Refactor active layer calculation to separate bottom-up, top-down, and rooting metrics - #45
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Refactor active layer calculation to separate bottom-up, top-down, and rooting metrics#45rfiorella wants to merge 2 commits into
rfiorella wants to merge 2 commits into
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…d rooting metrics Implements three distinct thaw depth calculations to improve representation of permafrost dynamics and rooting access: 1. ZTHAW_BU (bottom-up): Preserves original algorithm searching from bedrock upward for deepest thaw. Includes talik (deep thawed soil) in calculation. Used for subsidence and thermal state tracking. 2. ZTHAW_TD (top-down): New algorithm searching from surface downward for first frozen layer. Excludes isolated talik beneath frozen barriers. Represents surface-connected thawed zone accessible to roots and biogeochemical processes. 3. ALT (active layer): Defined as max(ZTHAW_TD, ZTHAW_TD_lastyear) to implement rooting memory. Allows roots to access the deeper of current year or prior year maximum top-down thaw depth. Maintains backward-compatible variable names (altmax_col, altmax_lastyear_col) so external modules (RootDynamicsMod, etc.) require no changes. ## Key Features - Algorithms converge to same value when no talik exists (seasonally frozen regions, open taliks) - Algorithms diverge only when frozen layer separates two thawed zones (closed talik) - During growing season with full column thaw, ZTHAW_TD correctly captures entire thawed depth - Rooting memory preserves access to previously-thawed depths that remain surface-connected - Polygonal tundra subsidence now responds to ALT (max of top-down thaw) rather than bottom-up - Backward-compatible restart I/O: reads old format and initializes new variables conservatively - New history fields (ZTHAW_BU, ZTHAW_TD, etc.) default to inactive to avoid output bloat ## Modified Files - ActiveLayerMod.F90: Implements three sequential algorithms in single timestep - CanopyStateType.F90: Expands from 10 to 24 variables organized by algorithm type ## Scientific Justification Closed talik (deep thaw isolated by frozen permafrost) is hydraulically disconnected from roots when surface-connected thaw is shallower. Frozen soil reduces hydraulic conductivity by 4-6 orders of magnitude, creating an effective aquiclude. Top-down algorithm correctly represents surface-connected thawed zone that roots can functionally access, while bottom-up captures deepest thermal thaw important for subsidence modeling.
The bottom-up 1989 baseline variables were declared, allocated, initialized, and included in restart I/O but never computed or read in any logic. Remove them from CanopyStateType and the alt_calc associate block. Retain zthaw_bu_max_ever and altmax_1989, which remain in use.
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This one should probably get a pretty robust discussion, since it will not be BFB. |
rfiorella
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August 28, 2026 05:49
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Refactor active layer calculation to separate bottom-up, top-down, and rooting metrics
Summary
Implements three distinct thaw depth calculations to improve representation of permafrost dynamics and rooting access:
ZTHAW_BU (bottom-up): Preserves original algorithm searching from bedrock upward for deepest thaw. Includes talik (deep thawed soil). Included mainly for backward compatibility.
ZTHAW_TD (top-down): New algorithm searching from surface downward for first frozen layer. Excludes isolated talik beneath frozen barriers. Represents surface-connected thawed zone accessible to roots.
ALT (active layer): Defined as max(ZTHAW_TD, ZTHAW_TD_lastyear) to implement rooting memory. Allows roots to access the deeper of current year or prior year maximum top-down thaw depth.
Key Features
Modified Files
components/elm/src/biogeophys/ActiveLayerMod.F90: Implements three sequential algorithmscomponents/elm/src/biogeophys/CanopyStateType.F90: Expands from 10 to 24 variables organized by algorithm