The Climate Characteristics of the First Date of ≤0 °C Temperature in East China

摘要

In this paper the climate characteristics of the first date of ≤0 °C temperature are analyzed; furthermore, the farming responses to climate warming are discussed using a climate diagnosis analysis and the least squares methods, which are based on the daily minimum temperature data in East China from 1961 to 2009. It was found that over the past 50 years there has been a trend of the first date of ≤0 °C temperature being delayed at a rate of 1.6 days per 10 years; however, between 1961 and 1990 the first date of ≤0 °C temperature arrived early at a rate of 1.8 days per 10 years, and then was delayed at a rate of 3.3 days per 10 years. Furthermore, the average first date of ≤0 °C temperature is 30 October in northern regions, and the frequency of the first date of ≤0 °C temperature is greater in October and November than in other months; however, the boundary of the first date of ≤0 °C temperature shifts from south to north during September to December, and this has been especially evident since the 1990s. It was also found that in some southern stations, ≤0 °C temperature never occurs. The first date of ≤0 °C temperature occurs earlier in the north than in the south, and the interannual variation of the first date of ≤0 °C temperature is large in low latitudes and small in high latitudes. Additionally, the sustained period of ≤0 °C temperature, from beginning to end, decreased at a rate of 5 days per 10 years, which leads to a reduction in the length of the frost periods and causes a structural adjustment to the type of crops that can be planted. Therefore, the study reveals the significant effects that the first date of ≤0 °C temperature can have on the length of frost periods and farming and provides useful findings with regard to the prevention of frost damage and agricultural management.