Quantifying the effects of climate trends in the past 43 years (1961-2003) on crop growth and water demand in the North China Plain

This paper explores changes in climatic variables, including solar radiation, rainfall, fraction of diffuse radiation (FDR) and temperature, during wheat season (October to May) and maize season (June to September) from 1961 to 2003 at four sites in the North China Plain (NCP), and then evaluates the effects of these changes on crop growth processes, productivity and water demand by using the Agricultural Production Systems Simulator. A significant decline in radiation and rainfall was detected during the 43 years, while both temperature and FDR exhibit an increasing trend in both wheat and maize seasons. The average trend of each climatic variable for each crop season from the four sites is that radiation decreased by 13.2 and 6.2 MJ m(-2) a(-1), precipitation decreased by 0.1 and 1.8 mm a(-1), minimum temperature increased by 0.05 and 0.02A degrees C a(-1), maximum temperature increased by 0.03 and 0.01A degrees C a(-1), FDR increased by 0.21 and 0.38% a(-1) during wheat and maize season, respectively. Simulated crop water demand and potential yield was significantly decreased because of the declining trend in solar radiation. On average, crop water demand was decreased by 2.3 mm a(-1) for wheat and 1.8 mm a(-1) for maize if changes in crop variety were not considered. Simulated potential crop yields under fully irrigated condition declined about 45.3 kg ha(-1) a(-1) for wheat and 51.4 kg ha(-1) a(-1) for maize at the northern sites, Beijing and Tianjin. They had no significant changes in the southern sites, Jinan and Zhengzhou. Irrigation, fertilization development and crop variety improvement are main factors to contribute to the increase in actual crop yield for the wheat-maize double cropping system, contrasted to the decline in the potential crop yield. Further research on how the improvement in crop varieties and management practices can counteract the impact of climatic change may provide insight into the future sustainability of wheat-maize double crop rotations in the NCP.