SUMMARYThe sensitivity of predicted final grain yield to changes in the mean and variance of daily temperature and daily log(radiation) was studied for the arcwheat1 crop model of winter wheat. These two climatic variables were each simulated by each of two stochastic models, the parameters of which were estimated from 12 years' data from Rothamsted Experimental Station.When arcwheat1 was run with systematic changes in daily temperature from – 2 °C to +2 °C in steps of 0·1 °C, there were abrupt changes in predicted final grain yield which coincided with predicted increases in leaf number. These effects were smoothed out when the stochastic climate models incorporating simulated daily variation were used as inputs, in multiple runs of arcwheat1.In such runs, the response of predicted yield to changes in the means of temperature and log(radiation) was studied both for individual developmental stages and over the entire growing season. Yield was insensitive to changes in temperature and radiation during the stage between sowing and emergence, and to changes in radiation before terminal spikelet formation.