Abstract:

Based on frost date data at 110 weather stations of He’nan province from 1971 to 2010, spatial and temporal distribution characteristics of the first and latest frost dates and frost-free period as well as its response to air temperature changes were analyzed by methods of a linear trend and a single correlation, and its abrupt change feature was also discussed based on the analysis using a Mann-Kendall method. The results show that average frost-free period is 221.3 days. Latitude is significantly negative correlation with the first frost date and frost-free period, and both correlation coefficients are -0.806 and -0.707 respectively; it is significantly positive correlation with the latest frost date, and correlation coefficient reaches 0.557. The first frost date delays at the rate of 2.6 days per decade (p<0.01); the latest frost date has no significant trend; the frost-free period increases at the rate of 4.7 days per decade (p<0.01). The abrupt change of the first frost date, last frost date and frost-free period all appear in 1998. Trends of the first frost date, last frost date and frost-free period differ in different regions. The first frost date delays in all six regions, especially in the west of He’nan province with 3.5 days per decade (p<0.01). The latest frost date only advances in the west and south of He’nan province. The frost-free period extends obviously except in the east of He’nan province, especially in the west with 7.7 days per decade (p<0.01). For the spatial distribution of frost period at 110 weather stations, the areas in which the first frost date is postponed significantly, in which the last frost date appears obviously earlier and in which the frost-free period extends obviously mainly include the western and southern parts of He’nan province. The first frost date is significantly related to temperature of October, while the last frost date is markedly correlated with temperature of March. Changes of the first frost and latest frost dates are mainly attributed to increasing air temperature, especially increasing average minimum air temperature in He’nan province. The first frost date delays and the latest frost date is in advance, which leads to frost-free period extending.

Key words: The first frost date, The latest frost date, Frost-free period, Abrupt change, Climate response