Additional changes to streamline the phenology code (not bit-for-bit)

[mpaiao]

Description:

This pull request is part of the #1385 task, and it introduces multiple changes in the phenology code aiming at making the logic and the code itself a bit simpler. Because there were (mostly minor) changes in the logic, this is not expected to be bit-for-bit, though these are not expected to cause major changes in results.

In short, these are the changes implemented:

1. Moved the updates for days since last flushing and abscission events to the cumulative time subroutine.
2. Changed the initialisation of the dates of the last flushing/abscission deciduous events, so they can start at negative values. This change should eliminate the need for a few if statements in the main phenology subroutine.
3. Added a fourth case for cold deciduous phenology, which forces leaf flushing if plants remain dormant due to cold for a very long time. This should cause these plants to be vulnerable to frost in climates that are too cold for them to survive.
4. Saved some phenology transition tests to logical variables to make the code a bit more readable.
5. Restructured the cold-deciduous phenology code so the different checks are inside an if/elseif/else block (so only one change can happen at any time).
6. Replaced some additional checks for growing degree days that should be taken care by change 2 plus the definition of a growing season.

In addition, the phenology status constants (stored in currentSite%phen_status(ipft)) were updated, and cold-deciduous state names were renamed similarly to the drought deciduous so the code is more easily interpretable (I personally found the original naming a bit confusing). The table below includes all the statuses, original names (except for new statuses) and new names, along with the description.

Code	New name	Original name	Description
0	phen_estat_evergreen	—	Dummy phenology state for evergreen PFTs
1	phen_cstat_timeoff	phen_cstat_nevercold	Leaves off, leaves exceeded life span without cold days
2	phen_cstat_tempoff	phen_cstat_iscold	Leaves off after reaching multiple cold days
3	phen_cstat_tempon	phen_cstat_notcold	Leaves on after exceeding the growing degree day threshold
4	phen_cstat_timeon	—	Leaves on after extended cold period, forced flushing
5	phen_dstat_timeoff	phen_dstat_timeoff	Leaves off, leaves exceeded life span without desiccation
6	phen_dstat_moistoff	phen_dstat_moistoff	Leaves off, moisture availability fell below the threshold
7	phen_dstat_moiston	phen_dstat_moiston	Leaves on, moisture availability went above the threshold
8	phen_dstat_timeon	phen_dstat_timeon	Leaves on after extended dry period, forced flushing
9	phen_dstat_pshed	phen_dstat_pshed	Leaves partially abscissing due to drying conditions

This pull request should be integrated only after #1355 #1389 and #1392 are integrated.

Collaborators:

@glemieux @rgknox @rosiealice @XiulinGao @lmkueppers @ckoven

Expectation of Answer Changes:

There are some minor changes in logic, so this is unlikely to be bit-for-bit.

Checklist

If this is your first time contributing, please read the CONTRIBUTING document.

All checklist items must be checked to enable merging this pull request:

Contributor

• The in-code documentation has been updated with descriptive comments
• The documentation has been assessed to determine if updates are necessary

Integrator

• FATES PASS/FAIL regression tests were run
• Evaluation of test results for answer changes was performed and results provided
• FATES-CLM6 Code Freeze: satellite phenology regression tests are b4b

If satellite phenology regressions are not b4b, please hold merge and notify the FATES development team.

Documentation

• Technical Note update:
• User's Guide update:

Test Results:

CTSM (or) E3SM (specify which) test hash-tag:

CTSM (or) E3SM (specify which) baseline hash-tag:

FATES baseline hash-tag:

Test Output: