The negative impact of increasing temperatures on rice yields in southern China.

China is the main producer and consumer of rice in the world, and rice is a major staple food grain for more than half of the world's population. Reduced rice yields caused by climate factors not only affect the food security of China, but also has global repercussions. Thus, it is vital to assess the potential impact of climate warming on rice production. Using daily temperature and phenology records of double-cropping rice from agro-meteorological stations in southern China, the influence of increased temperatures on rice yields during the last several decades was investigated. Associated with an increase in average daily mean temperatures by 0.7 °C during 2009-2018 relative to 1961-1970, Killing Degree Days (KDD), an indicator for damaging high temperature, for early and late rice increased by 110% and 88.6% respectively. However, the negative influence of KDDs on yields was mainly evident for early rice, because high temperatures occurred frequently during the sensitive grain-filling period; early-rice yields showed a decrease of 8% per 1 °C increase in mean growing season air temperature. Late rice yields, on the other hand, were not as negatively influenced by increasing temperatures as early rice, because high temperature usually occurred during the vegetative growth stage, which was not so sensitive to high temperature.