The Indian Monsoon and Climate Change

1. June-Sept rainfall changes for 2xCO2 850mb wind changes for 2xCO2 Surface temperature changes for 2xCO2 The Indian Monsoon and Climate Change The Indian and South Asian monsoon affects the lives of more than one third of the world’s population. How might it change in the future? • Climate models suggest an increase in summer rainfall over India – on average • Simulations with the Met Office coupled ocean-atmosphere model (HadCM3) suggest a robust Asian summer monsoon - indeed precipitation increases by around 5% over India. • The strengthening occurs due to a warmer Indian Ocean that provides additional moisture for convection. • Model errors may prevent more authoritative projections of the future climate. Tests to examine such errors in this model suggest increases in the monsoon are qualitatively correct. Of much greater interest to the agrarian societies of South Asia is the effect of climate change on annual and intraseasonal variations in the monsoon… Water consumers need advanced warning of long and short term variations in the monsoon in order to adapt their requirements. PDF of daily rainfall anomalies in HadCM3. An increased number of very wet and dry days are predicted during the monsoon season. Intraseasonal variability:during the summer, active and break periods of intense and reduced precipitation have a dramatic impact on water supplies available for agriculture. The dramatic break of July 2002. PDF of summer rainfall totals in HadCM3 shows increased interannual variability. The risk of sustained heavy rain is particularly enhanced. Interannual variability: seasonally persistent floods or droughts can be devastating to the Indian economy if not correctly forecast. Mumbai flooding in August 2005. Climate change may not manifest itself in simple changes alone. Variations on decadal timescales can also influence the monsoon system… • Interdecadal variability:observed relationships between the monsoon and the El Niño-Southern Oscillation over the Pacific have waxed and waned over the last century. Some measure of ENSO is often used in statistical forecasts of the monsoon. • One version of the HadCM3 model suggests that ENSO may change between distinct regimes at 2xCO2. • The regimes and their impact on the monsoon demonstrate that climate change may have more profound effects than previously thought. East Pacific sea-surface temperatures show long periods of irregular and biennial oscillation in HadCM3 at 2xCO2. Correlations between monsoon rainfall and ENSO are very different in each regime. Dr Andrew Turner, Dr Pete Inness and Prof Julia Slingo Contact:a.g.turner@rdg.ac.uk