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Global catchment based comparison of observed and HadGEM modelled precipitation, temperature and Köppen climate type

This study compares observed catchment data with data from the HadGEM climate model to assess its accuracy in simulating precipitation, temperature, and Köppen climate types. The results show that while the model performs well in reproducing mean annual temperature, it struggles to capture the observed range of precipitation. Additionally, cold bias in the model leads to fewer tropical catchments and errors in map data affect arid catchments. Overall, the study provides valuable insights into the performance of the HadGEM model for future hydrologic analysis.

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Global catchment based comparison of observed and HadGEM modelled precipitation, temperature and Köppen climate type

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  1. 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

  2. Outline • Background • Observed catchment data • HadGEM data • Comparison • Mean annual • Precipitation • Temperature • Köppen climate type • Conclusions EGU 2008 - Session CL21, Peel et al

  3. 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

  4. BackgroundObserved catchment data • Globally 686 catchments. EGU 2008 - Session CL21, Peel et al

  5. 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

  6. 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

  7. 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

  8. BackgroundHadGEM data • Area weighted grid cell to form catchment average values EGU 2008 - Session CL21, Peel et al

  9. Comparison • Compare observed and HadGEM catchment average • Mean Annual P & T • Köppen climate type EGU 2008 - Session CL21, Peel et al

  10. Global catchment mean annual temperature • GCM has ~1oC cool bias, but overall very good. EGU 2008 - Session CL21, Peel et al

  11. Hemisphere catchment mean annual temperature • NH better than SH EGU 2008 - Session CL21, Peel et al

  12. Global catchment mean annual precipitation • GCM not capturing the observed range. EGU 2008 - Session CL21, Peel et al

  13. Hemisphere catchment mean annual precipitation • Again NH better than SH EGU 2008 - Session CL21, Peel et al

  14. 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

  15. Köppen climate type - Tropical • Cold bias of GCM reduces the number of Tropical catchments (coldest month ≥ 18oC) EGU 2008 - Session CL21, Peel et al

  16. Köppen climate type - Arid • Errors in NH & SH GCM MAP leads to more Arid catchments EGU 2008 - Session CL21, Peel et al

  17. Köppen climate type - Temperate EGU 2008 - Session CL21, Peel et al

  18. Köppen climate type - Cold EGU 2008 - Session CL21, Peel et al

  19. Köppen climate type - Polar EGU 2008 - Session CL21, Peel et al

  20. 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

  21. 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

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