Abstract: According to the air temperature data over the last 50 years in Longhai weather station,the freezing damage for Litchi trees could be avoided. But in the year of 1991/1992 and 1999/2000,the Litchi trees were suffered serious freezing damage in Shuangdi Overseas Chinese Farm,11 km away to south-southwest of Longhai Station. To make clear of cause for freezing damage,the air temperature data in winter of 2008/2009 in Longhai weather station and auto weather station of Shuangdi Overseas Chinese Farm (lied in lower parts of landlocked mountain slopes) were comparatively analyzed. The results showed that the average temperature and the minimum temperature of weather station of Shuangdi Overseas Chinese Farm were lower than those of Longhai weather station. However,the maximum temperature observed by the latter station was higher and the daytime temperature differences between the two weather stations were wider accordingly. Moreover,there was linear relation of minimum daytime temperature of two weather stations (r=0.9468>r0.001,n=90),and with the decreasing of the minimum temperature of Longhai weather station,the difference value of the minimum temperature between the two weather stations presented increasing trend,and the minimum temperature of Shuangdi Overseas Chinese Farm was even lower than that of Longhai county. Furthermore,the annual extreme minimum air temperature data from the new and old weather stations in Longhai were adjusted homogeneously by difference method. By using the linear regression analysis,the minimum temperature of weather station of Shuangdi Overseas Chinese Farm in 1991/1992 and in 1999/2000 were -5.8℃ and -4.8℃ respectively,which was the real reason for the freezing damage to Litchi trees.

Key words: Minimum air temperature, Minimum air temperature, Landlocked mountain slopes, Analyzed comparatively, Freezing damage to Litchi trees