Abstract:

Low−temperature disasters during the jointing−flowering stage severely impact wheat growth and yield formation in the Huang−Huai plain. The identification of the frequently−occurring and severely−affected areas can enhance the monitoring and defense capabilities against such disasters. To more accurately identify the low−temperature risk regions and assess low−temperature disaster severity in Henan province, authors utilized hourly temperature data of Stevenson screen from national meteorological stations in 118 counties of Henan province from 2006 to 2024. Besides, hourly wheat fields (10−70cm above ground) temperature data from four agrometeorological stations from 2023 to 2024 were used to analyze the temperature differences between wheat fields and Stevenson screen and establish the temperature indicators of low−temperature disaster. Based on dual temperature indicators of ≤4℃ and ≤2℃ from Stevenson screen, the spatiotemporal characteristics of low−temperature events during the jointing−flowering stage of winter wheat were analyzed at different severities. The results showed that: (1) temperatures at different heights within the field exhibited a highly significant correlation with Stevenson screen temperatures (P=0.001) during the jointing−flowering period. When the wheat field temperatures dropped below 0°C, the Stevenson screen temperatures were on average 3.7°C higher than the field temperatures measured at the height of 10−50cm. (2) The Stevenson screen temperatures ≤4℃, ≤2℃ and daily minimum temperatures occurred most frequently at 06:00, with corresponding frequencies of 13.1%, 15.5% and 35.0%, respectively. For most stations, the latest termination dates for ≤4℃ and ≤2℃ events were April 20−25 and April 16−20, respectively. (3) The most prolonged low−temperature durations (Stevenson screen temperatures ≤4℃and ≤2℃) and highest accumulated chilling injury indices were concentrated in central−southern area (Zhumadian and Luohe) and eastern area (Shangqiu). In the two high−risk zones, the low−temperature durations exceeded 200h (≤4℃) and 120h (≤2℃) respectively, while the accumulated chilling surpassed 50.0℃·h (≤4℃) and 10.0℃·h (≤2℃) respectively. Moreover, low−temperature duration exhibited a highly significant correlation with both daily minimum temperature and daily accumulated chilling. However, the correlation between low−temperature duration and the decrease of daily minimum temperature was comparatively weak. (4) During the jointing−flowering stage of winter wheat in Henan province, the maximum decreases of daily minimum temperature ranged from 5.8 to 9.2℃·d⁻¹, with the maximum decrease rates of temperature ranging from 1.0 to 2.0℃·h⁻¹. Based on the accumulated low−temperature frequency and perennial jointing dates, northern and western regions exhibit lower spring low−temperature frequency, while central and southwestern regions‌ show lower frequency of severe low temperatures but higher frequency of mild events. In contrast, eastern and central−southern regions experience relatively high frequencies of both mild and severe low−temperature events, which require prioritized preventive measures against low−temperature disasters.

Key words: Hourly temperature, Low?temperature disaster, The micro meteorology of field, Harmful accumulated chilling, Winter wheat