Input data set: N-Deposition (ISIMIP4)

The nitrogen deposition datasets provide atmospheric inputs of reactive nitrogen for ISIMIP4b impact simulations. They include both wet and dry deposition of reduced nitrogen (NHx) and oxidized nitrogen (NOy) and the totals, representing the deposition of nitrogen originating from anthropogenic and natural emissions. Nitrogen deposition is required by terrestrial ecosystem, vegetation, and biogeochemical impact models to represent nutrient inputs and associated ecosystem responses. Unlike atmospheric CO₂ concentrations, nitrogen deposition is not diagnosed by emission-driven Earth System Models in CMIP7. Consequently, the same prescribed nitrogen deposition forcing is used for both concentration-driven and emission-driven climate simulations to ensure a consistent representation of atmospheric nitrogen inputs across all ISIMIP4 simulations.

The dataset provides monthly gridded deposition fluxes of oxidized (NOy) and reduced (NHx) nitrogen for wet deposition, dry deposition, and total deposition on a global 0.5° × 0.5° grid. The total deposition fields are calculated as the sum of the corresponding wet and dry deposition components. Nitrogen deposition is prescribed as an external forcing and is identical for concentration-driven and emission-driven simulations.

For ISIMIP4a, the historical forcing is constructed from two Input4MIPs releases:

FZJ-CMIP-nitrogen-2-0 (v20260318) for 1850–2022
FZJ-CMIP-nitrogen-m-1-0 for 2023–2025

This provides a continuous historical nitrogen deposition time series through 2025.

For ISIMIP4b, nitrogen deposition is taken directly from the CMIP7 Input4MIPs datasets:

FZJ-CMIP-nitrogen-2-0 (v20260318) for the historical period
FZJ-CMIP-nitrogen-vl-1-0 (v20260706) for very-low forcing scenarios
FZJ-CMIP-nitrogen-h-1-0 (v20260409) for high forcing scenarios.

Nitrogen deposition forcing is taken from the CMIP7 Input4MIPs nitrogen deposition dataset FZJ-CMIP-nitrogen-2-0, developed by Forschungszentrum Jülich and distributed through the Input4MIPs infrastructure. Specifically:

Historical: FZJ-CMIP-nitrogen-2-0 (v20260318)
Future scenarios: FZJ-CMIP-nitrogen-vl-1-0 (v20260706) and FZJ-CMIP-nitrogen-h-1-0 ( v20260409)

This dataset provides globally gridded monthly fields of wet and dry deposition for NHx and NOy for historical and scenario simulations. In addition to the wet and dry deposition components provided by the Input4MIPs datasets, ISIMIP distributes total NOy and NHx deposition fields, computed as the sum of the respective wet and dry deposition fluxes.

Documentation is available at:

https://input4mips-cvs.readthedocs.io/en/latest/dataset-overviews/nitrogen-deposition/

The prescribed deposition fields are used unchanged for both concentration-driven and emission-driven CMIP7 simulations because atmospheric nitrogen deposition is an external forcing and may not be interactively calculated by the emission-driven Earth System Models.