Page 256 - 《高原气象》2022年第1期

高 原 气 象 41 卷
254

Characteristics and Possible Causes for Extreme Precipitation in

Summer over the Loess Plateau

LU Shan 1，2，3，4 ，HU Zeyong 1，3 ，FU Chunwei 1，3，4 ，FAN Weiwei 1，3，4 ，WU Di 1，3，4

（1. Key laboratory of Land Surface Process and Climate Change in Cold and Arid Regions，Northwest Institute of
Eco-Environment and Resources，Chinese Academy of Sciences，Lanzhou 730000，Gansu，China；
2. Shaanxi Meteorological Service Center，Xi’an 710014，Shaanxi，China；
3. Nagqu Station of Plateau Climate and Environment，Northwest Institute of Eco-Environment and Resources，
Chinese Academy of Sciences，Nagqu 852000，Xizang，China；
4. University of Chinese Academy of Sciences，Beijing 100049，China）

Abstract：Using the daily precipitation datasets from 64 meteorological monitoring stations in the Loess Plateau
and NCEP/NCAR reanalysis data during the period of 1961-2016，the spatial-temporal variations of the extreme
precipitation were investigated in the Loess Plateau. In addition，the similarities and differences in atmospheric
circulation situation corresponding to strong and weak years of extreme precipitation，and in different ages were
compared. Results showed that extreme precipitation was the major type in summer in the Loess Plateau，which
accounted for about 70% of the total summer precipitation，and presented spatial decreases from east to west of
the plateau. Under the background of overall decline of summer precipitation in the Loess Plateau from 1961 to
2016，the proportion of extreme precipitation showed an increasing trend among almost 70% of the stations.
Comparison of atmospheric circulation between strong and weak year indicated that when Baikal low strength‐
ened and the subtropical high extended northward in summer，the warm and humid northward air flow from the
Northwest Pacific Ocean and South China Sea intensified，leading to the convergence of cold and warm air over
the Loess Plateau and consequently more extreme precipitation in summer. In strong extreme precipitation years，
there were positive water vapor income anomalies in summer in the Loess Plateau. The positive contribution to
water vapor mainly originated from the northern and southern boundaries in June. The water vapor at northern
boundary was converted to an output part in July and August，while the water vapor input at the western and
southern boundaries increased and more pronounced in August. The more obviously convergence of cold and
warm air in summer was detected in strong extreme precipitation years，which was beneficial to the release of un‐
stable energy and the increase of extreme precipitation in study area. Moreover，extreme precipitation in summer
was found to have experienced a transition from wet condition to dry condition in the Loess Plateau in the 1980s，
and had begun to increase in recent years. Based on the analyses of the characteristics of summer atmospheric cir‐
culation in different ages，it can be observed that positive net income of water vapor and obvious convergence of
cold and warm air in summer typically resulted in more extreme precipitation in the Loess Plateau in the corre‐
sponding year，and vice versa.
Key words：The Loess Plateau；extreme precipitation；atmospheric circulation