Spatial Estimation of the Northern Taiwan Rainfall Erosion Index Derived from Distrometer
Date Issued
2016
Date
2016
Author(s)
Liu, Tai-Yuan
Abstract
Soil erosion has been a serious problem in Taiwan due to special hydrological and physiographic conditions, and human activities. Rainfall erosion index (the R factor) is an important factor for soil erosion. Because of the limited number of rainfall observation stations and the different lengths of rainfall observation period, it is necessary to conduct spatial estimation of the R for the areas without rainfall observation station or lack of rainfall data. To accomplish this goal, the northern Taiwan was selected as the study area. The R values used in this study was obtained from the observed data using distrometer. There are three methods for spatial estimation. The first is interpolation method: isoerodent map method or inverse-distance weighting method computed using the data of the three near rainfall observation stations. This method is currently applied to the technical specification of soil and water conservation in Taiwan. The second is Kriging method: the observed rainfall data in the whole study area are used to estimate the R value using the Kriging method. Compared to Method 1, Method 2 is more accurate and more often used in recent years. The third is delimiting homogeneous region method accompanied with the Kriging method: firstly, delimit homogeneous regions of rainfall erosion properties, then using the Kriging method with each homogeneous region’s rainfall observation station data to estimate the R vales in each homogeneous region. This method is proposed and utilized in this study. By comparing Method 2 with Method 3, the effects of delimiting homogeneous regions of rainfall erosion properties on the R estimation in the areas without observed rainfall data are investigated in this study. While Method 3 is used for analysis, principal components analysis(Principal components include longitude, latitude, elevation, rainfall erosion index and its coefficient of variation.) is firstly conducted and two step cluster analysis is then carried out. Through the procedures, the northern Taiwan could be clearly delimited, while each region maintain its spatial dependence. Finally, in each rainfall erosion property region, the Kriging method is applied to estimate the R values for the areas without observed rainfall data. From the results of cross validation, it is found the R values estimated using Method 3 is more accurate than that using Method 2, i.e., Method 3 is better than Method 2.
Subjects
distrometer
rainfall erosion index
delimiting the homogeneous regions
principal components analysis
kriging method
cross validation
Type
thesis