Climate Change & Indian Monsoon : Some Key Issues

1. Climate Change & Indian Monsoon : Some Key Issues B. N. Goswami (goswami@tropmet.res.in) Indian Institute of Tropical Meteorology, Pune

2. What is the Indian Summer Monsoon? A manifestation of seasonal northward migration of the Rain Band or Tropical Convergence Zone (TCZ )

4. Long term mean JJA precipitation and DJF precipitation Monsoon ? Wet- summer Dry - winter

5. Characteristic features of summer monsoon circulation Low level, cross-equatorial flow, south-westerlies, westerly jet in Arabian sea Upper level easterlies, Monsoon Easterly Jet Deep Baroclinic vertical structure

6. All India Rainfall (AIR) JJAS Mean Interannual Variability AIR Mean : 86 cm AIR S.D. : 8.6 cm No increasing trend in Monsoon rainfall past 100 yrs.

7. Global mean temperatures are rising faster with time Period Rate Years  /decade IPCC 150 0.045  0.012 100 0.074  0.018 50 0.128  0.026 25 0.177  0.052 Warmest 12 years: 1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999, 1990 ,2000

8. Trend in temp. is similar to global temp. trend. Much faster during past 50 years Annual mean Temp. over India 1875-2004

9. Indian Ocean temperature also shows warming trend

10. All India Rainfall (AIR) Interannual Variability No increasing trend in Monsoon rainfall past 100 yrs.

12. Blue : 1950-1970 Red : 1980-2000

13. Time series of count over CI Low & Moderate events Heavy events (>10cm) V. Heavy events (>15cm) Goswami et al. 2006, Science, 314, 1442

15. Why no trend in the seasonal mean ?

22. Future Scenarios for Summer Monsoon Rainfall and Annual Temperature over South Asia under A2 Scenario (High Emissions) based on IPCC AR4 Simulations of AOGCMs (Anomalies relative to current period) Model spread-a rough measure of uncertainty

23. South Asia Kripalani et al. 2007, Theor. Appl. Clmatol.

24. South Asia Kripalani et al. 2007, Theor. Appl. Clmatol.

27. Rignot et al. GRL, 2008

28. Climate on a threshold! Monsoon may tip to a persistent drought phase! Back Melting of Greenland Ice due to Global Warming Persistent Weak Monsoon Fresh water addition to North Atlantic Ocean Weakening of Atlantic Thermohaline Circulation Weak north-south Atmos. Temp. Gradient over Indian Longitudes

29. Mean=5.2 mm/day S.D. =14.7% mean LTA monsoon rainfall (JJAS) decreases by 20%!

31. Projections of monsoon under climate change scenarios by current climate models are not reliable! Because current climate models are unable to simulate the present mean monsoon climate and its variability with fidelity

32. Wavenumber-frequency spectra of twice daily OLR in tropics showing Kelvin, Rossby and MRG waves (Wheeler and Kiladis, JAS,1999, vol.56,374pp)

34. Lin et al. 2006, J. Climate

35. NICAM

36. Obs. (Takayabu et al. 1999) NICAM (7-km) Matsuno (AMS, 2007)

37. Cloud distribution simulated by ECMWF forecast model on a given day

38. Tools required for reliable answer to Regional Climate Change Questions: Atmosphere GCM With Stratospheric Chemistry, Aerosol , Dynamic vegetation, resolve trop. Meososcale clouds Ocean GCM With biogeochemistry model Carbon Cycle Model

43. Thank You !

44. Unprecedented fast Variations in recent past

46. Basic energy spectrum (thick curve) and error energy spectrum (thin curves) Lorenz 1969 Predictability limit in any scale is the time required for the error to propagate “upscale” from very, very small initial scale to that scale and become as large as the variance in that scale.

47. South Asia Kripalani et al. 2007, Theor. Appl. Clmatol.

48. Space-time spectra of tropical waves from anti-symmetric component of precipitation simulated by some AR4 models