Warming temperatures and precipitation changes are expected to alter water availability and increase drought stress in western North America, yet uncertainties remain in how concurrent changes in the amount and seasonality of precipitation interact with warming to affect hydrologic partitioning. We combined over a century of streamflow (Q) and climate observations with two decades of tree growth data and remotely sensed vegetation activity to quantify how temperature and precipitation interact to control hydrologic partitioning in the Front Range of Colorado, Boulder Creek Watershed. Temperature and precipitation significantly increased over the last five decades, with precipitation increasing primarily in winter (11.2 mm decade⁻¹) and temperature increasing primarily during the growing season (0.12°C decade⁻¹). In response to wetter winters and warmer summers, streamflow decreased −9.8 mm decade⁻¹, with largest declines occurring during summer and autumn baseflow (−8.4 mm decade⁻¹). Spring warming was associated with increases in episodic, short spring melt events, earlier and slower snowmelt and an increase in fraction of precipitation available to plants (catchment wetting or W). Warming during the growing season resulted in an increase in the fraction of W lost as evapotranspiration (ET), earlier and lower peaks in remotely sensed normalized difference vegetation index (NDVI) and lower tree ring width index (RWI). These analyses highlight that vegetation is becoming increasingly water limited even as increases in precipitation and slower melt increase plant water availability. Further, catchment‐derived metrics like the Horton Index (ET/W) provide insight in to how simultaneous changes in temperature, precipitation and melt impact vegetation across complex watersheds.

中文翻译：

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在季节性积雪的森林中，由于气候变暖和湿润，植物水分胁迫增加，夏季溪流减少

预计气温升高和降水变化将改变北美西部的水资源供应并增加干旱压力，但仍存在不确定性，即降水量和季节性的同时变化如何与变暖相互作用以影响水文分配。我们结合了一个多世纪以来的水流（Q）和气候观测结果以及数十年的树木生长数据以及遥感植被活动，以量化温度和降水如何相互作用以控制科罗拉多州博尔德溪分水岭前缘的水文分区。在过去的五十年中，温度和降水显着增加，降水主要在冬季（11.2毫米十年^-1）增加，温度主要在生长季节（0.12°C十年）增加^-1）。为了应对冬天的湿润和夏天的温暖，水流下降了-9.8毫米十年^-1，最大的下降发生在夏季和秋季的基流（-8.4毫米十年^-1）。春季变暖与间歇性，春季融化事件增加，融雪较早和变慢以及植物可获得的降水分数增加有关（集水区湿润或W）。生长季节的变暖导致蒸发蒸腾量（ET）导致的W损失比例增加，遥感归一化差异植被指数（NDVI）和较低的年轮宽度指数（RWI）的峰值更早和更低。这些分析表明，即使降水增加和融化速度降低，植物的水分利用率也越来越高，植被正变得越来越受水限制。此外，诸如霍顿指数（ET / W）等来自流域的度量标准可洞悉温度，降水和融化的同时变化如何影响复杂流域的植被。