survey results at Providence
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Evapotranspiration (ET) across a Southern Sierraelevation transect
Mid-elevation forests show neither summer nor winter shutdown: ̶Q deep rooting & resiliency to moisture stress ̶Q warmer canopy-level temperatures despite snow
From Goulden et al., 2012
ET, ft
per
yea
r
1
2
3
Oak savannah
Mixed conifer
Red fir
Elevation, ft0 3000 6700 10,000
Winter dormancy
Summer moisture
deficit
Sweet spot for mixed conifer
Photo courtesy SSCZO
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Jun Jul Aug Sep
Monthly dry season evapotranspiration at mixed conifer site (Providence Creek)
~7000 ft elev.
After Goulden et al., 2012, courtesy Roger Bales
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Jun Jul Aug Sep
Monthly dry season evapotranspiration at mixed conifer site (Providence Creek)
~7000 ft elev.
The trees are moisture stressed & are vulnerable to insects, disease & fire starting in 2012
After Goulden et al., 2012, courtesy Roger Bales
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Precip based on
PRISMRunoff by difference
Fraction of runoff by elevation band
From Goulden & Bales, 2014
Rain-snow transition
ET extended using satellite
indices
Kings River Basin: Precip = Evapotranspiration + Runoff
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What we know: science 1. Vegetation removal generally results in more runoff, initially2. Vegetation regrowth means less runoff3. Clear cutting or wildfire means more sublimation & earlier
snowmelt – runoff could go up or down4. Less-dense forests (up to a point) can retain snow longer and
are more fire-resistant.5. Colder, snow-dominated areas produce more runoff that
lower, rain-dominated areasPath forward: Water Security1. Sustained forest management that provides measurable
benefits for water supply & forest health will require investment, verification, & maintenance
2. Better information is a critical foundation for water security, especially in a warming & more-variable climate