A RCM bias correction method for climatic indices expressed in a daily based frequency applied to

temperature projections of the North Iberian Peninsula

Iratxe González Dr. Julia Hidalgo

TECNALIA – LABEIN. Environment Unit. Spain.

BIAS models vs. observations

Adjustment datato a probability density

function

- Piani et al, 2009- Collins 2007- Planton et al, 2008- Kjellstrom et al, 2005- Alexander et al, 2005-Chauvin and Devil 2005

Adjustment data distribution to a delta change temperature

- Roossmalen et al 2009- Kjellstrom et al 200 7- Christensen and Christensen 2007

The goodness of fit, or bias, summarize the discrepancy between the observations and the model outputs. It should be evaluated before analysing future climatic scenarios from such models.

• Seasonally frequency based indices• Daily frequency based indices

OUTLINE

USED DATA REGIONAL SERIES

STATISTICAL INDICESCORRECTION BIAS

RCM vs. OBSERVATIONS

ANALYSIS RESULTS CONCLUSIONS

METHODOLOGY.

Summer:- 90th percentile Tmax- days with T > 90th p Tmax- Human Comfort Index (THI)

Winter:- 10th percentile Tmin-Days with T < 10th p Tmin- Number of frost days

Summer:Heat waveDuration

WMO

Winter:Cold waveDuration

WMOBasque Country

North Iberian Peninsula.

Climate Scenarios:ENSEMBLES project

Observed data:Spanish Meteorological Agency (AEMET)

Time period : 1978-2000 ; 2000-2100

PRUDENCE resultsAbanades et al. 2007

RCM Models 10th percentile (ºC) Tmin Figure

90th percentile (ºC) Tmax Figure

HIRHAM-ARPEGE 4  a2 4 a1 

ALADIN-ARPEGE 4  a2 4 a1

PROMES-HadCM3  1  a2 4 a1

CLM-HadCM3  1  a2  4 a1

REMO-ECHAM5 10  b2  - 2 b1

RACMO-ECHAM5 10  b2  - 2 b1

METHODOLOGY. Evaluation of models

METHODOLOGY. Bias correction

Correction Seasonally indices

∆T (ºC)

.. ObskModk TTT

(T10thp model corrected)i = (T10thp model not corrected)i – (∆T)associated

to this temperature

in the calibration curve

1th 99th… Percentiles(21 in total)

*

* *

* * **

* * * *

*

*

1

.

.

.

10

K- pecentile 1:99th

; i- daily datan

TT

TTT

n

ji

jim

iimimcorr

1

))((

)()(

Correction daily indices

Christensen et al 2008 Jacob et al, 2007 Kjellstrom et al 2007

CORRECTION OF MODELS: Mean Maximum TemperaturesFor Summer

Obs.

20-27ºC

M. REFERENCE

22-32ºC

19-27ºC

RESULTS. Bias correction90

th

per

cen

tile

max

imu

m t

emp

erat

ure

wit

ho

ut

corr

ecti

on

co

rrec

ted

RESULTS. Summer time 90th percentile Tmax

EnsembleAv. 35.6ºC

Spread:3.5ºCStdv:1.41ºC

EnsembleAv. 39.7ºC

Spread: 4.6ºCStdv:1.87ºC

Future projection: 2000-2100trend: 3ºCStdv . 1.41 ºCSpread: 4.2ºC

EnsembleAv. 37.8ºC

Spread:6.52ºCStdv:2.54ºC

RESULTS. Summer time Heat Waves duration

EnsemblesFreq. 1-2 heat wavesAv. 9-11 days [12%]

EnsemblesFreq. 1-2 heat wavesAv. 13-16 days [16%]

EnsemblesFreq. 1-3 heat wavesAv. 18-22 days [22%]

Temp involved 34.7 ºC Temp involved 34.3 ºC Temp involved 34.2 ºC

Obs.Av. 1.3 heat wavesFreq: 13.7 daysTemp: 29 ºC

RESULTS. Summer time Thermal Comfort Index (THI)

THI % population uncomfortable70 1075 5080 90

(Gates, 1972)

EnsembleAv. 67.91

Stdv:1 .60

EnsembleAv. 67.99

Stdv:1 .64

EnsembleAv. 69.34

Stdv: 3.97

RESULTS. Winter time 10th percentile Tmin

EnsembleAv. - 0.72ºC

Spread:1.5ºCStdv: 0.92ºC

Future scenario: 2000-2100trend: 3ºCStdv . 0.83 ºCSpread: 1.83ºC

EnsembleAv. -3.04ºC

Spread: 1.8ºCStdv: 0.71ºC

EnsembleAv. -1.70ºC

Spread: 1.72ºCStdv:0.68ºC

RESULTS. Winter time

Future scenario (2000-2100)Decrease 50% of daysRespect with Ref. Period

EnsembleAv. 7.5 d

Stdv: 3.57 d

EnsembleAv. 20.6 dStdv: 3.5 d

EnsembleAv. 11.5 dStdv: 3.9 d

Number of frost days

RESULTS. Winter time

EnsemblesFreq. 1-3 cold wavesAv. 7-19 days [14%]

EnsemblesFreq. 1-2 cold wavesAv. 6-10 days [9%]

RACMO/REMO/ALADINFreq. 1 cold waveAv. 6- 9 days [8%]HIRHAM/CLM/PROMES: 0

Temp involved 2.7 ºC Temp involved 3.3 ºC Temp involved 1.3ºC

Cold Waves duration

Obs.Av. 1.25 cold wavesFreq: 11.1 days [12%]Temp: 3.3 ºC

Conclusions & Discussions

Methodology to correct the bias based on the percentiles approach

Proposed method to correct indices when absolute values are required (daily based frequency)

Correction methodology suitable for interdisciplinary groups

Applicability for the Basque Country case study: indices indicate that for summer and winter periods the maximum and minimum temperature tend to increase. The duration of the heat episodes tend to increase and for cold episodes tend to decrease ; as well for the number of the frost days in winter.