| Summary: | 博士 === 國立中興大學 === 水土保持學系所 === 94 === Rainfall caused by typhoon is not only the important income of water resources, but also the key factor of disturbing the spatial distribution of soil and water resources in Taiwan. It will be help to realize the spatial distribution of soil and water resources and movement of sedimentation for our homeland by studying the spatial variations of typhoon rainfall.
Watershed is a unit of topography and an elementary area that applied for the topics of spatial hydrology and sediment movement. This study first used the first law of geography and nonparametric statistics test, and then chose 19 rain gauge stations to analyze the spatial variations of typhoon rainfalls by areal reduction factor curves in the Nam Shih Creek watershed of Northern Taiwan for different durations and return periods.
The results of typhoon rainfall spatial distribution from semivariograms analysis of different durations and return periods showed that the range is about 7.4km, and the spatial variation increasing by durations and return periods under the range in this site.
The semivariogram models built by former analysis used as the input functions for Kriging that making isohyetal maps by integrating GIS. From the isohyetal maps, we can display the spatial distribution of rainfall caused by typhoons in Nan Shih Creek watershed. The spatial distributions of typhoon rainfall lessen gradually from east to west and south to north in this area. Such being the cases, the apparent spatial variations of typhoon rainfall is in the eastern and southern parts of this watershed.
For the sake of understanding the relationship between typhoon rainfall degradation and area of distribution, this study applied the isohyetal maps that drawn in the former part to extract areal reduction factors of different durations and return periods, and forming the areal reduction factor curves. As a result of areal reduction factor curves, the areal reduction factors of typhoon rainfalls decayed with accumulative areas of spatial distribution by the power law. The areal reduction factor curves decrease mildly with the rainfall durations on increasing in the fixed return period. In the condition of fixed durations, the areal reduction factor curves also grow less mildly with the return periods extend. In previously description, it shows that the spatial variations of typhoon rainfall trend unvarying in Nan Shih Creek watershed.
|
|---|
