Abstract Snowmelt is a major source for summer soil water storage that supports tree growth in the Mediterranean climate of the Sierra Nevada, California. The timing and magnitude of snow-water contributions to soil moisture are controlled by energy and water availability that varies based on climate (and thus weather) and topography (i.e. elevation, slope, and aspect). Few studies, thus far, have explored how transpiration rate is affected by differences in the timing and magnitude of snowmelt across years and locations. Here we used meteorological and hydrological measurements on north and south aspects in the Sagehen Creek catchment (Sierra Nevada, California) to investigate the controls on the timing of conifer sap flow, a proxy for transpiration rate, in response to the timing and magnitude of snowmelt. We found that sap flow prior to its seasonal peak in July was largely controlled by air temperature and that spring sap flow was reduced by cloudy conditions. Years with earlier snow disappearance caused earlier peak sap flow, which was nearly coincident with the beginning of soil moisture limitations than years with later snow disappearance. Because Sagehen Creek receives little summer rainfall, years with earlier snowmelt and peak sap flow had more total days with soil moisture limitation on sap flow. Overall, our results suggest that earlier snow disappearance and more spring rain (both expected to result from climate change) will potentially shift the peak of sap flow earlier in the growing season and increase the duration of water limitations during summer. These insights about the timing and duration of water limitations could be used as benchmarks to test physically based models and better constrain predictions of transpiration rates in snow-dominated landscapes similar to the study site.

中文翻译：

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融雪对内华达山脉针叶林的蒸腾作用造成不同的限制

摘要 融雪是夏季土壤蓄水的主要来源，支持加利福尼亚内华达山脉地中海气候中的树木生长。雪水对土壤水分贡献的时间和大小受能源和水资源可用性的控制，这些能源和水资源根据气候（以及天气）和地形（即海拔、坡度和坡向）而变化。迄今为止，很少有研究探讨不同年份和地点的融雪时间和程度的差异如何影响蒸腾速率。在这里，我们使用了 Sagehen Creek 集水区（加利福尼亚州内华达山脉）北部和南部的气象和水文测量，以研究对针叶树液流时间的控制，这是蒸腾速率的代表，以响应融雪的时间和幅度. 我们发现 7 月份季节性高峰之前的树液流量在很大程度上受气温控制，而春季树液流量因多云条件而减少。积雪较早的年份导致树液流量峰值较早，与积雪较晚的年份相比，这几乎与土壤水分限制的开始一致。由于 Sagehen Creek 夏季降雨量很少，因此融雪和树液流量高峰期较早的年份总天数较多，土壤水分限制了树液流量。总体而言，我们的结果表明，更早的雪消失和更多的春雨（预计均由气候变化引起）可能会在生长季节更早地改变树液流量的峰值，并增加夏季水分限制的持续时间。