Initial Development for Simulating Land Surface Change Impacts on Climate in the Northern Great Plains

Over the past several decades, the coverage of crops has changed dramatically over the Northern Great Plains (NGP). In North Dakota for example, barley and wheat acreages have decreased while leafier plants such as corn and soybeans have seen increases in planting. The leafier crops are more effective at evapotranspiration, and this interaction between the soil and the atmosphere modifies the atmospheric boundary layer. Most notably, recent decades have seen increases in precipitation and minimum temperatures across the region. Prior studies suggest that at least some of this signal is due to land cover (crop) changes and warrants further study on the regional climate impact of land surface changes in the NGP.

Most modeling strategies use look-up tables to prescribe parameters such as leaf area index (LAI) to predict surface energy fluxes of a model’s lower boundary. Typically, this strategy does not produce the most accurate land surface parameters. In this study, the Weather Research and Forecasting (WRF) model is employed to simulate historical periods (2011-2015) across the NGP. A dynamic crop model from the Noah-MP land surface model is used to simulate the crop growing season. The crop model uses plant growth stages (PGS) to simulate the crop growth process, and PGS are estimated by accumulated growing degree days (GDD). Since PGS are a function of GDD and the relationship can change yearly and by geographical region, a linkage between PGS and GDD is first established for the NGP region. After GDD thresholds for PGS are established, year-long 12-km WRF simulations are investigated with and without the crop model to elucidate changes in surface energy fluxes and to study their impact onto the atmosphere between the differing land surface simulations. In addition, documentation is developed describing the crop model process used within WRF.