Hence there are broadly four scenarios where model simulations of cold induced sterility will be inaccurate: 1) The site experiences a large range of diurnal temperature fluctuation and any threshold based on Tmean cannot accurately capture cool temperatures experienced by the crop, 2) phenology is not accurately modeled,so the simulated crop experiences a different set of temperatures than the observed crop, 3) phenology is accurately modeled, but climate data does not reflect the micro-climate experienced by the developing spikelets, and 4) a short period of cool temperatures coincides with peak spikelet sensitivity, which will have little impact on the total accumulated cooling degree days in the model but a large impact on observed sterility. The structure of ORYZA’s subroutine for cold-induced sterility is poorly equipped to counter these sources of error. Taken together, these issues suggest that the sub-routine ORYZA uses to simulate cold effects on sterilityrequires substantive revision.