1. http://www.ncas.ac.uk NCAS Conference 2007 10-11 December 2007, Park Inn Hotel, York The Indian monsoon and climate change Andrew Turner, Julia Slingo & Pete Inness NCAS-Climate Walker Institute for Climate System Research, University of Reading

2. http://www.ncas.ac.uk NCAS Conference 2007 Introduction Indian summer monsoon affects the lives of more than 2 billion people across South Asia, and provides more than 75% of total annual rainfall. Agricultural and industrial consumers require reliable source of water, together with an appropriate forecast on seasonal and intraseasonal timescales. How monsoon characteristics may change in the future is a key goal of climate research.

3. http://www.ncas.ac.uk NCAS Conference 2007 Outline Introduction Model details The mean monsoon Extremes & active-break cycles Interannual variability and predictability Decadal-timescale uncertainties Summary

4. http://www.ncas.ac.uk NCAS Conference 2007 Model experiments Hadley Centre coupled model HadCM3 run at high vertical resolution (L30). This better represents intraseasonal tropical convection 1 and has an improved atmospheric response to El Niño 2. Control (1xCO 2 ) and future climate (2xCO 2 ) integrations used to test the impact of increased GHG forcing. Further integration of each climate scenario to test the role of systematic model biases. 1 P.M. Inness, J.M. Slingo, S. Woolnough, R. Neale, V. Pope (2001). Clim. Dyn. 17: 777--793. 2 H. Spencer, J.M. Slingo (2003). J. Climate 16: 1757--1774.

5. http://www.ncas.ac.uk NCAS Conference 2007 Mean response of the monsoon to 2xCO 2

6. http://www.ncas.ac.uk NCAS Conference 2007 Mean monsoon response in the AR4 models Fig 10.9 1 : some consistency in the JJA response of precipitation over India to A1B forcing with 2xCO 2 result (but within inter- model spread). Fig 10.12 1 : less than 80% of models agree on annual mean change in precip over India. 1 G. Meehl et al. (2007) Global Climate Projections. In: Climate Change 2007: The Physical Science Basis. 10.9 10.12 Of the six AR4 models which reasonably simulate the monsoon precipitation climatology of the 20 th century, all show general increases in seasonal rainfall over India in the 1pctto2x runs 2. 2 H. Annamalai, K. Hamilton, K. R. Sperber (2007). J. Climate 20: 1071--1092

7. http://www.ncas.ac.uk NCAS Conference 2007 Systematic model bias and the uncertain response to 2xCO 2

8. http://www.ncas.ac.uk NCAS Conference 2007 Uncertainty in monsoon precipitation response to 2xCO 2 Systematic bias seems to mask full impact of changing climate 1 A.G. Turner, P.M. Inness, J.M. Slingo (2007a). QJRMS 133: 11431157.

9. http://www.ncas.ac.uk NCAS Conference 2007 Intraseasonal variability & extreme events Intraseasonal modes represent the largest variations of the Indian summer monsoon. 2002 2007

10. http://www.ncas.ac.uk NCAS Conference 2007 Subseasonal precipitation extremes Heavy (95th) and very heavy (99th) percentiles of precipitation are calculated for each season in 1xCO 2 and 2xCO 2 climates. Extreme precipitation increases are larger than those in the seasonal mean. 1xCO 2 2xCO 2 95th 99th 2xCO 2 minus 1xCO 2

11. http://www.ncas.ac.uk NCAS Conference 2007 Active-break index Simple active-break index constructed from All- India rainfall. Active-break events defined as rainfall anomaly to seasonal cycle lying outside ±1σ, persisting for at least five days.

12. http://www.ncas.ac.uk NCAS Conference 2007 Absolute precipitation in active & break events Clear intensification of active and break events at 2xCO 2. Intensification of break anomalies at 2xCO 2 is tempered by wetter climatological seasonal cycle.

13. http://www.ncas.ac.uk NCAS Conference 2007 Interannual variability Year-to-year variability increases at 2xCO 2 (+24% using Webster-Yang index). Increases are predominantly tied to ENSO. 1xCO 2 2xCO 2 strong-weak monsoon precip and 850hPa wind

14. http://www.ncas.ac.uk NCAS Conference 2007 Monsoon-ENSO teleconnections: lag correlations The teleconnection is generally robust with increased CO 2 forcing. Systematic model bias can have a dramatic impact on the teleconnection to ENSO. 1 A.G. Turner, P.M. Inness, J.M. Slingo (2007a). QJRMS 133: 11431157. JJAS Indian rainfall vs. Niño-3 SST

15. http://www.ncas.ac.uk NCAS Conference 2007 Monsoon-ENSO teleconnection: moving correlations Recent decades have seen a marked decline in the strength of the teleconnection. HadISST vs. All-India gauge data Model teleconnection varies with similar amplitude to observations despite fixed CO 2 forcing. model rainfall

16. http://www.ncas.ac.uk NCAS Conference 2007 Interdecadal uncertainty? One possible source of uncertainty lies in El Nino, which is known to consist of different mechanisms 1,2 which vary in strength over time. 1 A.V. Federov, S.G. Philander (2001). J. Clim. 14: 30863101. 2 E. Guilyardi (2006). Clim. Dyn. 26: 329348. Such changes to the nature of El Nino have been found in 2xCO 2 model integrations, with associated impacts on the monsoon 3. 3 A.G. Turner, P.M. Inness, J.M. Slingo (2007b). QJRMS 133: 11591173.

17. http://www.ncas.ac.uk NCAS Conference 2007 Summary Some qualitative agreement on future increases in the mean monsoon. Systematic model biases may mask the full climate change signal in monsoon regions. Increases in monsoon variability on interannual and intraseasonal timescales. Interdecadal variations in the monsoon and its drivers add additional uncertainty to climate change projections.