天津夏季降水演变规律及其城市效应

利用1956~2005 年天津25 个雨量站的月降水数据， 借助累积距平、相关分析、Mann- Kendall 秩次相关检验 法等， 分析了夏季降水的时空演变规律。在此基础上， 结合ARCGIS 空间分析功能， 研究了天津雨岛效应的时空特 征。结果表明: 25 个站点的年降水量70%以上集中在夏季， 夏季降水倾向率均为负， 60%的站点通过了显著水平检 验。从加权平均得到的全市夏季降水序列得出1956~2005 年倾向率为- 24.7mm/10a， 其中1956~1988 年倾向率为 7.6mm/10a， 1989~2005 年倾向率达- 28.6mm/10a， 由此可见天津夏季降水减少主要发生在近17 年。又比较其不同 历史时段的空间演变规律发现， 夏季降水减少趋势北部山区大于南部平原， 南部平原的市区大于市郊， 呈现城市雨 岛效应， 特别是在20 世纪70 年代初期之后雨岛效应更加明显， 且受降水的丰枯影响较大， 丰水年雨岛现象明显， 枯水年雨岛消失。

Variation of Summer Precipitation in Tianjin Region and Its Urbanization Effect

The precipitation data of 25 rain gauges in Tianjin from 1956 to 2005 were selected to analyze the spatial and temporal variation using accumulated variance,correlation analysis and Mann-Kendall method.Furthermore,the spatial and temporal characteristics of the urbanization effect on summer precipitation were revealed by the spatial analysis tool of GIS.The result showed that:more than 70% of the rainfall in a whole year concentrates in summer,and the summer precipitation exhibited a decreasing trend during the past 50 years.The summer precipitation slopes of the 25 sites were below zero,and 60% of them reached the significant level of.The weighted average of summer precipitation showed the slope from 1956 to 2005 was 24.7 mm/10a,the slope was 7.6 mm/10a from 1956 to 1988,and it was -28.6 mm/10a from 1989 to 2005.So it was concluded the decline of summer precipitation mainly happened in recent 17 years.After an advanced study,it was found that the down trend of summer precipitation differed between northern and southern,between urban and suburban areas,which showed rain island effect.The effect turned more significant after the early 1970s,and had a strong relation with amount of the rainfall.The rain island effect was more apparent in high rainfall years than that of low rainfall years.