Drought effects and critical groundwater recharge

A race against time: is the rate of rainfall managed aquifer recharge fast enough for drought recovery?

Published in the Journal of Hydrology, new research by University of California, Riverside (UCR) environmental scientists shows that on average, groundwater takes three years to recover from drought — if recovery occurs. In addition, this recovery time only applies to aquifers untouched by human activity.

For groundwater levels to recover from a drought, rainfall needs time to percolate through the soil and recharge the depleted aquifer. The recovery process may be several years longer in regions with excessive pumping and thus, more declined levels of groundwater.

Continual pumping “without first letting (groundwater) recharge” means “the cost of pumping goes up and the land sinks,” explained Dr. Hoori Ajami, Associate Professor of Groundwater Hydrology and principal investigator on this project.

The study is the first to examine groundwater response to droughts on a continental scale. Past investigations of drought effects on groundwater have focused on smaller areas, and they mostly relied on model simulations. The UCR study takes into account 30 years of daily measurements from 600 wells across the U.S.

Researchers determined about two years for rainwater drought trigger groundwater drought. In some cases, up to 15 years of rainfall drought occurred before an aquifer was affected. Like the majority of things underground, effects aren’t observable even though they can be severe.

“Subsidence causes irreversible damage to infrastructure,” said Ajami who added that the gradual, uneven lowering of the land surface is being “exacerbated by climate factors.”

Another concern is groundwater quality. As ground shifts and water level declines, contaminants from soil can be transported into the water. Coastal communities also contend with sea water intrusion, contaminating underground freshwater supplies.

The Public Policy Institute of California reports that groundwater supplies “nearly 40% of water used by farms and cities in the state and that 85% residents rely on groundwater for some portion of their water supply.”

On a global scale, an estimated two billion people depend on it. Excessive groundwater use combined with droughts has caused land surface to sink, damaging critical infrastructure including roads, buildings, and sewage and water pipes beyond California.