World food security faces severe challenges under the background of climate change. According to the Sixth IPCC Assessment Report, climate change is already affecting every region of the earth in many ways, and the changes we experience will intensify with global warming [1
]. Climate change can directly affect the crop growth environments (e.g., temperature, water and light) [2
], and the crop planting areas are extremely sensitive to climate change, especially temperature increase [3
]. Since the 1960s, the annual average temperature of China has risen by 1.22–1.66 °C with global climate change, which may have a significant effect on crop planting regions in China, the world’s largest developing economy [4
]. Therefore, accurate information about the suitable crop planting regions especially northern planting boundaries under climate change, is of great importance to ensure food security and formulate sound agricultural policies.
Temperature is a key factor in crop growth and development [7
]. The increase in temperature will make some areas that were not suitable for planting crops due to the lack of heat resources become potential planting regions, thus causing planting boundaries to move. China is a sensitive area that is significantly impacted by global climate change, and the heating rate has been significantly higher than the global average level in the same period since 1950s [10
]. It should be noted that, although, many researchers have outlined the northern boundaries of different crops in China under climate change, most of them have only used climate data before 2010. However, the latest Blue Book on Climate Change in China reported that 2011–2020 was the warmest decade since 1850, and 2020 was the warmest year in Asia since 20th century [11
]. Consequently, it is necessary to update the potential northern boundaries of different crops in China, especially considering the climatic conditions in last ten years.
The northern planting boundaries of various crops have been delineated by previous studies, and the effect of climate change on these boundaries has also been analyzed. Yang et al. compared the planting limits of winter wheat during 1950s–1980 and 1981–2007 [12
]. They found that the planting limits moved to north and west about 20 km to 200 km in China. Liu et al. analyzed the effects of past climate change on the northern limits of maize planting in Northeast China, and results showed that temperature increase led to a northward expansion of the northern limits of maize, which allowed these areas to be planted with new cultivars that have a longer growing season [13
]. Research conducted by Ye et al. showed that in the context of climate warming, the northern planting boundaries for rice cropping systems in China moved northward and extended westward [14
]. Sun et al. used the CMIP5 (Coupled Model Intercomparison Project Phase 5) historical simulation test (1850–2005) to simulate the historical climate evolution process, and used the Representative Concentration Pathway 4.5 (RCP4.5) to present the future climate change. They then analyzed the planting boundaries of winter wheat in China [2
]. Results showed that the northern planting boundaries of winter wheat in China will likely move northward and expand westward in the future.
However, most of these studies only used meteorological data from about 600 national basic weather stations of China to present the results, which may cause large uncertainties at the national scale when using fewer meteorological data to determine suitable planting areas of crops in China. As shown in Figure 1
, there were only less than 500 national weather stations in the early 1950s, and the number of stations increased to more than 2000 in the 1960s. The red color represents the amount range (500–700) of weather stations that most previous studies used, which is much less than the existing national weather stations. Therefore, it is better to consider more weather stations for a more accurate result when analyzing the effect of climate change on the potential planting boundaries at the national scale.
In summary, the objectives of this study are to (1) analyze the climate change effect on crop northern planting boundaries and update the time period to 1961-2020 to include the latest ten years; (2) determine the northern planting boundaries of three main grain crops (winter wheat, spring maize, and rice) in China based on their own growth criteria; (3) compare and analyze the changes of the northern planting boundaries between the first 30 years (1961–1990) and the last 30 years (1991–2020); and (4) present a more accurate and real-time information about the northern planting boundary changes of three main grain crops by integrating more weather stations (the 2437 national weather stations in China).
In this study, we analyzed the potential planting boundaries of three main crops in China during the periods of 1961–1990 and 1991–2020 under the background of climate warming. Our study shows that the extreme minimum temperature, mean minimum temperature in the coldest month and the accumulated temperature during the period of 1991–2020 significantly increased compared with those during the period of 1961–1990, both at the weather station level and the regional (province and national) level. The rising temperature caused a northward movement of the potential planting boundaries of these crops. Moreover, the boundaries of winter wheat and spring maize also showed a trend of expansion to high-altitude areas (e.g., the Qinghai–Tibet Plateau), and the boundaries of double and triple rice cropping systems present a western expansion. In general, the boundaries of winter wheat, spring maize, double and triple rice cropping systems changed significantly due to climate warming. Our study presents more accurate and recent results regarding the potential planting northern boundaries of the three main grain crops in China and demonstrates the effect of climate change on them, potentially providing a reference for policy makers seeking to pay more attention and assign greater priority to the design of agricultural strategies adapted for the sake of crops in sensitive regions.