Add PEcAn-to-ILAMB GeoTIFF conversion pipeline (GH-4019)

Adds a Python pipeline in PEcAn.benchmark to convert downscaled SDA
reanalysis GeoTIFF ensemble maps into ILAMB-compatible CF-1.8 netCDF
for cVeg, cSoil, mrsol, and lai, with unit conversions and 13 unit tests.

Author: Tejas7007

CHANGELOG.md

@@ -9,6 +9,7 @@ For more information about this file see also [Keep a Changelog](http://keepacha
 ## Unreleased
 
 ### Added
+- Added `inst/ilamb/` pipeline in PEcAn.benchmark to convert downscaled SDA reanalysis GeoTIFFs into ILAMB-compatible CF netCDF for carbon-cycle benchmarking (#4019).
 - Added PEcAn.PEPRMT model, including a demo run with example data
 - Add `format_try_for_ma()` and `try_trait_mapping()` to `PEcAn.data.remote` to convert trait data from the external TRY database into the tabular format required by the PEcAn meta-analysis module (#3717).
 - Add function `qsub_sda()` for submitting SDA batch jobs by splitting a large number of sites into multiple small groups of sites (#3634).

CITATION.cff

@@ -30,6 +30,7 @@ authors:
   - given-names: David LeBauer
     affiliation: University of Arizona
     orcid: 'https://orcid.org/0000-0001-7228-053X'
+  - given-names: Tejas Dahiya
   - given-names: Michael Dietze
     orcid: 'https://orcid.org/0000-0002-2324-2518'
     affiliation: Boston University

modules/benchmark/NEWS.md

@@ -1,5 +1,9 @@
 # PEcAn.benchmark 1.7.5.9000
 
+## Added
+
+* Added Python pipeline (`inst/ilamb/`) to convert PEcAn SDA reanalysis GeoTIFFs to ILAMB-compatible CF netCDF (cVeg, cSoil, mrsol, lai) with unit tests (#4019).
+
 ## Fixed
 
 * `metric_PPMC()`: added `use = "pairwise.complete.obs"` to `stats::cor()` so the Pearson correlation is computed on available pairs rather than returning `NA` whenever any observation is missing. This matches the behaviour of `metric_cor()` in the same package.

modules/benchmark/inst/ilamb/README.md

@@ -0,0 +1,105 @@
+# PEcAn-to-ILAMB Conversion
+
+Converts PEcAn SDA carbon reanalysis outputs (downscaled GeoTIFF ensemble maps)
+into ILAMB-compatible CF-convention netCDF files for benchmarking against
+TRENDY, CMIP, and observational datasets.
+
+## Overview
+
+The PEcAn North American carbon reanalysis (Zhang et al. 2026) provides
+downscaled 1 km ensemble maps of four state variables. This tool reads those
+GeoTIFFs, computes the ensemble mean, coarsens to ILAMB's default 0.5 degree
+resolution, applies unit conversions, and writes CF-1.8 compliant netCDF that
+ILAMB can ingest directly.
+
+## Input
+
+GeoTIFF ensemble maps organized as:
+
+```
+<input_dir>/<year>/<variable>_<year>/ensemble_<n>_<year>_<variable>.tiff
+```
+
+- 13 years (2012-2024), annual snapshots fixed to July 15
+- 4 variables, 100 ensemble members each
+- 1 km resolution (9360 x 19080), EPSG:4326
+
+## Variable mapping and unit conversions
+
+| PEcAn variable | CMOR name | Source units | Conversion | ILAMB units |
+|----------------|-----------|--------------|------------|-------------|
+| AbvGrndWood    | cVeg      | Mg C ha-1    | x 0.1      | kg m-2      |
+| TotSoilCarb    | cSoil     | kg C m-2     | none       | kg m-2      |
+| SoilMoistFrac  | mrsol     | vol. percent | x 9.98     | kg m-2      |
+| LAI            | lai       | m2 m-2       | none       | m2 m-2      |
+
+**Aboveground biomass** is already a carbon density (Mg C ha-1), so the
+conversion to kg m-2 is purely unit scaling: 1 Mg ha-1 = 0.1 kg m-2.
+
+**Soil moisture** is volumetric water content expressed as percent over the
+0-100 cm root zone. Conversion to mass per area:
+
+```
+kg m-2 = percent / 100 x 1.0 m depth x 998 kg/m3  =  percent x 9.98
+```
+
+The 0-100 cm root-zone depth was confirmed with the dataset author
+(D. Zhang, pers. comm.), and matches the depth span of the ILAMB Wang2021
+soil-moisture benchmark (0-10, 10-30, 30-50, 50-100 cm layers).
+
+## Output
+
+CF-1.8 compliant netCDF on a 0.5 degree regular grid (156 x 318) covering the
+North American study area (7-85N, 179-20W):
+
+- `<output_dir>/<cmor_name>/<cmor_name>_<year>.nc` (one file per year)
+- `<output_dir>/<cmor_name>.nc` (merged multi-year file)
+
+Latitude is monotonically increasing (south to north); coordinates are rounded
+to 0.01 degrees; time is encoded as days since 1850-01-01 with full-year
+bounds.
+
+## Usage
+
+```bash
+module load python3 gcc/13.2.0
+export PATH=$HOME/.local/bin:$PATH
+
+# Convert all variables, all years
+python convert_geotiff_to_ilamb.py \
+    --input_dir /path/to/NA_SDA_maps_zipped \
+    --output_dir /path/to/output
+
+# Single variable / year range
+python convert_geotiff_to_ilamb.py --variables AbvGrndWood --years 2014 2014
+
+# Skip the merge step
+python convert_geotiff_to_ilamb.py --skip-merge
+```
+
+On an HPC system, reading 100 full-resolution members per variable exceeds
+interactive CPU limits; submit the full run as a batch job.
+
+## Testing
+
+```bash
+pytest test_convert.py -v
+```
+
+13 tests cover file existence, CMOR variable naming, all four unit
+conversions, output grid shape, CF-1.8 compliance, latitude direction,
+spatial coverage, chronological multi-year merging, and ILAMB `ModelResult`
+loading. Set `ILAMB_OUTPUT_DIR` to point the tests at your output directory.
+
+## Dependencies
+
+`numpy`, `xarray`, `rasterio`, `netCDF4`, and `ILAMB` (for the loading test).
+
+## Notes
+
+- Fluxes (GPP, NEE) are not included; the downscaled product covers only the
+  four state variables above. Flux benchmarking will draw from the raw SDA
+  netCDF outputs in a later contribution.
+- A known structural discontinuity exists in the underlying LandTrendr input
+  around 2017-2018 (see the ORNL DAAC documentation); it is preserved as-is in
+  the converted output rather than adjusted here.