Alpine regions are generally referred to as water towers for the lowlands, yet the water balance has not been quantified for alpine catchments with different vegetation types. This paper presented a multi-year time series of evapotranspiration (ET) and water supply (precipitation minus ET) during the warm-season (June to September), measured using eddy covariance techniques for an upper alpine shrub (3400 m) and for a lower alpine meadow (3200 m), on the northeastern Qinghai-Tibetan Plateau. The monthly ET for the shrub averaged 71.8 ± 10.1 mm (Mean ± SD), which was 22.7% lower than for the meadow. ET peaked at 89.0 ± 3.0 mm for the shrub and at 113.9 ± 2.6 mm for the meadow both in July. The monthly water supply was nearly neutral from June to July and represented a surplus in August and September at both sites. The mean warm-season ET and water supply were 287.0 ± 17.6 mm and 59.6 ± 16.3 mm for the shrub, and 352.2 ± 15.7 mm and 22.5 ± 32.5 mm for the meadow, respectively. Piecewise structural equation models showed that variability of daily ET was dominated more by net radiation (R_n) than by vapor pressure deficit (VPD) at both sites. However, net radiation was 32.6% higher for the shrub than for the meadow, but this did not drive higher ET for the shrub. This was explained by the difference in the energy partitioning strategy (Bowen ratio), which was attributable to the difference in the bulk surface resistance, rather than the difference in the climatological resistance (which is proportional to VPD/R_n). The seasonal and annual variability of water supply was determined by precipitation rather than by ET. The linear slopes of water supply with precipitation were all close to one, regardless of vegetation type. This suggested that the water yield efficiency was consistent at the two sites. Our results highlighted the different effects of vegetation type on ET and water supply for humid alpine regions. The lower ET loss and consequent higher water yield, but with less digestible forage in the shrub, would present a dilemma for the balance between water supply and forage production under current shrub expansion in alpine rangeland.

高山地区通常被称为低地水塔，但尚未对不同植被类型的高山集水区的水平衡进行量化。本文介绍了在暖季（6月至9月）期间的蒸散量（ET）和供水量（降水量减去ET）的多年时间序列，使用涡度协方差技术对高海拔灌木（3400 m）和高海拔灌木进行了测量。位于青藏高原东北部的低高山草甸（3200 m）。灌木的月平均ET为71.8±10.1mm（平均值±标准差），比草地低22.7％。灌木的ET峰值在89.0±3.0 mm，草甸的ET峰值在113.9±2.6 mm。从6月到7月，每月的水供应几乎是中性的，这两个地点在8月和9月表示过剩。灌木的平均暖季ET和供水量分别为287.0±17.6 mm和59.6±16.3 mm，草甸的分别为352.2±15.7 mm和22.5±32.5 mm。分段结构方程模型表明，每日ET的变化主要受净辐射的影响（R _n）大于两个位置的蒸汽压差（VPD）。但是，灌木的净辐射比草地高32.6％，但这并没有推动灌木的ET升高。能量分配策略的差异（博文比）可以解释这一点，这归因于体表电阻的差异，而不是气候阻力的差异（与VPD / R _n成正比））。供水的季节和年度变化取决于降水量而不是ET。不论植被类型如何，带降水的供水线性斜率都接近于一。这表明在两个地点的产水效率是一致的。我们的结果强调了湿润高山地区植被类型对ET和供水的不同影响。较低的ET损失和随之而来的较高的水产量，但灌木中易消化的草料较少，这将给目前高寒草原上灌木扩展下的供水和草料生产之间的平衡带来难题。