Can CMIP6 Models Reproduce the Decadal-to-Seasonal Variabilities in Nitrogen Deposition Across Major Emission Hotspots?

Abstract

Atmospheric nitrogen deposition modulates carbon sequestration by terrestrial ecosystems via nitrogen-carbon interactions. The intertwined chemical and physical processes in nitrogen deposition and subsequent nitrogen-carbon interactions pose challenges for Earth system model (ESM) in quantifying them. Here, we combine 30-year nitrogen wet deposition measurements (1980–2014) with Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations to disentangle the nitrogen wet deposition variabilities across different scales. We show that observed decadal trends in nitrogen deposition can be reproduced by ESMs for the United States and Europe, but diverge in East Asia. Models generally fail to capture nitrogen deposition seasonality, with distinct driving factors of model errors for different nitrogen forms. The incorrect ammonia emission seasonality explains the bias in reduced nitrogen deposition, whereas precipitation scavenging and nitrogen oxides chemical oxidation collectively determine the seasonal bias of oxidized nitrogen deposition. Our results can facilitate the informed assessment of nitrogen-carbon-climate interactions under changing human activities.