Evaluating morphological estimates of the aerodynamic roughness of debris covered glacier ice

Aerodynamic roughness length (z₀), the height above the ground surface at which the extrapolated horizontal wind velocity profile drops to zero, is one of the most poorly parameterised elements of the glacier surface energy balance equation. Microtopographic methods for estimating z₀ have become prominent in the literature in recent years, but are rarely validated against independent measures and are yet to be comprehensively analysed for scale or data resolution dependency. Here, we present the results of a field investigation conducted on the debris covered Khumbu Glacier during the post‐monsoon season of 2015. We focus on two sites. The first is characterised by gravels and cobbles supported by a fine sandy matrix. The second comprises cobbles and boulders separated by voids. Vertical profiles of wind speed recorded by a tower comprising five cup anemometers and deployed over both sites enable us to derive measurements of aerodynamic roughness that reflect their observed surface characteristics (0.0184 m and 0.0243 m, respectively). At the second site, z₀ also varied through time following snowfall (0.0055 m) and during its subsequent melt (0.0129 m), showing the importance of fine resolution topography for near‐surface airflow. To compare the wind profile data with microtopographic methods, we conducted structure from motion multi‐view stereo (SfM‐MVS) surveys across each patch and calculated z₀ using three previously published approaches. The fully three‐dimensional cloud‐based approach is shown to be most stable across different scales and these z₀ values are most correct in relative order when compared with the wind tower data. Popular profile‐based methods perform less well providing highly variable values across different scales and when using data of differing resolution. These findings hold relevance for all studies using microtopographic methods to estimate aerodynamic roughness lengths, including those in non‐glacial settings. Copyright © 2017 John Wiley & Sons, Ltd.     

Heterogeneous water storage and thermal regime of supraglacial ponds on debris‐covered glaciers

The water storage and energy transfer roles of supraglacial ponds are poorly constrained, yet they are thought to be important components of debris‐covered glacier ablation budgets. We used an unmanned surface vessel (USV) to collect sonar depth measurements for 24 ponds to derive the first empirical relationship between their area and volume applicable to the size distribution of ponds commonly encountered on debris‐covered glaciers. Additionally, we instrumented nine ponds with thermistors and three with pressure transducers, characterizing their thermal regime and capturing three pond drainage events. The deepest and most irregularly‐shaped ponds were those associated with ice cliffs, which were connected to the surface or englacial hydrology network (maximum depth = 45.6 m), whereas hydrologically‐isolated ponds without ice cliffs were both more circular and shallower (maximum depth = 9.9 m). The englacial drainage of three ponds had the potential to melt ~100 ± 20 × 10³ kg to ~470 ± 90 × 10³ kg of glacier ice owing to the large volumes of stored water. Our observations of seasonal pond growth and drainage with their associated calculations of stored thermal energy have implications for glacier ice flow, the progressive enlargement and sudden collapse of englacial conduits, and the location of glacier ablation hot‐spots where ponds and ice cliffs interact. Additionally, the evolutionary trajectory of these ponds controls large proglacial lake formation in deglaciating environments. Copyright © 2017 John Wiley & Sons, Ltd.     

淮北平原覆盖区土壤采样密度及其环境质量研究——以1∶5万高炉集幅为例

以1∶5万高炉集幅为研究对象,在6个点/km2及4个点/km2两种采样密度条件下,土壤元素在地球化学参数特征及空间分布上均相近,表明该图幅内采样密度4个点/km2可以满足1∶5万土地质量调查评价工作的要求.基于不同采样密度下土壤元素地球化学特征的对比分析,提出淮北平原覆盖区地质背景相对单一的连片耕地区开展1∶5万土地质...     

黄土覆盖区金矿深部地质结构大地电磁探测——以河北怀来颜家沟金矿为例

基于岩体和矿体的电性差异,应用大地电磁测深法在河北怀来颜家沟金矿进行地球物理勘探,通过对采集原始数据的处理分析,建立电性剖面模型,依据电性剖面中的电阻率梯度分布特征,结合钻探勘查成果和高精度磁测发现的成矿异常等地质资料,预测在测区西部11号测点、南部54号测点、东部21号测点深部及附近发育的低阻异常带是有利成矿位置,并已得到部分工程验证,该成果为覆盖区隐伏矿体预测提供了科学依据。     

湿地沉积物-水界面营养盐交换的定量估算

为有效控制湖泊内源营养盐的释放,探讨了不同物理改良措施(覆沙、底质疏松)对沉积物-水界面营养盐的释放通量控制效果。利用原位孔隙水采样技术(Peeper)来获得沉积物孔隙水剖面,对改良后湿地沉积物孔隙水营养盐的垂向分布及其扩散通量进行了研究。结果发现,改良后沉积含水率、孔隙率分别提高了91%和54%。水土界面附近,随剖面深度增加,孔隙水中PO₄3-、NH₄+、NO₃-及NO₂-浓度分布符合指数关系,PO₄3-、NH₄+在8 cm左右达到最大值。种植芦苇后沉积物孔隙水中PO₄3-、NH₄+均有不同程度的下降,改良措施能有效降低表层弱结合态磷在总磷中比例但增加铁磷的比例,种植芦苇可强化这一效应。运用Fick第一定律对剖面孔隙水营养盐的扩散通量进行估算,发现沉积物经疏松后,NH₄+、PO₄3-的扩散通量由57.47~72.19μg/(m2·d)和2.55~3.21μg/(m2·d)变为-95.54~-130.94μg/(m2·d)和1.50~2.05μg/(m2·d),可考虑疏松沉积物-水界面附近沉积物来作为控制湖泊内源污染的有效手段之一。     

东台西瓜大棚内外温度关系及高低温预警方法研究

根据东台大棚西瓜生产普遍模式和研究目的,建立相应的试验观测站,分别选择夜间低温样本和白天晴天条件样本,对资料序列进行分析。结果表明：夜间塑料大棚内温度与外界温度密切相关;白天晴天条件下大棚内温度与外界温度、太阳高度角、太阳光通过大气对流层的斜距等因子有着显著的相关关系。运用统计回归方法建立夜间低温条件下和白天晴天条件下大棚内外温度关系,达到较高的准确率和精度;结合冻害温度指标和发生冻害的可能性大小,确定夜间低温预警指标等级及温度范围,并对白天晴天条件下大棚内指标温度出现时间进行尝试性预测,有针对性地服务于大棚西瓜的生产过程。     

THE MORPHODYNAMICS OF THE MONT BLANC MASSIF IN A CHANGING CRYOSPHERE: A COMPREHENSIVE REVIEW

One of the most glacierized areas in the European Alps, the Mont Blanc massif, illustrates how fast changes affect the cryosphere and the related morphodynamics in high mountain environments, especially since the termination of the Little Ice Age. Contrasts between the north‐west side, gentle and heavily glaciated, and the south‐east side, steep and rocky, and between local faces with varying slope angle and aspect highlight the suitability of the study site for scientific investigations. Glacier shrinkage is pronounced at low elevation but weaker than in other Alpine massifs, and supraglacial debris covers have developed over most of the glaciers, often starting in the nineteenth century. Lowering of glacier surface also affects areas of the accumulation zone. While modern glaciology has been carried out in the massif for several decades, study of the permafrost has been under development for only a few years, especially in the rock walls. Many hazards are related to glacier dynamics. Outburst flood from englacial pockets, ice avalanche from warm‐based and cold‐based glaciers, and rock slope failure due to debuttressing are generally increasing with the current decrease or even the vanishing of glaciers. Permafrost degradation is likely involved in rockfall and rock avalanche, contributing to the chains of processes resulting from the high relief of the massif. The resulting hazards could increasingly endanger population and activities of the valleys surrounding the Mont Blanc massif.     

Modelling the hydrological response of debris‐free and debris‐covered glaciers to present climatic conditions in the semiarid Andes of central Chile

We apply the process‐based, distributed TOPKAPI‐ETH glacio‐hydrological model to a glacierized catchment (19% glacierized) in the semiarid Andes of central Chile. The semiarid Andes provides vital freshwater resources to valleys in Chile and Argentina, but only few glacio‐hydrological modelling studies have been conducted, and its dominant hydrological processes remain poorly understood. The catchment contains two debris‐free glaciers reaching down to 3900 m asl (Bello and Yeso glaciers) and one debris‐covered avalanche‐fed glacier reaching to 3200 m asl (Piramide Glacier). Our main objective is to compare the mass balance and runoff contributions of both glacier types under current climatic conditions. We use a unique dataset of field measurements collected over two ablation seasons combined with the distributed TOPKAPI‐ETH model that includes physically oriented parameterizations of snow and ice ablation, gravitational distribution of snow, snow albedo evolution and the ablation of debris‐covered ice. Model outputs indicate that while the mass balance of Bello and Yeso glaciers is mostly explained by temperature gradients, the Piramide Glacier mass balance is governed by debris thickness and avalanches and has a clear non‐linear profile with elevation as a result. Despite the thermal insulation effect of the debris cover, the mass balance and contribution to runoff from debris‐free and debris‐covered glaciers are similar in magnitude, mainly because of elevation differences. However, runoff contributions are distinct in time and seasonality with ice melt starting approximately four weeks earlier from the debris‐covered glacier, what is of relevance for water resources management. At the catchment scale, snowmelt is the dominant contributor to runoff during both years. However, during the driest year of our simulations, ice melt contributes 42 ± 8% and 67 ± 6% of the annual and summer runoff, respectively. Sensitivity analyses show that runoff is most sensitive to temperature and precipitation gradients, melt factors and debris cover thickness. Copyright © 2016 John Wiley & Sons, Ltd.     

Implications of decadal to century scale glacio‐hydrological change for water resources of the Hood River basin,OR, USA

In glacier‐fed rivers, melting of glacier ice sustains streamflow during the driest times of the year, especially during drought years. Anthropogenic and ecologic systems that rely on this glacial buffering of low flows are vulnerable to glacier recession as temperatures rise. We demonstrate the evolution of glacier melt contribution in watershed hydrology over the course of a 184‐year period from 1916 to 2099 through the application of a coupled hydrological and glacier dynamics model to the Hood River basin in Northwest Oregon, USA. We performed continuous simulations of glaciological processes (mass accumulation and ablation, lateral flow of ice and heat conduction through supra‐glacial debris), which are directly linked with seasonal snow dynamics as well as other key hydrologic processes (e.g. evapotranspiration and subsurface flow). Our simulations show that historically, the contribution of glacier melt to basin water supply was up to 79% at upland water management locations. We also show that supraglacial debris cover on the Hood River glaciers modulates the rate of glacier recession and progression of dry season flow at upland stream locations with debris‐covered glaciers. Our model results indicate that dry season (July to September) discharge sourced from glacier melt started to decline early in the 21st century following glacier recession that started early in the 20th century. Changes in climate over the course of the current century will lead to 14–63% (18–78%) reductions in dry season discharge across the basin for IPCC emission pathway RCP4.5 (RCP8.5). The largest losses will be at upland drainage locations of water diversions that were dominated historically by glacier melt and seasonal snowmelt. The contribution of glacier melt varies greatly not only in space but also in time. It displays a strong decadal scale fluctuations that are super‐imposed on the effects of a long‐term climatic warming trend. This decadal variability results in reversals in trends in glacier melt, which underscore the importance of long‐time series of glacio‐hydrologic analyses for evaluating the hydrological response to glacier recession. Copyright © 2016 John Wiley & Sons, Ltd.     

2000—2020年中国荒漠化潜在发生范围区林草覆被时空变化特征

干旱地区林草植被生长动态变化是研究荒漠化形成发展和演变过程的重要依据。本文基于改进方向性像元二分模型构建的2000—2020年中国荒漠化潜在发生范围区（PEDC）年植被覆盖度数据集,采用Sen+Mann-Kendall时间序列趋势变化检测方法,分析了2000—2020年PEDC,特别是林草覆盖区的植被生长状况时空变化特征。研究结果表明：① 2000—2020年,PEDC平均植被覆盖度为0.284,改进的植被覆盖度估算结果能够较好地反映研究区植被覆盖状况,估算精度为86.98%。PEDC植被生长状况不断趋好,其中干旱区表现最为突出,显著增加区域达到了48%,而亚湿润干旱区平均增长量最大为0.1。② 林草生态恢复工程措施效果显著,但植被恢复是个长期缓慢的过程,特别是林草面积的恢复。2000—2010年林草面积增加较少（0.002%）;2010—2020年增加较多（0.371%）。③ 2000—2020年PEDC林地植被改善最明显,草地则较为稳定,植被覆盖度显著性增加区域分别为76.4%和71.8%。其中林地植被覆盖度在亚湿润干旱区增长量最大为0.15,而整个研究区草地增长了0.06。本文更深入地掌握PEDC林草覆盖区长时间序列植被生长状况,为进一步制定和实施各项生态工程提供重要信息参考。