Rising and falling river flows: contrasting signals of climate change and glacier mass balance from the eastern and western Karakoram

Abstract

Field observations and geodetic measurements suggest that in the Karakoram Mountains, glaciers are either stable or have expanded since 1990, in sharp contrast to glacier retreats that are prevalently observed in the Himalayas and adjoining high-altitude terrains of central Asia. Decreased discharge in the rivers originating from this region is cited as a supporting evidence for this somewhat anomalous phenomenon. Here, we show that river discharge during the melting season of the glaciers in the eastern and western Karakoram, respectively, exhibits rising and falling trends. We have implemented a statistical procedure involving non-parametric tests combined with a benchmark smoothing technique that has proven to be a powerful method for separating the stochastic component from the trend component in a time series. Precipitation patterns determined from ERA-40 and GPCP data indicate that summer-monsoonal precipitation has increased over the Karakoram Mountains in recent decades. Increasing flows in June and July in the eastern Karakoram are due to an increase in summer-monsoonal precipitation. The rising trend of August discharge is due to an increase in the loss of glacier storage at an approximate average rate of 0.186–0.217 mm d^-1 year^-1 during the period 1973–2010. Moreover, this rate is higher than the rate of increase in monsoonal snowfall during the months of August and September. Therefore, most plausibly, glacier mass balance in the eastern Karakoram is negative. In the western Karakoram, river flows show declining trends for all summer months for the period 1966–2010, corresponding to a rate of increase of glacier storage by approximately 0.552–0.644 mm d^-1 year^-1, which is also higher than the rate of increase in summer-monsoonal precipitation. The gain of the cryospheric mass in the western Karakoram is in the form of increased thickness of the glaciers and perennial snowpacks instead of areal expansion. This investigation shows two contrasting patterns of trends of river flows that signify both negative and positive mass balance of the Karakoram glaciers. Trends of river flows are spatially and temporally integrated responses of a watershed to changing climate and thereby are important signals of the conditions of the cryospheric component of a watershed where it is highly significant. However, they cannot unequivocally provide indications of the state and fate of the glaciers in the complex hydrometeorological setting of the Karakoram. Extreme caution and care must be exercised in interpreting trends of river discharge in conjunction with climatic data.     

Sensitivities of the equilibrium line altitude to temperature and precipitation changes along the Andes

Equilibrium line altitudes (ELAs) of alpine glaciers are sensitive indicators of climate change and have been commonly used to reconstruct paleoclimates at different temporal and spatial scales. However, accurate interpretations of ELA fluctuations rely on a quantitative understanding of the sensitivity of ELAs to changes in climate. We applied a full surface energy- and mass-balance model to quantify ELA sensitivity to temperature and precipitation changes across the range of climate conditions found in the Andes. Model results show that ELA response has a strong spatial variability across the glaciated regions of South America. This spatial variability correlates with the distribution of the present-day mean climate conditions observed along the Andes. We find that ELAs respond linearly to changes in temperature, with the magnitude of the response being prescribed by the local lapse rates. ELA sensitivities to precipitation changes are nearly linear and are inversely correlated with the emissivity of the atmosphere. Temperature sensitivities are greatest in the inner tropics; precipitation becomes more important in the subtropics and northernmost mid-latitudes. These results can be considered an important step towards developing a framework for understanding past episodes of glacial fluctuations and ultimately for predicting glacier response to future climate changes.     

Characteristics of DDF at Baishui Glacier No.1 Region in Yulong Snow Mountain

Based on observed mass balance and meteorological data since September 2008 and ablation data by the expedition team of Tibetan plateau from June to August 1982 at Baishui(白水) Glacier No.1 region,we analyzed the spatial and temporal changes of degree-day factor(DDF) of the Baishui Glacier No.1 following the changes of space,time,and temperature,which lays a theoretical foundation to establish DDF model.The results indicate that the melting DDF of ice showed a significant down-ward trend with rising temperat...     

祁连山冰川服务价值评估及其时空特征

冰川为干旱区人类福祉和社会经济发展提供必不可少的资源与服务,开展冰川服务价值评估及时空特征研究对于区域社会经济可持续发展和环境保护具有重要意义.基于祁连山第一次和第二次冰川编目数据,通过构建冰川服务价值评估体系,并结合单位面积服务价格法、价值当量因子法和冰川服务价值变化指数等方法,评估祁连山冰川服务价值及时空变化.结果...     

现代冰川中的微粒研究与气候环境变化

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中国典型季风海洋性冰川区"冰川-径流"系统的全球变化敏感性研究

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中国班公湖流域区冰川补充编目及冰川特征

论述了中国班公湖流域区冰川补充编目的结果及冰川特征.1988年公布的中国班公湖流域区总共有冰川834条,冰川总面积642.77km²,冰储量为33.9246km³;经过补充编目,更正了以往部分简易目录后的冰川是959条,冰川总面积665.35km²,冰储量为39.2316km³.冰川数量增加的结果主要是利用小比例尺卫星相片编目时遗漏了面积≤1.00km²的小冰川所致.     

雪冰中生物有机酸研究的历史与现状

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