How bad is climate change going to impact water delivery?

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How bad is climate change going to impact water
delivery?
Kevin Richards and K.T.Shum, EBMUD - California
Water and Environmental Modeling Forum Annual
Meeting, 2004
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Known facts about climate change

• Average global surface temperature has increased
  by 0.6C since the late 19th century.
• Evidence of reduction in Artic sea ice and
  continental glaciers.
• 1.0 to 2.0 mm/yr of global average sea level rise
  during the 20th century.

Likely reductions in California water supply
Most global climate models estimate an average
increase of at least 2oC over the next century
under business-as-usual scenario. This could

• Reduce spring snowmelt ? increase need for water
  storage in reservoirs
• Increase urban water use, increase evaporation
  and evapotranspiration
• Etc.

But by how much?
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Some quantitative results on potential water
delivery impacts in California

• Warming (i.e. early snowmelt)
• Preliminary studies using CALSIM II, Bardini
  et.al. 2001
• 20th century diminishing snowmelt trend extended
• 2.5 reduction in total CVP/SWP exports during
  1928-34 drought
• Preliminary studies using EBMUDSIM, Richards 2003
• Shift 28 of historical Apr-Jul runoff to Nov-Mar
• lt1 reduction in Mokelumne deliveries during
  1928-34 drought
• Reduced precipitation
• Brekke et.al. 2003
• PCM scenario w/ 13 reduction in San Joaquin
  River region annual runoff
• Negligible reduction in dry-year deliveries to
  east-side contractors 14 reduction in dry-year
  deliveries to west-side contractors (Delta
  exporters)
• Richards 2003
• 10, 20, 30 reduction in annual runoff
• 4, 6, 12 reduction in dry-year deliveries to
  Mokelumne water users

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Not many, and by not as much. Why?
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Some apparent reasons for relatively small water
delivery impacts simulated

• Use of historical hydrology
• Climate models project long term trends and may
  not account for all critical factors influencing
  climate variability (year-to-year and
  month-to-month).
• Most of the studies utilize a climate change
  forecast superimposed on the 20th century
  hydrologic sequence. This presents no new
  information about potential climate variability
  and more critical hydrological sequences.
• Smart flood control
• Models (e.g. EBMUDSIM) know when to begin
  reservoir refill according to how much snowpack
  remains in the watershed.
• Depending on the systems rainflood requirements,
  there is enough snowmelt to refill in all but a
  few years of the historical record due to a 28
  shift of runoff.
• If those years were to precede a critical drought
  then results could be more substantial The
  sequence of wet and dry years is important!

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What are some alternate approaches?
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Focus on critical factors affecting water
delivery

• Climate research and modeling
• Climate variability Quantify linkage between
  precipitation and major drivers (e.g. PDO, ENSO)
  identify factors influencing extreme events
  (e.g. Pineapple Express) and quantify
  probability of occurrence in each watershed.
• Watershed hydrology Quantify relationships
  between climate variables and hydrology variables
  (e.g. temperature and snowpack, precipitation and
  runoff) in each watershed.
• Water delivery impacts research and modeling
• Reservoir operations Quantify potential changes
  in hydrology-based rules and agreements under
  climate changes (e.g. flood control, target
  storage, water use, instream flows). Develop
  models to relate project operations to hydrology
  rather than utilizing historical data and
  empirical formulations.
• Mitigation strategies - Lund et. al., 2003 and
  VanRheenan et.al., 2004 have explored mitigation
  strategies to cope with climate change impacts.
  This is an important aspect of understanding the
  problem.
• Conduct more comprehensive sensitivity analyses.

and break the problem into smaller pieces.
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Preliminary results from EBMUDSIM
Kevin Richards, EBMUD