Thermal resource change dynamics for single-season rice in China under RCP scenarios

Rice production is affected by current climate change, but future changes are rarely mentioned. A better understanding of the thermal resource dynamics of rice production is important for future optimization. Changes in the spatial-temporal dynamics of the thermal resources for future single-season rice was analyzed under two representative concentration pathways (i.e., RCP4.5 and RCP8.5), using the mean air temperature, accumulated temperature above 10 ℃, and temperature suitability as indices. The analysis was based on daily reproduction data from 20 global climate models at a high resolution of 0.25°×0.25°, which was downscaled by Bias Correction Spatial Disaggregation. The results indicated that the mean air temperature, accumulated temperature above 10 ℃, and temperature suitability differed spatially. During the baseline period from 1986-2005, a higher mean air temperature and accumulated temperature above 10 ℃ were detected in the Sichuan Basin, as well as in the middle and lower reaches of the Yangtze River. Relative to the baseline, the mean air temperature and accumulated temperature above 10 ℃ during the future periods (i.e., 2021-2040, 2041-2060, 2061-2080, and 2081-2100) under RCP4.5 and RCP8.5 increased by varying magnitudes in different regions (increment magnitudes under RCP8.5 were larger than RCP4.5). Increasing mean air temperature and accumulated temperature suggest that more thermal resources will be available for rice in the future, making it appropriate to replace the early-mid rice variety with the mid-late variety. However, increasing temperature is not always beneficial to rice growing. Temperature suitability based on the temperature requirements were implemented for different rice-growing periods. During the baseline years, the temperature suitability was greater than 0.95 in the Sichuan Basin, as well as in the middle and lower reaches of the Yangtze River, which was higher than the other regions (i.e., Northeast China, Ningxia, and the southern and southeastern regions of Southwest China). No obvious (or negative) temperature suitability trends were observed in the Sichuan Basin or the middle and lower reaches of the Yangtze River, but positive trends were observed in other regions. Under future period predictions, there was a decreasing temperature suitability trend in the Sichuan Basin and in the middle and lower reaches of the Yangtze River, with a tendency of -0.03 - 0·(10a)^-1 and -0.11- -0.03· (10a)^-1 under RCP4.5 and RCP8.5, respectively. This was attributed to more days in the future with maximum temperatures greater than 35 ℃ and implies that a significant increase in heat stress would threaten rice growing. Comparatively, temperature suitability in Northeast China, Ningxia, the southern and southeastern regions of Southwest China increased at a rate of 0.00-0.03·(10a)^-1 under RCP4.5, which was smaller than under RCP8.5. This, combined with increasing mean air temperature and accumulated temperature above 10 ℃, would benefit rice growing in these regions. Understanding the thermal characteristics can help to optimize rice production among regions in response to climate change.