Temperature-index modelling of runoff from adeclining Alpine glacier

The Gornera River, in the Pennine Alps, Switzerland, drains meltwater fromGornergletscher and its tributary glaciers, which contribute a large proportion of therunoff from this highly-glacierised basin. As the mass of ice has declined, recessionof many smaller tributary glaciers has resulted in their separation from the trunkGornergletscher. Declining glacier surface area might be expected to have reduced theice melt contribution to runoff, and since the Little Ice Age Maximum extent,Gornergletscher has revealed a strong link between climatic change and ice-cover.Glaciers in the Swiss Alps have revealed a total ice volume loss since the 1870s ofabout 13 km3. Approximately 8.7 km3 of ice loss occurred since the 1920s, and afurther 3.5 km3 of ice mass were lost between 1980 and the present day.This study aims to address three aspects of how changing temperatures and reducingice areas influence meltwater runoff.1. Modelling runoff response from scenarios of modified air temperatures and iceareas (e.g. a +1°C scenario with 20% reduced ice area), with the aim of finding theextent to which the modified conditions influence ice melt. In order to model runoffresponse, a temperature index model called RRM (Runoff Response Model) was setup. RRM uses formulae to calculate runoff by inputting the following forcingvariables to the model: positive air temperature values, and ice area measurements byelevation band, together with a degree day factor (DDF), and an air temperature lapserate.2. By using the same method, the effects of climate variations on ice area wereinvestigated by generating modelled runoff quantities from each elevation band. Thepurpose of doing this was to indicate how various areas of the glacier contributediffering quantities of melt to runoff during the ablation season, and the potentialimpact of loss of areas of ice. Using the model to show the highest contributing areaswas applied to Gornergletscher using the hypsometry of the basin – the second largestglacier in the Alps. Gornergletscher differs from other Alpine glaciers as a result ofits wide and relatively flat trunk.3. The study aims to calculate whether there is a linear or non-linear trend in ice areachange with elevation following model tuning. It is generally thought withGornergletscher that greatest ice areas are distributed at mid-elevations around thetrunk, where the tributaries join or joined the main ice body. Ice area in theory shouldbe most liable to melt at low and mid-elevations where both positive degree days andexposed ice areas exceed those of higher elevations. The influence of basinhypsometry on ice area change was studies by modifying the model to respond todiffering scenarios of energy availability and ice area available for melt.The investigation aimed to calculate whether there is a linear/non-linear relationshipbetween ice area change and elevation in a modified climate scenario. It is consideredfor Gornergletscher, that surface ice area distribution is greatest at mid-elevations,where tributaries connect to the main glacier body. Ice melt in theory should beproduced most at mid-elevations where both - more ice area is exposed than that oflower elevations and positive degree days exceed those of higher elevations.Basin hypsometry is of interest for ice area changes because of the irregular ice areadistribution with elevation in the basin. The relationship between the wide and flathypsometry of the Gornera Basin and ice melt at elevation was considered bymodifying the model input values to reflect different scenarios of energy availabilityand ice area available for melt.

Level dc:type.qualificationlevel

Master's Level (Level 7)

Year dc:date.issued

2026

Author dc:creator

• Bradley, JD

Language dc:language

en

Identifier

oai:salford-repository.worktribe.com:1406034

OAI identifier oai:identifier

oai:salford-repository.worktribe.com:1406034