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Agricultural water resource security is faced with serious challenges in the background of climate change. It is important to study the trend of evapotranspiration (ET) for future planning and management of agricultural water resources. On the basis of the 19612004 weather data, the trends of six meteorological variables were analysed. Also, the potential ET (PET) of maize (Zea mays L.) in the growing season was simulated by the World Food Study (WOFOST) model. Results indicated that the maximum and minimum temperatures increased significantly, and the daily minimum temperature increased much faster than the daily maximum temperature, which resulted in the decrease in the diurnal temperature range (DTR). The precipitation showed an increasing trend, whereas the sunshine duration and wind speed (WS) showed a declining trend. No remarkable linear tendency was found on vapour pressure. As a result, the simulated maize PET showed a significant decrease by 1 mm year-1, and it was mainly as a result of decreased sunshine duration and WS. This may provide valuable information on the aspect of water resource management in the Yellow River basin. Copyright (c) 2011 John Wiley & Sons, Ltd.