…as well as lakes and wetlands outside of the landmask

with new code:

<        ! Assume wetland, glacier and/or lake when dataset landmask implies ocean

<           if (pctgla(n) < 1.e-6_r8) then
<               pctwet(n)    = 100._r8 - pctlak(n)
<               pctgla(n)    = 0._r8
<           else
<               pctwet(n)    = 100._r8 - pctgla(n) - pctlak(n)
<           end if

from

>        ! Assume wetland and/or lake when dataset landmask implies ocean

>           pctwet(n)        = 100._r8 - pctlak(n)
>           pctgla(n)        = 0._r8

Update cime to next version being used in cesm2.1.0 release. And fix the XML for f05
surface dataset for 1850 and non-crop. Test that all six f05 cases work (1850/2000/Hist,crop/non-crop).

…rrecting that now allows each one to work correctly

Option for rain-to-snow to immediately run off in some regions

Up until now: When repartition_rain_snow is .true. (which is the default
for CLM5), rain that falls when the near-surface temperature is cold is
converted to snow. This repartitioning was put in place for two
reasons: (1) Downscaling to elevation classes: changing the balance
between rain and snow for different elevation classes; (2) Correcting
problems in CAM. However, members of the Land Ice Working Group would
like to change this behavior so that, when CAM produces cold-temperature
rain, this rain immediately runs off rather than being converted to
snow. The purpose of this is to reduce the too-high SMB over portions of
Greenland in CESM2 coupled runs (which results in part from CAM's
generation of liquid precipitation despite very cold temperatures).

This new behavior is implemented in a glacier region-specific manner,
based on a new namelist flag, glacier_region_rain_to_snow_behavior. It
is not at all ideal to make this aspect of the physics differ by region,
but this has been requested by members of the Land Ice Working Group in
order to address biases over Greenland while having minimal impact on
the climate (so that the climate can stay very similar to that of the
official CMIP6 runs). Note that, unlike other glacier region-specific
behaviors, this one applies to all landunits, not just glaciers. This
also seems a bit non-ideal, but we want the physics to be the same for
all landunit types in a given region, and we also want this behavior to
apply to vegetated columns because they are used for glacial
inception (and we want this alternate behavior to apply to glacial
inception, too, in order to decrease some instances of inception).

The justification for this new physics is: In the case of (1) above: If
CAM is generating rain at a given elevation / temperature, that doesn't
necessarily imply that an equal water equivalent of snow would be
generated at a higher elevation / lower temperature: indeed, in reality,
there might not be any precipitation falling at that higher elevation /
lower temperature. In the case of (2) above: There seem to be problems
with CAM's microphysics that cause it to produce too much rain when
temperatures are very cold; it seems (at least to some people) equally
justifiable to throw this cold rain away (by sending it to the ocean as
runoff) as it is to convert this cold rain to snow.

Note: I don't think any changes are needed in
BalanceCheck (unfortunately), since BalanceCheck currently uses the
post-downscaling precipitation fluxes, and the pre-lnd2atm runoff
fluxes (i.e., the new runoff flux isn't included in the terms in
BalanceCheck, and it doesn't need to be because BalanceCheck uses the
post-downscaling precipitation fluxes). (See also
ESCOMP#201 (comment) .)

CTSM Master Tag This Corresponds To: N/A

   At least for now, we are bringing this to the release branch but not
   to master. Here is an excerpt from the email explaining this
   rationale:

   My question is: Should I do this:

   (1) Just on a branch off of the release-clm5.0 branch, with no plan
       to bring it back to release-clm5.0 or master

   (2) On the release-clm5.0 branch, but not bring it back to master

   (3) On the release-clm5.0 branch and master

   My inclination right now is towards (2). I don't really like (1)
   because this change will be wanted for a number of CMIP6-related
   experiments, and it feels like it could be a pain to keep this branch
   up-to-date with the evolving release-clm5.0 branch. However, the
   changes are going to be a bit messy and having this be
   region-specific isn't really physically justifiable (it's just being
   done that way to keep the climate as close as possible to the
   official CMIP6 runs), so I'm not sure we really want this on
   master. If we did anything on master, I could imagine having a
   globally-applicable switch controlling this behavior, rather than
   having it apply to just certain glacier regions.

   Bette: The main reason I could see for bringing this to master is if
   you imagine needing to use this new option in isotope-enabled runs,
   since the isotope-enabled version of CTSM won't be on the
   release-clm5.0 branch. Do you think it's likely that you'd need to do
   that, or would the isotope-enabled runs use the standard CMIP6
   physics settings in this respect?

…as sim_year for clm4_5