Abstract: High-temperature and heat damage is the major agricultural meteorological disasters in southwest China, and it is important to study them to ensure rice production. Based on daily meteorological data from 351 meteorological stations in the southwestern region from 1980 to 2022, this study focused on the critical growth stages of rice (heading-milk grain stage and milk grain-mature stage) to analyze the spatial and temporal variations and risk of high-temperature and heat damage using the heat damage cumulative index. The results provide a theoretical basis for the rational placement of rice cultivation. The results showed a significant increase in the number of stations experiencing high temperatures and heat damage between 1980 and 2022 during two critical growth stages of rice, with the increasing rates of 6.4 and 4.1 percentage points per decade. Taking a decade-by-decade perspective, heat stress and damage were relatively light in the 1980s, with the total number of stations experiencing heat stress during the two growth phases being 16.3% and 7.8% of the total number of stations, respectively. However, the high-temperature and heat damage were more severe in the last 13 years, with a total number of stations experiencing heat damage accounting for 38.1% and 22.2% of the total stations. The year with the highest occurrence of high-temperature and heat damage during both growth stages was in 2022, with the total number of stations experiencing heat stress accounting for 51.6% and 37.6% of the total stations, respectively. The annual tendency rate during the heading and milking stage had inceased significantly in the southwestern region, mainly concentrated in the central and western parts of Chongqing, the eastern part of Guizhou, and the northeastern and southern parts of the Sichuan basin. Only a few stations showed a decreasing trend. The tendency rate during the ripening stage of rice increased significantly in most areas of the Sichuan basin and Chongqing. The spatial distribution of the number of days, frequency, and risk of high-temperature and heat damage during the two critical growth stages of rice were generally consistent, showing a high concentration in the northeast and a low concentration in the southwest. The high-risk areas of high-temperature and heat damage were mainly concentrated in the central and western parts of Chongqing, the northern part of Chongqing, the northeastern part of the Sichuan basin, and the central and southern parts of the basin. This study achieved a quantitative assessment of high temperature and heat damage, improved the fineness of spatial distribution, and provided more guidance for actual rice production.

Key words: Rice, Heat damage cumulative index, Spatial and temporal variation, Risk