Development and Evaluation of Nitrogen Cycling in the Noah-MP-CN Land Surface Model

Abstract:

In climate and biosphere models, terrestrial nitrogen impacts the carbon cycle processes through limiting plant growth; while in operational environmental models, nitrogen is the leading nutrient causing eutrophication in rivers, lakes, and coastal water. The community Noah land surface model with multi-parameterization options (Noah-MP) was designed as the next-generation land surface model for the Weather Research and Forecasting meteorological model and for the operational weather/climate models in NOAA’s National Centers for Environmental Prediction. To improve Noah-MP’s support for weather/climate modeling and enable its new capability for environmental predictions, we developed a terrestrial dynamic nitrogen model for Noah-MP (hereafter Noah-MP-CN). Noah-MP-CN incorporates the state-of-the-art carbon cost theory from the Fixation and Uptake of Nitrogen plant model and the soil nitrogen dynamics from the Soil and Water Assessment Tool, which features its strength in representing the impacts of agricultural management on the nitrogen cycle. Evaluated at a Long Term Ecological Research site within the US Corn Belt—the Kellogg Biological Station—Noah-MP-CN performed well in capturing the major nitrogen state/flux variables (e.g., soil nitrate and nitrate leaching). Compared to the original model without dynamic nitrogen processes, the addition of nitrogen dynamics improved the modeling of net primary productivity and evapotranspiration. In addition, applied to the entire China region, Noah-MP-CN also showed large improvement in carbon cycle simulations (e.g., leaf area index and gross primary productivity) and slight improvement in water cycle simulations (e.g., soil moisture and evapotranspiration). Lastly, Noah-MP-CN showed similar improvements in the San Antonio and Guadalupe Basins in Texas. The study further showed Noah-MP-CN was capable of reproducing the observed nitrogen leaching in these two river basins. In summary, the model development here showed the great potential for Noah-MP-CN to be used in a fully coupled Earth system model for simultaneous weather/climate and environmental predictions.