What is the glacier contribution to the global water cycle?

Any life on Earth is directly connected to the availability of water. The water cycle describes the continues fluxes of water between different storages at, above, and below the Earth’s surface (Figure 1). Glaciers are one important storage within the global water cycle and store about 160.000 km3 of water. Water storage in glaciers cannot be directly measured but is assessed from inventories (glacier area) and glacier thickness estimates (compare GTN-G datasets (www.gtn-g.org).

Fig. 1 & 2 Global water storages and fluxes, from Dorigo et al. 2021.

At decadal to annual time scales, glaciers act as storages with related changes, while at annual scales, their annual mass turnover corresponds to hydrological fluxes. As such, glaciers contribute to runoff during dry/summer seasons even in years with positive annual mass balances. Annual glacier mass turnover can be measured at individual glaciers, however, at regional to global scale corresponding estimates are only available from modelling studies (Dorigo et al. 2021).
With changing and vanishing glaciers, more and more reliable data is needed for the assessment of this storage component. So far, no operational long-term global observation system of glacier-related water fluxes is available, neither from in-situ measurements, nor from remote sensing. In their study, Dorigo et al. 2021 suggest the following strategy for glaciers to cover the demands regarding water cycle monitoring:
– maintain and expand the worldwide in-situ network with a focus on long-term monitoring programs.
– use spaceborne altimetry.
– increase the availability of large-scale high-resolution DEMs.
– unlock national archives of aerial surveys and photogrammetric processing of early optical satellite data.

References

Dorigo, W., Dietrich, S., Aires, F. et al. (2021): Closing the water cycle from observations across scales. Where do we stand? BAMS Article, American Meteorological Society. https://doi.org/10.1175/BAMS-D-19-0316.1