DOI: 10.5061/dryad.0k6djhb73
title: Coupled PPE model output - land parameter impacts on the mean climate state

description: Terrestrial processes influence the atmosphere by controlling
 land-to-atmosphere fluxes of energy, water, and carbon. Prior research has
 demonstrated that parameter uncertainty drives uncertainty in land surface
 fluxes. However, the influence of land process uncertainty on the climate
 system remains underexplored. Here, we quantify how assumptions about land
 processes impact climate using a perturbed parameter ensemble for 18 land
 parameters in the Community Earth System Model (CESM2) under preindustrial
 conditions. We find that an observationally-informed range of land
 parameters generate biogeophysical feedbacks that significantly influence
 the mean climate state, largely by modifying evapotranspiration. Global
 mean land surface temperature ranges by 2.2°C across our ensemble
 (standard deviation = 0.5°C) and precipitation changes were significant
 and spatially variable. Our analysis demonstrates that the impacts of land
 parameter uncertainty on surface fluxes propagates to the entire Earth
 system, and provides insights into where and how land process uncertainty
 influences climate.
description: We ran PPEs under preindustrial conditions using two
 configurations of CESM2: a partially coupled configuration (“coupled”) and
 an uncoupled, land only configuration (“land-only”). In both the coupled
 and land-only PPE, the land model (CLM5) was run with prognostic leaf
 area. The land was initialized with the spun-up land state from the
 default model parameterization which includes the carbon content of soil
 and vegetation pools.  In the coupled ensemble, we ran preindustrial
 simulations with constant greenhouse gas concentrations using an active
 atmosphere (CAM6) and a slab ocean which is based on q-fluxes from
 preindustrial simulations of the full dynamic ocean model. Because these
 simulations have fixed concentrations of greenhouse gasses including CO2,
 they capture the biogeophysical impacts of land parameters which is the
 focus of this project, but they do not capture biogeochemical feedbacks.
  The land-only simulations used a custom atmospheric forcing, which was
 generated by CAM6 in the reference coupled simulation that used default
 parameters. Each parameter perturbation simulation,
 which we refer to as an ensemble member, was run for 140 years under
 constant preindustrial greenhouse gas concentrations and land use
 conditions. Our PPEs sampled 18 land parameters (see https://github.com/czarakas/coupled_PPE/blob/main/code/02_set_up_ensemble/CLM5PPE_coupledPPE_crosswalk.csv), and our parameter selection was informed by the CLM5 PPE project (data and methods description are available via https://github.com/djk2120/clm5ppe). The 18 parameters we selected span nine functional categories: soil hydrology, stomatal conductance and plant water use, snow, photosynthesis, boundary layer / roughness, radiation, canopy evaporation, biomass heat storage, and temperature acclimation. For each parameter, we ran two simulations, where the parameter was perturbed to a minimum and maximum value (ensemble n = 36). We used the parameter ranges from the CLM5 PPE, which were determined by domain-area experts based on literature review and expert judgement. Because some parameters have larger ranges than others, our analysis includes both the sensitivity of the climate system to a change in a parameter combined with the uncertainty in that parameter’s range.
description: # Coupled PPE model output - land parameter impacts on the mean climate
 state ## Description of
 the data and file structure This dataset is organized into three folders:
 `coupled_PPE`, `landonly_PPE`, and `doubling_CO2`. `coupled_PPE`
 and`landonly_PPE` contain monthly model output from the coupled and land
 only PPEs, respectively, for all output variables used in our analysis.
 These output variables are land surface temperature (TSKIN), land
 precipitation (PREC_FROM_ATM), latent heat flux (EFLX_LH_TOT), sensible
 heat flux (FSH), downwelling shortwave radiation (FSDS), and reflected
 shortwave radiation (FSR). Data filenames for the PPE are formatted as
 `VARIABLENAME_timeseries_PPETYPE.nc` (e.g. for the TSKIN data from the
 coupled PPE, the filename is `TSKIN_timeseries_coupled.nc`). PPE data has
 dimensions of [time, lat, lon, ensemble_key]. The ensemble keys correspond
 to different parameter perturbation ensemble members, which are described
 at
 . Data from the reference simulation are also included, in the format `ref_VARIABLENAME_timeseries_PPETYPE.nc`. The `doubling_CO2`contains one file, `Reponse_TS_2xCO2_AnnualMean.nc`, which is the annual mean change in surface temperature between a simulation with preindustrial CO2 concentrations and a simulation with 2x preindustrial CO2 concentrations. ## Code/Software Code used to run simulations and analyze model output are available at