Assessing climate change impacts on water resources in Chile

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Assessing climate change impacts on water
resources in Chile
Reunión profesores Estadounidenses
Fulbright Valparaiso, Chile 15 setiembre 2011
Ed Maurer Civil Engineering Department
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Global Climate is Changing

• Temperatures are increasing globally
• Most recent warming attributed to human-driven
  GHG emissions
• Some impacts already evident and attributable to
  warming

Source U.S. Global Change Research Program
(USGCRP)
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Observed Changes 1970-2004

• High confidence changes in
• rainfall intensity
• extreme temperatures
• regional drought
• glacier melt
• early snowmelt
• lake warming
• Changes are consistent with observed warming, if
  not attributable

Source IPCC Climate Change 2007 Impacts,
Adaptation, and Vulnerability -- Summary for
Policymakers.
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Projections of Global Change

• Range of likely warming by end of 21st century
  variable
• By mid-21st century most differences smaller

1.8
3.4
4.0
2.4
2.8
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Which pathway are we on?

• Current emissions are tracking above the most
  intense IPCC emission scenario

Raupach et al., PNAS, 2007 Global Carbon Project,
2009

• Scenarios trends are averages across all models
  available for each scenario class.

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Looking toward the future end of 21st century
21 modeled changes for A1B emissions 2080-2099
minus 1980-1999 Warming is large-scale,
certain Precipitation changes more regional, less
confident Regional changes drive regional
impacts .
Precipitation
number of models out of 21 that project increases
in precipitation
source IPCC, 2007
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How do changes in Chile compare to the California
Case?
21 modeled changes for A1B emissions 2080-2099
minus 1980-1999 Warming is large-scale,
certain Precipitation changes more regional, less
confident Regional changes drive regional
impacts .
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Regional Changes

• Projected changes non-uniform
• Impacts also non-uniform

Median runoff change, 2041-2060 minus 1901-1970
Source U.S. Global Change Research Program
(USGCRP)
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Estimating regional impacts
2. Global Climate Model
4. Land surface (Hydrology) Model
1. GHG Emissions Scenario
5. Operations/impacts Models

1. Downscaling

Adapted from Cayan and Knowles, SCRIPPS/USGS, 2003
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Availability of GCM Simulations

• 20th century through 2100 and beyond
• gt20 GCMs
• Multiple Future Emissions Scenarios

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Need for Downscaling

• Dynamic
• Better representation of terrain captures local
  processes and feedbacks
• Computationally expensive
• Still contain biases
• Statistical
• Assumes stationary transfer function

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Downscaling for Impacts Models

• Bias correct and spatially downscale GCM output
• Run hydrology model with projected climate

Raw GCM Output
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Multi-Model Ensemble Projections for Feather River

• Increase Dec-Feb Flows
• 77 for A2
• 55 for B1

• Decrease May-Jul
• 30 for A2
• 21 for B1

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Impact Probabilities for Planning
Snow water equivalent on April 1, mm

• Combine many future scenarios, models, since we
  dont know which path well follow (22 futures
  here)
• Choose appropriate level of risk

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Translating this approach to Chile
Four key basins Ecologically and economically
important
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Mataquito Basin
Tmed, Tmax, Tmin, P
Qdía

• Series diarias
• Se rellenan de series incompletas de P y Q
• Análisis (1) estacional, (2) periodo pluvial y
  nival, (3) anual
• Variables hidroclimatológicas e índices
  representativos
• Tendencias (Mann-Kendall y Regresión Lineal)

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Escenarios de Cambio Climático específicos cuenca
Mataquito
Para un solo escenario (A1b) pero ahora
estudiando un poco cambios en variabilidad
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Snow Cover and Extreme Events
2002 2008
P 2 días previos (mm) 103.6 83.9
Caudal Máximo (m3/s) 931 2690
Tmax promedio (C) 13,0 17,4
Cota estimada línea de nieve (m) 1700 2200

• Two events
• 23 may 2008
• 27 may 2002

A partir de Ps y Ts en Curicó, adoptando una
tasa de lapso de 9 C/Km
2002
2008
2008, with lower total rain produced greater peak
stream flow.
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Capturing Uncertainties in an Ensemble -
Temperature

• Internal variability (forecast) important first
  few years
• Model Uncertainty dominates through mid-21st
  century
• Uncertain emissions pathway most important after
  that

Hawkins Sutton, BAMS, 2009
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Does this capture the range of uncertainties?

• Perturbed physics experiments and theoretical
  feedback analyses extend tail to right
• Uncertainty in emissions is on same order if
  planning horizon includes end of 21st century or
  beyond

Roe and Baker, 2007
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Thanks!
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Caudales (mm/año)
Temperatura Media Anual (Celsius)
Precipitaciones (mm/año)