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

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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.