Dynamic Crop Life Cycles in the CCSM

The dynamic crop life cycle parameterizations in the Community Climate System Model (CCSM) simulate improved vegetation phenology and ground cover relative to the stress-deciduous phenology parameterization traditionally used with grasses to represent a generic crop. This means better timing of leaf emergence and senescence and better leaf and stem area index values when representing corn, spring wheat, and soybean explicitly, rather than with the generic crop. For places like Nebraska, USA, the generic crop and C3 grasses green up earlier than corn, spring wheat, and soybean (reasonable for unmanaged grasses) and retain leaf area index values of 4 or more through December (not reasonable even for unmanaged grasses). Areas of corn, spring wheat, and soybean remain almost bare after summer's harvest usually through May. Such different representations of agriculture affect the surface albedo, evapotranspiration, and roughness. We explore the climate sensitivity to alternate representations of crop.