Abstract:

To avoid the damage of frost to agricultural production, the study used the daily minimum ground temperature data of 46 meteorological stations in southern Shanxi from 1961 to 2020, to analyze the variation characteristics of the first frost day, the last frost day and the frost free period in southern Shanxi by using the methods of linear trend, abruption test and wavelet analysis. The results showed that in the 60 years, the average first frost day and last frost day in southern Shanxi was October 17 and April 17, respectively, and the average frost free period was 184 days. At the rate of 2.18, 2.07 and 4.4 days per decade, there were obvious delay, advance and extension of the average first frost day, the average last frost day and the average frost free period, respectively, and there were obvious abrupt years. The abrupt change year of the first frost day, the last frost day and frost free period was respectively 2005, 2002 and 2001; and there were obvious periodic changes in frost duration. As to the spatial characteristics, the first frost day was early in the northeast and late in the southwest, the last frost day was opposite to the first frost day, early in the southwest and late in the northeast, and the frost free period decreased from southwest to northeast. The occurrence probability of extremely early frost day was higher in the southeast and northwest, and lower in the northeast and southwest, and the occurrence probability of extremely late last frost day was lower in Linyun basin and the river valley at the junction of Linfen and Jincheng, and higher in other areas. Altitude was the key geographical factor affecting the change of the frost period in southern Shanxi, and the minimum ground temperature in spring and autumn was the key climatic factor affecting the change of the frost period. In summary, the change of the frost period has a great impact on agriculture. The frozen area of crops does not change significantly with the change of frost frequency and intensity, and this might be related to the rapid improvement of modern facility agriculture protection measures. But the obvious increase of accumulated temperature could lead to the early development of crops and increase the probability of frost damage.

Key words: southern Shanxi, the first frost day, the last frost day, frost free period, climate characteristics