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[AHW22-13] Development of a method to reconstruct past winter monsoon variability based on the inter-annual variabilities of river discharges and snowfall in Hokkaido, northern Japan
Keywords:winter monsoon, river discharge, snowfall, Hokkaido, principal component analysis
Monsoon is the seasonally alternating wind due to heat contrast between continents and ocean by solar radiation (Tada, 2005), and one of the most characteristic seasonal variation of climate in east Asia. Winter monsoon, which is characterized by cold and dry wind and blows from continents, promotes heavy snowfall along the Japan Sea side of Japanese Islands, while summer monsoon wind characterized by wet airmass turning around the north Pacific Ocean flows to Bai-u front and brings seasonal rain 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, to examine how the seasonal precipitation affects the spatiotemporal 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-years 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 Principle Components (PC) 1, 2, and 3. PC1 score represents a common seasonal pattern of discharges in Hokkaido, while PC2 and 3 represent differences of discharge patterns among the areas of Japan Sea, Okhotsk Sea, and Pacific. Based on the PC scores, each PC could be summarized like below, from shape of the maxima and minimum value of scores (the inter-annual variabilities of each principle component) and period of occurring.
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
We also compared three PC scores with inter-annual snowfall or summer precipitation in drainage area of each river, and the results were below.
1.Positive values of PC2 loadings correspond to inter-annual variability of summer precipitation in Takinoue, and the negative values correspond to those of snowfall in Iwamizawa
2.Positive values of PC3 loadings correspond to inter-annual variability of snowfall inTakinoue, and the negative values correspond to those in Noboribetsu
In order to utilize the knowledge for the reconstruction of past variability of winter monsoon, we need to further examine not only precipitation and snowfall but also the other climatological data.
We collected 10-years 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 Principle Components (PC) 1, 2, and 3. PC1 score represents a common seasonal pattern of discharges in Hokkaido, while PC2 and 3 represent differences of discharge patterns among the areas of Japan Sea, Okhotsk Sea, and Pacific. Based on the PC scores, each PC could be summarized like below, from shape of the maxima and minimum value of scores (the inter-annual variabilities of each principle component) and period of occurring.
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
We also compared three PC scores with inter-annual snowfall or summer precipitation in drainage area of each river, and the results were below.
1.Positive values of PC2 loadings correspond to inter-annual variability of summer precipitation in Takinoue, and the negative values correspond to those of snowfall in Iwamizawa
2.Positive values of PC3 loadings correspond to inter-annual variability of snowfall inTakinoue, and the negative values correspond to those in Noboribetsu
In order to utilize the knowledge for the reconstruction of past variability of winter monsoon, we need to further examine not only precipitation and snowfall but also the other climatological data.