Observations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (∼42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations (∼5200 since 1850) show that the rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable.

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[1] We have developed a physically based, distributed surface energy balance model to simulate glacier mass balance under meteorological and climatological forcing. Here we apply the model to estimate summer ablation on South Cascade Glacier, Washington, for the 2004 and 2005 mass balance seasons. To arrive at optimal mass balance simulations, we investigate and quantify model uncertainty associated with selecting from a range of physical parameter values that are not commonly measured in glaciological mass balance field studies. We optimize the performance of the model by varying values for atmospheric transmissivity, the albedo of surrounding topography, precipitationelevation lapse rate, surface roughness for turbulent exchange of momentum, and snow albedo aging coefficient. Of these the snow aging parameter and precipitation lapse rates have the greatest influence on the modeled ablation. We examined model sensitivity to varying parameters by performing an additional 10 3 realizations with parameters randomly chosen over a ±5% range centered about the optimum values. The best fit suite of model parameters yielded a net balance of À1.69 ± 0.38 m water equivalent (WE) for the 2004 water year and À2.10 ± 0.30 m WE up to 11 September 2005. The 2004 result is within 3% of the measured value. These simulations account for 91% and 93% of the variance in measured ablation for the respective years.

The more than 40 year record of net and seasonal mass balance records from measurements made by the U.S. Geological Survey on South Cascade Glacier, Washington, and Wolverine and Gulkana Glaciers, Alaska, show annual and interannual fluctuations that reflect changes in the controlling climatic conditions at regional and global scales. As the mass balance record grows in length, it is revealing significant changes in previously described glacier mass balance behavior, and both inter-glacier and glacier-climate relationships. South Cascade and Wolverine

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This manual provides a series of standard designs for streamgaging cableways used by the U.S. Geological Survey (USGS). It also provides helpful information on construction, inspection, and maintenance of cableways. Users of design recommendations are cautioned to follow sound engineering practice in selection of system components for a specific site. Accepted industry standards are referenced to facilitate procurement of materials where appropriate.

Relation that describes mass balance, in meters water equivalent, as either varies with glacier surface altitude, evaluated at altitude Z i x Symbol Meaning c Daily accumulation c  Accumulation rate c 0 Factor relating precipitation at a reference site to precipitation at a particular glacier site d 0 , d 1 Emperical coefficients DDF i Degree-day factor for ice melt DDF s Degree-day factor for snow and firn melt PDD Positive degree days m Slope of a rating curve segment on a logarithmic plot n Number of glacier altitude grid points p Discharge when the quantity (S-S 0) equals 1 P ref Daily precipitation at a reference site q Stream discharge S Water stage S 0 Stage of effective zero stream discharge T Daily average air temperature T 2 Daily average air temperature at 2-m height at a given mass balance site T crit Air temperature at and below which precipitation falls as snow

Symbols Symbol Meaning  a Ablation rate b Mass balance for a period beginning with time t 0 and ending with time t 1 b Glacier mass balance b 0 Glacier initial balance increment, the glacier balance between the time of the beginning of the water year and the beginning of the balance year. b 1 Glacier final balance increment, the glacier balance between the time of the end of the water year and the end of the balance year b a Annual (water year) balance b a Glacier annual (water year) balance b n Net balance b n Glacier net balance b s Summer balance b s Glacier summer balance b w Winter balance b w Glacier winter balance b m (s) Measured winter snow balance b m (s) Glacier measured winter snow balance b w (s) Maximum winter snow balance b w (s) Glacier maximum winter snow balance b(Z i) A relation that describes snow water equivalent or mass balance, in meters water equivalent, as either varies with glacier-surface altitude, evaluated at altitude Z i  c Accumulation rate m Slope of a rating curve segment on a logarithmic plot n Number of glacier altitude grid points p Discharge when the quantity (S-S 0) equals 1 q Stream discharge S Water stage S 0 Stage of effective zero stream discharge T Average June-through-September air temperature at the Hut X Position in local horizontal coordinate system along the X-axis, which increases from west to east Y Position in local horizontal coordinate system along the Y-axis, which increases from south to north Z Altitude Z i Altitude of a grid point in a glacier altitude grid