Developing methods for estimating regional-scale evapotranspiration using forest inventory data

Abstract:

Quantifying evapotranspiration (ET) from forests is important for understanding the rainfall runoff process and for sustainable water resource management. Numerous studies in field-based investigation and monitoring in small catchment scales have been conducted for estimating effects of vegetation on internal hydrological processes in forested landscapes. Hence, application for these findings in small scales to regional scales, which is important for water resources management, is always challenges. Spatial heterogeneity of management unit of forest including stand density and species compositions needs to be included for scaling up hydrological processes to the regional scales. This study firstly developed models for interception loss, canopy evapotranspiration, and understory evapotranspiration based on review the previous studies. Then, we applied the models for prefectures and national forests GIS database for estimating the evapotranspiration. Estimated ET by the model was also validated by monitoring data in research watersheds located and transpiration of Japanese cypress forest in the FM Karasawa-yama, Tokyo University of Agriculture and Technology. Estimated value of interception loss was 349 mm/year compared to the measured interception of 415 mm/year. Estimated and measured transpiration were 441 mm/year and 441.0 mm/year, respectively. Estimated understory ET became 179 mm/year as compared to measured one by 124 mm/year. This analysis permits us for spatial extrapolation of monitoring data to the regional scales.