Global catchment based comparison of observed and HadGEM modelled precipitation, temperature and...
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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