北海道有珠山における泥流発生にかかわる降雨特性(I) : 総雨量・日雨量

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Rainfall properties related to the occurrence of mudflows in Mt. Usu area were studied by using rainfall amount data obtained from a special mesoscale raingauge network set up by the present workers and raingauge networks operated by other organizations. The magnitude of rainfall amount in Mt. Usu area is as follows. The annual mean rainfall amount during the warm period (April〜October) was about 800 mm and this value was equal to the annual mean rainfall amount in Hokkaido. Accordingly it is not considered that Mt. Usu area is a pluvial area. It is generally said that disasters of mud or rock debris flows begin to occur when the daily rainfall amount exceeds 80 mm. Based on the past rainfall amount data in Mt. Usu area, the return period of over 80 mm in daily rainfall amount was about three years in Mt. Usu area. It was obtained from the data in Mt. Usu observation point that the maximum daily rainfall amount for the past ten years was 136 mm. There were large rainfall amounts in the periods from the second decade of August to the second decade of September and from the second decade of July to the third decade of July, and heavy rainfalls were also concentrated in these periods. It was considered that the former corresponded to Shuurin period and the latter corresponded to Baiu period. While a weather forecast is made for this area regarding all Iburi district as a unit area, it is known that the distribution pattern of rainfall amount in the Iburi district is not uniform. When there were large rainfall amounts in Mt. Usu area, the distribution patterns of rainfall amount were analyzed and classified as follows. There were four distinct distribution patterns ; "Seaside rainfall" in which the maximum peak of rainfall amount was concentrated on the seaside region in the central Iburi district, "Orographic rainfall" in which the maximum peak was concentrated on the southeastern slope in the Orofure Mountain Range, "Mt-Usu rainfall" in which the maximum peak was concentrated in Mt. Usu area and "Other rainfall type" in which the peak showed an overly spacious distribution or when the maximum peak could not be classified. When there were large rainfall amounts that caused mud or rock debris flows which occurred in 1980, the pluvial areas in Mt. Usu area corresponded to both vertical side portions of the flank against the prevailing wind and their lee portions, that is to say, the pluvial areas were determined by the wind direction. In the case of 1980, the areas of mud or rock debris flows corresponded to the areas which exceeded 30 mm in accumulated rainfall amount.
北海道大学の論文
1982-03-25

北海道有珠山における泥流発生にかかわる降雨特性(I) : 総雨量・日雨量

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