Modelling of Glaciers

WaSiM offers two different glacier model approaches: the (old) static and (newer) dynamic glacier model.

The static model glacier

Glacier areas must be excluded into separate sub-basins. An input grid contains codes for glacier ice and firn, thus enabling a spoatailly differenciated calculation of ice and firn melt and runoff. Such a subbasin must consist of glaciers cells only, either firn or ice. It is not possible to define partly glacierized cells.

Ice, firn and snow melt are modelled after Hock (1997). There are two methods with or without radiation correction available.

Runoff concentration for glaciers is calculated separately for ice, firn and snow melt by using separate single linear storages. The total glacier runoff is the sum of these three components, which is then be routed into the next (usually glacier-free) subbasin.

Please note that no glacier area and glacier mass changes are simulated by this static glacier model.

The dynamic glacier model

The dynamic glacier model does not use fix assignments of individual cells as glaciers. Rather, for each cell the glaciated fraction can be defined. Consequently, it is also not necessary that every glacier is assigned its own subbasin. However, it is recommended to model individual glaciers or groups of similar glaciers in sparated subbasins in order to investigate the outflows separately later during post processing.

Each glacier is assigned an ID (new input grid), so the dynamic shrinking or growing can be done separately for each glacier. Once a model year, for example at the end of September, the size of all the glaciers is re-calculated (separately for each glacier - because of the IDs) by evaluating the accumulated mass balance for the last year. According to the resize amount, cells or fractions thereof are added to the glaciers or taken away. Thus, in long-term simulations glacier advances and retreats can be modelled.

Furthermore, the dynamic glacier model incorporates a module to model the metamorphosis of snow to firn and then to ice (after a specified number of years).

The glacier melt and runoff concentration algorithms are identical to those of the static glacier model

Details on the modeling of Glacier Runoff can be found in the WaSiM model documentation.

References