Hello,

For crop modeling under future climate scenarios, I need to provide DSSAT
CSM with CO2 levels from different emissions scenarios.

There appears to be an option in the File X simulation controls to let CO2
be read from the weather file when the switch is set to "W". However,
looking through associated documentation (weather.cde, DSSAT manuals, source
code for CO2val.for), I don't see how one provides CO2 as a variable in the
.WTH file (which is what I assume the setting means).  We have tried
entering a "CO2" (width=6 characters) variable in a .WTH file also
(WTHMOD.FOR suggests this might be possible?), but the model doesn't take it
and defaults to the 380 ppm value.

Besides, the only other solutions I can see are:

1. Define CO2 as a weather variable to be listed alongside the others in
weather.cde, but I presume this means changes to source code for this to
work.

2. Appending CO2 values onto C02o45.WDA, then changing the appended values
in order to capture different emissions scenarios (e.g. A2 versus B1,
etc.).

The latter seems the most straightforward, although I wonder if this would
make the model unhappy, and it is unappealing to have to edit this file
multiple times (which precludes testing multiple CO2 levels in a single
batch run).

It seems that there is already a solution built in, but I can't figure out
how to implement it (maybe I am missing something in the manuals--apologies
if it is blindingly obvious).  I would greatly appreciate any advice on
this.

Thanks in advance,


Lyndon