Ecosystem Service Assessment in Agricultural Watershed by Using Topmodel

Abstract

In Millennium Ecosystem Assessment established by the United Nations, the ecosystem services (ES) provide benefits for human life as well as the environment. There is "regulating services" among all the supporting services. As a regulatory service, forests alleviate the flood risk after heavy rain by storing rainfall temporarily into forestlands and prevent the sudden increase in river discharge. The purpose of this research is to develop a hydrological modelling to assess this service in a watershed where consists of not only forestland but also grassland. TOPMODEL is applied for the quantification. This model was invented to forecast river discharge in watersheds where the land use is uniform. However, the model has not been applied to a watershed where agricultural and forest area are mixed in Japan. This research aimed to develop TOPMODEL to apply to such complexed land use. Because the targeted watershed is consisted of two land-use types, TOPMODEL was applied in each grassland and forestland. It predicted the river discharge by combining the predicted discharge from the different types of land calculated by TOPMODEL. The result confirmed that by developing the model, it was able to assess the water discharge from the both grassland and forestland in a watershed. The developed model also showed the better reproducibility of river-discharge prediction than the conventional TOPMODEL. In addition, it clarified that the forestland stores more water than grassland into the ground. Therefore, the effect of flood control which is the regulatory service of ES was assessable through the developed model.