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

为了解日本全境森林对水资源和泥沙排放的作用的空间分布，开发和讨论了各种GIS数据的处理方法。对覆盖日本全国的现有方格网数据集的利用进行了回顾性研究。本研究使用的数据包括海拔数据、气象数据（温度、降雨量和积雪深度）、植被/土地利用和地表地质数据，根据植被/土地和降雨数据，森林区、农业区和城市区的年降水量分别为1900 mm、1566 mm和1575 mm。林地的年平均降水量大于其他土地利用方式。这种差异是由两个事实造成的。森林面积一般分布在海拔较高的地区，降水量随海拔升高而增加。同一海拔高度的年平均降水量比较，林区的降水量大于其他土地利用方式。因此，在比较森林地区和其他土地利用的水资源和蒸散量时，应该考虑到这种差异。此外，还利用日本全国的数据集，分析了地貌特征与地质带的关系。本研究使用两个指数的组合作为计算每个b1 km网格的参数，以显示地理形态差异。一个是1 km梯度，另一个是50 m网格拉普拉斯。第二个指标代表1 km网格内的地表不平整度。

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.