cc: Mike Hulme date: Fri, 14 Nov 2003 16:35:28 +0000 from: Tim Mitchell subject: Flooding paper to: Sari Kovats Sari, Quantification of uncertainty in precip projections: This must be regionally specific to be useful, and lies beyond the scope of this background document. I advise researchers to quantify for themselves using: http://www.cru.uea.ac.uk/~timm/grid/TYN_SC_2_0.html Which countries/regions most affected: This is not a relevant question unless it is contextually embedded. A country with currently low rainfall but a small increase in the future may be 'more affected' than a country with high rainfall and the same small increase. Again, individual regions must be examined. Probabilistic approaches: Yes - I agree, but there is no global data available. Or even continental data. For the UK, see: Osborn TJ and Hulme M (2002) Evidence for trends in heavy rainfall events over the United Kingdom. Philosophical Transactions of the Royal Society London series A 360, 1313-1325 Asian monsoon: Summary from IPCC WG1 TAR p568 " One of the most significant aspects of regional interannual variability is the Asian Monsoon. Several recent studies (Kitoh et al., 1997; Hu et al., 2000a; Lal et al., 2000) have corroborated earlier results (Mitchell et al., 1990; Kattenberg et al., 1996) of an increase in the interannual variability of daily precipitation in the Asian summer monsoon with increased greenhouse gases. Lal et al. (2000) find that there is also an increase in intra-seasonal precipitation variability and that both intra-seasonal and inter-annual increases are associated with increased intra-seasonal convective activity during the summer. Less well studied is the Asian winter monsoon, although Hu et al. (2000b) find reductions in its intensity with a systematic weakening of the north-easterlies along the Pacific coast of the Eurasian continent. However, they find no change in the interannual or inter-decadal variability. "The effect of sulphate aerosols on Indian summer monsoon precipitation is to dampen the strength of the monsoon compared to that seen with greenhouse gases only (Lal et al., 1995; Cubasch et al., 1996; Meehl et al., 1996; Mitchell and Johns 1997; Roeckner et al., 1999), reinforcing preliminary findings in the SAR. The pattern of response to the combined forcing is at least partly dependent on the land-sea distribution of the aerosol forcing, which in turn may depend upon the relative size of the direct and indirect effects (e.g., Meehl et al., 1996; Roeckner et al., 1999). There is still considerable uncertainty in these forcings (Chapter 6). To date, the effect of aerosol forcing (direct and indirect) on the variability of the monsoon has not been investigated. "In summary, an intensification of the Asian summer monsoon and an enhancement of summer monsoon precipitation variability with increased greenhouse gases that was reported in the SAR has been corroborated by new studies. The effect of sulphate aerosols is to weaken the intensification of the mean precipitation found with increases in greenhouse gases, but the magnitude of the change depends on the size and distribution of the forcing." regards Tim _____________________________________ Dr. Tim Mitchell Tyndall Centre for Climate Change Research email: t.mitchell@uea.ac.uk web: http://www.cru.uea.ac.uk/~timm/ phone: +44 (0)1603 59 1378 = CHANGED JULY fax: +44 (0)1603 59 3901 post: Tyndall, ENV, UEA, Norwich, NR4 7TJ, UK _____________________________________