芦生演習林の気象観測資料の解析 (1) : 事務所構内と長治谷の観測所の比較解析を中心に

Abstract

1) 京都大学芦生演習林の70年間の気象観測資料から気温, 湿度, 降水量, 積雪の各項目について検討を行った。2) 芦生観測所の気象は, 最近15年間の観測結果から年平均気温 (9時) は11. 0℃, 真夏の最高気温 (極) は34℃, 真冬の最低気温 (極) は－10℃前後となり, 年平均湿度 (9時) は83％, 年降水量は2370mm, 降水日数は173日, 最大積雪深は108cm, 積雪日数は88日となった。京都市内に比べて, 年平均気温 (9時) は4℃低く, 夏の最高気温は1℃, 冬の最低気温は5℃低く, 冬期の気温の低下が著しかった。年降水量は800mm以上多く, 年降水日数は1. 5倍となり, 湿度は年間を通じて10％以上高くなり, ともに冬期にその差が大きくなった。3) 芦生観測所より海抜高が277m高い長治谷観測所では, 年平均気温 (10時) は2℃, 真夏の最高気温は5℃, 真冬の最低気温は4℃低かった。冬期の降水量は50mm/月多くなり, 年降水量は400mm多かった。最大積雪深は200cmを超え, 積雪日数は40日多くなった。4) 芦生観測所と京都府下の京都気象台の各観測所の観測結果を比較すると, 芦生は年平均気温は低く, 年降水量は多く, 最大積雪深は大きかった。15km離れた美山観測所より年平均気温は2℃低く, 年降水量は400mm多く, 最大積雪深は70cm大きかった。5) 芦生では降水量, 積雪などの気象観測値が異常値に達することが多く, 特に夏期の集中豪雨に起因する気象災害が多発した。6) 日降水量100mm, 総降水量200mm以上となると, 車道, 林道, 軌道では崩壊が起こり易く, 日降水量200mm以上では由良川は危険水位となり, 道路, 建物, 諸施設の被害は激甚となった。雪による被害は最大積雪深が150cm以上, 積雪100cm以上の日数が20日を超えると建物や道路の崩壊などの被害が現れはじめ, 特に185cmを超え, 日数が50日以上になると被害が大きくなった。

1) Meteorological data of air temperature, humidity, precipitation and snow cover, which have observed in Kyoto University Forest of Ashiu located at northern east part of Kyoto Prefecture for 70 years were analyzed. 2) The average annual temperature at 9 o'clock was 11.0℃ with the average extreme maximum temperature 34℃ in summer and the average extreme minimum temperature - 10℃ in winter; the average annual humidity at 9 o'clock was 83%; the average precipitation was 2370 mm with 173 days above 1 mm/day a year; the average annual maximum depth of snow cover was 108 cm with 88 days of snow cover above 1 cm in winter in Ashiu observation station at 363 m above sea level. 3) Observed values of Ashiu were 4℃ lower in the average annual temperature, 1℃ lower in the extreme maximum temperature in summer and 5℃ lower in the extreme minimum temperature in winter; above 10% higher in the average annual humidity; 800 mm more in the average precipitation a year than that of Kyoto University Experimental Forest Station on the Campus, which was located in Kyoto City and about 30 km distance from Ashiu in a straight line towards the south. And it has scarcely snown in a period of observation there. 4) Observed values of Chojidani observation station at 640 m above sea level, which was about 5 km distance from Ashiu towards the north were 2℃ lower in the average annual temperature at 10 o'clock, 5℃ lower in the average extreme maximum temperature in summer and 4℃ lower in the average extreme minimum temperature; 50 mm/month more in winter and 400 mm more a year in the average precipitation; 40 days of snow cover with the annual maximum snow depth above 200 cm more than that of Ashiu observation station. 5) Observed values of Ashiu were lower in the average annual temperature and more in the average precipitation and in the snow cover than that of any observation by Kyoto meteorological observatory in Kyoto Prefecture. The average annual temperature was 2℃ lower, the precipitation was 400 mm more a year and snow cover was 80 cm more than that of Miyama observation station, which was about 15 km distance from Ashiu towards the west at 200 m above sea level. 6) Many peculiar data were observed, for example heavy or long rain and snow in Ashiu. Ashiu has often suffered from many disasters especialy caused by heavy rain in summer in a period of observation. 7) The breaking downs of road were happened easily by over 100 mm/day or over 200 mm of total amount of precipitation. If the daily amount of precipitation was over 200 mm, heavy disasters, for example, washing away of Yuragawa Bridge and many damages of roads, hauses and facilities occurred by the flood. And damages of hauses and roads were happened easily by over 150 cm of snow cover and 20 days of snow cover above 100 cm. Over 185 cm of snow cover and 50 days of snow cover above 100 cm caused heavy damage.