Global catchment based comparison of Global catchment based comparison of observed and HadGEM modelled observed and HadGEM modelled

precipitation, temperature and Köppen precipitation, temperature and Köppen climate typeclimate type

Murray Peel1, Thomas McMahon1 & Ian Smith2

1 Civil & Environmental Engineering, The University of Melbourne, Victoria, Australia

2 CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia

EGU 2008 - Session CL21, Peel et al

OutlineOutline

Background– Observed catchment data– HadGEM data

Comparison– Mean annual

Precipitation Temperature

– Köppen climate type

Conclusions

EGU 2008 - Session CL21, Peel et al

BackgroundBackground

Long-term water resources management will depend upon projections of future climate change.

How well do CGCMs reproduce past & present hydroclimate at the catchment scale?

EGU 2008 - Session CL21, Peel et al

BackgroundBackgroundObserved catchment dataObserved catchment data

Globally 686 catchments.

EGU 2008 - Session CL21, Peel et al

BackgroundBackgroundObserved catchment dataObserved catchment data

Catchment boundary, within 5% of known area using 1km DEM (HYDRO1k),

Monthly streamflow data,– Unregulated for the period of record,

Catchment average monthly Temperature (T) & Precipitation (P),– For the period of runoff record,– Theissen polygon area weighting using GHCN v2 P &

T station data. Missing P & T infilled from nearby stations with best monthly

correlation

EGU 2008 - Session CL21, Peel et al

BackgroundBackgroundObserved catchment dataObserved catchment data

Elevation correction to Catchment P– Since station elevation is usually low relative to the

catchment area, catchment average P underestimated,– Corrected using Budyko like relationship of Fu (Zhang

et al., 2004, WRR 40, W02502).

The 686 catchments are a subset of 900 catchments– modelled adequately with a monthly rainfall-runoff

model– Some confidence in the P & T data.

EGU 2008 - Session CL21, Peel et al

BackgroundBackgroundHadGEM dataHadGEM data

HadGEM a coupled global climate model from the Hadley Centre, UK.– IPCC AR4 run– 20C3M scenario

Monthly P & T for 1/1860 – 12/1999

– Extract catchment average P & T from raw HadGEM (no downscaling) for the concurrent period of observed streamflow

Ideally an ensemble average of GCM runs would be better than the single run used here

EGU 2008 - Session CL21, Peel et al

BackgroundBackgroundHadGEM dataHadGEM data

Area weighted grid cell to form catchment average values

EGU 2008 - Session CL21, Peel et al

ComparisonComparison

Compare observed and HadGEM catchment average– Mean Annual P & T– Köppen climate type

EGU 2008 - Session CL21, Peel et al

Global catchment mean annual Global catchment mean annual temperaturetemperature

GCM has ~1oC cool bias, but overall very good.

y = 1.001x - 1.191

R2 = 0.914

-20

-10

0

10

20

30

-20 -10 0 10 20 30

Observed mean annual temperature (deg C)

GC

M m

ean

an

nu

al

tem

per

atu

re (

deg

C)

EGU 2008 - Session CL21, Peel et al

Hemisphere catchment mean Hemisphere catchment mean annual temperatureannual temperature

NH better than SH

y = 1.0219x - 1.7672

R2 = 0.9579

y = 0.6319x + 5.205

R2 = 0.4564

-20

-10

0

10

20

30

-20 -10 0 10 20 30

Observed mean annual temperature (deg C)

GC

M m

ean

an

nu

al t

emp

erat

ure

(d

eg C

)

NHSH

EGU 2008 - Session CL21, Peel et al

Global catchment mean annual Global catchment mean annual precipitationprecipitation

GCM not capturing the observed range.

y = 12.7x0.612

R2 = 0.325

100

1000

10000

100 1000 10000

Observed mean annual precipitation (with Fu adjustment) (mm)

GC

M m

ean

an

nu

al p

reci

pit

atio

n (

mm

)

EGU 2008 - Session CL21, Peel et al

Hemisphere catchment mean Hemisphere catchment mean annual precipitationannual precipitation

Again NH better than SH

y = 76.07x0.346

R2 = 0.1064

y = 4.2953x0.7738

R2 = 0.5234

100

1000

10000

100 1000 10000

Observed mean annual precipitation (with Fu adjustment) (mm)

GC

M m

ean

an

nu

al p

reci

pit

atio

n (

mm

)

NHSH

EGU 2008 - Session CL21, Peel et al

KKööppen climate typeppen climate type

Köppen climate classification rules as used in Peel et al (2007, HESS, 11: 1633-1644.)

EGU 2008 - Session CL21, Peel et al

KKööppen climate type - Tropicalppen climate type - Tropical

Cold bias of GCM reduces the number of Tropical catchments (coldest month ≥ 18oC)

Sub-Class

Obs Freq.

Obs All

GCM Freq.

GCM Freq.

Af 22

110

11

83Am 16 14

Aw 72 58

EGU 2008 - Session CL21, Peel et al

KKööppen climate type - Aridppen climate type - Arid

Errors in NH & SH GCM MAP leads to more Arid catchments

Sub-Class

Obs Freq.

Obs Freq.

GCM Freq.

GCM Freq.

BWh 0

19

2

49BWk 0 0

BSh 13 21

BSk 16 26

EGU 2008 - Session CL21, Peel et al

KKööppen climate type - Temperateppen climate type - Temperate

Sub-Class

Obs Freq.

Obs Freq.

GCM Freq.

GCM Freq.

Csa 17

340

12

313

Csb 23 29

Csc 1 0

Cwa 21 40

Cwb 36 11

Cfa 83 64

Cfb 153 156

Cfc 6 1

EGU 2008 - Session CL21, Peel et al

KKööppen climate type - Coldppen climate type - ColdSub-Class

Obs Freq.

Obs Freq.

GCM Freq.

GCM Freq.

Dsa 1

211

1

230

Dsb 1 10

Dsc 4 3

Dwa 3 5

Dwb 2 4

Dwc 4 9

Dwd 0 3

Dfa 3 22

Dfb 105 73

Dfc 85 98

Dfd 3 2

EGU 2008 - Session CL21, Peel et al

KKööppen climate type - Polarppen climate type - Polar

Sub-Class

Obs Freq.

Obs All

GCM Freq.

GCM Freq.

ET 6 11

EGU 2008 - Session CL21, Peel et al

ConclusionsConclusions

Comparison of observed and raw HadGEM catchment average P & T.– Globally MAT good

NH better than SH– Globally MAP not very good

Again, NH better than SH– Köppen climate type

Less Tropical & more Arid Temperate & Cold (mainly NH) good

Useful assessment of GCM performance for later hydrologic analysis

EGU 2008 - Session CL21, Peel et al

AcknowledgementsAcknowledgements

The analysis presented forms part of a paper in currently in preparation.

Funded by– Australian Research Council Discovery Grant