How frost is formed
Freezing refers to the sudden drop in the temperature of the soil or plant surface to a temperature that causes crop damage or death during the plant growing season.
Xinjiang has frequent cold air activities in spring and autumn, and the temperature changes are very unstable. Autumn frost often comes too early, and spring frost often ends late, resulting in varying degrees of frost in various parts of Xinjiang over the years. occur. The main crops affected include corn, sorghum, rice, cotton, potatoes, vegetables, fruits, etc.
1. Standards
Various crops or different development stages of the same crop have different low-temperature tolerance capabilities, but the critical freezing temperature of most thermophilic crops is around 0°C. In order to simplify the frost indicators, when analyzing the climate patterns of frost, the daily minimum temperature of 0℃ is always used as the indicator.
2. Occurrence time and geographical distribution
(1) First frost day
The first frost in Xinjiang is almost always associated with a strong cold air or cold wave invasion related. The average first frost day is generally in late September and early October in the Altay and Tacheng areas of northern northern Xinjiang, early October in the Ili Valley and along the Tianshan Mountains, the first half of late October in the northeastern part of southern Xinjiang, and the first half of late October in the southwestern and southwestern parts of Xinjiang. Turpan is late October or early November; southern Dongjiang and the Maonao Lake depression in Yiwu County are mid-October; and Barkol Basin is early September. The average first frost date in northern Xinjiang is about one month earlier than in southern Xinjiang. The average date of first frost and the earliest date can differ from half a month to one month in northern Xinjiang, and the difference between southern Xinjiang and eastern Xinjiang is 10 to 20 days. The longest difference between the earliest and latest dates of first frost in northern Xinjiang is nearly 2 months, and the shortest difference is more than half a month, usually around 1 month. In southern Xinjiang, the longest difference is 1 month to 1 and a half months ( See Table 3-4 in Part 3). When the first frost occurs, immature crops will be affected, such as cotton, late-maturing corn and re-sowed corn, melons and vegetables. The impact of the first frost on crops is more serious than that of the final frost, and the losses are also greater.
(2) Final frost day
Final frost is mainly caused by cold air activity in northern Xinjiang, while it is formed by the simultaneous effects of cold air activity and radiative cooling in southern Xinjiang. On average, The last frost day is generally in early May in Altay and Tacheng areas, in mid-April in the Ili Valley and along the Tianshan Mountains, in late March in eastern southern Xinjiang, in mid-to-late March in southwestern southern Xinjiang and Turpan, and in southern eastern Xinjiang. It is mid-April for the Naomao Lake Depression in Yiwu County, and as late as mid-May for the Barkol Basin. The average last frost date in northern Xinjiang is about one month later than in southern Xinjiang. The difference between the average date and the latest date of final frost in northern Xinjiang is generally half a month to one and a half months, and that in southern Xinjiang is generally one month to one and a half months. The difference between the earliest and latest final frost days is even greater, and the longest in northern Xinjiang can be 74 days, the shortest is 29 days, usually around 40 days.
If the first day when the daily average temperature stably passes through 10℃ is used as the starting date of the sowing period of thermophilic crops, then in most areas of Xinjiang and in most years, the last frost day occurs before the sowing of thermophilic crops. In a few areas, although it occurs after the sowing of thermophilic crops, appear, but the crop has not yet emerged