Potential Climate Change Impacts in the San Francisco BayDelta Estuary and Watershed Noah Knowles, U

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Potential Climate Change Impacts in the San
Francisco Bay-Delta Estuary and WatershedNoah
Knowles, USGS Menlo Park

• Hydrologic impacts of warming
• Runoff-driven estuarine changes
• Sea level rise and inundation risks
• Combined impacts of hydrologic and sea
  level changes in Delta

The Bay-Delta watershed
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Multiple climate models project a range of
possible futures.
A strong majority of these projections fall
within relatively narrow ranges.
Figures courtesy Mike Dettinger
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A 1.6C warming would diminish snowpacks by about
1/3rd and shift runoff timing earlier.
Knowles and Cayan, 2002
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A key challenge will be mitigating the impact on
Delta flows.
2060 Delta flows 2000 Delta flows
Knowles and Cayan, 2004
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An altered Delta outflow pattern would result in
increased salinity intrusion.
Knowles and Cayan, 2004
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Sea level has been projected to rise 20-90cm by
2100, but those estimates could be conservative.
projections
observed
Envelopes of modeled global sea level rise from
several GHG emission scenarios
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To study inundation risks associated with SLR, we
needed highly accurate elevation data.

• Patchwork of datasets, based mainly in
  photogrammetry and LIDAR
• 10-30 cm vertical accuracy
• Horizontal resolution 1-5m
• Work by Tom Coons, USGS (funded by CALFED)
• Napa R. watershed provided by Bill
  Dietrich and Ionut Iordache, UCB
• no longer missing Petaluma R., Suisun marsh
  elevation data
• Preliminary Delta LIDAR data courtesy of
  Joel Dudas

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A 1.0m sea level rise would put an additional
150 km2 at risk of monthly inundation
(red). Existing shallow-water habitats and
intertidal ecosystems would also be threatened.
below present mean water level
below present monthly mean high tide
below monthly mean high tide with 1.0m sea
level rise
Most of these areas are currently protected by
levees. They would be inundated only if those
levees fail or are overtopped.
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below present mean water level
In the Delta, about 300 km2 would be newly at
risk of monthly inundation under a 1.0 m sea
level rise (red).
below present monthly mean high tide
below monthly mean high tide with 1.0m sea
level rise
Most of these areas are currently protected by
levees. They would be inundated only if those
levees fail or are overtopped.
A key concern is the increased pressure on the
levee system due to sea level rise and
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Increased winter runoff, if unmitigated, would
lead to higher Delta flood peaks.
Knowles and Cayan, 2004
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below present mean water level
In the Delta, about 300 km2 would be newly at
risk of monthly inundation under a 1.0 m sea
level rise (red).
below present monthly mean high tide
below monthly mean high tide with 1.0m sea
level rise
Most of these areas are currently protected by
levees. They would be inundated only if those
levees fail or are overtopped.
A key concern is the increased pressure on the
levee system due to sea level rise and
higher winter flood peaks.
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• Summary
• Most climate models project 2-6C warming and
  little precipitation change by 2100 in
  Northern California.
• This would lead to dramatic reductions in
  snowpack and earlier runoff to reservoirs.
• If mitigated only partially, this would lead to
  higher winter flood peaks and reduced
  dry-season flows.
• Sea level rise would combine with runoff changes
  to produce increased salinity intrusion in
  the Bay and increased risk of levee failure
  in the Delta.