关键词: 农业气象学, 淮河流域, 气候变暖, 异常初、终霜日, 频率

Abstract:

The abnormal first frost date and last frost date that occur in the critical period of crop growth will cause great losses to crop yields. It is of great significance to know and grasp the changing rules of abnormal frost date index accurately in the Huaihe River Basin to ensure the stable, high and safe grain yield of China. Ground 0 cm daily minimum temperature collected at 61 meteorological stations were used to identify the first and the last frost dates. The standard deviation was used to calculate the stability of the first and the last frost dates and the probability density function was used to define abnormal first and last frost dates. Meanwhile, IDW interpolation method was adopted to reflect the stability of first and last frost dates and the frequency of abnormal frost date before and after the transition of climate state. Moreover, linear trend estimation, Mann-Kendall mutation test, sliding t-test and cumulative averaging method were employed to obtain the mutation year in temperature. And the effect of the circulation index and air temperature on the first and the last frost dates was analyzed by correlation coefficient method. The following conclusions can be drawn from the analysis above: (1) The mean temperature of Huaihe River Basin in the period 1960-2015 showed a significant upward trend at a rate of 0.18 ℃·10 a^-1 (P<0.01) and the mutation year happened in 1993. The transition of climate state promoted the postponement of the first frost date and the advancement of the last frost date. (2) The transition of climate state led to the decrease of the stability of first and last frost dates. The stability of first and last frost dates became much better with the increase of latitude and longitude. The stability of the first frost date became better with the increase of elevation. But the change of the last frost date is not significant even when the elevation increases. The stability of the last frost date is better than that of the first frost date. (3) There was a descending order among the frequency of earlier first frost date, later last frost date, special early first frost date, and special late last frost date. And after the transition of climatological state, the frequency of abnormal first and last frost days tends to decrease and be stable at 0-20%. On the whole, the frequency of abnormal first frost date is higher than that of abnormal last frost date. The impact of climate warming is greater on the first frost date than on the last frost date. (4) The spatial distribution of abnormal first and last frost dates was significantly different, the high frequency of which was observed in the 1970s and the 1960s, respectively, and the low frequency of which was found in the 2000s. Although the frequency of abnormal first and last frost dates was gradually stabilized and remained at a low level, the transition of climate promoted the increase of the frequency of special early first date in the southeast and south parts, partial early first frost date in the south, partial late last frost date in the northeast, and special late frost date in the southeast of the Huaihe River Basin respectively. (5) The smaller the polar vortex area is in September in the northern hemisphere, the later the first frost date is (R=-0.41, P< 0.01); the smaller the polar vortex area is in February, the earlier the last frost date would be (R=0.29, P<0.01); the larger the subtropical high is in October, the later the first frost date is (R=0.39, P<0.05); the larger the subtropical high is in April, the earlier the last frost date is (R=-0.15, P>0.05). Moreover, the tendency ahead of schedule was accelerated after 1990. The result of this article is good for frost forecast services and mitigation of frost disasters.

Key words: agro- meteorology, Huaihe River Basin, climate change, abnormal first and last frost date, frequency