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How far can global models predict extreme hydrological events Hervé Le Treut

10/09/2014. How far can global models predict extreme hydrological events Hervé Le Treut. 10/09/2014. Plan of the talk: French interest on the subject Remarks on AR4 models One test case: South-East South-America. LMDZ-Mediterranean (IPSL, Paris). Arpege-Mediterranean

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How far can global models predict extreme hydrological events Hervé Le Treut

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  1. 10/09/2014 How far can global models predict extreme hydrological events Hervé Le Treut

  2. 10/09/2014 • Plan of the talk: • French interest on the subject • Remarks on AR4 models • One test case: South-East South-America

  3. LMDZ-Mediterranean (IPSL, Paris) Arpege-Mediterranean (Météo-France, Toulouse) Two French zoomed climate models

  4. Global buffer zone buffer zone Regional • Global O-A coupled model: LMDZ-global / ORCA2 • Regional O-A coupled model: LMDZ-regional / MED8 • Two atmospheric models are coupled through buffer zones • Two oceanic models are also coupled through buffer zones Schematic of the quardruple coupling in IPSL

  5. Applications to:EuropeHYmex (Hydrology in the Mediterranean area)AMMA (West Africa)ChinaSouth America Wüst, 1961

  6. A downscaling study for France (Li et al): Three versions: Global / Europe / France Two-way nesting between Global/Europe One-way nesting from Europe to France

  7. Annual-mean precipitation (mm) in three LMDZ models: Globe (top), Europe (middle) and France (bottom)

  8. Intense precipitations (mm/day), return level at 50 years Observations and three versions LMDZ

  9. Goubanova et al. 2007, Planetary and Global Change Future evolution of extremes Precipitation (mm/day) averages SON DJF MAM JJA 30-year return levels 2070/2099 minus 1970/1999

  10. Added values of LMDZ-regional: extremes (a) Normalized frequency and (b) amount of precipitation as a function of daily intensity for observation and the reference simulations of LMDZ-Global、LMDZ/CTRL and LMDZ/CTRL2. Chen et al. 2010, Cli Dyn

  11. Hadley mass transport (DJF, winter cell) and its dependence on CO2 doubling AR4 models

  12. Hadley cell latitudinal extension (JJA, Southern limit) and its dependence on CO2 doubling AR4 models S JJA (en ° latitude) • Extension vers les pôles des branches subsidentes, Gastineau et al, 2008

  13. Main features of tropical response to CO2 increase in current GCMs • Hadley cell intensity diminished (consistent with changes in vertical stability of the atmosphere, with radiative forcing) • Precipitation rates are increased (increase in water vapour, in convective precipitation) • The position of the main tropical system undergoes only moderate changes SENTIVITY EXPERIMENTS in reponse to prescribed SSTS show that these agreements between models reflect a response to globally average SST changess, or zonally averaged SST changes. The impact of zonal asymmetries is much more complex and involves competition between Walker and Hadley cells.

  14. A useful paradigm to understand tropical circulations: the two-column model.

  15. R-2 R-1 The dynamic link between two cells determines specific scales (Bellon, Ghil, Le Treut, GRL, 2006)

  16. Coupling two adjacent cells sharing a common subsidence zone (through a modification the low level heat transport) clearly shows the possibility of non-linear behaviour (Le Treut and Bellon, 2005)

  17. Differences of simulated seasonal mean precipitation between 2079-2999 and 1979-1999 periods from IPCC-AR4 models (see list in table 1). Color scale interval is 0.2 mm day-1. The black contour indicates the 0 level. (Vera, Junquas, Li and Le Treut)

  18. EOF1 of DJF (2001-2098) rainfall from IPCC-AR4 model. Color scale interval is 0.2 non-dimensional units. The black contour indicates the 0 level.

  19. Figure 14: Composite differences of mean DJF geopotential height (zg) at 500hPa between the positive and the negative EOF1-SE for (2001-2049) (a) and (2050-2098) (b) from 8 of the 9 selected models . Color scale and contour interval is 10 m. The black contour indicates the 0 level. a. b.

  20. 10/09/2014 • Conclusions: • Inceasing Model resolution is a necessity • But the scale interactions are complex, and non-linearity can arise from the large-scale synoptic circulations • Using a GCM for regional studies, and more so for the deterination of extreme events, requires a combination of approaches, and careful process studies

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