Effects of vegetation and soil on evapotranspiration, flow regime, and basin storage in three nearby catchments in northeast Japan

Abstract. Vegetation and soil determine evapotranspiration, flow regime, and basin storage in forested catchments. We conducted hydrological observations at three nearby catchments (catchments nos. 1, 2, and 3) in the Nagasaka experimental watershed located on the green tuff region in northeast Japan. Diameter-at-breast height (DBH) of all trees > 3 cm DBH was recorded. In addition, we measured soil depth at 170 locations and investigated 45 soil pits. Based on these detailed vegetation and soil measurements, we examined evapotranspiration, flow regime, and basin storage during the no-snow-cover period (May–November). More than 80.9 % of stands in the catchment were comprised of Cryptomeria japonica. Stand volume (122.0 m³ ha⁻¹) and sapwood area (10.7 m² ha⁻¹) in catchment no. 3 were smaller than those in the other two catchments (no. 1: 255.7 m³ ha⁻¹; 16.0 m² ha⁻¹, no. 2: 216.5 m³ ha⁻¹; 14.2 m² ha⁻¹). Consequently, evapotranspiration was lower in catchment no. 3 than that in catchments nos. 1 and no. 2. In addition, low and scanty runoffs in catchment no. 3 were larger than those in nos. 1 and 2. The order of magnitude for soil storage was catchments no. 1 (104.2 mm) < no. 3 (115.7 mm) < no. 2 (123.1 mm), which was similar to the order of magnitude for basin storage: catchments no. 1 (65.9 mm) < no. 3 (69.7 mm) < no. 2 (115.8 mm). Deep soil storage contributed to increased basin storage and decreased the ratio of plentiful runoff to scanty runoff.