Assessment of risk and yield loss of rice in Sichuan Province due to heat stress

Under global climate change, agricultural meteorological disasters have been increasing. Heat stress has been one of the most important agrometeorological disasters in Sichuan Province, the affected area, frequency and intensity of heat stress have significantly changed. Therefore, research on the impact of heat stress on rice is critical for sustainable agricultural development and safe production in Sichuan Province. In this study, the following data were used to evaluate the risk of cultivation and yield loss of rice in Sichuan Province due to heat stress:1) daily climate variables (average temperature, maximum temperature and relative humidity) from 84 meteorological stations in Sichuan Province for the period 1981-2015; 2) developmental stages (from heading to flowering, and from grain-filling to harvest) of rice in 84 agro-meteorological observation stations in Sichuan Province for the period 1981-2015; 3) rice yields for the 84 stations in Sichuan Province during the period 1981-2015. The hazard index of heat stress at different rice developmental stages were calculated based on the Chinese National Standard, GB/T 21985-2008 Temperature Index of High Temperature Harm for Main Crops. The meteorological yield of rice was separated from actual yield. And then the risk evaluation model for rice in Sichuan Province due to heat stress was constructed by using rice hazard index for the critical development stages and the whole growth period, and rice yield loss due to heat stress was evaluated. The results showed the average hazard index of heat stress in the period 1981-2015 was highest (6.0) for grain-filling to harvest growth stage, medium (5.0) for the whole growth period and lowest (4.0) for heading to flowering growth stage in Sichuan Province. For the heading-flowering stage, most of the northeast basin and parts of the southern basin were under high or sub-high-risk of heat stress. Dazhou, Guang'an and Luzhou were under high-risk. The western basin, southern basin and southwest Sichuan were under low-risk. For the filling to harvest stage, most of the northeast basin and the southern basin were under high or sub-high-risk of heat stress. Luzhou, part of Nanchong and Yibin were high-risk areas. Most of the western basin, northern basin and southwest Sichuan were low-risk areas. For the whole growth period, most of the northeast basin and southern basin were under high or sub-high-risk. Luzhou, Nanchong and Dazhou were high-risk areas. Most of the western basin, northern basin and southwest Sichuan were low-risk areas. The statistical model for rice yield loss due to heat stress was simple and practicable. Using Yanjiang, Yingshan, Longchang, Yanting and Dazhu as the case study, the differences in historical statistical yields and simulated yields of rice for the years of heat stress were analyzed. The relative error between the statistical yield and the simulated yield of rice affected by heat stress was less than 1.5%. The verification results showed that the model was synthetically reflective of the impact of heat stress on rice yield and that it highly accurately evaluated rice yield loss. The assessment showed that the range of yield loss of rice in typical areas of Sichuan due to heat stress was 5.6%-10.2%.