Temporal and Spatial Variations of the First and Last Frost Date During 1961—2013 in Henan Province and Their Responses to Climate Changes

In this study, the annual first and last frost date for each station was defined on the basis of daily minimum ground temperature at17 meteorological stations over the period from 1961 to 2013 in Henan Province. The spatial and temporal changes of first and last frost date,as well as their responses to seasonal temperature variations, were analyzed. The results showed that: The regional mean first frost date showed a significantly delaying trend, with a linear trend of 2.2 d·10 a-1during the most recent 53 years. The strongest delaying regions occurred in western mountain areas, with the maximum value in Lushi(4.0 d·10 a-1). However, the regional mean last frost date indicated a notably advancing trend, with a linear trend of 2.3 d·10 a-1over the period from 1961 to 2013. The greatest advancing regions were detected in central and southern Henan, with the maximum value in Zhumadian(4.9 d·10 a-1). The regional mean first and last frost dates were significantly correlated with seasonal mean temperatures. The regression coefficient between first(last)frost date and seasonal mean temperature was 6.5 d·℃-1(-3.5 d·℃-1), representing that the first(last)frost day was delayed(advanced)by 6.5(3.5)days if spring temperature(mean temperature of February, March, and April)increased by 1.0 ℃, suggesting that the first frost date was more sensitive to climate change than last frost date in the context of global warming background.