Projection of Climatic Change over Japan Due to Global Warming by High-Resolution Regional Climate Model in MRI

Abstract

performance was evaluated in seven local areas of Japan (Fig. 1). Precipitation amount was reproduced adequately in each area, compared with the climatic amount of observed precipitation that was calculated from data by observation stations of JMA (e.g., Fig. 2). In Fig. 2, monthly mean precipitation amounts from the result of RCM20 and from observations are indicated for areas of NJ (North Japan/Japan Sea side) and WJ (West Japan/Japan Sea side). The observed climatic precipitation amount was calculated by averaging data at observation stations included in each area. To calculate the model climate, model grid data nearest each observation station was chosen. The chosen data were gathered and averaged in each area to obtain the areal model climate. In the figure, differences between model climates and observations were seen. However, Fig. 2 shows that total differences were not too large. Model results agreed to observations mostly with a significance level of 95%. In other areas, climatic precipitation amounts were reproduced with similar accuracy as Fig. 2 for most cases. We can conclude that the model could reproduce the annual change of precipitation for each area of Japan with adequate accuracy. The exception was the area of SWI, where observation stations are few and reproducibility was not adequate. In this paper, results of SWI are not discussed. Surface air temperatures are plotted in scatter diagrams in Fig. 3. One dot represents data at each observation station. From the figure, high correlations between model results and observations can be seen for January and July. The temperatures had warm biases of 2°C in all areas for summer and winter. For reduction of this bias, we may need further sophistication of surface process of RCMs in the future. However, high correlation coefficients exceeding 0.95 were attained between model results and observations for all months. The coefficient was 0.95 for January and 0.97 for July, as presented in Fig. 3. These results indicated that RCM20 was able to reproduce present climate over Japan with adequate accuracy.