Stochastic control of Indian megadroughts and megafloods
- 231 Downloads
A multi-millennial run of the CSIRO Mark2 coupled climatic model has been used to investigate megadroughts and megafloods during the Indian summer monsoon (June–September). These extreme events were defined as having rainfall anomalies at least two standard deviations from normal. More than ten megafloods and more than twenty megadroughts, so-defined, were found to occur in a 5,000-year period of the simulation. The simulation replicated most of the major features of the observed summer monsoon, but a comparison of observed and simulated probability density functions suggests that the limited observed rainfall time series to date does not adequately sample the possible range of Indian monsoonal rainfall. An investigation of causal mechanisms of Indian rainfall variability reproduced the observed negative correlation with ENSO events, but it was found that neither extreme ENSO events or extremes of a range of other climatic phenomena coincided with the simulated, extreme megadroughts and megafloods. This disconnect between these events is succinctly illustrated with examples related to ENSO events in particular. Autoregressive and FFT analysis of observed and simulated Indian summer monsoon rainfall time series revealed them to consist of white noise. Since these time series therefore consist of random outcomes, it is apparent that these Indian megadroughts and megafloods are the consequence of stochastic influences. Thus, it is concluded that the interannual variability of Indian summer monsoonal rainfall cannot be predicted in general, nor can megadroughts and megafloods in particular.
KeywordsMegadroughts Megafloods Multi-millennial simulation Indian monsoon
I would like to thank the Indian Institute of Tropical Meteorology for making available the observed Indian rainfall time series used in this paper.
- Gadgil S, Joseph PV (2003) On breaks of the Indian monsoon. Proc Indian Acad Sci 112:529–558Google Scholar
- Goswami BN, Krishnamurthy V, Annamalai H (1997) A broad scale circulation index for the interannual variability of the Indian summer monsoon. COLA Tech. Rep. 46, p 52. Center for Ocean-Land-Atmosphere Studies, CalvertonGoogle Scholar
- Hunt BG, Elliott TI (2003) Secular variability of ENSO events in a 1000-year climatic simulation. Clim Dyn 20:689–703Google Scholar
- McGregor JL, Gordon HB, Watterson IG, Dix MR, Rotstayn LD (1993) The CSIRO 9-level atmospheric general circulation model. CSIRO Division of Atmospheric Research Tech Paper 26, p 89Google Scholar
- Rajeevan M, Unnikrishnan CK, Preethi B (2011) Evaluation of the ENSEMBLES multi-model seasonal forecasts of Indian summer monsoon variability. Clim Dyn. doi: 10.1007/s00382-011-1061-X (published on line)
- Saji NH, Goswami BN, Vinayachandran PN, Yamagata T (1999) A dipole mode in the tropical Indian ocean. Nature 401:360–363Google Scholar