ABSTRACT The altitudinal variation of precipitation, evapotranspiration, and runoff was quantified at 16 different grassland sites between 580 and 2550 m a.s.l. in the Austrian Alps. Along this altitudinal transect annual evapotranspiration decreased from roughly 690 mm at low elevation sites to 210–220 mm at the upper limit of the alpine grassland belt. A detailed analysis of the data showed that the observed reduction in the annual sum of evapotranspiration could be mainly explained by the altitudinal decline of the length of the snow-free period (i.e. the vegetation period). Daily mean sums of evapotranspiration showed no altitudinal trend and averaged 2.2 mm d−1 independent of elevation, although the leaf area index, growing season mean air temperature, and vapor pressure deficit declined with increasing altitude. As precipitation increased with elevation, evapotranspiration seems to be of secondary importance when compared to runoff. Inter-annual variability of evapotranspiration was fairly low across contrasting dry and wet years (coefficient of variation = 7%), indicating that even during dry years water availability was not limiting evapotranspiration.

中文翻译：

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奥地利阿尔卑斯山草原生态系统的水平衡

摘要 在奥地利阿尔卑斯山海拔 580 到 2550 米之间的 16 个不同草地地点量化了降水、蒸散和径流的高度变化。沿着这个高度样带，年蒸散量从低海拔地区的大约 690 毫米下降到高寒草原带上限的 210-220 毫米。对数据的详细分析表明，观测到的年蒸散总量减少的主要原因是无雪期（即植被期）长度的高度下降。尽管叶面积指数、生长季节平均气温和水汽压差随着海拔的升高而下降，但日平均蒸散总量没有显示出海拔趋势，平均为 2.2 mm d-1，与海拔无关。随着降水随海拔升高而增加，与径流相比，蒸散似乎是次要的。在对比的干湿年份，蒸发蒸腾的年际变化相当低（变异系数 = 7%），这表明即使在干旱年份，水的可用性也不会限制蒸发蒸腾。