High quality of long-term daily weather data is essential for simulating crop production and its variability. However, daily weather data with adequate duration and required quality are not available in many regions. This study has evaluated the suitability of AgMERRA (The Modern-Era Retrospective Analysis for Research and Applications) weather data for simulating rainfed wheat evapotranspiration (ETc) and yield. Daily AgMERRA were compared with corresponding observed weather data of 11 land stations across the northeast Iran, considering the different periods from 1980 to 2010. Cropwat and CSM-CERESWheat models were used to simulate ETc and yield of rainfed wheat, respectively. The comparison of daily AgMERRA with observations resulted in the highest correlation (r2 > 70%) and good agreement (d > 0.77 and NRMSE < 30%) between climate variables, except for daily wind speed and precipitation at all locations. However, when daily precipitation data were aggregated into 15-day periods, agreement and correlation improved. According to the monthly comparison, the largest bias between AgMERRA temperature and radiation with land observations was obtained from June to August (summer season). Results also indicated that the distribution of simulated ETc and yield using AgMERRA was within 10% of the simulated yield using observations at 73% and 100% of locations, respectively. The degree of variation of AgMERRA-simulated ETc and yield was very similar to the calculated coefficient of variation in simulated ETc and yield based on observations at 73% of locations. However, simulation of ETc and yield using AgMERRA for single years was more uncertain when compared with simulated ETc and yield based on observations for the same year. It is concluded that AgMERRA can provide a robust estimate of long-term average ETc and yield of wheat than the ETc and yield of a single year in regions that there is no long-termweather data available.

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