cc: Keith Briffa <k.briffaatXYZxyz.ac.uk>
date: Thu, 23 Jun 2005 14:49:36 +0100
from: "Betts, Richard" <richard.bettsatXYZxyzoffice.gov.uk>
subject: RE: sudden response to vegetation change?
to: Tim Osborn <t.osbornatXYZxyz.ac.uk>, "Tett, Simon" <simon.tettatXYZxyzoffice.gov.uk>
Yes, this probably is due to land use, and is probably an artifact of
the particular diagnostic chosen for the run rather than being a result
of climate change.
That particular soil moisture diagnostic represents soil moisture in the
root zone. When deforestation is imposed, the root zone shrinks so that
diagnostic shows less soil moisture. The soil moisture content per unot
root depth may not have actually changed though.
There is an alterntive diagnostic (soil moisture content in layers)
which is independent of the plant roots, but unfortunately I think that
wasn't included in the run.
Dr Richard Betts
Manager, Ecosystems and Climate Impacts
Hadley Centre for Climate Prediction and Research
Met Office, Fitzroy Road, Exeter, EX5 2SN, UK
Tel: +44 (0)1392 886877 Fax: +44 (0)1392 885681
From: Tim Osborn [mailto:email@example.com]
Sent: Thursday, June 23, 2005 2:35 PM
To: Betts, Richard; Tett, Simon
Cc: Keith Briffa
Subject: sudden response to vegetation change?
Dear Simon and Richard,
I have a question regarding some very sudden changes in soil moisture in
the ALL250 HadCM3 run. Please see the attached PDF plots. They all
from 9 grid boxes in and around Fargo in North Dakota. The exact
coordinates for the 9 boxes are given in the header of the ASCII data
which contains the soil moisture data only.
If you look at the soil moisture plots, you'll see very sudden
in some boxes at different times. Why? If "real", I can only guess
this is due to vegetation change imposed during ALL250. These are
means with a 30-yr filter also shown. If you look at the data file
see that the second time series (from 97.5 W, 50 N) has the change
1910 and 1911 affect all months. And it is huge relative to the
mean and relative to interannual variability. The first time series in
file doesn't show such a change.
Should such changes be so sudden, and with such contrast between
neighbouring grid boxes? I guess it might if the Ramankutty & Foley
use data have such discontinuities in.
For interest I've also included time series of new surface SW radiation
air temperature from the same 9 boxes. They show trends rather than
changes, perhaps more related to tropospheric sulphate aerosol cooling
to vegetation change? Anyway, there's apparently no anthropogenic
here in HadCM3.
Any comments on the apparent discontinuities? I'm wondering whether I
should use these grid box time series? I could average the 9 together
get a North Dakota time series, which would smooth the change out, but
given the underlying behaviour, I'm not sure I'd be confident in this