Assessing the Impact of Climate Change and Land Use Change on Water Environment in Tokoro River Basin, Japan.

This study aims to assess the impact of climate change and land use change on the water environment using SWAT model in Tokoro river basin, which lies in north Japan.

Water pollution is a severe problem in Tokoro river basin, due to the limited amount of precipitation and large amount of agricultural drainage. Considering the fact that the precipitation patterns are projected to change significantly in north Japan, and that depopulation is advancing at high speed in this area, it is meaningful to evaluate the impact of these factors.

We created the future climate and land use scenario and simulated the impact of them using Soil and Water Assessment Tool (SWAT) model. For the climate scenario, the Database for Policy Decision making for Future climate change (d4PDF), which consists of 3000 years historical ensemble simulation and 5400 years future projections under 4 degree warming　was used. For Land use scenario, patterns and areas of agricultural land use was changed, based on recent trends of upsizing and abandonment of croplands.

As a preliminary analysis, for historical scenarios, 150 years ensemble simulations were selected out of 3000 years, and for future scenarios, 180 years future projections were selected out of 900 years in each of the 6 SST change patterns under 4 degree warming.

From the comparison of the results between historical and 4 degree warming scenario, it is indicated that annual mean flow is reduced in 5 out of 6 patterns under the 4 degree warming scenarios, and sediment concentration in all patterns. The annual mean flow was reduced to 80% at the most, while the only pattern with the increasing value was expanded to 102%.

In the presentation, we will show the result of the whole analysis, which takes into account the impact of land use change in addition to climate change.