Abstract:

Shaanxi Province, China is located to the northeast of the Qinghai-Tibet Plateau. It is narrow from north to south and spans three climatic zones of Shanbei, Guanzhong, and Shannan according to the ecological and climatic characteristics of the three regions. Thus, the agricultural planting structure and ecological diversity are complex in Shaanxi. The Qinling Mountains across Shaanxi are the dividing line between the north and south climates in China, indicating that Shaanxi is one of the sensitive areas affected by climate change. Studying the characteristics of the occurrence of cold and warm winter climate events in Shaanxi could provide a theoretical basis for improving the facts of regional climate change. Based on the observational facts of 94 weather stations in Shaanxi from 1960 to 2019, the trend analysis of climatic regions was investigated using linear regression and five-year trend sliding. The factor average and change tendency rate in each climatic region were also calculated. The mutation analysis of winter average temperature in different climatic regions was conducted using the Mann-Kendall non-parameter statistical test method and sliding T-test method. The spatial and temporal change results of cold and warm winter events in Shaanxi show that the climatic change has caused a significant increase in the average winter temperature in Shaanxi and its abrupt changes occurred near 1987. The abrupt change time was earlier in Shanbei and slightly later in Shannan. The 0 °C isotherm of zonally average in winter moved north 1°-2°. The maximum temperature increase in Shanbei is 0.45 °C·(10a) ^-1, while the minimum temperature increase in Shannan is only 0.23 °C·(10a) ^-1. The regional warm winter index increased by 9.5%·(10a)^-1, and the cold winter index decreased by 9.6%·(10a)^-1 in the past 60 a. The cold and warm winter events in most sites occurred 17-20 times. Simultaneously, the strong cold and warm winter events occurred 4-7 times. The frequency of cold and warm winter events changed significantly before and after the abrupt time, of which 16 out of 20 warm winter events occurred after the abrupt change of winter temperature. Moreover, 16 out of 19 regional cold winters occurred before the abrupt change of winter temperature, especially the strong cold winter that occurred five times before 1980 and never happened again. In the spatial distribution, the frequency of cold and warm winters in Shanbei and Shannan are relatively high. However, the strong warm winter events occur mainly in Guanzhong, while the strong cold winters occur mainly in Shannan and Guanzhong. The winter temperature variation characters with time are consistent with the national results. However, in the spatial distribution, there are some differences between this research and the national results, mainly in the regional and strength changes. The reason for this is that the underlying surface, the terrain conditions, and the impact of urbanization of the study area are extremely complex, leading to a strong regional response to the cold and warm winter events. In the later period, we will focus on adverse effects, such as crop safety overwintering, disease spread, and pests occurrence and diseases caused by regional warm winter events caused by climate change.

Key words: warm winter, cold winter, climate change, Shaanxi