川渝地区夏季极端降水日变化特征分析

Analysis of Diurnal Variation Characteristics of Summer Extreme Precipitation in Sichuan and Chongqing

利用川渝地区1991~2012年夏季逐小时降水资料,分析该地区总降水、极端降水时空分布特征,特别是极端降水的日变化特征。结果表明,川渝地区受西高东低的地形影响,降水量总量(precipitation amounts,简称PA)也呈西少东多分布,具体是川西北高原少、川西南山地及东部盆地多,盆周山区多、盆中丘陵区少;降水频率(precipitation frequency,简称PF)则呈西高东低的相反分布,高原地区PF较高;降水强度(precipitation intensity,简称PI)的分布与PA较为一致,自西向东逐渐增强。极端降水的PA、PF、PI空间分布特征与总降水的空间分布特征相似。东部的四川盆地乐山、雅安地区和达州、广元地区,以及西南山地区的西昌、攀枝花地区的PA大主要是由于PI大。西昌地区北方小部分西南山地区的PA大主要是由于PF大。川西高原区PA小是因为PI小。PA日峰值自西向东递增,PF日峰值呈相反变化趋势,自西向东递减。两者几乎全部都出现在夜间,“夜雨”特征显著。海拔较高的地区日峰值大多出现在前半夜,而海拔较低的地区大多出现在后半夜,自西向东日峰值出现时间逐渐推迟,因此川渝地区的降水系统可能存在自西向东传播的特征。聚类得到四类区域站点的典型形态降水日变化曲线分析表明,一区主要为川西高原地区,二区主要为高原向盆地过渡的南部山区,三区为盆地区域,四区为盆地向东部过渡的丘陵地区,PA、PF和PI的日变化曲线均有“一峰一谷”的特征,区域一到四的PA峰值在午夜到凌晨,谷值在午后到傍晚,且自西向东逐渐推迟,PF峰谷值时间均与PA峰谷值接近,PI日变化波动较PA和PF的曲线大。位于高海拔地区的第一区PA小,主要是其PI小,高原向盆地过渡的南部山区的PA较大主要是PF较大,盆地区域及其向东部过渡的丘陵地区的PA的主要贡献是PI大。极端降水日峰值及其出现时间的分布特征都与总降水相似。川渝地区夏季小时极端降水的阈值西低东高,自西向东逐渐增大,极端降水量占总降水量的比重自西向东呈增大趋势,极端降水量对川渝地区东部总降水量贡献大,对西部贡献较少。

Hourly precipitation data in the summer of 1991–2012 in Sichuan and Chongqing were used to analyze the spatial and temporal distribution characteristics of total precipitation and extreme precipitation,especially the diurnal variation characteristics of extreme precipitation.The results show that the area’s precipitation amount(PA)is low in the west and high in the east influenced by the terrain,which is high in the west and low in the east.Specifically,there is more precipitation in the eastern Sichuan Basin and southwestern mountains than in the northwest plateau and more precipitation in the mountains around the basin than in the basin.The precipitation frequency(PF)was higher in the west and the plateau but lower in the east.The precipitation intensity(PI)distribution is similar to that of PA,which increases gradually from west to east.The spatial distribution characteristics of PA,PF,and PI of extreme precipitation are similar to those of total precipitation.Greater precipitation in the eastern Sichuan basin,such as Leshan,Ya’an,Dazhou,and Guangyuan,and in the southwestern mountains,such as Xichang and Panzhihua,is mainly because of greater PI.The larger precipitation in a small part of the southwest mountain in the north of Xichang is mainly because of high PF.Less precipitation in the western plateau of Sichuan is due to lower PI.The daily peak of PA increased from west to east,while the daily peak of PF showed an opposite trend,decreasing from west to east.Almost all of them occur at night,and the“night rain”feature is very prominent.Most of the daily peaks in the high-altitude areas occur in the early midnight,whereas the peaks in the low-altitude areas occur in the later midnight.The time of the daily peaks from west to east delays gradually,which is indicative of the precipitation system spreading from west to east in Sichuan and Chongqing.Four regions are obtained by clustering of the typical form of precipitation area site daily change curve analysis.The first region is the plateau,the second is the southern mountains transitioning from the plateau to the basin,the third is the basin,and the fourth is the transition area from the basin to the eastern hills.The diurnal variation of the PA,PF,and PI curves has the same characteristics as“one peak and one valley.”The peak values of PA from regions one to four are from midnight to early morning,and the valley ones are from afternoon to evening,which gradually delays from west to east.The peak and valley time of PF is close to those of PA,and the diurnal fluctuation of PI is larger than that of PA and PF.The small PA of the first region is mainly due to its weaker PI.The PA of the second region is high mainly because of its higher PF.The higher PA of the third and fourth regions is mainly due to their stronger PI.The distribution characteristics of the daily peak of extreme precipitation and its occurrence time are similar to that of total precipitation.The threshold value of extreme hourly precipitation in summers in Sichuan and Chongqing was low in the west and high in the east and gradually increased from west to east.The proportion of extreme precipitation to total precipitation increased from west to east.The extreme precipitation contributed more to the total precipitation in the eastern parts of Sichuan and Chongqing but less to the western part.