暖候性積雪地域の山地流域における気象要素の空間的分布 : 降雨量・気温・積雪深

Abstract

芦生演習林の気象・水文の空間分布を把握するために、演習林全体を含むおよそ4, 700haの由良川源流域において調査用施設を配置し, 観測を開始した。芦生集水域の地質は丹波帯の中生層で頁岩を主体としてチャート, 砂岩を含んでいる。植生はスギと広葉樹 (ブナ, ミズナラ, ウラジロガシ) が混交し, 標高は355 - 959mの流域である。本報告では, この集水域における広域的な降水量・気温・積雪深などの気象要素の分布の3年間の観測結果を示し, 各観測点の観測値を比較・検討することによって, 事務所の観測値から林内の各地点の気象要素を推定する方法を提案した。

Hydrological observations have been made in the Ashiu Experimental Watershed situated on the source area of the Yura River in Kyoto Prefecture, for understanding the meteorological and hydrological conditions of the University Forest in Ashiu. The Ashiu Watershed is underlain by Mesozoic Era formations and is covered with natural forests of Cryptomeria japonica, Fagus crenata and Quercus salicina. The basin area of this watershed is about 4, 700 ha. The altitude of the watershed ranges from 355m to 959m. The results are as follows, 1) Precipitation in Ashiu is able to be presumed by the observed data of Office and Chojidani point. 2) It is possible to adopt the reduction rate of temperature (0.6℃/100m) to presume the mean temperature of high land which has no streams, owing to the observations of temperature in Ashiu. But it is necesarry to use another equation for presumption of the temperature of valley parts. The reduction rate of temperature is 1.2℃/100m in the high-land part which has streams. The reduction rate of temperature is 3.0℃/100m in the valley parts along Naisugi River and that is 5.0℃/100m in the valley parts along Yura River. 3) The maximum snow depths become langerin proportion to altitudes in the valley parts and slope parts. The maximum snow depths are nearly constant in the high-land part of Ashiu. The authors get the equations as MSHob=a･(Aob-360)+MSHAJ Aob‹600 MSHob=a･240+MSHAJ Aob≧600 where, MSHob : maximum snow depth at an observation point (cm) Aob : altitude of an observation point (m) MSHAJ : maximum snow depth at Office (cm) a : coefficient number (0.2~0.4)