CCLM-CLM: A new tool to investigate biosphere-atmosphere interactions.

1. CCLM-CLM: A new tool to investigate biosphere-atmosphere interactions. Edouard L. Davin, Reto Stöckli, Sonia I. Seneviratne

2. Outline • Presentation of CCLM-CLM • Evaluation of CCLM-CLM and comparison with the standard CCLM

3. Community Land Model (CLM) • The CLM is the land surface component of the NCAR CCSM climate model. • Latest generation of LSM representing biogeophysics, hydrology, C/N cycles and vegetation dynamics. Bonan, 2008

4. Coupling strategy CCLM (Atmosphere) • The coupling strategy is meant to minimize changes made in both CCLM and CLM (facilitate version updates). • A coupling interface enables communication between CCLM and CLM. • A switch controlling the use of TERRA versus CLM has been introduced in CCLM. Coupling interface CLM (Land)

5. Coupling strategy • TERRA-ML calculates the surface state (surface temperature, humidity…) not surface fluxes. • Transfer coefficients for sensible and latent heat (Ch and Cq) and then surface fluxes are calculated as part of the boundary layer scheme. • But CLM provides directly surface fluxes to the atmosphere!! H = Ch |vh| ( Ta – Ts ) LE = Cq |vh| ( qa – qs ) Solution: Surface fluxes are first calculated by CLM. Fluxes are inverted to retrieve the transfer coefficients, which are then passed to the atmospheric model. Surface fluxes are finally recalculated in the atmospheric part.

6. Performances Performances on the Cray XT5 at CSCS

7. Outline • Presentation of CCLM-CLM • Evaluation of CCLM-CLM and comparison with the standard CCLM

8. Experiments • CCLM4.0-TERRA • CCLM4.0-CLM3.5 • Same atmospheric model, same boundary conditions, isolate the effect of the Land Surface Model (and its parameters). Driven by ERA40 reanalysis

9. CLM configuration Bonan, 2008

10. Datasets • CRU TS 2.1 (Mitchell and Jones, 2005)  T2m, precip, clouds • GSWP-2 (Dirmeyer et al., 2006)  surface fluxes Period from 1986 to 1995 is used

11. Mean climate in CCLM 2-m temperature Precipitations JJA K % DJF

12. Summary of CCLM deficiencies • Too cold in summer north of 45N. • Too wet in winter (also in summer over northern Europe) • Related to the model itself and not to the driving data

13. 2-m temperature Model minus CRU CCLM-CLM CCLM RMSE=1.9 RMSE=1.2 JJA K RMSE=1.7 RMSE=1.7 DJF

14. Precipitations Model versus CRU CCLM-CLM CCLM RMSE=18.8 RMSE=15.8 JJA % RMSE=34.8 RMSE=33.7 DJF

15. Typical errors (RMSE) are smaller in CCLM-CLM for both temperature and precipitation at both seasons • The coupling has a stronger effect in summer than in winter • Summer cold/wet bias suppressed

16. Net shortwave radiation Model minus GSWP-2 CCLM CCLM-CLM W/m2 Shaded area = error is smaller than the std of the GSWP models

17. Net longwave radiation Model minus GSWP-2 CCLM CCLM-CLM W/m2

18. Net radiation Model minus GSWP-2 CCLM CCLM-CLM W/m2

19. Sensible heat Model minus GSWP-2 CCLM CCLM-CLM W/m2

20. Latent heat Model minus GSWP-2 CCLM CCLM-CLM W/m2

21. Evaporative fraction CCLM-CLM CCLM Model minus GSWP-2

22. Surface albedo Model minus GSWP-2 CCLM CCLM-CLM %

23. Incoming shortwave radiation Model minus GSWP-2 CCLM CCLM-CLM W/m2

24. Total cloud cover Model minus CRU CCLM CCLM-CLM %

25. Cloud cover CCLM-CLM versus CCLM High clouds Low clouds Mid clouds

26. Summary • Most aspects of the simulated climate are improved in CCLM-CLM: • Less clouds (and less rain) • More incoming SW • Higher net radiation • Lower evaporative fraction • Higher temperature • ...but SW flux is still underestimated, with consequences on net radiation and evapotranspiration.