Critical groundwater supplies may never recover from drought
Let this sink in

Date:
September 30, 2021
Source:
University of California - Riverside
Summary:
New research shows groundwater takes an average of three years to
recover from drought -- if it ever recovers at all. In the largest
study of its kind, scientists found that this recovery time only
applies to aquifers that aren't touched by human activity, and
the recovery time might be even longer in regions with excessive
pumping.



FULL STORY ========================================================================== Along with hurricanes and wildfires, there's another important, but
seldom- discussed effect of climate change -- toxic water and sinking
land made worse by groundwater drought.


========================================================================== Water from snow and rain seeps deep into the ground between layers
of soil and accumulates in sponge-like underground bathtubs, called
aquifers. Farmers rely heavily on this groundwater to irrigate their
crops when they can't get enough water from surface water sources.

Roughly 85 percent of Californians also rely on groundwater for some
portion of their water supply. Worldwide, an estimated two billion people depend on it.

However, excessive groundwater use combined with droughts has caused
land surface to sink, damaging critical infrastructure including roads, buildings, and sewage and water pipes.

New UC Riverside research shows groundwater takes an average of three
years to recover from drought -- if it ever recovers at all. In the
largest study of its kind, scientists found that this recovery time
only applies to aquifers that aren't touched by human activity, and the recovery time might be even longer in regions with excessive pumping.

For groundwater levels to recover after a drought, new precipitation
requires time to percolate through the soil and recharge the depleted
aquifer. The researchers show that this process can take several years
longer in areas with deeper groundwater levels.

"If people pump groundwater without first letting it recharge, groundwater levels keep going down, the cost of pumping goes up, and the land sinks," explained Hoori Ajami, UCR groundwater hydrologist and study co-author
and principal investigator on this project.



========================================================================== Published in the Journal of Hydrology,the new study is the first to
examine groundwater response to droughts on a continental scale. Previous investigations of groundwater drought have mostly relied on model
simulations and covered smaller areas. This study relied on 30 years of
daily measurements from 600 wells across the country.

On average, the researchers determined it takes about two years for
rainwater drought to become groundwater drought, though in some cases
it takes as long as 15 years. Because of the long lag time, the effects
aren't felt or seen immediately. However, they can be severe.

Groundwater drought combined with pumping can cause a gradual, uneven
lowering of the land surface called subsidence. "It is a known problem
in California's Central Valley, exacerbated by climate factors and
excessive water pumping," Ajami said. "Subsidence causes irreversible
damage to infrastructure, buildings and roads." As the ground shifts
and water level declines, contaminants in the soil, like arsenic, can
mobilize and poison the water. In coastal areas, aquifers depleted by
drought and pumping can fill up with salty sea water, making groundwater unusable for drinking or farming.

"You start with a problem of water quantity, and you end up with a
problem of water quality," Ajami said.

"Excessive pumping lowers the groundwater level, creating a downward
spiral in which restoring the aquifer becomes harder and harder," added
study co-author Adam Schreiner-McGraw.

To reduce the damage from prolonged droughts that are an inevitability
as the planet continues to warm, the researchers have several
recommendations. Most climate models show rain becoming more
intense. Storing rain waters could recharge aquifers, speeding up the
recovery process.

The researchers also suggest that farmers improve irrigation efficiency
and switch perennials like almonds, pistachios, and walnuts to annual,
less water- intensive crops in areas where groundwater depletion is
severe.

"We need to improve our climate projections to include groundwater,
so that we can better assess what we have and how to protect
it," Ajami said. "There are ways to better manage what we have." ========================================================================== Story Source: Materials provided by
University_of_California_-_Riverside. Original written by Jules
Bernstein. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Adam P. Schreiner-McGraw, Hoori Ajami. Delayed response of
groundwater to
multi-year meteorological droughts in the absence of anthropogenic
management. Journal of Hydrology, 2021; 603: 126917 DOI: 10.1016/
j.jhydrol.2021.126917 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210930082352.htm

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