RESEARCH
BRIEF
Credit: Courtesy Terranova Ranch Inc.

POINTS FOR POLICY MAKERS

MAY 2021

New Modeling
Framework Guides
Managed Aquifer Recharge
Under Climate Change
Combining a climate-informed hydrological model withnew basin classifications leads to better quantification andmanagement of water available for groundwater recharge.
Background
Current and future climate change effects are intensifying thehydrological cycle, leading to increased variability of bothprecipitation and runoff. This heightened pattern results in more
frequent and severe droughts and floods, as well as more recurrent
swings between these two extremes. Harvesting floodwaters using
managed aquifer recharge to replenish depleted groundwateraquifers can simultaneously reduce flood and drought risks.
However, the uncertainty around how much water will be available
for recharge has made it difficult to determine where efforts to
deploy this approach will have significant benefits – both at presentand in an unpredictable future climate.
Managed aquifer recharge (MAR) provides an innovative way toachieve integrated water management by improving the connectionsof surface-built infrastructure (e.g., reservoirs or canals) andunderground infrastructure (e.g., groundwater aquifers or wells) toManaged aquifer recharge or Flood-MAR is arelatively underutilized management strategy
compared with traditional surface water
infrastructure such as reservoirs. Growing
evidence has demonstrated the large potential
for underground water storage solutions suchas Flood-MAR, particularly when facing climatechange uncertainties. Flood-MAR augments
groundwater supply while also providing
multiple benefits, including flood risk reductionand ecosystem services enhancement. As
additional burdens are placed on California’s
aging water infrastructure systems,
incorporating strategies like Flood-MAR can be
more cost-effective, sustainable and adaptative.
Integrated water management strategies
can mitigate flood risk while also conserving
floodwater from wet periods to utilize during
future drought. Strategies that mitigate eachhazard in isolation tend to be less effective thanintegrated ones. In California, the geographic
mismatch between north and south in termsof water availability, as well as the changing
timing and magnitude of floodwaters, createsa challenge in moving flows from where they
are available to where they are needed. Making
the most of high-magnitude-flows for recharge
could provide balance and bring a large portionof depleted groundwater aquifers into balance inareas such as the San Joaquin Valley.
Climate-informed hydrological modelingcombined with basin-specific infrastructureassessments can inform management options.
This can also help prioritize the development
or enhancement of diversion infrastructure
despite significant uncertainties. It is critical tounderstand how water available for recharge islikely to vary depending on different policy andinfrastructure assumptions and the extent towhich these assumptions are subject to climate
and other hydrologic uncertainties. In addition,socio-technological, financial and environmental
feasibility may play equally or more importantroles in investment decisions.

transfer floodwater across regions and store it locally. Compared toconventional surface storage options, using floodwater for MAR –known as Flood-MAR – can be more cost-effective, sustainable andadaptive while also offering benefits such as flood risk reduction andecosystem services enhancement.
Despite increases in future projected water availability, differences
between existing infrastructure capacity and policy uncertainties
constrain how much water can be captured. To tap anticipatedrecharge potential through infrastructure expansion while dealing
with increasing uncertainties, a Stanford-led research teamdeveloped a climate-informed and policy-relevant framework
to quantify floodwater availability in California. The researchers
additionally devised a basin classification system that considers
existing constraints on deployment together with hydrologic
potential under uncertain climate futures to identify priority areas ofinfrastructure investment needs.
Adapting to heightened climate-related risk will requiretransformational changes to existing water management practices
to successfully manage droughts, floods and restore depleted
groundwater aquifers simultaneously. Employing a modelingframework based on water available for recharge can inform effective
investment decisions by policy makers and water resource managers.
It also allows for adaptation to future climate-fueled drought andflood risk over depleted aquifers in California, as well as in similarhydrologic regions across the U.S.

An aerial of the East Branch California Aqueduct in northern Los Angeles County.

ABOUT THE AUTHORS

Xiaogang He
Xiagang He is a researchcollaborator with Water inthe West.

Benjamin Bryant
Benjamin Bryant is a researchcollaborator with Water in
the West.

Tara Moran
Tara Moran is a researchcollaborator with Water inthe West.

David Freyberg
David Freyberg is anassociate professor ofcivil and environmental
engineering at Stanford andsenior fellow at the Stanford
Woods Institute for theEnvironment.

This brief is based on Climate-informed hydrologic
modeling and policy typology to guide managed
aquifer recharge published in Science Advances.

FOR MORE INFORMATION
Water in the West
Stanford University
waterinthewest@stanford.edu
waterinthewest.stanford.edu
Credit: California Department of Water Resources