Development of the Bio-Geographical and GeoChemical (BGGC) Model for Assessments of Climate Change Impacts on the Terrestrial Ecosystem in Japan

Abstract

This study developed the Bio-Geographical and GeoChemical model (BGGC model) to assess the future impacts of global climate change, as prescribed by the IPCC-SRES, on the distribution and functioning of terrestrial ecosystems in Japan. The BGGC model simulates the cycling of carbon, nitrogen, and water in vegetation, soil ecosystems and the atmosphere. Some modules in the model borrow most of their basic structures from the sub-model of CENTURY4 (Parton et al., 1993) and the modified BIOME3 (Ishigami et al., 2002). The BGGC model is broadly divided into two sub-models, the vegetation competition sub-model and the soil organic matter sub-model. The vegetation competition sub-model consists of the photosynthesis model and the canopy model. The photosynthesis model estimates the optimized net primary productivity (NPP) and leaf area index (LAI) to satisfy the soil nitrogen, and annual moisture. The canopy model considers the canopy structure for forest vegetation types. On the other hand, the soil organic matter sub-model, which is linked to the vegetation competition sub-model, simulates carbon, nitrogen, and water dynamics in the soil ecosystem. The distribution of potential natural vegetation types was determined by the estimated NPP and LAI. In order to assess the impact of climate change on the terrestrial ecosystem, this study estimated the distribution of potential natural vegetation in Japan using NPP. The GCMs experimental data used were the CSIRO-Mk2 and ECHAM4/OPYC3 for each of A2 and B2 scenarios in the SRES. Comparison of the averages of simulated NPP under each scenario with the average NPP under current climate conditions showed that the average NPP could increase about 19 to 33 percent by the year 2050 and 25 to 53 percent by the year 2080.