How does land-cover change alter land-surface fluxes and recharge?

Clearing or planting forests, ploughing, irrigating and paving all change how much water evaporates, runs off or soaks down to aquifers. A century of catchment experiments has not yet made these effects predictable.

Question

What are the impacts of land-cover change (such as deforestation, afforestation, conversion to cropland and urbanisation) and soil disturbance (such as tillage, compaction and sealing) on the water and energy fluxes at the land surface, and on the resulting groundwater recharge?

Background

The topic has been on the hydrological agenda for over a century: experimental catchments studying forests and streamflow began in Emmental, Switzerland, in 1900 and at Coweeta, North Carolina, around 1930. Yet the authors of the twenty-three unsolved problems in hydrology note that despite almost 500 paired-watershed studies, the effects of forest harvesting and afforestation remain largely unpredictable [1].

What is known

• A review of about 312 watersheds worldwide found that forest loss raises annual runoff significantly at several spatial scales, whereas the effect of forest gain is statistically inconsistent; runoff is more sensitive to forest change in water-limited than in energy-limited watersheds [2].
• In the southwestern USA, replacing natural rangeland (no recharge, water moving upward) with agriculture reversed the flow direction: recharge reached about 130–640 mm per year under irrigation and 9–32 mm per year under dryland farming, flushing stored salts towards the aquifers [3].
• In a global dataset of more than 5,000 recharge estimates, precipitation and the seasonality of temperature and precipitation are the strongest predictors, but vegetation and soil structure add explanatory power, so climate-only estimates can mislead [4].

What would count as progress

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

• A meta-analysis of paired-catchment and land-use change experiments that predicts the sign and size of the runoff and recharge response from climate, soil and vegetation, tested on catchments held out of the fit.
• Tracer or unsaturated-zone profiles that document recharge before and after a dated land-use change at the same site.
• Land-surface models whose simulated recharge response to land-cover change is evaluated against these data, not only against streamflow.

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. Zhang, M. et al. (2017). A global review on hydrological responses to forest change across multiple spatial scales: importance of scale, climate, forest type and hydrological regime. Journal of Hydrology 546, 44–59.
3. Scanlon, B. R. et al. (2005). Impact of land use and land cover change on groundwater recharge and quality in the southwestern US. Global Change Biology 11(10), 1577–1593.
4. Moeck, C. et al. (2020). A global-scale dataset of direct natural groundwater recharge rates: a review of variables, processes and relationships. Science of the Total Environment 717, 137042.

Source

Imported from Twenty-three unsolved problems in hydrology, question 4, 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.