PMP估算中地形对山地暴雨增幅作用的影响

在山区可能最大降水(PMP)估算中,当确定移置附近气候相似区某场灾害性特大暴雨后,就必须定量估算山地地形对暴雨的增幅作用,以便在移置之前定量消除地形对被移置暴雨的影响。为了定量估算辐合雨分量及其时空分布形态,以福建莆田地区和香港地区两场不同类型的暴雨为例,基于福建东南沿海地区84个站点和香港地区77个站点1、3、6、12、24h的5个时段的历史年最大雨量资料和实测降雨资料,应用"分时段地形增强因子(SDOIF)"暴雨分割技术分割香港20080607和莆田19991009两场暴雨,探讨山区暴雨期间地形对暴雨的定量影响及其空间分布模式。研究发现山区地形对暴雨有着增幅作用,且随历时增加而逐渐增强,越靠近暴雨中心增强幅度也越显著。同时地形增强因子也受高程的影响,低海拔处地形增强因子的增速高于高海拔处。经暴雨分割后的辐合雨空间分布形态与实测降雨的形态也基本一致。可见基于极值暴雨历史系列统计特性分析及暴雨天气背景和地形地貌特征分析相结合的SDOIF暴雨分割技术,能够有效地反映特定地形对暴雨的增幅作用及其空间分布形态,为山区暴雨移置提供了可靠依据。

Enhancement Effect of Topography on Orographic Storm Rainfall in PMP Estimation

Quantitative estimation of the effect of topography on orographic storm rainfall is very important in PMP estimation. It can quantitatively determine the influence of topography before storm transposition took place. In this paper, the step duration orographic intensification factor (SDOIF) method is adopted to determine the quantitative effect of topography on orographic storm rainfall and analyze its spatial distribution in Putian and Hongkong region based on the precipitation data at 84 stations in Fujian Province and 77 stations in Hongkong for a time period of 1 h, 3 h, 6 h, 12 h, 24 h. It is found that the enhancement effect of topography on storm rainfall increases with time. Furthermore, in the area where is closer to the rainfall center the enhancement effect shows more remarkable. SDOIF also increase with altitude of the mountain. The result also shows that the spatial pattern of the convergence rainfall component is similar to the pattern of the storm rainfall from which the convergence component was separated by the SDOIF, which provides reliable basis for mountainous storm transposition.