Mass Balance Data Research Articles

Can soil gas profiles be used to assess microbial CH 4 oxidation in landfill covers?

A method is proposed to estimate CH 4 oxidation efficiency in landfill covers, biowindows or biofilters from soil gas profile data. The approach assumes that the shift in the ratio of CO 2 to CH 4 in the gas profile, compared to the ratio in the raw landfill gas, is a result of the oxidation process and thus allows the calculation of the cumulative share of CH 4 oxidized up to a particular depth. The approach was validated using mass balance data from two independent laboratory column experiments. Values corresponded well over a wide range of oxidation efficiencies from less than 10% to nearly total oxidation. An incubation experiment on 40 samples from the cover soil of an old landfill showed that the share of CO 2 from respiration falls below 10% of the total CO 2 production when the methane oxidation capacity is 3.8 μg CH 4 g dw - 1 h −1 or higher, a rate that is often exceeded in landfill covers and biofilters. The method is mainly suitable in settings where the CO 2 concentrations are not significantly influenced by processes such as respiration or where CH 4 loadings and oxidation rates are high enough so that CO 2 generated from CH 4 oxidation outweighs other sources of CO 2. The latter can be expected for most biofilters, biowindows and biocovers on landfills. This simple method constitutes an inexpensive complementary tool for studies that require an estimation of the CH 4 oxidation efficiency values in methane oxidation systems, such as landfill biocovers and biowindows.

Removal of Silver and Lead Ions from Water Wastes Using Azolla filiculoides, an Aquatic Plant, Which Adsorbs and Reduces the Ions into the Corresponding Metallic Nanoparticles Under Microwave Radiation in 5 min

Pollution of water bodies with heavy metal ions is a major worldwide environmental problem. The objective of this study was to elucidate the mechanism in which metallic ions are adsorbed and reduced to metallic nanoparticles onto plant materials using microwave radiation. In this research, we have fabricated metallic silver and lead nanoparticles from their corresponding ions using the aquatic plants Azolla filiculoides and Pistia stratiotes (since identical results are obtained for both plants, the emphasis will be on the Azolla) under microwave radiation. Our data show that metallic silver and metallic lead nanoparticles were completely removed from the polluted solution and were embedded in the A. filiculoides surface after 5 min of microwave reaction. It was also found that, for both metals, reduction of the metallic ions was accomplished by the plant matrix without the need of an external reducing agent. Most of the particles had a spherical shape within the 10–50 nm size range. Mass balance data clearly indicate that most of the silver particles were found on the surface of the plant and not in the clean water. Pectin and α-glucuronic acid did not reduce the silver or lead ions under microwave radiation. We therefore hypothesize that perhaps the proteins or sugar alcohols in the plant matrix were serving as the reducing agents. We believe that this technique in which adsorption and reduction are combined using microwave radiation can be applied for removing and recycling metallic ions from contaminated water and industrial wastewater.

Effect of nutrients on the biodegradation of tributyltin (TBT) by alginate immobilized microalga, Chlorella vulgaris, in natural river water

The removal and degradation of tributyltin (TBT) by alginate immobilized Chlorella vulgaris has been evidenced in our previously published work. The present study was further to investigate the effect of spiked nutrient concentrations on the TBT removal capacity and degradation in the same alginate immobilized C. vulgaris. During the 14-d experiment, compared to the control (natural river water), the spiked nutrient groups (50% or 100% nutrients of the commercial Bristol medium as the reference, marked as 1/2N or 1N) showed more rapid cell proliferation of microalgae and higher TBT removal rate. Moreover, significantly more TBT was adsorbed onto the alginate matrix, but less TBT was taken up by the algal cells of the nutrient groups than that of the control. Mass balance data showed that TBT was lost as inorganic tin in the highest degree in 1N group, followed by 1/2N group and the least was in the control, but the relative abundance of the intermediate products of debutylation (dibutyltin and monobutyltin) were comparable among three groups. In conclusion, the addition of nutrients in contaminated water stimulated the growth and physiological activity of C. vulgaris immobilized in alginate beads and improved its TBT degradation efficiency.

Global-scale modeling of glacier mass balances for water resources assessments: Glacier mass changes between 1948 and 2006

Glaciers play an important role for freshwater resources, but in global-scale freshwater assessments, their impact on river flows has not yet been taken into account. As a first step, we developed a global glacier model that can be coupled to global land surface and hydrological models. With a spatial resolution of 0.5° by 0.5°, the glacier model HYOGA computes glacier mass balance by a simple degree-day approach for 50 m sub-grid elevation bands, modeling all glaciers within a grid cell as one glacier. The model is tuned individually for each grid cell against observed glacier mass balance data. HYOGA is able to compute glacier mass balances reasonably well, even those of summer accumulation type glaciers. Still, model uncertainty is high, which is, among other reasons, due to the uncertainty of global data sets of temperature and precipitation which do not represent well the climatic situation at glacier sites. We developed a 59-yr (1948–2006) time series of global glacier mass balance and glacier area by driving HYOGA with daily near-surface atmospheric data. According to our computations, most glaciers have lost mass during the study period. Compared to estimates derived from a rather small number of observed glacier mass balances, HYOGA computes larger glacier mass losses in Asia, Europe, Canadian Arctic islands and Svalbard. In accordance with the estimates, average annual mass losses have increased strongly after 1990 as compared to the 30 yrs before. The sea level equivalent of the melt water from glaciers is 0.76 mm/yr water equivalent after 1990 as compared to only 0.34 mm/yr water equivalent before. We computed an acceleration of glacier mass losses after 1990 for all world regions except South America, where the number of gauge observations of precipitation is very small after 1980.

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 downward trend with rising temperatures, and larger value of DDF only appeared at low temperature conditions. A larger value of DDF appeared in the high altitude areas, and as altitude rises, the value of DDF increased. The snow DDF is lower than the DDF of ice, and the DDF is higher in temperate glaciers than those in other glaciers. The melting DDF of snow has a more obvious seasonal variation than the melting DDF of ice.

Role of glaciers in watershed hydrology: a preliminary study of a "Himalayan catchment"

Abstract. A large number of Himalayan glacier catchments are under the influence of humid climate with snowfall in winter (November–April) and south-west monsoon in summer (June–September) dominating the regional hydrology. Such catchments are defined as "Himalayan catchment", where the glacier meltwater contributes to the river flow during the period of annual high flows produced by the monsoon. The winter snow dominated Alpine catchments of the Kashmir and Karakoram region and cold-arid regions of the Ladakh mountain range are the other major glacio-hydrological regimes identified in the region. Factors influencing the river flow variations in a "Himalayan catchment" were studied in a micro-scale glacier catchment in the Garhwal Himalaya, covering an area of 77.8 km2. Three hydrometric stations were established at different altitudes along the Din Gad stream and discharge was monitored during the summer ablation period from 1998 to 2004, with an exception in 2002. These data have been analysed along with winter/summer precipitation, temperature and mass balance data of the Dokriani glacier to study the role of glacier and precipitation in determining runoff variations along the stream continuum from the glacier snout to 2360 m a.s.l. The study shows that the inter-annual runoff variation in a "Himalayan catchment" is linked with precipitation rather than mass balance changes of the glacier. This study also indicates that the warming induced an initial increase of glacier runoff and subsequent decline as suggested by the IPCC (2007) is restricted to the glacier degradation-derived component in a precipitation dominant Himalayan catchment and cannot be translated as river flow response. The preliminary assessment suggests that the "Himalayan catchment" could experience higher river flows and positive glacier mass balance regime together in association with strong monsoon. The important role of glaciers in this precipitation dominant system is to augment stream runoff during the years of low summer discharge. This paper intends to highlight the importance of creating credible knowledge on the Himalayan cryospheric processes to develop a more representative global view on river flow response to cryospheric changes and locally sustainable water resources management strategies.

Glaciers and climate change: Interpretation of 50 years of direct mass balance of Hintereisferner

Direct mass balance data of Hintereisferner glacier annually measured for fifty years were reanalyzed and bias-corrected. The glacier area and the patterns of the spatial distribution of specific mass balance were homogenized using the measured data and the current methods of modern mass balance analysis on Hintereisferner. The homogenized mass balance shows a good agreement with the geodetic and the hydrological mass balance. The comparison with modelled mass balance and measured temperature data showed that the homogenized mass balance correlated best with TS sum ( R 2 = 0.76) followed by the simple degree-day sum ( R 2 = 0.60) and the mean summer temperature ( R 2 = 0.55). From that and from the calculation of the effects of albedo changes follows that the frequency and duration of summer snowfalls play an important role in the summer ablation of the glacier. The analysis of sub areas shows that at high elevations mass balance is dominated by the influence of winter precipitation. At low elevations, the increasingly negative mass balance was a result of the increase of the mean summer temperatures and the decrease of surface elevation. Between 1953 and 2003, the surface of the glacier tongue lowered by 160 m. This corresponds to a temperature increase of about 1 °C at the surface 2003 compared to the surface 1953. In the same period, the potential incoming solar radiation during the summer is reduced by the surface lowering. Comparing the effect of these two factors, the impact of the topographic temperature change on mass balance is much higher than the impact of increased shading. At higher elevations, the effect of topographic changes is small compared to changes in the mean surface albedo. The separation of glacier tributaries has been decreasing the inflow of ice to the main tongue. The mass balance of the glacier parts connected to the main tongue decreases faster than the mass balance of the total area. Therefore, the retreat of Hintereisferner is governed by a more negative mass balance than measured for the total area.

Outdoor weathering and dissolution of TNT and Tritonal

Low-order detonations of military munitions scatter cm-sized chunks of high-explosives onto military range soils, where rainfall can dissolve and then transport the explosives to groundwater. We present 1 year of mass-loss data obtained from cm-sized chunks of the frequently used explosives TNT (2,4,6-trinitrotoluene) and Tritonal (an 80:20 mixture of TNT and aluminum flakes) exposed outdoors to weather and dissolve under natural conditions. The explosive chunks rested on glass frits in individual funnels and all precipitation interacting with them was collected and analyzed. Mass balance data reveal that TNT in the water samples accounts for only about one-third of the TNT lost from the chunks. The creation of photo-transformation products on the solid chunks, and their subsequent dissolution or sublimation, probably accounts for the other two-thirds. Although these products cannot, as yet, be quantified they are intrinsic to the outdoor weathering and fate of TNT-based explosives. TNT in our water samples was not photo-transformed. Thus, we used the yearlong, dissolved-mass time-series to validate a drop-impingement dissolution model for TNT. The model used measured rainfall and air temperature data as input, and the results agreed remarkably well with TNT dissolved-mass time-series measured for the year. This model can estimate annual TNT influx into range soils using annual rainfall and particle-size distributions. Nevertheless, large uncertainties remain in the numbers and sizes of TNT particles scattered on military ranges and the identities and fates of the photo-transformation products.

Observed changes in streamflow at the headwaters of the Urumqi River, eastern Tianshan, central Asia

AbstractThe runoff records of streams draining basins with between 0 and approximately 54% glacier cover, located at the headwaters of the Urumqi River in eastern Tianshan, central Asia, have been examined for the purpose of assessing climatic and glacial influences on temporal patterns of streamflow for the period 1959–2006. Runoff in the highest glacierized basin is found to be inversely correlated with the glacier mass‐balance data and increased by 165·1 × 104 m3 or 1·5 times on average from 1959 to 2006, whereas flow from a glacier‐free basin reflects precipitation changes associated with temperature that may enable either ground ice formation or ice storage release. For the basin with a glacier cover of 18·5%, the runoff increased approximately 355·4 × 104 m3 or 29·6% on average from 1983 to 2006, which underscores expected results based on glacier melt and precipitation increase, especially after 2000. This is due to several possible reasons including enhanced evaporation, groundwater percolation, increased water consumption due to plant colonization and runoff decrease from glacier basins subject to area reduction. From the measurement at Urumqi glacier No. 1 gauging station and a simple water balance model, the glacial runoff during the period 1959–2006 was calculated and found to have increased by 145·5 × 104 m3 a−1 (a factor of 2) over the 48‐year span. A significant amount of the increase occurred after 1987, particularly after 1995, and coincides with increases in both temperature and precipitation. Copyright © 2009 John Wiley & Sons, Ltd.

On Asphaltene and Resin Association in Athabasca Bitumen and Maya Crude Oil

The mass fraction of resins in asphaltene-rich aggregates, present in crude oils, and the physics and chemistry associated with them are poorly defined because of the variability of the definitions of asphaltenes and resins but remain a subject of significant interest to practitioners who model asphaltene behavior in hydrocarbon resources. In this contribution, the mass fraction of resins in pentane−asphaltene-rich aggregates in nanofiltered Athabasca bitumen and Maya crude oil samples is evaluated using a mass balance model and data regression fits to saturates, aromatics, resins, and asphaltenes (SARA) analyses of permeate and retentate samples obtained by filtering these hydrocarbon resources directly through 5, 10, 20, 50, 100, and 200 nm filters. Solvents are not employed in the filtration experiments. At 473 K, the mass fraction of resins in pentane−asphaltene-rich aggregates and the fraction of resins present in aggregates are both found to be at or below the threshold for resin mass fraction measu...

A Minute Dose of 14C-β-Carotene Is Absorbed and Converted to Retinoids in Humans1–3

Our objective was to quantify the absorption and conversion to retinoids of a 1.01-nmol, 3.7-kBq oral dose of 14C-β-carotene in 8 healthy adults. The approach was to quantify, using AMS, the elimination of 14C in feces for up to 16 d after dosing and in urine for up to 30 d after dosing. The levels of total 14C in undiluted serial plasma samples were measured for up to 166 d after dosing. Also, the levels of 14C in the retinyl ester (RE), retinol (ROH), and β-carotene fractions that were isolated from undiluted plasma using HPLC were measured. The apparent digestibility of the 14C was 53 ± 13% (mean ± SD), based on the mass balance data, and was generally consistent with the area under the curve for zero to infinite period of 14C that was eliminated in the feces collections made up to 7.5 d after dosing. Metabolic fecal elimination, calculated as the slope per day (% 14C-dose/collection from d 7.5 to the final day), was only 0.05 ± 0.02%. The portion of the 14C dose eliminated via urine was variable (6.5 ± 5.2%). Participants [except participant 6 (P6)] had a distinct plasma peak of 14C at 0.25 d post-dose, preceded by a shoulder at ∼0.1 d, and followed by a broad 14C peak that became indistinguishable from baseline at ∼40 d. Plasma 14C-RE accounted for most of the absorbed 14C early after dosing and P1 had the longest delay in the first appearance of 14C-RE in plasma. The data suggest that plasma RE should be considered in estimating the ROH activity equivalent of ingested β-carotene.

Use of chloride mass balance and tritium data for estimation of groundwater recharge and renewal rate in an unconfined aquifer from North Africa: a case study from Tunisia

The scarcity of surface water resources in arid and semi-arid regions from North African countries contributes to the considerable increase of groundwater exploitation, which leads to the development of hydrogeological studies. However, due to the lack of hydrodynamic data in these regions, these studies focus more and more on the geochemical and environmental isotope techniques to insure a better understanding of the hydrodynamic functioning of subsurface systems. In this study, which interests an important unconfined aquifer in central Tunisia, tritium data and chloride mass balance (CMB) method were applied in order to (1) understand the mode of recharge of this aquifer and (2) obtain a reliable estimation of its recharge amount as well as (3) estimate its annual renewal rate. It has been demonstrated that the shallow groundwaters are classified into two groups according to their tritium contents. The first group includes wells located mainly downstream and highlights the significant role of the post-nuclear lineal recharge through Wadis courses. The second group encloses wells located practically overall the rest of the basin and refers to relatively modern waters originated from areal recharge of present-day rainfall. Based on the CMB method, the recharge to this unconfined aquifer is estimated to 31.7 mm year−1, which corresponds to 10.5% of the total rainfall. The annual renewal rate of groundwater, evaluated based on the tritium contents, is up to 16%.

Glacier fluctuations of Jostedalsbreen, western Norway, during the past 20 years: the sensitive response of maritime mountain glaciers

The steep outlet glaciers of Jostedalsbreen, western Norway, are good examples of sensitively reacting maritime mountain glaciers. Their changes in length, frontal position and lower tongue's morphology during the past 20 years have been well documented. At first they experienced a strong frontal advance. After AD 2000 glacier behaviour was dominated by a strong frontal retreat, in some cases causing a separation of the lowermost glacier tongue. In this paper, the glacier length changes are presented both visually and numerically, supplemented by mass balance and meteorological data. The glacier behaviour is interpreted and its causes are discussed. Whereas the factors controlling the advance during the 1990s seem clear, the interpretation of the most recent retreat still leaves some uncertainties. The actual glacier front behaviour cannot fully be related to the mass balance data. Terminus response times and relations between individual mass balance and meteorological parameters have changed. Some hypotheses are given, including disturbance of the `normal' mass transfer and dynamical response of the glacier front because of excessive ablation on the lowermost glacier tongues and summer back melting. These findings underline the sensitivity of maritime glaciers to climate changes. The empirical findings need to be taken into account in the interpretation of recent glacier length changes and their future modelling.

William “Bill” Back: An Incisive Geochemist and a Great Mentor

Introduction William ‘‘Bill’’ Back (Figure 1) was one of the great ‘‘idea people’’ in low-temperature geochemistry during the blossoming of ground water hydrology in the latter half of the twentieth century. Prior to the1950s, most of the research in ground water chemistry was related to water quality and was carried out by chemists who rarely ventured into the field. Bill, Ivan Barnes, Bruce Hanshaw, Blair Jones, and Don White of the USGS were among the first to change that by using aquifer systems to test models of natural solute evolution and thus changed the way people thought about water chemistry. Bill Back was an early leader in recognizing the importance of thermodynamics in ground water systems. He related ground water chemistry to flow in aquifers, and in what is now a benchmark paper (Back 1960), he introduced the concept of hydrochemical facies by drawing on the concept of geological facies (units of similar lithology and depositional history). Bill defined hydrochemcial facies as ‘‘the diagnostic chemical aspect of water solutions occurring in hydrologic systems,’’ which ‘‘reflect the response of chemical processes in the lithologic framework and the pattern of water flow in it.’’ In later work, he used geochemical mass balance and stable isotope data to constrain possible reactions and recognized the value of dating water and solutes in aquifer systems. He was among the first to investigate redox processes in iron-reducing aquifers and later turned to extreme geochemical environments such as landfills and investigation of the role of organics in solute evolution in ground water. Later in his career, he investigated the importance of ground water in the development of ancient cultures. Although his numerous publications reflect his many scientific accomplishments, he is perhaps most endearingly remembered as a mentor to young students and professionals, for encouraging and supporting women in hydrogeology, and for his contributions to professional societies and international hydrogeological activities.

Derivation of melt factors from glacier mass-balance records in western Canada

AbstractMelt factors for snow (ks) and ice (ki) were derived from specific mass-balance data and regionally interpolated daily air-temperature series at nine glaciers in the western Cordillera of Canada. Fitted ks and ki were relatively consistent across the region, with mean values (standard deviations) of 3.04 (0.38) and 4.59 (0.59) mm d−1 °C−1, respectively. The interannual variability of melt factors was investigated for two long-term datasets. Calculated annually, snow- and ice-melt factors were relatively stable from year to year; standard deviations for snowmelt factors were 0.48 (17%) and 0.42 (18%) at Peyto and Place Glaciers, respectively, while standard deviations of ice-melt factors were 1.17 (25%) and 0.81 (14%). While fitted values of ks are comparable to those presented in previous observational and modeling studies, fitted ki are substantially and consistently lower across the region. Fitted melt factors were sensitive to the choice of lapse rate used in the air-temperature interpolation. Melt factors fitted to mass-balance data from a single site (Place Glacier) provided reasonable summer balance predictions at most other sites representing both maritime and continental climates, although there was a tendency for under-prediction at several sites. The combination of regionally interpolated air temperatures and a degree-day model appears capable of generating first-order estimates of regional summer balance, which can provide a benchmark against which to judge the predictive ability of more complex (e.g. energy balance) models applied at a regional scale. Mass-balance sensitivity analyses indicate that a temperature increase of 1 K will increase summer ablation in the region by 0.51 m w.e. a−1 on average.

Six decades of glacier mass-balance observations: a review of the worldwide monitoring network

AbstractGlacier mass balance is the direct and undelayed response to atmospheric conditions and hence is among the essential variables required for climate system monitoring. It has been recognized as the largest non-steric contributor to the present rise in sea level. Six decades of annual mass-balance data have been compiled and made easily available by the World Glacier Monitoring Service and its predecessor organizations. In total, there have been 3480 annual mass-balance measurements reported from 228 glaciers around the globe. However, the present dataset is strongly biased towards the Northern Hemisphere and Europe and there are only 30 ‘reference’ glaciers that have uninterrupted series going back to 1976. The available data from the six decades indicate a strong ice loss as early as the 1940s and 1950s followed by a moderate mass loss until the end of the 1970s and a subsequent acceleration that has lasted until now, culminating in a mean overall ice loss of over 20mw.e. for the period 1946–2006. In view of the discrepancy between the relevance of glacier mass-balance data and the shortcomings of the available dataset it is strongly recommended to: (1) continue the long-term measurements; (2) resume interrupted long-term data series; (3) replace vanishing glaciers by early-starting replacement observations; (4) extend the monitoring network to strategically important regions; (5) validate, calibrate and accordingly flag field measurements with geodetic methods; and (6) make systematic use of remote sensing and geo-informatics for assessment of the representativeness of the available data series for their entire mountain range and for the extrapolation to regions without in situ observations; and (7) make all these data and related meta-information available.

Numerical modelling of historical front variations and the 21st-century evolution of glacier AX010, Nepal Himalaya

AbstractDue to the lack of measurements of ice velocity, mass balance, glacier geometry and other baseline data, model-based studies of glacial systems in the Nepal Himalaya are very limited. Here a numerical ice-flow model has been developed for glacier AX010 in order to study its relation to local climate and investigate the possible causes of its general retreat since the end of the Little Ice Age. First, an attempt is made to simulate the historical front variations, considering each climatic parameter separately. Good agreement between the observations and model projections can be obtained under the assumption that variations in glacier front position are a response to changes in temperature alone. The same assumption is made about future changes to explore the 21st-century evolution of the glacier. Under a no-change scenario, the glacier will retreat by another ∽600m by AD 2100, whereas it is projected to vanish completely during this century for all trends with a temperature rise larger than +2.5˚C by AD 2100 with respect to the 1980–99 mean. With constant precipitation at the 1980–99 mean, the model predicts that the glacier will cease to exist at AD 2083, 2056 or 2049 if the temperature rises linearly by 3˚C, 4.5˚C or 6˚C respectively by the end of this century. With an additional range of precipitation changes between –30% and +30%, the life expectancy of glacier AX010 varies by 18, 6 and 2 years for the respective temperature rises. Thus the role of precipitation becomes minimal for the higher trends of temperature rise.

Estimating equilibrium-line altitude (ELA) from glacier inventory data

AbstractA glacier’s most fundamental altitude is the equilibrium-line altitude (ELA) because it divides the glacier into ablation and accumulation areas. The best parameterization of the ELA for glacier inventory is the balanced-budget ELA. We discuss direct estimation of balanced-budget ELA from mass-balance data for individual glaciers, and indirect estimation of balanced-budget ELA from simple topographic parameters available from the World Glacier Inventory (WGI), i.e. the area-median and maximum and minimum altitudes. Mass balance and ELA for individual glaciers are usually strongly correlated and we calculate balanced-budget ELA from the regression equation linking the two. We then compare balanced-budget ELA with area-median and mid-range altitudes for the 94 glaciers for which we have all the necessary data. The different ELA estimates agree well enough (±82 to ±125 m) to describe geographical variations in ELA and for application of glacier–climate models to glacier inventory data. Mid-range and area-median altitudes are already available for tens of thousands of glaciers in the current WGI and should be evaluated in future inventories.

After six decades of monitoring glacier mass balance we still need data but it should be richer data

AbstractThis paper reviews data on glacier mass balance together with extra metadata on topography and climate to put the data into context. The 2007 Intergovernmental Panel on Climate Change (IPCC) estimates of global average glacier mass balance may not be much different from simple averages. A more mathematically correct approach is to analyse long and continuous mass-balance series measured in different regions, but there are few long series and they do not cover the globe in any representative way. However, 30 year series from 30 glaciers confirm a recent (1996–2005) trend to very negative mass balance after two decades of nearly zero mass balance. Climate data from a global gridded climatology are applied to datasets for global glacier cover, for 318 glaciers with mass-balance data for at least 1 year and for 30 glaciers with 30 year series of measurements. Results show that mean precipitation is relatively low in the global glacier-cover dataset and much higher for the observed glaciers. This shows that current mass-balance measurements are biased towards wetter conditions than are typical for global glacier cover. We urgently need to find better ways of analysing sparse datasets with ‘complex spatial and temporal patterns’ like the present mass-balance dataset.

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.