关键词: 四川盆地南部, 高温干旱, 复合胁迫, 2022年盛夏

Abstract:

In midsummer 2022, the southern Sichuan Basin (hereinafter referred to as Southern Sichuan) experienced the most severe high-temperature and drought event since meteorological records began in 1961, causing serious impacts on local agricultural production, particularly the ratooning rice industry. To reveal the regional characteristics of this extreme high-temperature and drought event and its potential impacts on ratooning rice production, this study analyzed the spatiotemporal evolution characteristics and extremity of high temperatures in midsummer 2022 based on data from 22 national meteorological observation stations in Southern Sichuan, evaluated the spatiotemporal dynamic changes of drought using the Meteorological Drought Composite Index (MCI), quantified the number of compound stress days combining high temperature and drought, and further investigated the causes of the extreme high temperatures from the perspectives of atmospheric circulation anomalies and land-atmosphere feedback effects using ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts. The results show that: (1) The regional average temperature in Southern Sichuan in midsummer 2022 was 31.9 ℃, 4.6 ℃ above the climatological mean, making it the highest on record for the same period. The regional average precipitation was only 101.4 mm, 69% less than the climatological mean, also the lowest on record for the same period. (2) The high-temperature event comprised two episodes: the first lasted 12 days and the second lasted 35 days, both covering the entire region. The number of days with temperatures exceeding 40 ℃ ranged from 6 to 31 days, with the longest duration (31 days) recorded at Hejiang. Among the 22 stations, 18 broke their historical maximum temperature records, with the highest value of 44.3 ℃ observed at Xuyong. The daily duration of high temperatures increased significantly, reaching up to 20 hours at some stations. Drought began in early July and peaked in late August, with Longchang experiencing the most severe conditions (53 days of severe drought and 10 days of extreme drought). During the second high-temperature episode, the average number of compound stress days (daily maximum temperature ≥35 ℃ combined with moderate drought or above) was 20 days, and the compound stress days was more than 33 d at stations such as Longchang and Gulin, indicating that the eastern and northern parts of the region are high-risk areas for compound stress on ratooning rice. (3) The western Pacific subtropical high area index anomaly reached 0.15×10⁵ km², which was the highest since 1990, and Southern Sichuan was controlled by persistent subsiding airflow with enhanced clear-sky radiation. Soil moisture anomaly dropped to its lowest value (-0.08 m³·m^-3), while surface sensible heat flux anomaly rose to its highest value of 12.15 W·m^-2, forming a positive “high temperature-drought” feedback mechanism that simultaneously amplified both the high-temperature and the drought.

Key words: the southern Sichuan Basin, high-temperature and drought, compound stress, midsummer 2022