Spatial and temporal chacracteristics of ice-freezing disasters and its relationship with meorological conditions from 1961 to 2010 in Zhejiang province

Using daily ice freezing data and corresponding temperature, wind speed as well as relative humidity data at 68 weather stations in Zhejiang province from 1961 to 2010, spatial and temporal distribution characteristics of ice freezing disasters were analyzed using methods of a linear trend analysis, a wavelet analysis and a correlation analysis. Meteorological conditions causing ice freezing disaster were studied. The results show that for temporal variations, annual average number of ice freezing day is in a significantly decreasing trend from 1961 to 2010, and an abrupt change point is observed in the late 1980s. Ice freezing disaster mainly occurs from December and February, especially in January. For spatial distributions, the number of ice freezing day is also in a decreasing trend from northwest to southeast, and it is a tonguelike distribution in the middle and northern regions of Zhejiang province. Ice freezing disaster occurs more frequent in Tianmu Mountains and hilly region of northern Zhejiang province than in Jinhua and Quzhou Basin although these areas are in the same latitudes. The number of ice freezing day is closely related to the minimum air temperature. It is easy to cause ice freezing disaster when the minimum air temperature is about -2℃, daily mean wind speed is equal or less than 4 m·s^-1, and daily mean relative humidity is about 80%.