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Temporal and Spatial Variation Characteristics of Low Temperature

Freezing Rain and Snow Events in the Eastern Qinghai-Xizang
Plateau and Southwestern China

XIANG Nan， GONG Yuanfa， LI Zhuomin
（School of Atmosphere Science， Chengdu University of Information Technology， Plateau Atmosphere
and Environment Key Laboratory of Sichuan Province， Chengdu 610225， Sichuan， China）

Abstract： Using the daily minimum temperature and precipitation data of 157 stations in the eastern Qinghai-Xi‐
zang Plateau and Southwestern China from 1961 to 2020 by the National Meteorological Information Center， a
standard for low temperature freezing rain and snow events is defined， using Mann-Kendall mutation test， slid‐
ing t test and EOF analyzed the climatic characteristics and spatiotemporal characteristics of low temperature
freezing rain and snow events in the eastern Qinghai-Xizang Plateau and southwestern China. The results show
that： （1） The frequency of low temperature freezing rain and snow and the climatic characteristics of the annual
variation of precipitation in the eastern Qinghai-Xizang Plateau and Southwestern China are significantly differ‐
ent. The Qinghai-Xizang Plateau shows an obvious double-period annual variation， with the maximum in early
spring in March and the second peak in autumn in October， while the southwest region shows a U-shaped single-
period annual variation， with the maximum in winter in January.（2） The areas with the most frequent occurrenc‐
es on the Plateau in the source of the Three Rivers in Qinghai and the source of the Nu River in northern Tibet，
and the most frequent areas in southwest China are the western part of Guizhou.（3） The first three modes of
EOF decomposition show that the spatial and temporal variations of the frequency of freezing rain and snow in
different seasons are significantly different. The spatial distribution of the first mode in spring and autumn over
the Plateau shows a consistent change in the whole region， and the time coefficient has obvious interdecadal os‐
cillation characteristics， with more frequency from the end of 1970s to 2000， and experienced the evolution of
"less-to-more-to-less" process； in autumn， the frequency of low temperature freezing rain and snow is more in
the 1960s and 1970s， with interdecadal mutation around 1981， and less frequency after that； the first spatial dis‐
tribution mode in winter is dominated by the winter variation in the Southwest China， indicating that the winter
in the southwest has obvious abrupt changes around 1985， and has experienced a “more-less” change process；
the second spatial distribution mode in winter is dominated by winter variation in the Plateau， and its temporal
variation is similar to that in the Plateau in spring， with an obvious mutation around 2009.
Key words： Qinghai-Xizang Plateau； Southwest China； low temperature freezing rain and snow events； tempo‐
ral and spatial variation