Defining Indices for the Extreme Snowfall Events and Analyzing their Trends in Northern Xinjiang, China

Northern Xinjiang (NX), China, located at the middle latitude of the Northern Hemisphere, has abundant snowfall and a long period of snow cover. In this study, to assess the impact of climate change in this region and to provide scientific knowledge for the resource management, analyses of the spatial and temporal variations in extreme snowfall events (ESEs) in NX was conducted based on five defined ESE indices: days of heavy snowfall (DHS), maximum 1-day snowfall amount (MASD), maximum 1-event snowfall amount (MASE), the maximum number of consecutive snowfall days (MDSE), and frequency of heavy snowfall events (HSE). To reconstruct the snowfall dataset, the relationship between air temperature and snowfall events was determined, and it was found that the daily minimum air temperature below 0 degrees C is the best indicator to identify snowfall days. ESEs in NX occupied an increasing proportion of snow events, although the number of snowfall days decreased. Consistent increasing trends in all ESE indices were found for the entire NX region, while different changes in these indices were noted between subregions. With highly increasing trends of these ESE indices in most of subregions, the Daxigou-Xiaoquzi and Qitai areas were the hotspots for ESEs. Since these hotspots are likely influenced by airflow from the Arctic Ocean, the changes in the Arctic Ocean and the associated atmospheric circulation resulting from climate change might be the main reasons for the increasing trend of ESEs in NX.