Declining summer flows of Rocky Mountain rivers: Changing seasonal hydrology and probable impacts on floodplain forests
Declining summer flows of Rocky Mountain rivers: Changing seasonal hydrology and probable impacts on floodplain forests
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DOI：
10.1016/j.jhydrol.2007.11.012
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发表时间：
2008-02-01
影响因子：
6.4
通讯作者：
Shepherd, Anita
中科院分区：
文献类型：
--
作者：
Rood, Stewart B.;Pan, Jason;Shepherd, Anita
在分析气候变化的水文后果时，我们以前发现，排出北美、落基山脉源头和邻近河流流入北冰洋、大西洋和太平洋的河流的年流量正在下降。在这项研究中，我们通过比较月平均流量和分析约一个世纪有记录的累积过程线，研究了径流季节模式的历史变化。我们测试了由于冬季和春季变暖而导致的变化预测，这将增加雨雪比例，并改变积雪和融化。我们分析了14条自由流动、融雪为主的河流的记录，这些河流排干了相对原始的公园和保护区，从而避免了河流筑坝、流量调节或流域开发的影响。综合结果表明：(1)冬季(尤其是3月)径流略有增加，(2)春季径流和(3)洪峰出现较早，最显著的是(4)夏季和初秋(7-10月)径流明显减少。落基山脉东坡流向北部草原和哈德逊湾的河流变化最大，夏末流量递减率约为0.2%/年。这将产生相当大的生态影响，因为这是一个温暖和干燥的时期，蒸发需求最大，内河流量减少将减少河岸地下水补给，给泛滥平原森林带来干旱压力。再加上年流量的下降，更早的高峰和夏季流量的减少将给河岸的棉杨和柳树带来长期的压力，特别是限制苗木的招募。我们预测，一些河段将失去洪泛区森林，其他河段的林带将缩小，这些生态系统对其他影响的脆弱性将增加，包括牲畜放牧、高地植被侵蚀和杂草入侵。(C)2007 Elsevier B.V.保留所有权利。
In analyzing hydrologic consequences of climate change, we previously found declining annual discharges of rivers that drain the hydrographic apex of North America, the Rocky Mountain headwaters region for adjacent streams flowing to the Arctic, Atlantic and Pacific oceans. In this study we investigated historic changes in seasonal patterns of streamflows, by comparing mean monthly flows and analyzing cumulative hydrographs over the periods of record of about a century. We tested predictions of change due to winter and spring warming that would increase the proportion of rain versus snow, and alter snow accumulation and melt. We analyzed records from 14 free-flowing, snow-melt dominated rivers that drained relatively pristine parks and protected areas, thus avoiding the effects of river damming, flow regulation, or watershed development. The collective results indicated that: (1) winter flows (especially March) were often slightly increased, (2) spring run-off and (3) peak flows occurred earlier, and most substantially, (4) summer and early autumn flows (July-October) were considerably reduced. The greatest changes were observed for the rivers draining the east-slope of the Rocky Mountains toward the northern prairies and Hudson Bay, with late summer flow decline rates of about 0.2%/year. This would have considerable ecological impact since this is the warm and dry period when evaporative demand is maximal and reduced instream flows would reduce riparian groundwater recharge, imposing drought stress on floodplain forests. In combination with the decline in annual discharge, earlier peaks and reduced summer flows would provide chronic stress on riparian cottonwoods and willows and especially restrict seedling recruitment. We predict a loss of floodplain forests along some river reaches, the narrowing of forest bands along other reaches, and increased vulnerability of these ecosystems to other impacts including livestock grazing, encroachment of upland vegetation, and weed invasion. (C) 2007 Elsevier B.V. All rights reserved.