How will cold-region runoff and groundwater change as climate warms?

Glaciers, snow and frozen ground store water and release it on a schedule that people and ecosystems downstream rely on. As they shrink and thaw, the amount and timing of river flow and groundwater recharge change, but how much, where and when is still uncertain.

Question

How will runoff and groundwater in cold regions change in a warmer climate, for example as glaciers melt and permafrost thaws? This covers the amount and timing of streamflow and recharge, and the water stored in ice, snow and aquifers, in high mountains and the Arctic.

Background

With the next question, on drylands, this is one of the two practical questions of the twenty-three unsolved problems in hydrology: cold and dry places are where the impacts of climate change on hydrology and society are potentially largest, and where some regime shifts have already been identified [1].

What is known

• Glaciers worldwide lost 273 ± 16 Gt of ice per year from 2000 to 2023, 36 ± 10% more in 2012–2023 than in 2000–2011 [2].
• The most important mountain "water towers" are also among the most vulnerable; climatic and socio-economic change could affect 1.9 billion people living in or directly downstream of them [3].
• In roughly half of 56 large glacierized basins, glacier runoff is still rising towards "peak water"; in the rest it has passed. By 2100 a third of the basins may lose more than 10% of runoff in at least one month of the melt season, most in central Asia and the Andes [4].
• Permafrost is a primary control on flow paths. Thaw alters soil moisture, the connectivity of inland waters, streamflow seasonality and the split between surface and subsurface storage, but predictions are limited by sparse baseline data and simplified models [5].

What would count as progress

No single result settles a question like this; contributions like these would move it forward:

• Basin-scale projections of peak water and monthly runoff that are checked against observed glacier mass balance and discharge, with their uncertainty quantified.
• Coupled permafrost–groundwater models evaluated at instrumented sites against winter baseflow, active-layer depth and groundwater levels.
• An open, harmonised compilation of discharge, groundwater and ground-temperature records for Arctic and high-mountain basins, so that trends can be compared across regions.

References

1. Blöschl, G. et al. (2019). Twenty-three unsolved problems in hydrology (UPH) – a community perspective. Hydrological Sciences Journal 64(10), 1141–1158.
2. The GlaMBIE Team (2025). Community estimate of global glacier mass changes from 2000 to 2023. Nature 639(8054), 382–388.
3. Immerzeel, W. W. et al. (2020). Importance and vulnerability of the world's water towers. Nature 577(7790), 364–369.
4. Huss, M. & Hock, R. (2018). Global-scale hydrological response to future glacier mass loss. Nature Climate Change 8(2), 135–140.
5. Walvoord, M. A. & Kurylyk, B. L. (2016). Hydrologic impacts of thawing permafrost—a review. Vadose Zone Journal 15(6).

Source

Imported from Twenty-three unsolved problems in hydrology, question 2, curated by Blöschl et al. Listed as open in the source (2019) and still an active research question as of 2026-10-20. The statement above is written in our own words; see the source for the original wording, history and discussion.