Increased groundwater recharge due to localized infiltration from impervious surfaces in an urban area

Groundwater recharge in urban areas is generally accepted to differ from that in natural landscapes. However, due to numerous artificial influences on groundwater recharge, it is often difficult to predict the groundwater recharge without proper monitoring. Meanwhile, data from urban areas is scarce because most built-up sites consist of private property where data collection is challenging. This is particularly problematic for settlements with individual water supply in hardrock regions, as they are highly dependent on local groundwater resources. Furthermore, the availability of groundwater in those areas is often threatened by the ongoing climate change.

We evaluated the impact of localized infiltration of rainwater from impervious surfaces on groundwater recharge in a small settlement in Czechia. As the settlement has no public water supply or wastewater collection, the only artificial influences on water balance are withdrawal from domestic wells, irrigation and rainwater discharge on individual estates. Therefore, localized infiltration can be observed with as little disturbance as possible. We monitored water table level in a well, and installed a piezometer next to an outlet from rainwater drainage of a house roof to observe the localized infiltration independently. Two lysimeters were installed at the site – one 35 cm deep with cut grass and one 94 cm deep with shrubs. They confirmed that evapotranspiration significantly reduces the amount of groundwater recharge in gardens. The profiles with grass and shrubs consumed 68% and 95% of precipitation, respectively. During a 2-year monitoring period, water percolated to the bottom of the deeper lysimeter very few times – only in winter or after extreme rainfall. Despite that, water table in the well rose even when there was no recharge through the soil profile with vegetation. As the water table rises corresponded to peaks in the piezometer, it is evident that they were caused by the localized infiltration from the rainwater drainage. We estimated groundwater recharge inside and outside the settlement using Water table fluctuation method and Soil moisture deficit model (Šabatová et al., 2025), and also compared it to an existing regional study of groundwater recharge. Our results suggest that groundwater recharge enhanced by the localized infiltration can be up to 4 times higher than natural recharge. Thus, localized infiltration from impervious surfaces can substantially improve the water balance in built-up areas. This is especially valuable in dry periods, because the localized infiltration appears to percolate rapidly, avoiding capture for evapotranspiration. Therefore, allowing the rainwater from impervious surfaces to infiltrate can contribute significantly to counter the increasing drought related to the climate change, especially in hardrock areas where groundwater is of local origin.

References

Šabatová, K., Bruthans, J., Weiss, T., 2025. New groundwater recharge model for water table fluctuation method calibration using easily available data. Journal of Hydrology 661, 133685. https://doi.org/10.1016/j.jhydrol.2025.133685

Acknowledgements

Contribution was supported by project SS02030040 "PERUN - Prediction, Evaluation and Research for Understanding National sensitivity and impacts of drought and climate change for Czechia", co-financed with state support of the Technology Agency of the Czech Republic as part of the Program Environment for Life.