Mapping reveals contrasting change patterns of rain-on-snow events in China during 2001–2018

Abstract

Rain-on-snow (ROS) events can accelerate snow melting, which in turn leads to disasters such as floods, avalanches, and landslides. However, little is known about the characteristics of and changes in ROS events in China. In this study, the temporal and spatial variations of ROS days in China from 2001 to 2018 were investigated using the improved Moderate Resolution Imaging Spectroradiometer snow cover data, and China Meteorological Forcing Dataset. The results suggested that ROS days in China mainly occurred from November to June and were mainly distributed in northern Xinjiang (6.1 days/year), Qinghai-Tibet Plateau (2.8 days/year), northeast China (3.5 days/year), and east China (1.1 days/year). ROS days in each region have different seasonal distribution patterns. In the past 18 years, ROS days have shown a trend of increasing at higher latitudes and decreasing at lower latitudes in China, especially in northern Xinjiang and the Qinghai-Tibet Plateau. ROS days are decreasing below 3000 m in northern Xinjiang (-0.16 days/year) and below 4000 m in the Qinghai-Tibet Plateau (-0.21 days/year), which is explained by the decrease of snow days and rain days. ROS days are increasing at 3000–4000 m altitudes (0.15 days/year) in the Tianshan Mountains and 4000–5500 m altitudes (0.06 days/year) in the eastern Tibetan Mountains, mainly explained by more snowfall converted to rainfall. The ROS days along the Greater Khingan Mountains in Northeast China showed a decreasing trend (-0.12 days/year), and along the Changbai Mountains showed an increasing trend (0.07 days/year). The variation of snow cover days is the dominant factor. East China as a whole shows a decreasing trend (-0.1 days/year), explained by a decrease in snow cover time. In China, ROS days at low altitudes are negatively correlated with annual average temperature, and positively at high altitudes. The changes of ROS were also correlated with Arctic Oscillation and North Atlantic Oscillation. This study reveals the response of ROS to climate change in China, and provides an important reference for coping with the related disasters and changes caused by ROS events.