SPATIO-TEMPORAL VARIATIONS AND COMPARATIVE ANALYSIS OF THE FROST-FREE PERIOD IN THE NORTHERN AND SOUTHERN REGIONS OF THE QINLING MOUNTAINS FROM 1960 TO 2014
It is of great significance to study the spatio-temporal variations of agricultural heat resources in ecological sensitive region under the background of global warming. Based on the meteorological data of 47 weather stations in the northern and southern regions of the Qinling Mountains(QLM) from 1960 to 2014, the spatial distribution, spatio-temporal variation and jump features were analyzed by using the methods of linear trend, Mann-Kendall test and Kriging interpolation. The results showed that, the frost-free period decreased with the increase of latitude in the northern and southern regions of QLM. The time trends were consistent in the four regions, namely the first frost date and the frost- free period declined slightly but increased dramatically thereafter, while the last frost date increased slightly but declined rapidly thereafter. Over the past 55 years, the frost- free period has significantly prolonged, with the increase of mutation. Among the northern areas to the QLM, southern slope of QLM, Hanshui River Basin and valleys in Daba and Wushan mountains, the prolonging rates of frost-free period were 0.4006d/a,0.2804d/a,0.3961d/a, and 0.4075d/a, respectively; the years of mutation were 1999, 2002, 2001 and 1990 respectively. The mean and standard deviation of the frost-free period in each station increased from south to north. It was also found that the first frost date lengthened, the last frost date advanced earlier and the frost-free period were extended over 80% stations. The frost-free period was prolonged by the delayed first frost date, together with an earlier last frost date. There were 28 stations with fluctuation characteristics and 19 stations with mutations in the northern and southern regions of QLM. The mutation timing of the frost-free period occurred primarily from 1990s to 2000s, and varied considerably in the 2000s, which had the largest regions of mutation and mainly concentrated in the north-east regions. The results are expected to provide referece for optimizing ecological environment change and agricultural production distribution under climate change.