青藏高原积雪与广西降水的相关关系

利用青藏高原资料序列长度均在30年以上的54个台站(1967～1997年)的积雪日数和积雪深度资料,与广西降水进行相关统计和分析研究,找出两者之间的相关统计事实及存在的联系:不管是上一年还是当年的青藏高原积雪与广西当年降水都有一定的相关,但大多是分散的个别显著相关,少数属于区域显著相关,没有全区性的显著相关。     

Snow water equivalent over Eurasia in the next 50 years projected by aggregated CMIP3 models

Based on remote sensing snow water equivalent (SWE) data, the simulated SWE in 20C3M experiments from 14 models attending the third phase of the Coupled Models for Inter-comparison Project (CMIP3) was first evaluated by computing the different percentage, spatial correlation coefficient, and standard deviation of biases during 1979–2000. Then, the diagnosed ten models that performed better simulation in Eurasian SWE were aggregated by arithmetic mean to project the changes of Eurasian SWE in 2002–2060. Results show that SWE will decrease significantly for Eurasia as a whole in the next 50 years. Spatially, significant decreasing trends dominate Eurasia except for significant increase in the northeastern part. Seasonally, decreasing proportion will be greatest in summer indicating that snow cover in warmer seasons is more sensitive to climate warming. However, absolute decreasing trends are not the greatest in winter, but in spring. This is caused by the greater magnitude of negative trends, but smaller positive trends in spring than in winter. The changing characteristics of increasing in eastern Eurasia and decreasing in western Eurasia and over the Qinghai-Tibetan Plateau favor the viewpoint that there will be more rainfall in North China and less in the middle and lower reaches of the Yangtze River in summer. Additionally, the decreasing rate and extent with significant decreasing trends under SRES A2 are greater than those under SRES B1, indicating that the emission of greenhouse gases (GHG) will speed up the decreasing rate of snow cover both temporally and spatially. It is crucial to control the discharge of GHG emissions for mitigating the disappearance of snow cover over Eurasia.     

黑河流域上游寒区水文遥感-地面同步观测试验

介绍了黑河流域上游寒区水文遥感-地而同步观测试验,论述了试验目标与研究内容、试验区的选择设计以及寒区水文长期观测试验.上游试验以理解寒区水文过程、提高寒区定量遥感水平为主旨,以积雪和冻土为主要研究对象,开展了微波辐射计、高光谱成像仪航空遥感和地面同步观测,并选择典型小流域进行长期寒区水文过程观测与研究.试验集中在冰沟积雪小流域、阿柔草场和扁都口裸露耕地3个不蚓地表覆盖区,以积雪和冻土变量与参数的测量为主.同步试验在流域尺度、重点试验区、加密观测区和观测小区4个尺度上展开,分别布置了加密的地面同步观测、通量和气象水文观测、降雨、径流及其它水文要素观测网络;航空飞行传感器分别采用微波辐射计、高光谱成像仪、热红外成像仪和多光谱CCD相机,收集获取了试验区丰富的可见光/近红外、热红外、主被动微波等卫星数据.通过试验,初步构建了上游寒区航空-卫星-地面综合数据集,可以应用于改进和验证寒区陆面/水文过程模型.     

渭干河流域"2002·7"特大洪水分析

渭干河是塔里木河流域第六大源流, 位于天山西部南麓, 渭干河干流起点有新疆最大的流域性控制工程--克孜尔水库. 2002年7月下旬天山中西部山区出现大暴雨(雪)过程, 渭干河流域山区降水持续时间长达30 h以上, 山区降水量50 mm左右, 导致5条支流和渭干河干流出现有水文记录以来的最大洪峰, 流量超过警戒流量和危险流量的2～3.5倍, 暴雨(雪)过程结束之后, 融雪型洪峰长时间居高不下. 洪水过程中, 各支流以及暴雨与融雪等多种洪峰遭遇现象很明显. 克孜尔水库入库洪峰流量达3 660 m3*s-1, 经水库调洪错峰, 出库峰值流量为1 000 m3*s-1, 削峰率72.7%.     

Coupling snow accumulation and melt rate modules of monthly water balance models with the Jazim monthly water balance model

Several models for simulation of water balance processes in semi-arid mountainous basins were developed by coupling different modules of existing water balance models (WBM). Snow accumulation and snowmelt rate relationships extracted from the McCabe-Markstrom, Guo, Rao-Al Wagdany and WASMOD-M WBMs, originally developed for basins with humid climate, were coupled with the Jazim WBM, primarily developed for arid basins. Karaj Basin, central Iran, with snowy autumn–winter and dry summer periods, was selected to assess model performance. The model parameters were optimized using a genetic algorithm (GA). All coupled models performed better than the non-modified (original) WBMs in the study basin. The coupled Jazim–McCabe-Markstrom model provided the best performance in simulating low and high monthly flows. It estimated the snowmelt runoff values more accurately than other proposed coupled models because the linear relationships used in the snow module of the McCabe-Markstrom model are more compatible with snow variations in the Karaj Basin.     

雪冰中NO_3~-浓度记录的研究进展

NO3-是雪冰中含量最高的含氮无机离子,雪冰中NO3-浓度记录的解读已成为研究全球变化的重要内容之一.近年来国内外已经就极地与中低纬高海拔地区雪冰中NO3-浓度记录开展了大量的研究,关于NO3-所指示的环境意义形成了一系列的认识.从雪冰中NO3-的可能性来源(包括太阳活动、陆源粉尘、闪电等自然源以及其他人类源)、时空变化特征以及气-雪-冰界面转化过程等方面综述了近年来该领域的研究成果,并结合全球变化的背景对其研究前景进行了展望.     

对青藏高原末次冰盛期降温值、平衡线下降值与模拟结果的讨论

1999年5期《第四纪研究》刊登的“青藏高原冰期环境与冰期全球降温”论文,内容丰富,提出了许多重大问题和新鲜讯息,发人深思。本文就部分内容进行讨论,认为根据新近若干冰期降温值较大的信息,就得出冰期降温幅度为过去认识的两倍的普遍性推断,还为时过早。青藏高原新近研究表明夏季降温值是较小的;冰川平衡线高度取决于以夏季温度为标志所提供的消融热量与全年降雪积累量的平衡,单纯就降温值,不能决定平衡线下降值;全球各地气候、地形差别很大,冰期变化也很悬殊,不存在全球均一的1000m左右平衡线下降值,干旱区的下降值多低于此数。青藏高原末次冰盛期(LGM)冰川堆积(终碛、侧碛)和侵蚀形态(冰斗、槽谷)一般保存良好、形态鲜明,较易识别,近年已获取测年资料,证明过去地貌法判别的LGM冰川规模,并以此决定的LGM平衡线位置基本恰当,当然也有误判者。     

Avalanche Risk During Backcountry Skiing – An Analysis of Risk Factors

Skier-triggered avalanches are the main cause of avalanche accidents in backcountry skiing. The risk of accidents during backcountry skiing was analysed statistically and related to factors such as elevation level, aspect, stability rating and the time of the year. The analysis is based on a database about terrain usage and avalanche accidents from a large heli-skiing operator in Canada, which makes it possible to study the conditional probability of accidents given the recorded pattern of terrain usage. This study shows that the historical risk of accidentally triggering an avalanche greater than size 1 depends highly on the stability rating, with the highest risk occurring during “poor” stability. The risk is greater at high elevations, and it is lower during the late season than earlier on. Skier risk does not depend as much on aspect as may be indicated from avalanche data alone. However, it is relatively high in the N–NE–E sector. These factors are not independent of each other and therefore analyses of combined factors were also performed. Questionnaires and interviews were used to gain knowledge about the terrain selection of professional mountain guides. These results indicate that when selecting terrain, guides first look at the overall shape and size of the terrain, but avalanche history of terrain and inclination are also important factors. Finally, remarks in avalanche reports were analysed, and common human factors identified.     

Climate variability,snow, and physiographic controls on storm hydrographs in small forested basins,western Cascades,Oregon

Large floods are often attributed to the melting of snow during a rain event. This study tested how climate variability, snowpack presence, and basin physiography were related to storm hydrograph shape in three small (<1 km²) basins with old‐growth forest in western Oregon. Relationships between hydrograph characteristics and precipitation were tested for approximately 800 storms over a nearly 30‐year period. Analyses controlled for (1) snowpack presence/absence, (2) antecedent soil moisture, and (3) hillslope length and gradient. For small storms (<150 mm precipitation), controlling for precipitation, the presence of a snowpack on near‐saturated soil increased the threshold of precipitation before hydrograph rise, extended the start lag, centroid lag, and duration of storm hydrographs, and increased the peak discharge. The presence of a snowpack on near‐saturated soil sped up and steepened storm hydrographs in a basin with short steep slopes, but delayed storm hydrographs in basins with longer or more gentle slopes. Hydrographs of the largest events, which were extreme regional rain and rain‐on‐snow floods, were not sensitive to landform characteristics or snowpack presence/absence. Although the presence of a snowpack did not increase peak discharge in small, forested basins during large storms, it had contrasting effects on storm timing in small basins, potentially synchronizing small basin contributions to the larger basin hydrograph during large rain‐on‐snow events. By altering the relative timing of hydrographs, snowpack melting could produce extreme floods from precipitation events whose size is not extreme. Further work is needed to examine effects of canopy openings, snowpack, and climate warming on extreme rain‐on‐snow floods at the large basin scale. Copyright © 2008 John Wiley & Sons, Ltd.     

Snow accumulation distribution inferred from time‐lapse photography and simple modelling

The spatial and temporal distribution of snow accumulation is complex and significantly influences the hydrological characteristics of mountain catchments. Many snow redistribution processes, such as avalanching, slushflow or wind drift, are controlled by topography, but their modelling remains challenging. In situ measurements of snow accumulation are laborious and generally have a coarse spatial or temporal resolution. In this respect, time‐lapse photography shows itself as a powerful tool for collecting information at relatively low cost and without the need for direct field access. In this paper, the snow accumulation distribution of an Alpine catchment is inferred by adjusting a simple snow accumulation model combined with a temperature index melt model to match the modelled melt‐out pattern evolution to the pattern monitored during an ablation season through terrestrial oblique photography. The comparison of the resulting end‐of‐winter snow water equivalent distribution with direct measurements shows that the achieved accuracy is comparable with that obtained with an inverse distance interpolation of the point measurements. On average over the ablation season, the observed melt‐out pattern can be reproduced correctly in 93% of the area visible from the fixed camera. The relations between inferred snow accumulation distribution and topographic variables indicate large scatter. However, a significant correlation with local slope is found and terrain curvature is detected as a factor limiting the maximal snow accumulation. Copyright © 2010 John Wiley & Sons, Ltd.