Contrasting long-term alpine and subalpine precipitation trends in a mid-latitude North American mountain system, Colorado Front Range, USA
Contrasting long-term alpine and subalpine precipitation trends in a mid-latitude North American mountain system, Colorado Front Range, USA
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美国科罗拉多州弗兰特山脉中纬度北美山区系统的长期高山和亚高山降水趋势对比
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
P. Blanken
中科院分区：
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作者：
T. Kittel;M. Williams;K. Chowanski;M. Hartman;T. Ackerman;M. Losleben;P. Blanken
背景：山区系统的长期气候趋势通常随海拔高度变化很大。目的：评估中大陆、中纬度北美山脉系统的亚高山森林和高山苔原地区长期降水趋势对海拔的依赖性，并将这种依赖性与大气环流模式联系起来。方法：我们对比了美国落基山脉科罗拉多前岭尼沃特岭两个高海拔气候站 59 年（1952-2010）的降水记录。这些地点一处位于森林（海拔高度 3022 米），另一处位于高山苔原（海拔 3739 米），位置相距较近（水平方向 7 公里以内，垂直方向约 700 米以内），但与山地系统顶部（大陆分水岭）的距离不同。结果：这些地点的年度和季节性降水趋势存在显着差异，这在很大程度上取决于它们的海拔和距大陆分水岭的距离。高山地区年降水量每十年增加 60 毫米（+6%），而亚高山地区没有显着变化。从季节性来看，高山地区的趋势主要是冬季的增加，我们认为这是由于高空（700 hPa）西北气流驱动的分水岭上地形产生的降水增加所致。这种变化在亚高山地区并不明显，受西北流地形降水的影响较小。结论：降水趋势的海拔依赖性似乎是由于高空气流从主要西南风向西北风的变化引起的。降水趋势对地形位置和季节的依赖性对尼沃特山脊和邻近流域的生态和水文学具有复杂的影响，涉及物理过程（例如积雪动力学）和生物反应（例如物候和生态系统生产力）之间的相互作用。
Background: Long-term climate trends in mountain systems often vary strongly with elevation. Aims: To evaluate elevation dependence in long-term precipitation trends in subalpine forest and alpine tundra zones of a mid-continental, mid-latitude North American mountain system and to relate such dependence to atmospheric circulation patterns. Methods: We contrasted 59-year (1952–2010) precipitation records of two high-elevation climate stations on Niwot Ridge, Colorado Front Range, Rocky Mountains, USA. The sites, one in forest (3022 m a.s.l.) and the other in alpine tundra (3739 m), are closely located (within 7 km horizontally, ca. 700 m vertically), but differ with respect to proximity to the mountain-system crest (the Continental Divide). Results: The sites exhibited significant differences in annual and seasonal precipitation trends, which depended strongly on their elevation and distance from the Continental Divide. Annual precipitation increased by 60 mm (+6%) per decade at the alpine site, with no significant change at the subalpine site. Seasonally, trends at the alpine site were dominated by increases in winter, which we suggest resulted from an increase in orographically generated precipitation over the Divide, driven by upper-air (700 hPa) north-westerly flow. Such a change was not evident at the subalpine site, which is less affected by orographic precipitation on north-westerly flow. Conclusions: Elevation dependence in precipitation trends appears to have arisen from a change in upper-air flow from predominantly south-westerly to north-westerly. Dependence of precipitation trends on topographic position and season has complex implications for the ecology and hydrology of Niwot Ridge and adjacent watersheds, involving interactions among physical processes (e.g. snowpack dynamics) and biotic responses (e.g. in phenologies and ecosystem productivity).