Estimation Of Glacier Mass Balance Research Articles

Estimation and Analysis of Glacier Mass Balance in the Southeastern Tibetan Plateau Using TanDEM-X Bi-Static InSAR during 2000–2014

In recent decades, glaciers in the southeastern Tibetan Plateau (SETP) have been rapidly melting and showing a large scale of glacier mass loss. Due to the lack of large-scale, high-resolution, and high-precision observations, knowledge on the spatial distribution of the glacier mass balance and the response to climate change is limited in this region. We propose a TanDEM-X bi-static InSAR (Interferometric Synthetic Aperture Radar) algorithm with a non-local mean filter method and difference strategy, to improve the precision of glacier surface elevation change detection. Moreover, we improved the glacier mass balance estimation algorithm with a correction method for multi-source system errors and an uncertainty evaluation method based on error propagation theory to reduce the uncertainty of estimations. We used 13 pairs of TanDEM-X bi-static InSAR images to obtain the glacier mass balance data for the entire SETP. The total area of glaciers monitored was 5821 km2 and the total number of glaciers monitored was 2321; the glacier surface elevation change rate was −0.505 ± 0.005 m/yr, and the glacier mass balance estimation was −454.5 ± 13.1 mm w.eq. during 2000–2014. Additionally, we analyzed the spatial distribution of the glacier mass balance within the SETP using the sub-watershed analysis method. The results showed that the mass loss rate had a decreasing trend from the southeast to the northwest. Furthermore, the temperature change and the glacier mass loss rate showed a positive correlation from the southeast to the northwest in this region. This study greatly advances our understanding of the regularities of glacier dynamics in this region, and can provide scientific support for major national goals such as the rational utilization of surrounding water resources and construction of important transportation projects.

Accelerated glacier mass loss in the southeastern Tibetan Plateau since the 1970s

The southeastern Tibetan Plateau (SETP) is a region in High Mountain Asia with the most serious glacier mass loss. However, long-term and large regional-scale studies that estimate glacier mass balance in this area remain limited. In this study, we generated a KH-9 Digital Elevation Model (DEM) (covering 87.6% of the glacier area) for the 1970s from KH-9 Hexagon imagery and quantified geodetic glacier mass over the SETP from the 1970s to 2020 using KH-9 DEM, NASADEM and ICESat-2 ATL06 data. The results show that the SETP was in a state of serious mass loss (at a rate of −0.35 ± 0.03 m w.e. per year) from the 1970s to 2020, and the rate of mass loss accelerated from −0.15 ± 0.05 to −0.56 ± 0.10 m w.e. per year between the 1970s–2000 and 2000–2020. Within the SETP, the glacier mass balance revealed a remarkable spatial heterogeneity. The maximum mean glacier mass loss rate was observed in the Hengduan Shan. Nyainqentanglha exhibited the highest acceleration in the mass loss rate since the 1970s. The warming of air temperature and decreasing snowfall can partly explain the accelerated glacier mass loss in the SETP. The study provides a new long-term glacier mass balance estimation covering almost the entire SETP that suggests the acceleration in glacier mass loss observed in the SETP since the 1970s is a regional tendency, which is crucial for understanding the relationship between glaciers and climate changes.

Estimation of glacier mass balance using remote sensing and GIS technology in the Hindu Kush region of northern Pakistan

The Hindu Kush range of northern Pakistan has a large variety of Alpine and valley glaciers. These glaciers are subjected to volumetric changes owing to a host of factors (i.e. altitude, slope, glacier types, and aspect). The geodetic survey and field-based data are not available for assessment of glacier’s Equilibrium Line Altitude (ELA) for Hindu Kush due to rough topography and rigorous climate. However, the mass balance of the alpine and valley glaciers can be obtained through ELA and Accumulation Area Ratio (AAR). Therefore, this study deals with the estimation of ELA, the hypsometrically controlled methods based on AAR and Accumulation Area Balance Ratio (AABR). Various ratios between 0.4–0.8 with 0.05 interval for AAR and 0.67–4.4 with 0.01 for AABR are applied to obtain the ELA of valley glaciers. Moreover, the glacier contours with the interval of 50 m ± 5 m were employed for these estimations. The constant AAR and AABR ratios rather than constant glacier area adjust glacier hypsometry based on ELA variations. The results show that for AAR (0.5), 50 m ELA declined from 5409 to 5359 m and reduced (4%) the geometric area. The maximum decrease of 150 m ELA for these glaciers is reported for the AAR-AABR ratio of 0.1–4.4, showing a significant decrease. The estimated decrease in the glacier area of Hindu Kush is extremely variable specifically in Phargam, Khorabohr and Gordoghan.

Glacier mass-balance estimates over High Mountain Asia from 2000 to 2021 based on ICESat-2 and NASADEM

AbstractHigh Mountain Asia (HMA) glaciers are critical water reserves for montane regions, which are readily influenced by climate change. The glacier mass balance during 2000–2021 over HMA was estimated by comparing the elevations from ICESat-2 and the NASADEM. Radar penetration depth could be one of the intrinsic error sources in estimating glacier mass balance by using NASADEM. Therefore, we doubled elevation differences between the X-band Shuttle Radar Topography Missions (SRTMs) and NASADEM to estimate the potential error. The spatial characteristics of the altitude-dependent penetration depth can be detected in most sub-regions of HMA. Relatively deep penetrations in the Himalaya (2.3–3.7 m) and Hissar Alay (4.3 m) regions and small penetrations in the south-eastern HMA (1.0 m) were observed. The HMA region experienced a significant mass loss at a rate of −0.18 ± 0.12 m w.e. a−1, in which the Hengduan Shan exhibited the highest mass loss of −0.62 ± 0.10 m w.e. a−1, the West Kun Lun experienced a substantial mass gain of 0.23 ± 0.13 m w.e. a−1, and the Karakoram showed a more or less balance. Our results are in agreement with previous studies that assessed the mass balance of HMA glaciers from different methods.

Glacier mass balance estimation in Garhwal Himalaya using improved accumulation area ratio method.

Water requirements of the mountain communities living in the Himalaya are supported by snow and glacier melt. The availability of water from the source depends on numerous climatic and glacier parameters. One key parameter is mass balance, which helps to assess the glacier health and future water availability. We have used the improved accumulation area ratio (IAAR) method to estimate mass balance in Alaknanda and Bhagirathi basins, constituting 1055 glaciers covering ~1609 km2. The mean Equilibrium Line Altitude (ELA) of the Alaknanda and Bhagirathi basins are estimated as 6147 ± 130 and 5985 ± 130m.a.s.l, respectively. The mass balance is estimated using the accumulation area ratio (AAR)-mass balance relationship. The mean specific mass balance of the Alaknanda and Bhagirathi for 2001-2013 is estimated as -1.1 ± 0.03m.w.e.a-1 and -1.01 ± 0.07m.w.e.a-1, respectively. Total mass loss from the study area is calculated as ~21.4 ± 1.1Gt during this period. The loss of glaciers in the mountain area will increase the vulnerability of communities living in the region. It suggests a need for better adaptation strategies to improve the resilience of high mountain communities.

Existence of Glacier Anomaly in the Interior and Northern Tibetan Plateau between 2000 and 2012

There was sufficient evidence to indicate a nearly balanced glacier mass change (termed glacier anomaly) for Karakoram Mts. since the 1970s, in contrast to worldwide glacier mass losses caused by climate warming. Recently, this anomalous phenomenon was detected over the neighboring western Kunlun and Pamir Mts. However, the southeastern limit of this glacier anomaly remains uncertain, owing to the paucity of glacier mass balance observations across the interior and northern Tibetan Plateau (INTP). In this study, we presented a decadal glacier mass balance estimation in the INTP by differencing the SRTM DEM with the topographic data produced from TanDEM-X bistatic InSAR images. From 2000 to 2012, decade-average glacier mass balances of between −0.339 ± 0.040 and 0.237 ± 0.078 m w.e. yr−1 were detected over 22 glacierized areas. Significantly, we found a gradient and switch of glacier mass loss over the southeastern portion to glacier mass gain over the northwestern portion. This varying spatial pattern illustrates that glacier anomaly has existed over the northwestern or even central zone of the INTP since the early 21st century. This study provides important evidence for the model simulation of both glacier evolution and atmospheric circulations in investigating the prevailing mechanism of the regional anomalous phenomenon.

Constraining the contribution of glacier mass balance to the Tibetan lake growth in the early 21st century

The Tibetan Plateau (TP) hosts numerous glaciers and lakes which are critical natural water reserves but highly vulnerable to changing climate. In contrast to general drying trends in global endorheic basins in recent decades, the widespread lake expansions across the endorheic TP stand out as a puzzling “anomaly”. To quantify the contribution of glacier mass changes to lake expansion at fine basin-scale details, we compute spatially resolved estimation of mass change in both glaciers and lakes across the endorheic TP between 2000 and 2010/14 based on multi-mission remote sensing observations. Our glacier mass balance estimates were based on the differences between the newly released global TanDEM-X DEM and the historical SRTM-C DEM, which provide nearly complete coverage (98%) of the glacierized area on the endorheic TP. We provide lake water storage changes of all lakes >1 km2 on the inner TP. These estimates reveal that the massive lake water increase (9.44 ± 1.43 Gt yr−1) was essentially not from the mass loss of glaciers which represents only about 4.7 ± 8.8% of the lake water change (0.44 ± 0.80 Gt yr−1). The relationship in individual basins was, however, highly heterogeneous. About 20% of total lake storage gain had no causality with glacier feeding. In comparison, for 28% of lake water surplus, mainly in the northwestern TP, the positive glacier mass balance infers that glaciers retained some precipitation surplus that could otherwise have been drained to downstream lakes. For the other 52% of lake storage gain, mostly in southern and eastern regions, the glacier mass loss varied among the basins with limited contributing levels (mostly <20%). Our analyses highlight remarkable spatial and temporal variabilities in lake/glacier changes on the endoreic TP and contribute to a better understanding of the role of glaciers in the recent Tibetan lake growth and the impact of climate change on the two types of water reserves.

Hot Spots of Glacier Mass Balance Variability in Central Asia.

The Tien Shan and Pamir mountains host over 28,000 glaciers providing essential water resources for increasing water demand in Central Asia. A disequilibrium between glaciers and climate affects meltwater release to Central Asian rivers, challenging the region's water availability. Previous research has neglected temporal variability. We present glacier mass balance estimates based on transient snowline and geodetic surveys with unprecedented spatiotemporal resolution from 1999/00 to 2017/18. Our results reveal spatiotemporal heterogeneity characterized by two mass balance clusters: (a) positive, low variability, and (b) negative, high variability. This translates into variable glacial meltwater release (≈1–16%) of annual river runoff for two watersheds. Our study reveals more complex climate forcing‐runoff responses and importance of glacial meltwater variability for the region than suggested previously.

Contrasting behaviour of temporal glacier changes and long term estimation of glacier mass balance across Himalayan–Karakoram range

Glacier dynamics and mass balance observations in Himalayan–Karakoram (H–K) region are important to monitor the effect of climatic perturbations over the highest cryospheric region of the world. Such studies can be accomplished by employing satellite based remote sensing technique as field measurements are difficult to obtain in these inaccessible region. In the present study, an attempt was made to investigate the retreat/advancement along with their mass fluctuations of 13 select glaciers from different sectors of H–K region over a continuous period from year 1996 to 2020 using satellite images. Variation in areal and snout fluctuations shown different patterns pertaining to gain/advancement and loss/retreat of each select glaciers. Mass loss for glaciers in Karakoram Range (–0.217 ± 0.017 m w e) was marginal when compared with Western (–0.26 ± 0.08 m w e), Central (–0.56 ± 0.067 m w e) and Eastern Himalayas (–0.625 ± 0.13 m w e). Contrasting relationship between glacier dynamics and mass balance has been obtained in the present study. Validation of results with existing field observations depicted the utility of satellite-based observation.

Regional and Altitude-Dependent Estimate of the SRTM C/X-Band Radar Penetration Difference on High Mountain Asia Glaciers

Radar penetration correction is essential for accurately estimating glacier mass balance when using the geodetic methods based on the radar-derived digital elevation model (DEM). Due to heterogeneous snow distribution and snowpack properties, the radar penetration depth varies by region and is basically dependent on the altitudes. However, a constant value is usually used to correct the radar penetration for regional glacier mass balance estimation in high-mountain Asia (HMA), because little is known about the detailed distribution of radar penetration depth of the glacierized area in HMA. In this study, the penetration depth difference (hereafter referred to as PDD) of the C/X-band radar signals on glaciers over the whole HMA region was first estimated by comparing the Space Shuttle Radar Topographic Mission (SRTM) C/X-band digital elevation models (DEMs), and the spatial characteristics of the altitude-dependent PDD were analyzed on a 1° × 1° grid. The C/X-band radar PDD (the X minus C band penetration) was calculated in each 50-m elevation bin, and a linear model was used to study the correlation between the altitude and the penetration difference. The results show that the difference of the SRTM C/X-band penetration depth in the HMA region is between −1.67 p 0.65 m and 7.63 p 0.99 m, with an average value of 2.40±0.04 m. A significant linear positive correlation between elevation and the PDD was found in most of 1° × 1° grid regions in HMA. These results can be used as important reference data for estimating glacier mass balance in HMA based on SRTM DEMs.

Spatiotemporal variability of surface velocities of monsoon temperate glaciers in the Kangri Karpo Mountains, southeastern Tibetan Plateau

AbstractInfluenced by the Indian monsoon, the Kangri Karpo Mountains (KKM) of the southeastern Tibetan Plateau is the most humid part of the plateau, and one of the most important regions with numerous monsoon temperate glaciers. Glacier mass balance estimates have been strongly negative in the KKM over recent decades, but the spatiotemporal characteristics of surface velocity are poorly understood. Using phase-correlation feature tracking on Landsat images, this study estimates spatiotemporal variabilities of monsoon temperate glaciers for the period of 1988–2019. Results show that a significant slowdown was observed below an elevation of 4900 m, while an accelerated ice flow was found at an elevation of 4900–5800 m over the past 30 years. The trend of slowdown was −0.1 m a−1dec−1during 1988–2000, and then it increased to −0.5 m a−1dec−1during 2001–2019.

The role of meteorological forcing and snow model complexity in winter glacier mass balance estimation, Columbia River basin, Canada

AbstractGlaciers are commonly located in mountainous terrain subject to highly variable meteorological conditions. High resolution meteorological (HRM) data simulated by atmospheric models can complement meteorological station observations in order to assess changes in glacier energy fluxes and mass balance. We examine the performance of two snow models, SnowModel and Alpine3D, forced by different meteorological data for winter mass balance simulations at four glaciers in the Canadian portion of the Columbia Basin. The Weather Research and Forecasting model (WRF) with resolution of 1 km and the North American Land Data Assimilation System with ~12 km resolution, provide HRM data for the two snow models. Evaluation is based on the ability of the snow models to simulate snow depth at both point locations (automated snow weather stations) and over the entire glacier surface (airborne LiDAR [Light Detection and Ranging] surveys) during the 2015/2016 winter accumulation. When forced with HRM data, both models can reproduce snow depth to within ±15% of observed values. Both models underestimate winter mass balance when forced by HRM data. When driven with WRF data, SnowModel underestimates winter mass balance integrated over the glacier area by 1 and 10%, whilst Alpine3D underestimates winter mass balance by 12 and 22% compared with LiDAR and stake measurements, respectively. The overall results show that SnowModel forced by WRF simulated winter mass balance the best.

Which heterogeneous glacier melting patterns can be robustly observed from space? A multi-scale assessment in southeastern Tibetan Plateau

Region-wide investigation of glacier change in High Mountain Asia marked the strongest recession in southeastern Tibetan Plateau (SETP) in recent decades. However, evident differences of quantitative glacier mass balance (MB) estimations on fine scales exist in the prior reports. The large uncertainties in current geodetic observations over this region highlight the need for more independent validations and investigations on the spatial variability of glacier change. This study enriched glacier MB estimates over the SETP by using the newly released global Digital Elevation Model (DEM) - the TanDEM-X and analyzed the spatial pattern of glacier change on multi-spatial scales by comparing available satellite-based geodetic observations. Results reveal that the TanDEM-X - SRTM elevation differences, which show no obvious horizontal shifts and no significant elevation-dependent bias, provide reliable elevation change information over this challenging area. On the regional scale, the geodetic datasets (the ASTER elevation change rates data, TanDEM-X- SRTM differences, ICESat) achieved a highly consistent estimate of glacier MB at −4.11 ± 1.52 Gt a−1 (−0.60 ± 0.16 m w.e. a−1) during 2000 and 2010s. On the subregional scale, the two gridded geodetic datasets revealed a clear contrast between moderate thinning of spring-accumulation type glaciers in the south and significantly more negative glacier MB of summer-accumulation type glaciers in the north. Glacier-wide MB showed high heterogeneity, which was closely related to the combined effect of topographic variation and climate forcings. We observed similar glacier thinning rates between debris-covered land-terminating glaciers and clean-ice glaciers (−0.50 ± 0.32 m w.e. a−1) but remarkable more negative MB (−0.89 ± 0.36 m w.e. a−1) of debris-covered glaciers connected with glacial lakes, which may indicate different evolution process of debris-covered glaciers in the monsoon-influenced region. This study demonstrates that current satellite-based geodetic observations achieve overall consistent patterns of glacier mass changes even over the most challenging mountainous areas (complicated terrain and climate). With the global TanDEM-X DEM and increasing observations from the mission, we expect improved consistency in glacier MB estimation on large spatial scales as well as detailed investigation of glacier mass change variability in the future.

Integrating Models and Remote Sensing Data for Distributed Glacier Mass Balance Estimation

This article presents an approach to improve the estimation of the glacier mass balance (GMB) of six selected alpine glaciers in the European Alps. This is achieved by combining three complementary data sources: hydroclimatological model, remote sensing (RS) data, and ground measurements. The hydroclimatological model provides spatially distributed mass balances. RS supplies spatially distributed surface characteristics. The ground point measurements provide the mass balance at the local scale. The combination of these data sources allows us to improve the spatial resolution of the model output and its GMB estimates. We used the alpine multiscale numerical distributed simulation engine model (AMUNDSEN), which considers the processes of accumulation and ablation of snow and ice for the area of the entire glacier (with a given spatial and temporal resolution). In the proposed integration approach, we first compute the deviations between the GMB simulation (afforded by the hydroclimatological model) and the ground measurements. Then, the RS data are used to define a feature space (which objectively characterizes the glacier surface properties). The method estimates the adjustment required to the model, for each unlabeled sample, leveraging on its neighboring labeled samples in the feature space. This allows us to apply similar adjustment to samples sharing similar glacier surface conditions. Experimental results show that the proposed integration approach achieves an average root-mean-square error of 460 mm (compared to 732 and 661 mm obtained by the hydroclimatological model and the standard regression models, typically used for parameters estimation).

Mass-balance modelling of Gangotri glacier

Abstract The sensitivity of glacier mass balance (MB) in response to climatic perturbations has made it an important parameter of study from hydrological, climatological and glaciological point of view. To monitor the health of any glacier system, long-term MB observations are required. These observations among Himalayan glaciers are not available consistently and large glaciers are not often monitored for mass balance due to logistical challenges. One such glacier is the Gangotri, situated in the western Himalaya. In the present study an attempt is made to model the MB over the Gangotri glacier, the biggest glacier in the Ganga basin and also the point of origin of the River Ganges. The mass balance of the Gangotri glacier is estimated during the time period 1985–2014 using two different methods: ice-flow velocity; and energy balance modelling using regional model (REMO) outputs and in situ automatic weather station (AWS) data. The geodetic method is used for the nearby Dokriani glacier, where field-based MB measurements are available. MB of Gangotri glacier estimated for 2001–14 using the ice-flow velocity method is −0.92 ± 0.36 m w.e. a −1 ; for 2006–07, MB using AWS and Tropical Rainfall Monitoring Mission (TRMM) data with the energy balance modelling approach is −0.82 m w.e. a −1 ; and for 1985–2005, MB using REMO data with the energy balance modelling approach is −0.98 ± 0.23 m w.e. a −1 . Using the surface velocity method, it is estimated that the glacier lost 9% of its volume during the period 2001–14. The glacier vacated an area of 0.152 km 2 from the snout region, and retreated by 200 m in the last 14 years. MB values estimated for the Gangotri glacier from different methodologies are remarkably close, suggesting them to be suitable methods of MB estimation. TRMM, High Asia Refined (HAR-10) and Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation of water resources (APHRODITE) data are used to estimate the precipitation over the glacier. The study suggests that the glacier-wide estimation of weather parameters needs to be improved for more accurate estimation of glacier mass balance.

An estimate of glacier mass balance for the Chandra basin, western Himalaya, for the period 1984–2012

ABSTRACTAn improved understanding of fresh water stored in the Himalaya is crucial for water resource management in South Asia and can be inferred from glacier mass-balance estimates. However, field investigations in the rugged Himalaya are limited to a few individual glaciers and short duration. Therefore, we have recently developed an approach that combines satellite-derived snowlines, a temperature-index melt model and the accumulation-area ratio method to estimate annual mass balance of glaciers at basin scale and for a long period. In this investigation, the mass balance of 146 glaciers in the Chandra basin, western Himalaya, is estimated from 1984 to 2012. We estimate the trend in equilibrium line altitude of the basin as +113 m decade−1and the mean mass balance as −0.61 ± 0.46 m w.e. a−1. Our basin-wide mass-balance estimates are in agreement with the geodetic method during 1999–2012. Sensitivity analysis suggests that a 20% increase in precipitation can offset changes in mass balance for a 1 °C temperature rise. A water loss of 18% of the total basin volume is estimated, and 67% for small and low-altitude glaciers during 1984–2012, indicating a looming water scarcity crisis for villages in this valley.

Estimation of Glacier Mass Balance on a Basin Scale:An Approach Based on Satellite-Derived Snowlines and a Temperature Index Model

Mass balance is an important metric to assess the growth or decline of water stored in a glacier. The Accumulation Area Ratio (AAR) method where mass balance is proportional to AAR has been used to estimate glacier mass balance by several studies in the past. Since field estimates of AAR are not feasible on every glacier, it is usually estimated by identifying the snowline at the end of ablation season as a proxy of Equilibrium Line Altitude (ELA) on satellite images. However, locating ELA on satellite images is challenging due to temporal gaps, cloud cover and fresh snowfall on glaciers. Hence, the highest observed snowline has been traditionally used to estimate AAR, which usually leads to an underestimate of mass loss. To rectify this problem we propose a method to estimate the position of ELA by combining satellite images with in situ meteorological observations and a snowmelt model. The main advantage of this method is that it can be used to estimate the mass balance of individual glaciers and basins. Application of the method to eight glaciers in the Chandra basin, Western Himalaya is found to reduce the bias in mass balance estimates compared to the traditional AAR technique and the modelled estimates are in good agreement with the geodetic method. When applied to 12 selected glaciers in the Chandra basin, the modelled cumulative mass balance is -1.67 ± 0.72 Gt (-0.79 ± 0.34 m w.e. a -1 ) during 1999/2000-2008/09. This method can also be used to estimate the future deviations in mass balance using climate change projections of temperature and precipitation.

Adjustment of regional climate model output for modeling the climatic mass balance of all glaciers on Svalbard.

Large‐scale modeling of glacier mass balance relies often on the output from regional climate models (RCMs). However, the limited accuracy and spatial resolution of RCM output pose limitations on mass balance simulations at subregional or local scales. Moreover, RCM output is still rarely available over larger regions or for longer time periods. This study evaluates the extent to which it is possible to derive reliable region‐wide glacier mass balance estimates, using coarse resolution (10 km) RCM output for model forcing. Our data cover the entire Svalbard archipelago over one decade. To calculate mass balance, we use an index‐based model. Model parameters are not calibrated, but the RCM air temperature and precipitation fields are adjusted using in situ mass balance measurements as reference. We compare two different calibration methods: root mean square error minimization and regression optimization. The obtained air temperature shifts (+1.43°C versus +2.22°C) and precipitation scaling factors (1.23 versus 1.86) differ considerably between the two methods, which we attribute to inhomogeneities in the spatiotemporal distribution of the reference data. Our modeling suggests a mean annual climatic mass balance of −0.05 ± 0.40 m w.e. a−1 for Svalbard over 2000–2011 and a mean equilibrium line altitude of 452 ± 200 m above sea level. We find that the limited spatial resolution of the RCM forcing with respect to real surface topography and the usage of spatially homogeneous RCM output adjustments and mass balance model parameters are responsible for much of the modeling uncertainty. Sensitivity of the results to model parameter uncertainty is comparably small and of minor importance.

Enhanced estimation of glacier mass balance in unsampled areas by means of topographic data

AbstractA new method was developed to estimate the mass balance in unsampled areas from existing datasets. Three years of mass-balance data from two glaciers in the central Italian Alps were used to develop and test a multiple-regression method based exclusively on a 10m resolution digital terrain model. The introduction of a relative elevation attribute, which expresses the degree of wind exposure of the gridcells, notably increased the amount of explainable variance in winter balance with respect to altitude itself. The summer balance is highly correlated with elevation, but, in order to obtain reliable extrapolations, the clear-sky shortwave radiation and the diurnal cloud-cover cycle had to be taken into account. The net annual mass balance on a glacier system comprising the two monitored glaciers was calculated by applying both a single regression of winter and summer balance with altitude and the new regression method. The consistency of results was assessed against measured net balances and snow-cover maps drawn in the ablation season. The results of the new method were in close agreement with observations and proved to be less sensitive to the spatial representation of the sampled areas.

Modeling Chinese cryospheric change by using GIS technology

The Chinese Cryospheric Information System (CCIS) is an integrated geographic information system (GIS) for storing, managing and analyzing the cryospheric data within China. Three regions were selected as the case study areas of CCIS. They are the Qinghai–Tibet Plateau, the regions along the Qinghai–Tibet Highway and the Urumqi River Basin of Tianshan Mountain. A draft geo-classification system that can express the logical hierarchy of cryospheric data was established. Based on this, CCIS stored large volumes of data, including maps of glacier, frozen ground and other environmental elements, digital elevation data, observation data of meteorological stations, hydrological gauges and permafrost boreholes and remote sensing data. CCIS is managed by ARC/INFO and can export data to other GIS environments easily, since data exchange interfaces were paid particular attention in the system. Based on CCIS, several GIS-based models about cryospheric processes and cryospheric response to global change have been developed. The models introduced are the following: a response model of high-altitude permafrost to global change, an evaluation model of engineering properties in permafrost regions along the Qinghai–Tibet Highway and a model of glacier mass balance estimation. The modeling results showed that the permafrost and glaciers in Chinese cryosphere will have significant changes under climatic warming.