Abstract:

Based on the hourly precipitation data from 71 meteorological stations in flood season (May-September) in Gansu Province from 1975 to 2016, the spatial and temporal distributions of hourly precipitation in different climatic zones (arid zone, semi-arid zone and semi-humid zone) of Gansu Province were analyzed by using the methods of linear trend analysis, spatial interpolation and so on, and the change rules were revealed. The results were as follows: (1) The distributions of the hourly precipitation ratio (the ratio of  hourly precipitation to the overall daily precipitation) and precipitation frequency in the whole province were uneven in a day. The non-uniform distribution of precipitation ratio was the most obvious in the arid zone, while the precipitation frequency distributed most non-uniformly in the semi-humid zone. (2) In the whole province, the hourly precipitation ratio was relatively lower from 11:00 BST to 15:00 BST and higher from 18:00 BST to 23:00 BST. The hourly precipitation frequency was relatively lower from 12:00 BST to 17:00 BST and higher from 20:00 BST to 11:00 BST. (3) There was little difference about the distribution of hourly precipitation ratio in different climatic zones. However, the precipitation frequencies in the semi-arid zone and semi-humid zone were larger and closer to each other.While the precipitation frequency was minimum in the arid region. In Gansu Province, there was no significant linear trend for the hourly precipitation ratio and precipitation frequency over time. (4) The precipitation was more unstable in the afternoon than that before-noon. During May-August, the proportion of daily precipitation before-noon was smaller than that in the afternoon, while the reverse was true in September. (5) In the arid zone, the hourly precipitation ratio played the leading role for the precipitation of this time, followed by the precipitation frequency, nevertheless, in the semi-humid zone, both the precipitation ratio and precipitation frequency played some roles to the hourly precipitation.

Key words: Gansu Province, hourly precipitation, precipitation ration, precipitation frequency

摘要：

利用甘肃省71个国家气象站1975—2016年汛期（5—9月）逐小时降水量数据，采用线性趋势分析、空间插值等方法，对比分析了甘肃省内不同气候区（干旱区、半干旱区和半湿润区）逐时降水量时空分布特征，揭示了其变化规律。结果表明：（1）全省小时降水比率（某小时降水量占日降水量的百分比）和降水频率一日内各时次分布不均匀，其中降水比率分布不均匀最明显的区域在干旱区，而降水频率分布不均匀最明显的区域在半湿润区。（2）全省小时降水比率低值集中在11:00—15:00，高值出现在20:00前后，主要在18:00—23:00；全省小时降水频率低值集中在12:00—17:00，高值主要在22:00至次日11:00。（3）小时降水比率的分布在3个不同气候区的差异不大；但小时降水频率半干旱区和半湿润区较大，数值也较为接近，而干旱区最小。甘肃省小时降水比率和降水频率均不存在明显的线性变化趋势。（4）全省午后降水的不稳定性要大于午前，5—8月午前降水量在一日中所占的比例小，而9月午前降水量大于午后降水量。（5）干旱区的小时降水比率对相应时次降水量的大小起主导作用，降水频率的作用次之；而半湿润区的降水比率和降水频率共同影响小时降水量。

关键词: 甘肃, 逐小时降水量, 降水比率, 降水频率