Thursday, May 10, 2012


cc: Mike Hulme <>
date: Fri, 14 Nov 2003 16:35:28 +0000
from: Tim Mitchell <>
subject: Flooding paper
to: Sari Kovats <>


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

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

Dr. Tim Mitchell
Tyndall Centre for Climate Change Research

phone: +44 (0)1603 59 1378 = CHANGED JULY
fax: +44 (0)1603 59 3901
post: Tyndall, ENV, UEA, Norwich, NR4 7TJ, UK

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