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[MIS12-01] Winters in Japan have not been getting warmer in recent years
Keywords:meteorological office, AMeDAS, temperature lapse rate, Mann-Kendall test, Omiwatari
The annual mean temperature deviation in Japan from 1898 to 2023 has risen at a rate of 1.35°C/100 years. However, since 1989, the rate of increase has been 2.56°C/100 years, with a remarkable rise in temperature in the recent time period. In this study, we considered the temperature fluctuations from 1989 to 2023. The seasonal mean temperature deviation has the highest rate of increase in the summer, but the fluctuation observed in winter is significantly different from that of the other seasons, with a rate of fluctuation of -0.28°C/100 years and exhibiting a decreasing trend. The monthly mean temperature deviation had the largest rate of increase in March and showed an overall large rate of increase from March to September, with an exception for the month of April. The monthly mean temperature deviations in December and January exhibit a decreasing trend.
The winter mean temperature observed at the meteorological offices around the Japanese Alps region did not show a statistically significant trend of fluctuations. At approximately half of these locations, there was a decreasing trend which was not statistically significant. Seasonal mean temperatures in spring and summer seasons showed statistically significant increasing trend at almost all locations. The annual minimum temperature observed in Suwa exhibited a statistically significant upward trend. This upward trend is not because the recent temperature rise in Suwa has been more pronounced than in the other locations. We believe that this observed trend at Suwa can be attributed to an increase in winter seasons in the past with particularly low temperature values. The average winter temperatures at the AMeDAS observation points showed no statistically significant trend of fluctuation at any of the points, and the upward trend in the seasonal average temperature from spring to autumn seasons was more gradual than that observed at the meteorological offices.
The winter mean temperature observed at the meteorological offices around the Japanese Alps region did not show a statistically significant trend of fluctuations. At approximately half of these locations, there was a decreasing trend which was not statistically significant. Seasonal mean temperatures in spring and summer seasons showed statistically significant increasing trend at almost all locations. The annual minimum temperature observed in Suwa exhibited a statistically significant upward trend. This upward trend is not because the recent temperature rise in Suwa has been more pronounced than in the other locations. We believe that this observed trend at Suwa can be attributed to an increase in winter seasons in the past with particularly low temperature values. The average winter temperatures at the AMeDAS observation points showed no statistically significant trend of fluctuation at any of the points, and the upward trend in the seasonal average temperature from spring to autumn seasons was more gradual than that observed at the meteorological offices.