Abstract: The changes in regional grain production and disaster situation were analyzed from 1949 to 2020 based on statistical data on the area of cultivated land, grain acreage, yields and agricultural disaster situation in the Yangtze river basin. Using the established disaster-yield assessment model, we estimated the loss and yield of grain due to disasters in 7 provinces (municipalities) from 1949 to 2020. The disaster-yield model of grain crops in Sichuan province was constructed. The major disaster species affecting regional grain yield were identified, and the major disaster species-yield assessment model was constructed to further test the generality of the model construction approach. The results showed that: (1) in the past two years, the average planting area of grain crops in China and the whole river basin was 11.60×10⁷ha and 2.70×10⁷ha respectively, accounting for 23.3% of the whole country, which showed a significant increasing trend (P<0.05). The planting area of grain crops in Shanghai, Jiangsu, Zhejiang and Sichuan showed a significant downward trend (P<0.05). The planting area of maize, wheat, other crops and rice accounted for 5.9%, 14.9%, 34.6% and 44.6% of the whole basin, respectively. The planting area of rice showed a significant increasing trend (P<0.05). (2) From 1949 to 2020, the average grain crop yield of the whole country and the whole river basin was 3.67×10⁸t and 1.38×10⁸t, respectively, accounting for 39.5% of the whole country, showing a significant increasing trend (P<0.05). The yield of corn, wheat, other crops and rice accounted for 6.0%, 12.0%, 11.9% and 70.1% of the total in the basin, indicating a significant increase in rice production. During the same period, the multiple cropping index for the whole river basin and the whole country was 138% and 214%, respectively, showing a downward trend. In particular, the crop multiplicity index in Zhejiang province dropped dramatically from 250% in the 1980s to 100% in the 2010s. (3) The average area of disaster covered, disaster affected and disaster destroyed area in the Yangtze River basin were 1.08×10⁷ha, 0.48×10⁷ha and 0.08×10⁷ha, accounting for 30.8%, 29.2% and 28.8% of the whole country, respectively. The variation rates were 51.5%, 64.4% and 115.5%, respectively. Drought and flood accounted for 74.3%, 74.0% and 66.9% of the total disasters, while low temperatures, hail and typhoons accounted for 36.6%, 32.4% and 25.5% of the total disasters. (4) Based on the extended data to 2020, the simulated grain yield of Jiangsu, Anhui, Zhejiang, Jiangxi and Hunan provinces from 1949 to 2020 showed a highly significant linear correlation with the actual grain yield, with the regression coefficient (R²) higher than 0.97, while the coefficient (R²) of Shanghai and Hubei provinces was slightly lower (0.78 and 0.80, P < 0.01). In the last 72y, the newly constructed model in Sichuan province has a high simulation accuracy, with a coefficient of determination of 0.99. The yield reduction rates of grain in Shanghai and Zhejiang were relatively high (27.4% and 33.4%), while the yield reduction rates of grain in Jiangsu, Anhui, Jiangxi, Hubei, Hunan and Xichuan were 13.0%, 15.5%, 9.0%, 10.3%, 6.47% and 0.14%, respectively. A new regression model for major disaster-grain yields has been developed after identifying key disaster-preventing species in regions. That still explains more than 95 percent of the reduction in grain production. After further regional evaluation, the modeling method is able to well model the loss of grain yield due to meteorological disasters, has a good performance in predicting grain yield, and is feasible for national operational application.

Key words: Regional agricultural disaster, Disaster loss assessment model, Grain production, Agrometeorological disasters, Disaster-covered area, Disaster-affected area, Disaster-destroyed area