Crop phenology feedback on climate over central US in a regional climate model

The moisture and CO2 fluxes over cropland represent local climate forcing and an important component of atmospheric energy and CO2 budgets. Since observed fluxes, especially for CO2, are rarely available over extensive areas the fluxes are mainly estimated by climate models. The carbon sequestration and water consumption by crops are only crudely represented in the models. For example, most climate models use climatological or static crop growth and development that do not change from year to year, indistinguishable between flood and drought years. To improve the moisture and CO2 fluxes (i.e., photosynthesis) from crops we coupled crop models (CERES for corn and CropGro for soybean) with the regional model (MM5) along with the land surface model (LSM). This crop-climate coupled model with interactive crop phenology can simulate interannual variations in CO2 and water fluxes from the surface. The coupled model was used to simulate CO2 and moisture fluxes in the past couple of growing seasons in the central U.S. Results were compared with available CO2 flux observations at some AmeriFlux sites. It is found that the coupled model gives more realistic seasonal accumulation of CO2 fluxes and that the dynamic crop development in the coupled model has a strong feedback on regional precipitation. The typical climate models using static crop phenology significantly overestimate CO2 fluxes during early growing season because of positive biases in specifying leaf area index.