# Modeling the Impact of Atmospheric Warming on Staple Crop Growth in China in the 1960s and 2000s
## 3 Results  
### Temperature Changes during Crop Growth  
Relative to the 1960s, temperatures did not change significantly during the summer maize growth period in Fengqiu in North China, but temperatures in other regions increased significantly during crop growth periods in the 2000s, and the temperature distribution shifted to the high-temperature direction (Figure 2).  
Figure 2: Frequency distributions of daytime temperatures for the 1960s (1960–1969) and 2000s (2000–2009) for the whole growing seasons of different crops at different sites: (**a**) rice, Changshu; (**b**) single rice, Sanjiang; (**c**) early rice, Taoyuan; (**d**) late rice, Taoyuan; (**e**) winter wheat, Changshu; (**f**) winter wheat, Fengqiu; (**g**) summer maize, Fengqiu; (**h**) spring maize, Hailun. The three green arrows in each graph represent the base, optimum and maximum temperatures, respectively, for crop photosynthesis, and the red rectangles highlight ranges of the optimum temperatures for crop photosynthesis.  
Compared to the 1960s, during the 2000s, the number of days with extremely low temperatures occurring in rice areas of Changshu in East China (Figure 2a) and in early (Figure 2c) and late rice (Figure 2d) areas of Taoyuan in Central China did not change significantly during growth periods, but the number of days with high temperatures of over 35 \({}^{\circ}\)C significantly increased from 73 to 118 days for late rice areas in Taoyuan (Figure 2d). While the number of optimum temperature days for early rice in Taoyuan slightly increased, numbers for rice in Changshu and late rice in Taoyuan showed no significant changes in the 2000s. However, the number of extremely low temperature days decreased from 36 to 13 days during single cropping rice growth periods in Sanjiang, Northeast China (Figure 2b), which was accompanied by an increase in the number of optimum temperature days (from 142 to 203 days), and the number of extremely high temperature days did not change significantly between the two periods. For wheat (Figure 2e,f), in Changshu in East China (Figure 2e) and Fengqiu in North China (Figure 2f), the number of low temperature days during the growth period in the 2000s decreased significantly relative to the 1960s, with Changshu decreasing from 214 to 112 days and Fengqiu decreasing from 374 to 298 days. While the number of optimum temperature days increased, with Changshu increasing from 582 to 641 days and Fengqiu increasing from 489 to 570 days, the number of extremely high temperature days did not change significantly, which had a positive effect on wheat growth as compared to the 1960s. For maize (Figure 2g,h), temperatures in Fengqiu of North China (Figure 2g) did not change significantly during the two growth periods, nor did the temperature frequency distribution, the number of extremely high and low temperature days or the number of optimum temperature days. For summer maize in Hailun in Northeast China (Figure 2h), the number of optimum temperature days significantly increased from 207 days in the 1960s to 318 days in the 2000s, while extremely high temperatures did not occur in the two periods.  
According to these results, the number of low temperature days decreased, and the number of optimum temperature days increased significantly for winter wheat in North and East China, rice and maize in Northeast China. The number of optimum temperature days did not change significantly for rice in South China, and the number of extremely high temperature days increased (Figure 2).