Changes of Crop Water Use and Crop Yields: A Case Study of Climate Impacts over 35 Years in the North China Plain.

The North China Plain (NCP) is one of the most important grain production regions in China. Winter wheat and summer maize form the annual double cropping system. For the past 35 years from 1980s to present, yields of the two crops were increased continuously, but with large seasonal yield variation around -40%-20%. A field experiment lasting 35 years from 1980s to present was used to analyse the changes in crop water use and yields for the double cropping system as related to the climate as well as to the management. The results showed that reference evapotranspiration (ETo, calculated by FAO Penmen-Monteith method) was slightly increased due to the continuous increase in air temperature. However, the actual seasonal ET of both winter wheat and maize under well-watered condition was increased quite significantly during the past 35 years. The increase in crop water use was mainly related to the increase in the crop yields. The increase in soil fertility, chemical fertilizer and the renewing in cultivars contributed to the increase in crop yields. Calibrated APSIM and CERES-Wheat were used to quantify the effects of weather on the yield change. The results showed that the yields of winter wheat and maize were reduced around 10% for the past 35 years solely affected by weather, indicating the deteriorating conditions of the climate for the growth of the two crops. Correlation analysis showed that sunshine hours and diurnal temperature difference (DTR) were both positively related to the yield of the two crops. The climatic change trends for the past 60 years in this area showed that the DTR and sunshine hours were declining. This type of climatic change trend might further negatively affect the crop production in this region.