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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 NCAS Conference 2007 http://www.ncas.ac.uk 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. NCAS Conference 2007 http://www.ncas.ac.uk Outline Introduction Model details The mean monsoon Extremes & active-break cycles Interannual variability and predictability Decadal-timescale uncertainties Summary NCAS Conference 2007 http://www.ncas.ac.uk Model experiments Hadley Centre coupled model HadCM3 run at high vertical resolution (L30). This better represents intraseasonal tropical convection1 and has an improved atmospheric response to El Niño2. Control (1xCO2) and future climate (2xCO2) integrations used to test the impact of increased GHG forcing. Further integration of each climate scenario to test the role of systematic model biases. 1P.M. 2H. Inness, J.M. Slingo, S. Woolnough, R. Neale, V. Pope (2001). Clim. Dyn. 17: 777--793. Spencer, J.M. Slingo (2003). J. Climate 16: 1757--1774. NCAS Conference 2007 http://www.ncas.ac.uk Mean response of the monsoon to 2xCO2 NCAS Conference 2007 http://www.ncas.ac.uk Mean monsoon response in the AR4 models Fig 10.91: some consistency in the JJA response of precipitation over India to A1B forcing with 2xCO2 result (but within intermodel spread). Fig 10.121: less than 80% of models agree on annual mean change in precip over India. 10.12 10.9 Of the six AR4 models which reasonably simulate the monsoon precipitation climatology of the 20th century, all show general increases in seasonal rainfall over India in the 1pctto2x runs2. 12G. H. Annamalai, Hamilton, K. Climate R. Sperber (2007). J. Climate 20: 1071--1092 Meehl et al. K. (2007) Global Projections. In: Climate Change 2007: The Physical Science Basis. NCAS Conference 2007 http://www.ncas.ac.uk Systematic model bias and the uncertain response to 2xCO2 NCAS Conference 2007 http://www.ncas.ac.uk Uncertainty in monsoon precipitation response to 2xCO2 Systematic bias seems to mask full impact of changing climate 1A.G. Turner, P.M. Inness, J.M. Slingo (2007a). QJRMS 133: 1143—1157. NCAS Conference 2007 http://www.ncas.ac.uk Intraseasonal variability & extreme events Intraseasonal modes represent the largest variations of the Indian summer monsoon. 2002 2007 NCAS Conference 2007 http://www.ncas.ac.uk Active-break index Simple active-break index constructed from AllIndia rainfall. Active-break events defined as rainfall anomaly to seasonal cycle lying outside ±1σ, persisting for at least five days. NCAS Conference 2007 http://www.ncas.ac.uk Absolute precipitation in active & break events Clear intensification of active and break events at 2xCO2. Intensification of break anomalies at 2xCO2 is tempered by wetter climatological seasonal cycle. NCAS Conference 2007 http://www.ncas.ac.uk Interannual variability Year-to-year variability increases at 2xCO2 (+24% using Webster-Yang index). Increases are predominantly tied to ENSO. strong-weak monsoon precip and 850hPa wind 1xCO2 2xCO2 NCAS Conference 2007 http://www.ncas.ac.uk Monsoon-ENSO teleconnections: lag correlations Systematic model bias can have a dramatic impact on the teleconnection to ENSO. JJAS Indian rainfall vs. Niño-3 SST The teleconnection is generally robust with increased CO2 forcing. 1A.G. Turner, P.M. Inness, J.M. Slingo (2007a). QJRMS 133: 1143—1157. NCAS Conference 2007 http://www.ncas.ac.uk Monsoon-ENSO teleconnection: moving correlations HadISST vs. All-India gauge data Recent decades have seen a marked decline in the strength of the teleconnection. model rainfall Model teleconnection varies with similar amplitude to observations despite fixed CO2 forcing. NCAS Conference 2007 http://www.ncas.ac.uk Interdecadal uncertainty? One possible source of uncertainty lies in El Nino, which is known to consist of different mechanisms1,2 which vary in strength over time. Such changes to the nature of El Nino have been found in 2xCO2 model integrations, with associated impacts on the monsoon3. 31A.G. Turner, P.M. J.M.(2001). Slingo J. (2007b). QJRMS 133: A.V. Federov, S.G.Inness, Philander Clim. 14: 3086—3101. 1159—1173. 2E. Guilyardi (2006). Clim. Dyn. 26: 329—348. NCAS Conference 2007 http://www.ncas.ac.uk 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. NCAS Conference 2007 http://www.ncas.ac.uk