Abstract:

Based on the daily meteorological data of 129 cities in 11 provinces and 2 municipalities in the Yangtze River Basin for nearly 20 years, the effective precipitation and water requirement of winter rapeseed during the whole growth period and various growth stages were calculated by empirical formulas, the improved HS data model recommended by Food and Agriculture Organization (FAO), and crop coefficients. Furthermore, the water surplus/deficit index and the frequency of droughts and waterlogging disasters over multiple years were analyzed. The results indicated that the effective precipitation during various growth stages of winter rapeseed in the Yangtze River Basin had a decreasing belt-like distribution from southeast to northwest. Specifically, the plains around Poyang Lake and Dongting Lake, as well as Hangzhou-Jiaxing-Huzhou Plain, had abundant effective precipitation, while the effective precipitation in the coastal areas of the middle and lower reaches of the Yangtze River mainstream was moderate. Conversely, the effective precipitation was relatively low along the line from Qinling Mountains to Huaihe River, in Sichuan Basin, and on Yungui Plateau. The water requirement during various growth stages exhibits a distribution pattern of high in the southwest, moderate in the southeast, and low in the northwest. Among them, the water requirement was the highest in Yunnan Province, moderate in the plains of the middle and lower reaches of the Yangtze River, and the lowest in the areas along the line from Qinling Mountains to Huaihe River, in Sichuan Basin and Guizhou province. The spatial distribution characteristics of water surplus/deficit over multiple years indicated moderate water supply in the coastal areas of the middle and lower reaches of Yangtze River mainstream, insufficient water supply along the line from Qinling Mountains to Huaihe River, in Sichuan Basin, and on Yungui Plateau. The temporal evolution characteristics of water surplus/deficit indicated that droughts are more frequent at seedling stage in the upper reaches of the Yangtze River, with the occasional occurrences of waterlogging disasters, while waterlogging disasters were more frequent in the middle and lower reaches, with the occasional occurrences of droughts. At other growth stages, droughts were frequent in the upper reaches, while both droughts and waterlogging disasters were frequent in the middle and lower reaches. To ensure appropriate water supply at various growth stages of winter rapeseed in Yangtze River Basin, it was recommended to focus on adequate irrigation in the upper reaches at seedling stage and timely drainage in the middle and lower reaches. At other growth stages, sufficient irrigation should be emphasized in the upper reaches, timely irrigation in the cities on the northern bank of the mainstream in the middle and lower reaches, and timely drainage in the cities on the southern bank of the mainstream in the middle and lower reaches, aiming to promote high and stable yields of winter rapeseed in Yangtze River Basin and ensure a stable supply of domestic rapeseed raw materials.

Key words: Yangtze River Basin, winter rapeseed, effective precipitation, water requirement, trend of change, water surplus/ deficit