基于区域自动站数据的兰州地区降水精细化特征

基于2012—2019年兰州地区146个区域自动气象站小时降水数据,从不同时间尺度分析兰州地区近8 a降水精细化特征。结论如下:(1)2012—2019年,兰州地区年均降水量总体呈"北少南多、外多内少"的空间分布特征;年降水量具有明显的年际变化,2018年降水异常偏多46%,而2015、2017年降水异常偏少,尤其2015年偏少30%。(2)兰州地区降水主要集中在7—8月,受环流形势影响,7—8月南部降水明显多于北部,其余月份南北降水差异不明显。(3)兰州地区降水量和降水范围分别表现为"朝少夕多"、"夜大日小"的日变化特征;受海拔高度影响,城区降水量总体比山区小,且因热岛效应,城区降水主要集中在午后至傍晚前后,多为对流性降水,而山区降水日分布较为均匀,整体日波动较小。(4)安宁区短时强降水发生频次最高,但短时强降水频发的站点出现在皋兰县六合站和永登县徐家磨村站,永登县是兰州地区短时强降水预报需重点关注的地区。

Refined characteristics of precipitation in Lanzhou based on regional automatic weather stations data

Based on hourly precipitation data at 146 automatic weather stations of Lanzhou from 2012 to 2019, the refined characteristics of precipitation in Lanzhou were analyzed from different time scales. The results are as follows:(1) The average annual precipitation was less in the north and more in the south of Lanzhou, and that was more in the edge and less in the interior from 2012 to 2019. The inter-annual change of precipitation was obvious from 2012 to 2019, the precipitation in 2018 was abnormally more by 46%, while that in 2015 and 2017 was abnormally less, especially in 2015 it was less by 30%.(2) The precipitation mainly concentrated in July and August in Lanzhou, and it in the south was obviously more than that in the north due to the influence of atmospheric circulation situations, while the spatial difference of precipitation wasn’t obvious in other months.(3) The diurnal variation of rainfall was obvious in Lanzhou, the precipitation was less in morning and more at night, and the range of rainfall was larger at night and smaller in the daytime. The precipitation in urban areas was generally less than that in mountain areas under the influence of altitude, and it mostly concentrated from afternoon to evening due to heat island effect, the convective rainfall was more, while the diurnal distribution of rainfall was more uniform in mountain areas, the fluctuation was smaller as a whole.(4) Overall, the frequency of short-time heavy rainfall in Anning district of Lanzhou was the highest, but the short-time heavy rainfall at Liuhe station of Gaolan county and Xujiamo station of Yongdeng county was the most frequent, and that in Yongdeng county was a critical concern.