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This study compares observed catchment data with data from the HadGEM global climate model to assess its ability to reproduce past and present hydroclimate at the catchment scale. The comparison includes mean annual precipitation, temperature, and Köppen climate type. The results show good agreement for mean annual temperature, with the northern hemisphere performing better than the southern hemisphere. However, the model has difficulty capturing the observed range of precipitation, and there are errors in determining the Köppen climate type, particularly for tropical and arid regions.
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Global catchment based comparison of observed and HadGEM modelled precipitation, temperature and Köppen climate type Murray Peel1, Thomas McMahon1 & Ian Smith2 1 Civil & Environmental Engineering, The University of Melbourne, Victoria, Australia 2CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
Outline • Background • Observed catchment data • HadGEM data • Comparison • Mean annual • Precipitation • Temperature • Köppen climate type • Conclusions EGU 2008 - Session CL21, Peel et al
Background • 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
BackgroundObserved catchment data • Globally 686 catchments. EGU 2008 - Session CL21, Peel et al
BackgroundObserved 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
BackgroundObserved 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
BackgroundHadGEM 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
BackgroundHadGEM data • Area weighted grid cell to form catchment average values EGU 2008 - Session CL21, Peel et al
Comparison • Compare observed and HadGEM catchment average • Mean Annual P & T • Köppen climate type EGU 2008 - Session CL21, Peel et al
Global catchment mean annual temperature • GCM has ~1oC cool bias, but overall very good. EGU 2008 - Session CL21, Peel et al
Hemisphere catchment mean annual temperature • NH better than SH EGU 2008 - Session CL21, Peel et al
Global catchment mean annual precipitation • GCM not capturing the observed range. EGU 2008 - Session CL21, Peel et al
Hemisphere catchment mean annual precipitation • Again NH better than SH EGU 2008 - Session CL21, Peel et al
Köppen climate type • Köppen climate classification rules as used in Peel et al (2007, HESS, 11: 1633-1644.) EGU 2008 - Session CL21, Peel et al
Köppen climate type - Tropical • Cold bias of GCM reduces the number of Tropical catchments (coldest month ≥ 18oC) EGU 2008 - Session CL21, Peel et al
Köppen climate type - Arid • Errors in NH & SH GCM MAP leads to more Arid catchments EGU 2008 - Session CL21, Peel et al
Köppen climate type - Temperate EGU 2008 - Session CL21, Peel et al
Köppen climate type - Cold EGU 2008 - Session CL21, Peel et al
Köppen climate type - Polar EGU 2008 - Session CL21, Peel et al
Conclusions • 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
Acknowledgements • The analysis presented forms part of a paper in currently in preparation. • Funded by • Australian Research Council Discovery Grant EGU 2008 - Session CL21, Peel et al