Climate Change and Its Impact on Winter Wheat Output in Nanjing during Recent 60 Years

Food is the foundation for the subsistence and development of human beings. The stability of the world food supply has been faced with increasingly more pressures in the context of growing global population. The process of food production is often impacted by environmental changes. Studying impact of climate change on grain production is therefore of great importance under global warming. Nanjing City is located in the monsoon region of eastern China, Jiangsu Province, as well as the lower reaches of the Yangtze River. It is well known for a relatively higher temperature compared to other cities, a large population, developed economy, and a high level of urbanization. The authors used monthly data of temperature and precipitation of Nanjing City collected from the National Meteorological Center of the China Meteorological Administration during the period 1951-2008. Meanwhile, acre yield data of winter wheat collected from Nanjing Statistical Yearbook for the same period was also obtained. Trends in climate change in Nanjing were analyzed using a linear regression model while the M-K mutation test was made by the Mann-Kendall (M-K) model. Furthermore, yields of winter wheat responding to climate change were comprehensively analyzed. Results showed that the temperature of Nanjing City exhibited an increasing trend at a linear tendency rate of 0.25℃/10a, starting from the year 1975. Remarkable changes in the temperature were primarily observed in spring; insignificant changes, however, occurred in autumn and winter. The temperature remained almost stable in spring. The precipitation showed a progressively decreasing trend at a linear tendency rate of 12.45 mm/10a. There was an obvious alternation of droughts and floods since late 1980s. In general, the precipitation showed a decreasing trend in spring and autumn while increasing in summer and winter, implying a mutation since 1973. The aridity index demonstrated a rising trend, suggesting a marked warming and drying trend. The spring, autumn and winter showed an obvious trend of warming and drying, whereas a humid trend occurred in summer since 1975. The production of winter wheat was highly correlated with climate change, showing a determination coefficient of 0.626 (p≤0.05). Yields of winter wheat showed a generally increasing trend with certain fluctuations. It can be drawn that: 1) the temperature of Nanjing showed an increasing trend with a linear tendency rate ranging from 0.08℃/10a to 0.39℃/10a; 2) the precipitation demonstrated an increasing trend at a rate ranging between -1.84 mm/10a and 6.44 mm/10a; 3) the aridity index showed an increasing trend at a linear tendency rate ranging between -0.04/10a and 0.11/10a; and 4) the yield of winter wheat showed a positive correlation with a change in temperature and a negative correlation with precipitation and aridity index.