Assessing climate change impacts on water resources in Chile

Assessing climate change impacts on water resources in Chile

Reunión profesores Estadounidenses FulbrightValparaiso, Chile

15 setiembre 2011

Ed MaurerCivil Engineering Department

Global Climate is ChangingGlobal 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)

Observed Changes: 1970-2004Observed 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.

Projections of Global ChangeProjections of Global Change

• Range of ‘likely warming’ by end of 21st century variable

• By mid-21st century most differences smaller

2010

1.8° 3.4° 4.0°2.4° 2.8°

Which pathway are we on?Which pathway are we on?

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

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

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

1990 1995 2000 2005 2010 2015

Fo

ssil

Fu

el E

mis

sio

n (

GtC

y-1)

5

6

7

8

9

10

A1B

A1FI

A1T

A2

B1

B2

Carbon Dioxide Information Analysis Center

International Energy Agency

Looking toward the future: end of 21st century

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

Figure 11.12Figure 11.12number of models out of 21 that project increases in precipitationsource: IPCC, 2007

How do changes in Chile compare to the California

Case?

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

.

Regional ChangesRegional Changes

• Projected changes non-uniform

• Impacts also non-uniform

Median runoff change, 2041-2060 minus 1901-1970

Greater water scarcityMore wildfiresAccelerating invasive speciesTourism, recreation impactsAgricultural vulnerability

Extreme urban heat eventsWorsening air quality episodes

Ocean fishery migrationIncreased severe flooding events

Source: U.S. Global Change Research Program (USGCRP)

Estimating regional impactsEstimating regional impacts

1. GHG Emissions Scenario

Adapted from Cayan and Knowles, SCRIPPS/USGS, 2003

2. Global Climate Model4. Land surface

(Hydrology) Model

3. “Downscaling”

5. Operations/impac

ts Models

Availability of GCM SimulationsAvailability of GCM Simulations

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

Need for DownscalingNeed for Downscaling

• Dynamic– Better representation of terrain

captures local processes and feedbacks

– Computationally expensive– Still contain biases

• Statistical– Assumes stationary transfer function

Image: Canadian Climate Change Scenarios Network Images: IPCC

Downscaling

Downscaling for Impacts ModelsDownscaling for Impacts Models

Raw GCM

Output

• Bias correct and spatially downscale GCM output

• Run hydrology model with projected climateP

reci

p,

Tem

p

Flow, Snow, etc.

Multi-Model Ensemble Projections for Feather River

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

Impact Probabilities for PlanningImpact Probabilities for Planning

Sn

ow

wa

ter

eq

uiv

ale

nt

on

Ap

ril

1,

mm

Point at:120ºW, 38ºN

2/3 chance that loss will be at least 40% by mid century, 70% by end of century

• Combine many future scenarios, models, since we don’t know which path we’ll follow (22 futures here)

• Choose appropriate level of risk

Translating this approach to ChileTranslating this approach to Chile

Four key basins

Ecologically and economically important

• 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)

Mataquito Basin

Tmed, Tmax, Tmin, P

Qdía

Escenarios de Cambio Climático específicos cuenca Mataquito

Para un solo escenario (A1b) pero ahora estudiando un poco cambios en variabilidad

Snow Cover and Extreme Events

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

* A partir de P’s y T’s en Curicó, adoptando una tasa de lapso de 9 °C/Km

• Two events: 23 may 200827 may 2002

2002 2008

2008, with lower total rain produced greater peak stream flow.

Capturing Uncertainties in an Ensemble - Temperature

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

Does this capture the range of uncertainties?

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

Caudales(mm/año)

Temperatura Media Anual(Celsius)

Precipitaciones(mm/año)