Representing sub-grid scale variations in nitrogen deposition associated with land use in a global Earth System Model: implications for present and future nitrogen deposition fluxes over North America

Abstract

Abstract. Reactive nitrogen (N) emissions have increased over the last 150 years as a result of greater fossil fuel combustion and food production. The resulting increase in N deposition can alter the function of ecosystems, but characterizing its ecological impacts remains challenging, in part because of uncertainties in model-based estimates of N dry deposition. Here, we leverage the tiled structure of the land component (LM3) of the Geophysical Fluid Dynamics Laboratory (GFDL) 5Earth System Model to represent the impact of physical, hydrological, and ecological heterogeneities on the surface removal of chemical tracers. We show that this framework can be used to estimate N deposition at more ecologically-relevant scales (e.g., natural vegetation, water bodies) than from the coarse-resolution global chemistry-climate model (GFDL-AM3). Focusing on North America, we show that the faster removal of N over forested ecosystems relative to cropland and pasture implies 10 that coarse resolution estimates of N deposition from global models systematically underestimate N deposition to natural vegetation by 10 to 30% in the Central and Eastern US. Neglecting the subgrid scale heterogeneity of dry deposition velocities also results in an underestimate (overestimate) of the amount of reduced (oxidized) nitrogen deposited to water bodies. Overall, changes in land cover associated with human activities are found to slow down the removal of N from the atmosphere, 15 causing a reduction in the dry oxidized, dry reduced, and total N deposition over the contiguous US of 8%, 26%, and 6%, respectively. We also find that the reduction in the overall rate of removal of N associated with land-use change tends to increase N deposition on the remaining natural vegetation and facilitate N export to Canada. We show that subgrid scale differences in the surface removal of oxidized and reduced nitrogen imply that near-term (2010-2050)

Influence of Dynamic Ozone Dry Deposition on Ozone Pollution

“…We conduct time‐slice simulations for the 2010s and 2090s with the NOAA GFDL atmospheric model version 3 (AM3) coupled to the NOAA GFDL land model version 3 (LM3) through not only carbon, water, and energy exchanges but also dry deposition of several atmospheric constituents (AM3DD) (Paulot et al, ). Each simulation contains 10 years.…”

“…Each simulation contains 10 years. Below we describe the model configuration and the dynamic dry deposition scheme for ozone, which we modify from the general dynamic dry deposition scheme described by Paulot et al ().…”

Dry Deposition of Ozone Over Land: Processes, Measurement, and Modeling

“…Later big-leaf schemes (e.g., Clifton, 2018;Emberson, et al, 2000;Erisman et al, 1994;Paulot et al, 2018;Pleim & Ran, 2011;L. Zhang et al, 2002L.…”

“…We recommend developing and archiving model diagnostics oriented toward processes ( Figure 10). Isolating simulated v d for a specific LULC type from the grid-box average (Figure 10), which combines multiple LULC types, is also helpful for more direct comparison with observations (e.g., Paulot et al, 2018;Silva & Heald, 2018). For evaluation with such diagnostics to be most instructional, a firm grasp on the relative roles of individual ozone deposition pathways and the mechanisms responsible for differences across LULC types as gleaned from observations is needed.…”

“…To reduce the impact of differences between site and model variables on model evaluation and thus separate input uncertainty from process and parameter uncertainty (e.g., Z. Wu et al, 2018), we recommend driving standalone schemes with observed Figure 10. Model diagnostics for process understanding of simulated ozone deposition velocity (v d ) as illustrated by regional monthly daily mean v d for the InterMountain West United States at the beginning and end of the 21st century under RCP8.5 (a climate and emissions scenario designed for the Coupled Model Intercomparison Project 5, or CMIP5), as simulated by the NOAA GFDL atmospheric model version 3 (AM3) with dry deposition calculated in the land component of the model (Clifton, 2018;Paulot et al, 2018). Colors indicate contributions from deposition pathways (top panel) and land use/land cover types (bottom panel).…”