Climate warming worsens thermal resource utilization for practical rice cultivation in China.

Rice production is sensitive to climate change and significantly affected by warming in recent years. To what extent climate warming shifted rice phenology and varied thermal resource condition were explored across five agro-ecological zones in China, based on up-to-date observations of meteorology and rice cultivation in 1981-2020. It was clearly signaled that there was a general advance of 0.3-3.8 days in observed sowing date and a delay of 0.4-3.5 days in observed maturity date in 2001-2020 relative to 1981-2000 in major zones. A vacant time slice of 2.6-28.8 days between observed sowing date and potential sowing date, and a lag of 15.4-56.7 days in potential maturity date compared to observed maturity date were identified in 2001-2020. Within longer growing season, useful accumulated temperature increased by 76.7-117.6 °C·d in 2001-2020 relative to 1981-2000, while disactive accumulated temperature also increased. In Northeast China, actual rice cultivation was undergoing earlier sowing date than potential sowing date and longer growing duration than potential duration, yet leading to upward disactive accumulated temperature. The decrease in the thermal resource utilization in 2001-2020 relative to 1981-2000 was highlighted at 55.3-78.3% stations in major zones, with a decrement of 0.006-0.018 in average magnitude. The changes in thermal resource utilization unveiled that the shifts in actual rice cultivation still could not compensate for the suitability in thermal resource utilization benefited from climate warming.