the canadian climate impacts scenarios (ccis) project is funded by the climate change action fund...

The Canadian Climate Impacts Scenarios (CCIS) Project is funded by the

Climate Change Action Fund and provides climate change scenarios and related information to the VIA community in Canada

Downscaling Tools

Introduction to LARS-WG and SDSM



LARS-WG stochastic weather generator

( http:\\www.iacr.bbsrc.ac.uk\mas-models\larswg.html )

• Generation of long weather time-series suitable for risk assessment

• Ability to extend the simulation of weather to unobserved locations

• A computationally inexpensive tool to produce climate change scenarios incorporating changes in means and in variability



LARS-WG stochastic weather generator

( http:\\www.lars.bbsrc.ac.uk\model\larswg.html )

• Generates precipitation, min and max temperature and solar radiation• Modelling of precipitation events is based on wet/dry series• Semi-empirical distributions are used for precipitation amounts, dry/wet

series and solar radiation• Temperature and solar radiation are conditioned on the wet/dry status

of a day• Temperature and solar radiation are cross-correlated

0

0.02

0.04

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1 4 7 10 13 16 19

(mean, sd)

Parametric- e.g., WGEN

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Semi-parametric - e.g., LARS-WG



LARS-WG

• Model calibration - SITE ANALYSIS• Model validation - QTEST• Generation of synthetic weather data -

GENERATOR



SITE ANALYSIS



QTESTCompare observed and synthetic data to evaluate LARS-WG performance

Precipitation

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mm

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Obs

WG

Minimum temperature

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Min

imu

m t

em

pe

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re (

°C)

Obs

WG

Maximum temperature

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25

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Max

imu

m t

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°C)

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WG

Solar radiation

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iati

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(M

Jm-2)

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WG

Precipitation variability

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(m

m)

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WG

Minimum temperature variability

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(°C

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WG

Maximum temperature variability

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1.8

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nd

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viat

ion

(°C

)

Obs

WG

Solar radiation variability

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0.5

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1.5

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2.5

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3.5

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nd

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viat

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(M

Jm-2)

Obs

WG



Base scenario file

GENERATORGenerate synthetic weather data: to extend time series, or

for climate change studies

Scenario file



GENERATORPrecipitation

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180

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Base

2050s

Maximum temperature

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25

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Feb

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May Jun

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Max

imu

m t

em

pe

ratu

re (

°C)

Base

2050s

Minimum temperature

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Feb

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Min

imu

m t

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°C)

Base

2050s

Days with maximum temperature > 30°C

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1.2

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mb

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of

day

s

Base

2050s

Days with minimum temperature < 0°C

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mb

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of

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s

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2050s



Limitations of LARS-WG (and weather generators in

general) ...

• Temporal downscaling only

• Designed for use at individual sites only (no spatial correlation)

• Can only represent events in calibration data set

• Generally underestimate variability



SDSM1. A decision support

tool for assessing local climate change impacts

2. Facilitates the rapid development of multiple, low-cost, single-site scenarios of daily surface weather variables under current and future climate forcing

3. Based on a multiple regression-based method



SDSM Structure

7 steps:• Quality Control and Data Transformation• Screening of Predictor Variables• Model Calibration• Weather Generation (using observed

predictors)• Statistical Analyses• Graphing Model Output• Scenario Generation (using climate model

predictors)



Model Verification



Victoria: Maximum temperature

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5

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25

30

Jan

Fe

b

Ma

r

Ap

r

Ma

y

Jun

Jul

Au

g

Se

p

Oct

No

v

De

c

(°C

)

1961-1990

CGCM1 GA1

Downscaled



Tmax > 25°C



Cautionary Remarks

• SDSM provides a parsimonious technique of scenario construction that complements other methods

• SDSM should not be used uncritically as a “black box” (evaluate all relationships using independent data)

• Local knowledge is an invaluable source of information when determining sensible combinations of predictors

• Daily precipitation amount at individual stations is the most problematic variable to downscale

• The plausibility of all SDSM scenarios depends on the realism of the climate model forcing

• Try to apply multiple forcing scenarios (via different GCMs, ensemble members, time–slices, emission pathways, etc.)

the canadian climate impacts scenarios (ccis) project is funded by the climate change action fund...

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