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Antropogenic changes of Sahel rainfall Reindert Haarsma Nanne Weber Frank Selten

Antropogenic changes of Sahel rainfall Reindert Haarsma Nanne Weber Frank Selten Royal Netherlands Meteorological Institute. Dutch Challenge Project Impact of global warming on extreme events and other questions that require good statistical sampling:

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Antropogenic changes of Sahel rainfall Reindert Haarsma Nanne Weber Frank Selten

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  1. Antropogenic changes of Sahel rainfall Reindert Haarsma Nanne Weber Frank Selten Royal Netherlands Meteorological Institute

  2. Dutch Challenge Project • Impact of global warming on extreme events and other questions that require good statistical sampling: • NAO, ENSO, THC, hydrological cycle, etc. • Period of investigation 1940-2080 • State-of-the-Art climate model: CCSM version 1.4, T30, 18 levels • Large ensemble (62 members). Different initial conditions • Until 2000: Observed forcing (GHG, Solar, Vulcanos, Aerolsols) • After 2000: GHG scenario: BAU (SRES A1b) • Experiment done on TERAS supercomputer SARA Amsterdam • Start experiment: 01-06-2003 Last run: 22-09-2003

  3. Project leaders: Frank Selten (VO/KNMI), Henk Dijkstra (IMAU/UU) Experiment was motivated by earlier studies with ECBilt (Schaeffer et al. 2003, vd Brink et al. 2003). Large number of scientists at KNMI, including Meteorological Research, and at other CKO institutes are involved in analyzing the runs. Global mean temperature Blue dots: observed (Clim, Res. Unit) Red dots: ensemble members Black line: ensemble mean

  4. Surface air temperature (SAT) Ensemble mean difference 2050-2080 minus 1950-1980 Precipitation

  5. Precipitation Sahel Seasonal Cycle Change in precipitation in August Seasonal cycle (1951-1980)-(2051-2080) 62 members for each period Red: 2051-2080 Blue: 1951-1980 month

  6. Model 62 ensembles 1950-1980 Annual cycle precipitation in West Africa NCEP

  7. Model EOF’s Precipitation JAS Giannini et al., Scienceexpress, 2003 25% obs. 15% obs.

  8. Inter-member variability Member 55 Correlation SAHEL precipitation with SAT. Member 56

  9. Projection of precipitation EOF’s on SAHEL rainfall

  10. Model ensemble mean Model ensemble mean Correlation EOF 1 with SAT Detrended 21 year running mean Difference SAT 2050-2080 minus 1950-1980 during JAS

  11. Model ensemble mean Correlation EOF 1 with MSLP Detrended 21 year running mean Difference MSLP 2050-2080 minus 1950-1980 during JAS

  12. Model ensemble mean Correlation EOF 1 with Soil moisture Detrended 21 year running mean

  13. PDF of seasonal mean (JAS) rainfall 1950-1980 2050-2080 rainfall mm/day

  14. CONCLUSIONS Increase of Sahel rainfall due to greenhouse warming This increase of Sahel rainfall is connected with dominant mode Sahel precipitation Mechanism is due to: enhanced warming of Sahara decrease MSLP over Sahara increased advection of moisture

  15. QUESTIONS Explained variance of EOF’s and correlation with SST’s: Hindcast run with observed SST’s. Role of clouds How crucial is the heating of the Sahara?

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