Impact model: CLASSIC-PEAT

CLASSIC-PEAT is a peatland-enabled version of CLASSIC (CLASS+CTEM) that represents peatland hydrology and carbon cycling and outputs peat-specific variables (e.g., peat soil carbon, peat depth, water-table related diagnostics) together with standard ecosystem carbon and energy fluxes.The model is applied here at global scale following the ISIMIP3a protocol and conventions.

ISIMIP3b
ISIMIP3a

Spin-up design: Spin-up was conducted using spinclim forcing for 1800–1900 until equilibrium was achieved. To avoid excessive peat loss (i.e., peatland burn-out) during spin-up, static peat depth was prescribed for this phase. Atmospheric CO₂ was fixed at the 1850 level. A final (last) spin-up was then performed using spinclim forcing for 1850–1900, with CO₂ concentrations set to the corresponding annual values, to better align model states with early historical conditions.

How to calculate global annual total outputs: Methodology: Calculating Global Annual Total Outputs To calculate global annual totals from CLASSIC monthly gridded files, the process follows a rigorous framework of temporal integration followed by spatial scaling: 1. Temporal Processing: From Rates to Annual Totals The first step involves addressing the time frequency of the data. The approach depends on the physical attributes of the variable: Flux Variables (e.g., NEP, Respiration, Precipitation): Model outputs are typically provided as "rates" (e.g., kilograms per square meter per second). To obtain the annual cumulative total, the average monthly rate is multiplied by the actual number of seconds in that specific month. This ensures that the variation in month lengths (ranging from 28 to 31 days) is accurately captured in the annual sum. State Variables (e.g., Water Table Depth, Soil Moisture): These variables represent a physical state at a given moment rather than an accumulative process. Therefore, when converting from monthly to annual scales, we typically calculate the arithmetic mean of the 12 months rather than a summation. 2. Spatial Scaling: From Simulated Values to Geographical Reality Since CLASSIC simulations for peatlands are conducted under a "Pure Peat" assumption (meaning the model simulates the grid cell as if it were 100% covered by peatland), the outputs must be scaled to reflect their actual geographical footprint. This process requires three essential pieces of information: Grid Cell Area: We utilize latitude-dependent area data. Because the Earth is a sphere, the actual surface area of a grid cell decreases as it moves from the equator toward the poles. An area file is required to convert "values per unit area" into "absolute mass." Landmask: This step defines the valid simulation domain. It excludes the open ocean, major inland water bodies, and permanent ice sheets, ensuring that calculations are restricted solely to terrestrial ecosystems. Peatland Fraction: This is the most critical step for peatland research. Since peatlands may only occupy a small fraction of a specific grid cell, the "Pure Peat" simulated value must be multiplied by the actual fractional peatland cover of that cell to determine its true contribution to the regional or global total. 3. Integration from PFT to Grid Level For data output at the Plant Functional Type (PFT) level, we first perform a weighted sum based on the fractional area of each vegetation type within the grid cell. Once the data is consolidated into a grid-level value, the area and mask processing described above are applied.