Evaluation of Forest influence on water resources and sediment discharge using a digitalized square-grid map

为了了解日本全区森林水资源和防沙功能的空间分布，开发和讨论了各种地理信息系统数据的处理方法。对覆盖全日本的现有正方形格网数据集的利用情况进行了回顾研究。数据集包括高程数据、气象数据(温度、降雨和积雪深度)、植被/土地利用和地表地质数据，基于植被/土地和降雨量数据，林区、农业区和城区年降水量分别为1900 mm、1566 mm和1575 mm。林区年平均降雨量大于其他土地利用类型。这种差异是由两个事实造成的。森林面积一般分布在较高海拔，降雨量随海拔升高而增加。同海拔地区年平均降水量比较，林区降雨量大于其他土地利用类型。因此，在比较林地和其他土地利用之间的水资源和/或蒸散量时，应该考虑这种差异。本研究使用这两个指数的组合作为参数，计算出每一个b1公里网格，以显示地理形态的差异。一个是1公里的梯度，另一个是50m网格的拉普拉斯。第二个指数表示1千米网格正方形内地面的不平整度。

To understand spacial distribution of forest function on water resources and prevention of sediment discharge in whole area of Japan, method to process various GIS data have been developed and discussed. A review study on the utilization of existed square grid dataset covering whole Japan is conducted. Datasets used in this study are elevation data, meteorological data (temperature, rainfall and snow depth), vegetation/land-use and surface geology.Based on vegetation/land and rainfall data, annual precipitation annual precipitation for forested area, agricultural area and urban area was 1900mm, 1566mm, and 1575mm, respectively. The average of annual precipitation amounts for forest area was grater than those for other land use. This difference was caused by two facts. Forest area is generally distributed at higher elevation and precipitation amounts increase with elevation. Comparing the average1 of annual precipitation in the same elevation, precipitation amounts for forest area was grater than those for other land use. Therefore, we should consider this difference, when comparing water resources and/or evapotranspiration between forested area and other land-use.Relationships between geo-morphological features and geological zones are also analyzed using dataset covering whole Japan. This study uses the combination of the two indices as parameters that calculated every b1km grid to show the geo-morphological differences. One is a 1km-gradient and the other is 50m-grid laplacian. The second index represents unevenness in ground surface within 1km grid square.