Characteristics and effects of climate warming on winter wheat/summer maize cropping system in recent 50 years in the piedmont of Mount Taihang

Climate warming and its impact on cropping systems constitute a major aspect of agricultural development research in countering climate change. While the North China Plain (NCP) is one of the most important crop production bases of China, the piedmont regions of Mount Taihang are the most productive zones in the plain. Winter wheat and summer maize constitute the basic cropping system in NCP. In such a tight double-copping system, heat condition is the main factor that controls both sowing and harvesting dates of the crops. This paper established a case study on temperature and agricultural heat resources data for the last 50 years in Shijiazhuang, a typical area of the piedmont regions of Mount Taihang, to discuss the characteristics of climate warming and the related impacts on winter wheat/summer maize cropping system in the piedmont regions of Mount Taihang. For the last 50 years, an obvious warming trend at 0.35 ℃·10a^-1 was noted in the studied area. The trends in climate warming at the seasonal cycle were unequal, while a sharp increase (0.51 ℃·10a^-1) in winter and a more moderate increase (0.20 ℃·10a^-1) in summer. Climate warming in the studied area caused an increase in effective accumulated temperature (AT). In the last 2 decades, annual >10 ℃ AT increased obviously compared with the period of 1961~1990. The increased heat accumulation in recent years resulted in about 10~20 days extension of the suitable growing season. That favored crop growth and higher potential grain productivity. The sharp and unbalanced seasonal warming patterns resulting from regional climate warming distinctly impacted winter wheat/summer maize cropping system in the studied area. The emergence and seedling stages of winter wheat were temperature sensitive periods, and the suitable >0 ℃ AT was about 500~600 ℃ before overwintering stage. After 1990, the >0 ℃ AT in wheat season increased by 10% and the warmer seedling stage in turn decreased the safety level of overwintering stage. For that reason, wheat seeding date had been postponed to adapt to climate warming. Due to the higher heat resources and longer growing seasons, total >10 ℃ AT in maize season increased beyond 2 900 ℃. This was sufficient for mid-late maturity maize varieties in the piedmont regions of Mount Taihang.