How do climate change and water use alter dryland rivers and aquifers?

In arid and semi-arid regions many rivers flow only after rain, and the water they lose through their beds often refills the aquifers people depend on. How are warming and human water use changing these rivers and the groundwater linked to them?

Question

By what mechanisms do climate change and water use alter ephemeral rivers and groundwater in arid and semi-arid regions? Water use includes groundwater pumping, diversions and dams.

Background

With the previous question, on cold regions, it is one of the two practical questions of the twenty-three unsolved problems in hydrology, aimed at the places where climate impacts on hydrology and society may be largest and where some regime shifts have already been identified [1]. Rivers that periodically stop flowing have long been overlooked [2].

What is known

• Water stops flowing for at least one day a year along an estimated 51–60% of the world's rivers by length; non-perennial rivers occur in all climates and biomes and on every continent [2].
• Groundwater records across sub-Saharan Africa show that aridity governs the dominant recharge process: in drylands recharge is episodic, increasingly fed by losses from ephemeral overland flow, and intense rainfall produces some of the largest recharge years [3].
• In the contiguous USA, 64% of 4.2 million wells have water levels below nearby stream surfaces, so streams can lose water to aquifers; such losing streams are more common in drier climates, flatter landscapes and heavily pumped regions [4].
• Rapid groundwater declines (over 0.5 m per year) are widespread this century, especially in dry cropland regions, and have accelerated over four decades in 30% of regional aquifers; some reversed after policy changes, managed aquifer recharge or surface-water diversions [5].

What would count as progress

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

• Long, open records of flow presence and transmission losses on instrumented dryland reaches, paired with groundwater levels beneath them.
• A focused-recharge model validated against such records and then used to separate the effects of rainfall change from those of pumping.
• A continental analysis attributing observed changes in flow intermittence to climate versus water use, first tested on basins where the drivers are known.

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. Messager, M. L. et al. (2021). Global prevalence of non-perennial rivers and streams. Nature 594(7863), 391–397.
3. Cuthbert, M. O. et al. (2019). Observed controls on resilience of groundwater to climate variability in sub-Saharan Africa. Nature 572(7768), 230–234.
4. Jasechko, S. et al. (2021). Widespread potential loss of streamflow into underlying aquifers across the USA. Nature 591(7850), 391–395.
5. Jasechko, S. et al. (2024). Rapid groundwater decline and some cases of recovery in aquifers globally. Nature 625(7996), 715–721.

Source

Imported from Twenty-three unsolved problems in hydrology, question 3, 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.