[AHW32-P19] Establishment and evaluation of a method to reconstruct the past snow fall and winter monsoon intensity based on the inter-annual variabilities of river discharges in Hokkaido, northern Japan
Monsoon is the seasonally alternating wind due to heat contrast between continents and ocean by solar radiation (Tada, 2005), and the one of the most characteristic seasonal variation of climate in east Asia. Winter monsoon, which is characterised by cold and dry wind and blows from continents, promotes heavy snowfall along the Japan Sea side of Japanese Islands, while Baiu, where moist tongue characterised by wet wind turning around the north Pacific Ocean, brings seasonal rain front along the Japanese Islands in summer. Although past summer monsoon has been successfully reconstructed in many studies (Ikehara and Itaki, 2005), researches on winter paleoclimate including winter monsoon have not been developed well. In this study, we analyzed the inter-annual variability of river water discharge in Hokkaido, subarctic Japan, to examine how the seasonal precipitation affects the spatio-temporal variability of sediment and water discharge, and tried to utilize it to reconstruct the past variability of winter snowfall from sediment archives.
We collected 10-year water discharge data of 13 class A rivers between 2006-2016 in Hokkaido from Water Information System of Ministry of Land, Infrastructure, Transport and Tourism. Then, we conducted principal component analysis (PCA) using R. Missing data was interpolated by the mean values. Out of 13 principle components, we examined PC1, PC2, and PC3 which occupy a large proportion of total variance. Based on the spatial distribution of the principle component loadings and the timings of maximum and minimum of principle component scores, these PCs are characterised like below.
1. PC1 represents average temporal discharge variation in Hokkaido, where the discharge depends on precipitation during summer to autumn and melting of snow in spring
2. PC2 loadings are significantly positive in the Okhotsk Sea side and negative in the Japan Sea side, where timing of maximum score is associated by summer precipitation in the Okhotsk Sea side and minimum score is associated by spring snow melt in the Japan Sea side
3. PC3 loading shows significantly positive in the Okhotsk Sea side and negative in the Pacific side, where timing of maximum score is associated with spring snow melt and minimum score occurs at heavy precipitation in summer and autumn
Considering the timing of maxima and minima in PC2 score, we suggest that the comparison of sediment discharge between the Okhotsk Sea and the Japan Sea may enable us to extract the information of spring snow melt discharge in the Japan Side as well as winter snow fall. However, when magnitude of both PC2 and PC3 scores becomes large, melting snow also depends on temperature that depends on insolation intensity (Chikita. 1994). Therefore, we need to further examine not only precipitation and snowfall but also data of temperature and insolation.
We collected 10-year water discharge data of 13 class A rivers between 2006-2016 in Hokkaido from Water Information System of Ministry of Land, Infrastructure, Transport and Tourism. Then, we conducted principal component analysis (PCA) using R. Missing data was interpolated by the mean values. Out of 13 principle components, we examined PC1, PC2, and PC3 which occupy a large proportion of total variance. Based on the spatial distribution of the principle component loadings and the timings of maximum and minimum of principle component scores, these PCs are characterised like below.
1. PC1 represents average temporal discharge variation in Hokkaido, where the discharge depends on precipitation during summer to autumn and melting of snow in spring
2. PC2 loadings are significantly positive in the Okhotsk Sea side and negative in the Japan Sea side, where timing of maximum score is associated by summer precipitation in the Okhotsk Sea side and minimum score is associated by spring snow melt in the Japan Sea side
3. PC3 loading shows significantly positive in the Okhotsk Sea side and negative in the Pacific side, where timing of maximum score is associated with spring snow melt and minimum score occurs at heavy precipitation in summer and autumn
Considering the timing of maxima and minima in PC2 score, we suggest that the comparison of sediment discharge between the Okhotsk Sea and the Japan Sea may enable us to extract the information of spring snow melt discharge in the Japan Side as well as winter snow fall. However, when magnitude of both PC2 and PC3 scores becomes large, melting snow also depends on temperature that depends on insolation intensity (Chikita. 1994). Therefore, we need to further examine not only precipitation and snowfall but also data of temperature and insolation.