Is the hydrological cycle accelerating, and are there tipping points?

A warmer atmosphere holds more moisture, so the water cycle is expected to speed up: more evaporation, heavier rain, faster turnover. Is that actually happening region by region, and could parts of the cycle shift abruptly and not come back?

Question

Is the hydrological cycle regionally accelerating or decelerating under climate and environmental change, and are there tipping points (irreversible changes)? Acceleration means larger water fluxes and shorter residence times; a tipping point is an abrupt transition of a regional water regime to another state.

Background

The question opens the "time variability and change" theme of the twenty-three unsolved problems in hydrology, drawn up in 2018 by about 230 scientists. The authors note that regime changes in complex systems are notoriously difficult to identify, even with longer records and better models [1].

What is known

• Near-surface water vapour rises by about 7% per °C of warming, but global precipitation and evaporation only by about 2–3% per °C; direct human water use and land-use change are already a significant part of regional change [2].
• Ocean salinity changes over 1950–2000 imply an intensification of 8 ± 5% per degree of surface warming, double the response of the climate models of the time [3].
• Hydroclimate "whiplash", rapid swings between very dry and very wet conditions, has increased by 31–66% at the 3-month scale since the mid-twentieth century and is projected to increase by 113% over land with 3 °C of warming [4].

What would count as progress

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

• Regional acceleration indicators (fluxes and residence times) computed consistently from station data, the ERA5 reanalysis and GRACE/GRACE-FO water storage, with uncertainties.
• Basin-scale attribution studies that separate climate forcing from irrigation, abstraction and land-use change.
• A regime-shift test for river-flow, lake and groundwater records that recovers known shifts in synthetic series, reports its false-alarm rate, and is then applied to real data.

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. Allan, R. P. et al. (2020). Advances in understanding large-scale responses of the water cycle to climate change. Annals of the New York Academy of Sciences 1472(1), 49–75.
3. Durack, P. J., Wijffels, S. E. & Matear, R. J. (2012). Ocean salinities reveal strong global water cycle intensification during 1950 to 2000. Science 336(6080), 455–458.
4. Swain, D. L. et al. (2025). Hydroclimate volatility on a warming Earth. Nature Reviews Earth & Environment 6(1), 35–50.

Source

Imported from Twenty-three unsolved problems in hydrology, question 1, 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.