Recent warm winter and decreasing of snow water storage in the snowy cold region and those effect to the basin water balance

在过去的15年里，在北方北海道的一个雪山流域（1.15平方公里），水文和气象观测一直保持良好的状态。利用这些数据集计算了流域水平衡，并对流域水储量的年际变化进行了评价。提出了流域水量平衡的概念性数学模型。在模型中只假定气温为一个变量，通过模型计算考察了冬季变暖引起的积雪蓄水量变化对流域水量平衡的影响。最近，据说日本的多雪地区出现了暖冬，积雪量明显减少。我们研究了这些趋势对非人为流域水平衡的影响。通过我们的研究获得了以下结果：1）积雪贮水量的年际变化范围很大，不仅取决于冬季降水量，还取决于积雪和消融初期的气温，（二）融雪期后，积雪蓄水量对干旱径流的影响不大。1999.以化学成分为示踪剂，分析了坡面地下水流成分的径流过程。由三组分模型（融雪水、地下水和混合水）分离的河流过程线表明，在整个融雪季节，地下水对河流流量的贡献几乎占总流量的40%。这就导致了积雪化学成分的输出量超过了总输入量。

During the past 15 years, hydrological and meteorological observations have been continued in good condition in a snowy mountainous watershed (1.15 km^2) of northern Hokkaido. Annual basin water balance was calculated every water year using these data sets, and inter-annual variations of basin water storage were evaluated. Moreover, a conceptual mathematical model for the basin water balance was proposed. Air temperature was assumed only one variable parameter within the model, and an effect of the changes of snow water storage on the basin water balance due to the winter warming was examined by this model calculation. Recently, it is said that the snowy region in Japan has warm winter and the snowpack amount is decreasing remarkably. We have studied what kinds of influence would be caused by these trends in the basin water balance of the non-anthropogenic watershed. Following results were obtained through our study : 1) the wide range of inter-annual variation in snow water storage depended on not only winter precipitation but also air temperature in the beginning of snow accumulation and ablation periods, 2) snow water storage did not affect so much on the drought flow after the snowmelt season.Water and material budgets were examined at the same watershed during the whole snowmelt season in 1999. Runoff process of the subsurface flow component on the hillslope was analyzed using chemical constituent as a tracer. Stream hydrograph separation by the three components model (snowmelt water, groundwater and those mixed water) showed that groundwater contribution to the stream discharge was almost 40 % of total flow during the whole snowmelt season. This leads to the excessive output of chemical constituent as compared with the total input in the snowpack.