午夜欧美大片免费观看,欧美激情综合五月色丁香,亚洲日本在线视频观看,午夜精品福利在线

Based on the tea planting area of 78 counties from 1980 to 2014, the paper divided the tea base counties into three main growing areas in Anhui province. Using the data of daily minimum temperature from 1980 to 2014 in the tea base counties， the last frost dates， the spring frost days, and the occurrence frequency of different grade frosts are calculated and its distribution characteristics are analyzed. The results show that the averaged last frost dates in the south is earlier than those in north, with the earliest occurred on 21 March, the latest on 6 April. In the three main growing areas, the Dabie mountain area has the most spring frost days, and Xuancheng is the next, and then Huangshan. The dates of extremelate frost and late frosts in Xuancheng appear obviously later than that in the Dabie Mountain and Huangshan. The extremely late frost mainly occurred in the 1980’s, and occurred only once in 2000. The late frosts appeared mainly in the 1980’s and 1990’s, and occurred only once after 2000. In recent 35 years, mild spring frost had the highest frequency in the Dabie Mountain (Lu’an), while moderate and severe spring frost had the highest frequency in Xuancheng (Jixi). The occurring frequencies of mild, moderate and severe spring frost show a declining trend. The tea frost damage risk in the base counties is analyzed according to the theory of risk analysis and the spatial distribution features are obtained. The conclusion can be a reference for disaster prevention and reduction.