Establishment and Verification of Single Threshold Temperature Model for Partition Precipitation Phase Separation

Precipitation is an important parameter to characterize climate characteristics and climate change in a region. It is a key link in global water cycle and energy cycle. Under the same rainfall conditions, effects of different-phase precipitation in the earth's surface system are significantly different. The social and economic impacts produced by them also have significant differences. It is of great theoretical and practical significance to distinguish and recognize snowfall characteristics, their anomalies and causes. In addition, when monitoring and studying the global climate change background and long-term changes of the extreme precipitation events above the sub-continental scale, it is also necessary to distinguish rainfall and snowfall information from historical precipitation data.A statistical model with single temperature thresholds is established for separating cold season rainfall and snowfall with independent samples of different climate zones to the north of the Yangtze River in mainland China (north of 30°N). The applicability of the model is tested, and the deviation of the model on sleet recognizing is analyzed.Results show that correlations between estimated temperature thresholds and actual thresholds pass the significance level test for three areas, i.e., Eastern Monsoon Region, Northwest Arid Region and Qinghai-Tibet Plateau. Models for three areas can well simulate the temperature thresholds, the range and regional characteristics. Simulations in East Monsoon Region and Qinghai-Tibet Plateau are better than those in Northwest Arid Region. Among all of the stations in three regions, stations with absolute bias of the simulated threshold temperature less than 1℃ account for more than 74%, and stations with standard deviation biases between -0.5-0.5℃ account for 77%, and those between -1.0-1.0℃ account for 90%. When the daily mean temperature gets lower than thresholds, ratios of sleet days and precipitation compared to snow days and actual precipitation are slightly smaller in the north and larger in the south. In the south of Eastern Monsoon Region, ratios are more than 1. Statistical models can also be used to determine the distribution of the ratio in different areas.Climate types to north of the Yangtze River include temperate monsoon climate, temperate continental climate, and high-cold climate. Results of the independent sample test in three climatic zones indicate that applying this model to estimate the threshold temperature of precipitation phase in sub-continental snow-rich areas, although still limited, is basically feasible.