CryoSheds: a GIS modeling framework for delineating land-ice watersheds for the Greenland Ice Sheet

Choice of watershed delineation technique is an important source of uncertainty for cryo-hydrologic studies of the Greenland Ice Sheet (GrIS), with different methods yielding different watersheds for a common pour point. First, this paper explores this uncertainty for the Akuliarusiarsuup Kuua River Northern Tributary, Western Greenland. Next, a standardized, semi-automated modeling framework for generating land-ice watersheds for GrIS land-terminating ice (henceforth referred to as CryoSheds) using geographic information systems (GIS) hydrologic modeling tools is presented. The framework uses ArcGIS and the ArcPy geoprocessing library to delineate two types of land-ice watersheds, namely those defined by: (1) a hydraulic pressure potential with varying water to ice overburden pressure ratios (k-value), which determines theoretical flow paths from the hydrostatic equation, using surface and bedrock digital elevation models (DEMs) and (2) a surface topography DEM alone. Lastly, a demonstration of the CryoSheds method is presented for seven remotely sensed proglacial pour points along the Aussivigssuit River (AR), Western Greenland, and its largest tributaries. GrIS meltwater runoff from these seven nested land-ice watersheds is estimated using Modele Atmospherique Regional (MAR) v.3.2 and runoff uncertainties due to watershed delineation parameter selection is estimated.     

2050年前气候变暖冰川萎缩对水资源影响情景预估

根据有不确定性的综合预测 ,到 2 0 5 0年左右青藏高原温度可比 2 0世纪末升高 2 .5℃左右 ,其导致冰川强烈消融的夏季升温为 1.4℃ ,将使平衡线上升 10 0m以上 .冰舌区消融冰量超过积累区冰运动来的冰量 ,冰川出现变薄后退 ,初期以变薄为主融水量增加 ,后期冰川面积大幅度减少 ,融水量衰退 ,至冰川消亡而停止 .考虑冰川大小 ,冰川类型响应气候变暖的敏感性有重大差别 ,应用新编中国冰川目录的统计数据 ,选择若干区域 ,预估 2 0 5 0年前冰川萎缩对水资源影响情景 .祁连山北麓河西地区 ,天山北麓准噶尔盆地南缘 ,天山南麓吐鲁番 哈密盆地的多数出山河流的冰川 ,以面积小于 2km2 者占绝对优势 ,对气候变暖最为敏感 ,衰退迅速 ,本世纪初期出现融水量高峰 ,中期融水量减少 ,对每条河流的影响以 10 6～ 10 7m3 ·a-1计 .少数流域如疏勒河、玛纳斯河等 ,冰川融水量占河川径流 1/ 3以上 ,有若干 5～ 30km2 左右中等规模冰川存在 ,预期至本世纪中期才出现融水高峰 ,融水增加值以 10 8m3 ·a-1计 .塔里木盆地周围高山冰川总面积达 2 2 0 0 9km2 ,有面积超过 10 0km2 、冰舌为厚表覆盖的大冰川 2 2条 ,退缩缓慢 ,冰川融水量在叶尔羌河、玉龙喀什河与阿克苏河等占 5 0 %～ 80 % .现在塔里木河干流主要靠天山西南部     

C chronology for ice retreat and inception of Champlain Sea in the St. Lawrence Lowlands, Canada

AMS radiocarbon cross-dating of plant debris and marine shells trapped in a lake basin on Mount St. Hilaire (Québec, Canada) provides a direct assessment of a reservoir effect totaling ca. 1800 ¹⁴C years during the early stage of Champlain Sea. Pollen-based extrapolation of bottommost ages on terrestrial plant macrofossils in sediments of this lake, and of another lake nearby support an estimate of 11,100 ± 100 ¹⁴C yr B.P. for marine invasion in the Central St. Lawrence River Lowlands. Results indicate a 400–1000 years younger regional chronology of ice retreat, now congruent with the one inferred from the New England varve chronology. This is a summary of a longer paper to be published in French.     

博格达山南坡黑沟8号冰川融水径流随机过程的模拟

冰川融水径流过程是由一个反映气温影响的确定性系统和一个反映时间序列随机特性的随机系统综合作用的结果。本文提出用一个以气温为自变量的多元回归模型和一个自回归类模型相结合的组合模型来描述冰川融水径流日平均流量过程。结果表明,模拟系列和实测系列间达到α=0.01的相关,7—8月平均拟合误差约为±20.0％。     

Late Devensian ice sheet characteristics: a palaeohydraulic approach

Glacial meltwater channels are incised into bedrock and diamicton along much of the length of the Mid-Cheshire Ridge. Detailed mapping of one such system near the town of Helsby reveals a dendritic channel network developed in the opposite direction to the regional ice flow during the last (Late Devensian) glaciation. The channels formed subglacially, under atmospheric and not hydrostatic pressure, presumably as the ice sheet downwasted during deglaciation. Morphological and palaeohydraulic evidence suggests that not all of the network was necessarily active contemporaneously. Former water levels in the channels can be estimated due to the presence of bar surfaces, giving a calculated palaeodischarge of at least 111 m³ s⁻¹. The ablation rates required to account for this large discharge are an order of magnitude greater than those obtained from theoretical calculations and those observed in modern glacial environments. This implies that some form of high-magnitude discharge, such as a seasonal flood event, must have taken place in this area during deglaciation. This picture of the Late Devensian ice sheet suggests that during recession the ice sheet was static, crevassed and relatively thin (<50 m). This study also shows that there is no simple relationship between meltwater channel direction and ice dynamics, and that care is required when using the former to make inferences about the latter. Copyright © 1998 John Wiley & Sons, Ltd.     

基于概率分布法的典型内陆河流域径流未来变化

基于黑河干流历史时期（1960 - 2012年）和RCPs（本文RCPs指RCP2.6、 RCP4.5和RCP8.5三种情景）情景下预估的未来（2013 - 2100年）月平均流量和冰川融水数据, 运用概率分布法和河道来水量距平法, 分析了黑河干流出山径流量与冰川融水径流量及其极值的未来变化趋势与程度、 径流丰枯变化以及冰川融水径流对黑河出山径流的补给与调节作用的变化。结果表明, 相较历史时期, 不同RCPs情景下未来黑河干流出山径流量将略呈增加态势, 但不显著; 月最大（7 - 8月）出山径流量将大幅度减少, 不确定性降低, 月最小（12月 - 翌年1月）出山径流量变化不明显。未来黑河干流, 不同RCPs情景下枯水年的发生概率将增加2～3倍, 偏枯水年在RCP2.6和RCP4.5情景下的发生概率亦将增大; 黑河干流未来可能进入平水年, 甚至枯水年。未来黑河干流年冰川融水径流与月最大冰川融水径流均显著减少, 对黑河径流的补给与调节作用均降低。     

基于多源遥感数据的玛纳斯河流域冰川物质平衡变化

冰川物质平衡变化是连接气候和水资源的重要纽带,对河川径流有重要的调节功能。本文采用MOD11C3和TRMM 3B43等多源遥感数据驱动度日模型,模拟了2000—2016年玛纳斯河（简称玛河）流域冰川物质平衡过程,并分析了冰川融水对径流的补给规律。结果表明： ① 通过构建气温及降水反演模型能有效校正气象遥感原数据的精度,且经降尺度后能较精细刻画冰川区气候变化特征。冰川区年均气温和降水量分别为-7.57 ℃和410.71 mm,海拔4200 m处为气候变化剧烈地带,气温直减率以其为界上下分别为-0.03 ℃/100 m和-0.57 ℃/100 m,降水梯度分别为-2.66 mm/100 m和4.8 mm/100 m,海拔大于4700 m后降水又以5.17 mm/100 m递增。② 研究期内流域冰川持续呈负平衡状态,累积物质平衡达-9811.19 mm w.e.,年均物质平衡介于-464.85~-632.19 mm w.e.之间。垂向物质平衡在消融区和积累区分别以244.83 mm w.e./100 m、18.77 mm w.e./100 m递增。2000—2002年、2008—2010年冰川消融减缓,2002—2008年、2010—2016年消融加剧,其中2005—2009年期间冰川亏损最为强烈。③ 年内河川径流对冰川物质平衡变化响应强烈,尤以7月、8月物质平衡亏损最为严重占全年总量的75.4%,使得同期河川径流量占全年径流总量的55.1%。年际冰川融水补给率波动于19%~31%之间,可能是不同年份降水和积雪融水补给率差异较大所致。玛河与天山北坡其他河流冰川融水贡献率非常接近,也进一步证实了本研究物质平衡估算结果的可靠性。本研究可为其他流域冰川物质平衡研究提供借鉴和参考。     

MELTWATER FEATURES THAT SUGGEST MIOCENE ICE-SHEET OVERRIDING OF THE TRANSANTARCTIC MOUNTAINS IN VICTORIA LAND, ANTARCTICA

ABSTRACT. We illustrate here spectacular meltwater features associated with outburst floods beneath an ice sheet that overrode the Transantarctic Mountains in southern Victoria Land. Because of long-term hyperarid polar climate, these features are part of an ancient landscape preserved for about 14 million years. Some channels are associated with areal scouring of basement rocks extending from sea level to as much as 1200–2100 m elevation in coastal regions. Scablands with scallops, potholes and plunge pools are cut in Beacon Super group sandstones and Ferrar Dolerite and cover wide areas of high western plateaus near the mountain crest. Subglacial channel systems commonly originate near divides and converge downhill toward the northeast. We argue that the landforms were created beneath a major Antarctic Ice Sheet that submerged the whole area, with the possible exception of the high peaks of the Royal Society Range, as it flowed northeastward toward the outer Antarctic continental shelf. Areal scouring, associated with warm-based regimes, is restricted to the lower slopes close to the coast. In the higher terra in, meltwater channels and scabland alongside preserved patches of regolith are best explained by the breaching of cold-based ice on the mountain rim by subglacial melt water outbursts. Melt from warm-based ice, along with subglacial lakes trapped upstream of the mountain rim, are possible sources of the meltwater necessary to form the channel systems and scablands.