Changes to this version include the recalibration of the Biome Properties Look-up Table (BPLUT) and soil organic carbon (SOC) re-initialization in response to updates to the upstream SPL4SMGP input datasets. Additionally, a major change was made to the carbon model litterfall allocation scheme. Specifically:

• How litterfall is allocated to soil organic carbon (SOC) pools has changed. Previously, a fixed fraction of mean annual net primary production (NPP) was allocated each day to SOC pools. In the new version, the amount of mean annual NPP allocated will vary depending on the calendar day-of-year. A day’s allocation is determined by pre-computed weights, for each pixel and 8-day span (corresponding to the length of a VIIRS leaf area index composite), based on a semi-empirical leaf loss function derived by satellite-observed changes in leaf-area index.
• The SPL4CMDL global BPLUT calibration and SOC initialization using soil moisture and soil temperature data from the latest SMAP L4SM Open Loop (OL8000) ensemble Catchment land model simulation has been revised. The revision results in a calibration that is more consistent with the ensemble SPL4SMGP inputs used in SPL4C production.
• The SPL4CMDL global BPLUT calibration is now based on an entirely new dataset of eddy-covariance tower fluxes, consisting of 410 towers from across multiple, global tower networks. The quality of the flux data is also expected to be an improvement, as previous versions of SPL4CMDL were calibrated against the La Thuile/ FLUXNET2015 dataset which is known to contain some errors and excessive smoothing of the data.
• The calibration of the SPL4CMDL global BPLUT parameters related to SOC decay were also updated and, in this new version, they are based on new reference data from the International Soil Carbon Network (ISCN).