ArticlePDF Available

Lessons from California’s 2012–2016 Drought

October 2018
Journal of Water Resources Planning and Management 144(10)

DOI:10.1061/(ASCE)WR.1943-5452.0000984

Authors:

Josué Medellín Azuara

University of California, Merced

John R. Durand

University of California, Davis

Kathleen Stone

The Ohio State University

California's 5-year drought has ended, even as its aftermath lingers. From 2012-2016 much or all of California was under severe drought conditions, with greatly diminished precipitation, snowpack, and streamflow and higher temperatures. Water shortages to forests, aquatic ecosystems, hydroelectric power plants, rural drinking water supplies, agriculture, and cities caused billions of dollars in economic losses, killed millions of forest trees, brought several fish species closer to extinction, and caused inconvenience and some expense to millions of households and businesses. The drought also brought innovations and improvements in water management, some of which will better prepare California for future droughts. This paper summarizes the magnitude and impacts of the 2012-2016 California drought. The paper then reviews innovations arising from the drought in the larger historical context of water management in California. Lessons for California and for modern drought management are then discussed. Droughts in modern, well-managed water systems serving globalized economies need not be economically catastrophic, but will always have impacts and challenges, particularly for native ecosystems. In California and every other water system, droughts usefully expose weaknesses and inadequate preparation in water management. In this regard for California, managers of ecosystems and small rural water supplies had the most to learn.

. Major water project deliveries 2011-2017

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. Summary of agriculture impacts of the 2015 California drought

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. Delta export pumping during drought

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. Historical droughts in California, their impacts, innovations, and leading innovators

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Lessons from California’s 2012–2016 Drought

Jay Lund, Dist.M.ASCE1; Josue Medellin-Azuara, M.ASCE2; John Durand3; and Kathleen Stone4

Abstract: California’s 5-year drought has ended, even as its aftermath lingers. From 2012–2016 much or all of California was under severe

drought conditions, with greatly diminished precipitation, snowpack, and streamflow and higher temperatures. Water shortages to forests,

aquatic ecosystems, hydroelectric power plants, rural drinking water supplies, agriculture, and cities caused billions of dollars in economic

losses, killed millions of forest trees, brought several fish species closer to extinction, and caused inconvenience and some expense to millions of

households and businesses. The drought also brought innovations and improvements in water management, some of which will better prepare

California for future droughts. This paper summarizes the magnitude and impacts of the 2012–2016 California drought. The paper then reviews

innovations arising from the drought in the larger historical context of water management in California. Lessons for California and for modern

drought management are then discussed. Droughts in modern, well-managed water systems serving globalized economies need not be

economically catastrophic, but will always have impacts and challenges, particularly for native ecosystems. In California and every other

water system, droughts usefully expose weaknesses and inadequate preparation in water management. In this regard for California, managers

of ecosystems and small rural water supplies had the most to learn. DOI: 10.1061/(ASCE)WR.1943-5452.0000984.This work is made

available under the terms of the Creative Commons Attribution 4.0 International license, http://creativecommons.org/licenses/by/4.0/.

Introduction

Drought is a temporary reduction in water availability below

normal quantities. Droughts can be for only a few weeks or endure

for years or centuries—in which they blend with changes in cli-

mate. In rain-fed agricultural systems, droughts of a few weeks

can be devastating. Places such as California, with a long summer

dry season and a Mediterranean climate, each year face what would

be the worst drought ever seen in more humid American states.

From 2012 to 2016, California experienced one of its deepest,

longest, and warmest historical droughts. Many effects from this

drought to forests, native fish populations, groundwater levels, and

land subsidence will endure for decades. Lessons and innovations

from the drought also will last for decades and improve California’s

ability to manage future droughts. Past and future droughts are

always present in managing water in California. California enters

each drought with management institutions, policies, infrastructure,

water storage conditions, and water demands influenced by past

droughts. Future droughts are also in the minds of water managers

as they make agreements, contracts, storage, infrastructure, and

marketing decisions to dampen potential drought impacts.

Drought has always been a risk to humans and natural organ-

isms. Historically, drought has shaped and destroyed civilizations

and ecosystems. Droughts and sometimes-accompanying climate

change have been implicated in the decline and fall of civilizations

(Shimada et al. 1991;Douglas et al. 2015;Krieger 2014;

Staubwasser et al. 2003;Drysdale et al. 2005;Fagan 2009;Weiss

1997). For ecosystems, droughts can be pivotal events when

invasive species become established or shifts occur in species

composition (Winder et al. 2011). Yet, western US water manage-

ment systems have become much more robust and adaptive than is

commonly thought (Fleck 2016).

The onset of drought is slow. The water stored in soils, slowly

diminishing springs, reservoirs, and aquifers dampens the onset of

drought. The duration of droughts in California can be long and

uncertain, perhaps lasting years, decades, and even centuries,

compared with hours to days for fires and floods or minutes for

earthquakes (Stine 1994). Therefore, signaling the onset and end

of drought can be messy. Drought onset is usually slow, varying

in local intensity, with an uncertain and often varying duration. Like

all forms of disaster, preparation greatly diminishes drought losses,

and organization is central to effective preparation and response.

For humans, the impacts of drought vary with economic, infra-

structure, and institutional conditions, as well as the drought’s

hydrologic characteristics. The economic effects of drought depend

on the economy’s reliance on water and the extent of regional and

global trade. Global economic connections greatly reduce the

impacts of drought (Sumner 2015;Lund 2016a). Global food

trade largely eliminates the existential threats of drought to civili-

zations, and greatly eases drought’s economic and public health

impacts. Infrastructure networks and institutions that store, move,

and reallocate water flexibly also greatly reduce drought impacts

(Lund 2016a). Regional hydrologic characteristics, such as large

freshwater aquifers, can dampen drought effects.

However, actions taken to minimize the impact of drought for

humans often further jeopardize vulnerable ecosystems and other

environmental resources. California has arguably restructured its

infrastructure and economy to accommodate droughts, but many

of these actions have further altered habitats and streams in ways that

harm native species, which once were well adapted to California’s

droughts using once-vast habitats connected to snowmelt, springs,

groundwater, and seasonal floodplains. Losses to native species

populations during drought are often not recovered before the next

drought.

1Professor, Dept. of Civil and Environmental Engineering, Univ. of

California, Davis, CA 95616 (corresponding author). Email: jrlund@

ucdavis.edu

2Acting Associate Professor, Environmental Systems Engineering,

Univ. of California, Merced, CA 95343. Email: jmedellin-azuara@

ucmerced.edu

3Assistant Research Scientist, Center for Watershed Sciences, Univ. of

California, Davis, CA 95616. Email: jrdurand@ucdavis.edu

4Graduate Student, Dept. of Civil and Environmental Engineering,

Univ. of California, Davis, CA 95616. Email: katstone@ucdavis.edu

Note. This manuscript was submitted on January 2, 2018; approved on

April 24, 2018; published online on July 30, 2018. Discussion period open

until December 30, 2018; separate discussions must be submitted for

individual papers. This paper is part of the Journal of Water Resources

Planning and Management, © ASCE, ISSN 0733-9496.

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

This paper reviews California’s most recent drought, and places

it in an historical and global context. Lessons are drawn for

California and for drought management globally. Despite problems

and revealed weaknesses, well-prepared water systems within

globalized economies usually weather drought fairly well and

improve over time with exposure to such extremes.

2012–2016 Drought’s Hydrology

The California drought of 2012–2016 was unusually dry and warm

with a frequency estimated between once in 20–1,200 years. As a

large diverse state, this range of estimates is reasonable. The drought’s

unusually high temperatures depleted soil moisture more rapidly,

yielding a drought frequency estimate of 1 in 1,200 years, relative

to past temperatures (Griffin and Anchukaitis 2014). Snowpack also

diminished from high temperatures, witha frequency estimate of 1 in

500 years, assuming past temperatures (Belmecheri et al. 2016). The

drought was frequently the worst of record by many metrics, but local

assessment varies widely with location, area, and drought metric. Far

longer and more severe droughts occurred in the Middle Ages (Stine

1994). Regional precipitation, streamflow, and water delivery reduc-

tions, relevant for regional water supplies, were often new lows, but

more frequently have been seen with approximate frequencies of 1 in

15–30 yearsacross the state (Lund 2016a). The drought was unusually

dry, hot, and severe, by any reckoning.

The drought’s higher temperatures are important for how man-

agers, engineers, and scientists prepare for future droughts. Warmer

temperatures accounted for as much as 25% of the drought’s

cumulative moisture deficit (M. Dettinger, personal communica-

tion, 2017) and certainly reduced soil moisture and snowpack,

reduced cold water in reservoirs, and increased river temperatures

(Hanak et al. 2015b;Mount et al. 2017).

The California drought was caused largely by the formation of a

“ridiculously resilient ridge”of high pressure in the Pacific Ocean off

California, diverting atmospheric moisture away from California.

The climatological causes of this ridge will be debated for some time

(Swain 2015;Singh et al. 2016;Swain et al. 2017). The persistence

of such a deep drought for several years over California is unlikely to

be entirely random and is likely to have connection with some more

Pacific-wide and global climate processes (Teng and Branstator

2017). Climate warming is thought to have had some role

(Diffenbaugh et al. 2015) and the pattern is consistent with predic-

tions of climate change downscaled to California (Cayan et al. 2008;

Dettinger 2005).

California already has an unusually variable climate. The litera-

ture suggests that climate warming will magnify both the frequency

and magnitude of floods and droughts in California. The warmer

temperatures of the most recent drought might be a harbinger

for future drought and nondrought years with climate warming.

Higher temperatures will worsen many drought impacts, especially

for soil moisture, snowpack, streamflow, and temperature-sensitive

ecosystems.

Water Deliveries

The drought reduced water deliveries from local, regional, state,

and federal water projects at a time of historically high water

demands. Table 1summarizes the reductions in Central Valley

Project and State Water Project deliveries for each year of the

drought (2012–2016) as well as the wet years before and after

the drought (2011 and 2017), showing the drought’s development.

Even in wet years (2011 and 2017), the water projects cannot

satisfy all water demands. In addition, different water users are

often shorted differently, reflecting different legal priorities due to

legislation and/or preproject water rights (e.g., Sacramento Valley

“Settlement”and San Joaquin River “Exchange”contracts).

As the drought wore on, the water projects had less stored water

and reduced their deliveries, reaching a low in 2014 and 2015. In

these years, some water contractors (particularly Friant) received

zero deliveries for the first time since the project began in the

1950s, and sometimes lacked alternative water sources, forcing

users to drill new wells or purchase water from others with a

contract allocation. Such adaptations reduced shortages and costs

for many areas but brought their own costs and consequences.

Many other local and regional water suppliers, which provide

most water used by Californians, were affected by the drought.

Some were less affected, due to sizable upstream reservoirs

Table 1. Major water project deliveries 2011–2017

Year State water project (SWP)aCentral Valley project (CVP)b

2011 80% 100%, except south of Delta junior agricultural contractors (e.g., Westlands) 80%

2012 65% 100%—North of Delta, wildlife refuges, San Joaquin Exchange,

and Eastside (New Melones) contractors

75%—South of Delta urban

50%—Friant; 40%—south of Delta junior agricultural contractors

2013 35% 100%—Wildlife, San Joaquin Exchange, and Eastside contractors

75%—North of Delta agriculture and settlement

70%–75%—Urban; 62%—Friant; 20%—south of Delta agricultural

2014 5% 75%—Sacramento Valley settlement and wildlife refuges

65%—San Joaquin Exchange contracts and wildlife refuges

55%—Eastside (New Melones) contractors; 50%—urban

0%—Other agricultural contracts (including Friant, Westlands)

2015 20%, except north of

Delta urban 22–28%

75%—Sacramento Valley settlement, wildlife, San Joaquin Exchange

contracts; 25%—urban

0%—Eastside (New Melones) and other agricultural contracts

2016 60%, except north of

Delta urban 60–100%

100%—North of Delta, wildlife, San Joaquin Exchange contracts

75%—Friant; 55%—urban; 5%—south of Delta agriculture

0%—Eastside (New Melones) contractors

2017 85%, except north of

Delta urban 100%

100%, all

aData from California Department of Water Resources (2018a).

bData from US Bureau of Reclamation (2018).

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

(e.g., Solano County and Colorado River users), banked ground-

water, or water market transfers and conservation (particularly in

cities in southern California and the San Francisco Bay areas). Some

isolated local water supplies were more deeply affected.

Major Problem Areas

Droughts test water systems. The 2012–2016 drought was broad and

deep enough to test all water management sectors in California.

Areas with the most severe impacts, in rough economic order, were

agriculture (particularly San Joaquin Valley), forests, hydropower,

rural groundwater supplies, recreation, the Sacramento-San Joaquin

Delta, aquatic ecosystems, protected fisheries management, and

cities (particularly hydraulically isolated cities). The state’s water

accounting and water rights administration systems were also tested.

Agriculture

The drought was statewide and much of California’s agriculture

saw substantial drought effects, although local groundwater buf-

fered most agricultural impacts (Howitt et al. 2014,2015a,b;

Medellín-Azuara et al. 2015a;Medellín-Azuara et al. 2016). Of

the approximate 30% drought reduction of surface water available

for agriculture statewide, about two-thirds was replaced by addi-

tional groundwater pumping, adding approximately $600 million

per year in pumping costs (Table 2for 2015). The remaining

10% shortage in statewide agricultural water use was accommodated

by fallowing or idling about half a million acres (approximately 6%

of statewide irrigated crop area) and through stress irrigation of

crops, shifting crops, and improving irrigation efficiencies.

Total direct statewide economic losses to agriculture from the

drought were approximately $3.8 billion for 2014–2016 (Howitt

et al. 2014,2015b;Medellín-Azuara et al. 2016). Estimates are

unavailable for the less severe years of 2012–2013. This included

lost net revenues from crop production, dairy and livestock, and

additional pumping costs.

Statewide crop revenue losses were approximately $1.7 billion

in 2014–2015, the deepest 2 years of the drought (Howitt et al.

2014,2015a,b), for an approximate $45 billion dollar/year agricul-

ture industry. Seventy-two percent of these losses were in the

southern Central Valley (15% in the San Joaquin basin and 57%

in the Tulare basin). These losses were concentrated in parts of

the Valley lacking access to good groundwater. Agricultural areas

adapted to the drought by fallowing sizable acres of annual crops,

reducing irrigation applications to some crops (stress irrigation),

and shifting some annual crops to new orchards (with approxi-

mately 40% less water use in their first years) (Sanchez 2017).

Lower groundwater elevations from the drought will increase

groundwater pumping costs for many years in parts of the southern

Central Valley, with higher costs for dry wells and lost infrastruc-

ture capacity from subsiding land above heavily overdrafted aqui-

fers (MacEwan et al. 2017).

The drought greatly increased overdraft-related land subsidence,

a long-term problem in parts of the San Joaquin Valley (Faunt and

Sneed 2015;Sneed et al. 2013;Borchers et al. 2014). In some

areas, new land subsidence approached several feet during the

drought. The greatest economic impact of subsidence has been

reduced conveyance capacities for some major San Joaquin Valley

canals by up to 60% (Farr et al. 2017;Friant Water Authority

2017). Ironically, another major impact of drought-related sub-

sidence is disrupting slopes that reduce floodway capacities. This

groundwater-caused land subsidence is mostly from one-time

dewatering of aquifer clay layers with little reduction in ability to

recharge aquifers (Borchers et al. 2014).

Forests

Perhaps the greatest impact of California’s drought was the death of

102 million forest trees, which depend on soil moisture accumulated

in the wet season for growth during the spring and summer (US

Forest Service 2016;Stevens 2016). Low precipitation and snow-

pack greatly reduced soil moisture, and higher temperatures accel-

erated soil moisture depletion. Drier, weakened trees became more

susceptible to disease and insect infestations. Similar losses of forest

trees occurred from the shorter 1976–1977 drought (DWR 1978).

With a warming climate, this drought might be pivotal for eco-

logical changes in California’s forests, particularly in tree density

and species composition (Young et al. 2016). The millions of dead

trees in California’s forests has implications for wildfires, erosion,

and public safety. The economic costs of these forest impacts from

drought have not been estimated, but will continue to affect eco-

systems, fire, and public safety for many years. Costs from addi-

tional wildfires and their public health impacts could become the

largest economic and public health impact of the drought, spread

years after the drought ends.

Hydropower

California’s hydropower production is closely tied to annual runoff

upstream of hydropower plants, with little over-year water storage

(Madani and Lund 2009). Higher energy prices in the summer

encourage hydropower reductions in other seasons, which is fortu-

nately compatible with summer releases for downstream water

supplies.

The deepest years of the drought (2014–2015) reduced hydro-

power production by more than 50% from its long-term average,

going from about 13% of California’s electricity use to about 5%

(Table 3). The economic cost of this lost hydropower from substitut-

ing more expensive gas–turbine generation was approximately

$2 billion, plus additional air pollution and greenhouse gasses

(Gleick 2016). California’s 2015 hydropower production was almost

as low as in the short deep drought of 1976–1977 (DWR 1978).

Rural Groundwater Supplies

The drought increased attention to problems of small water systems

and rural domestic wells (Grossi 2017). These smaller systems lack

Table 2. Summary of agriculture impacts of the 2015 California drought

Description Base year Drought change % change

Surface water supply

(109m3)

22.2 10.7 loss −48%

Groundwater use (109m3) 10.4 8.0 increase 72%

Net water use (109m3) 32.6 3.3 reduction −10%

Drought-related idle

land (hectares)

500,000a225,000 more 45%

Crop revenue ($) $35 billion $900 million loss −2.6%

Dairy and livestock

revenue ($)

$12.4 billion $350 million loss −2.8%

Groundwater pumping

cost ($)

$780 million $590 million rise 75.5%

Direct costs ($) N/A $1.8 billion loss N/A

Total economic impact ($) N/A $2.7 billion loss N/A

Direct farm jobs 200,000b10,100 loss 5.1%

Total job losses N/A 21,000 loss N/A

Source: Data from Howitt et al. (2015b).

aNASA-ARC estimate of normal Central Valley idle land.

bTotal agriculture employment is about 412,000, of which 200,000 is farm

production.

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

economies of scale and are frequently poorer and less well organ-

ized. These factors make rural water systems (and rural public

services generally) more vulnerable to high costs, contamination,

operation and maintenance problems, and drought. Rural water

systems typically depend on shallower wells. Unlike larger water

systems, small systems are not required to have drought contin-

gency plans. Additionally, most small systems lack emergency

or permanent connections to other water systems that can help

during droughts.

As nearby water users with deeper wells pumped more during

the drought, many rural households and small communities found

their wells going dry. Tulare County alone reported almost 2,000

domestic well failures in 2015 (Tulare County 2017). Costs for

additional pumping and rehabilitation for domestic and community

wells in Tulare County from drought-related groundwater declines

were estimated to be $10–$18 million. Further costs occurred from

actual dry wells. Overall, these costs are greater than for previous

droughts due to lower initial groundwater levels (Gailey 2018;

Kwon 2017;Medellín-Azuara et al. 2016).

Many small water systems were unprepared for the drought

(Fencl and Klasic 2017). Bottled water was often used or potable

water was delivered by trucks for household storage tanks (Hanak

et al. 2015b). Various state departments provided financial and

technical assistance for private domestic well owners and small sys-

tems with drought-related issues (Fencl and Klasic 2017). The

Draft Executive Order Framework, issued by the California Depart-

ment of Water Resources, gives counties 2 years to determine how

to provide drought supplies for households currently outside of the

drought contingency plans (Fencl and Klasic 2017).

Recreation

Outdoor recreation also suffered from the drought. The skiing

industry was particularly affected by the lack of snow and higher

temperatures, particularly in 2014–2015, with shorter seasons and

significantly fewer customers (Barber 2015;Kirkpatrick 2015).

Whitewater rafting was somewhat buffered by upstream reservoirs.

Lake recreation was affected by lower reservoir levels, particularly

in 2014–2015. Some marinas in the Delta were overrun by alien

aquatic plants prohibiting boat passage (Durand et al. 2018). No

detailed analysis or quantification has been done on the effects

of drought on recreation for the 2012–2016 drought. A California

Department of Water Resources report on the 1976–1977 drought

demonstrates such an analysis (DWR 1978).

Sacramento–San Joaquin Delta

The Sacramento–San Joaquin Delta is the major hub of California’s

water system and a continuing source of controversy (Lund et al.

2010;California Department of Water Resources and US Bureau

of Reclamation 2016). During the drought, low inflows from

northern California greatly reduced the ability to move water

from wetter northern California to drier southern regions and

San Francisco Bay area cities. Water exports from the Delta were

greatly reduced. In 2011, before the drought, Delta water exports

peaked at 6.5 MAF, dropping to 1.8 MAF during the worst year of

the drought (Table 4).

In May 2015, DWR installed a temporary rock barrier to close

False River in the western Delta to reduce the need for additional

freshwater outflow to San Francisco Bay to maintain low salinity in

the central Delta. The barrier was removed in October 2015. This

followed decades of permanent flow barrier studies from the 1920s

(Lund et al. 2010) and annual use of seasonal barriers in the

southern Delta for fish and agricultural water quality purposes since

the 1990s, use of temporary drought barriers in the 1976–1977

drought, and proposals for drought barriers in the 2009 and

2014 drought years (California Department of Water Resources

2009). The barrier helped maintain only slightly relaxed water-

quality standards for Delta agriculture and urban use and some

south of Delta water exports with reduced fresh water releases from

upstream dams. The barrier affected in-Delta water quality and flow

circulation, which continue to be studied (Durand et al. 2018).

Export of zooplankton from the south Delta to Suisun Bay may

have slightly reduced summer food resources for the Delta smelt.

In addition, reduced water circulation may have increased salinity

in the lower San Joaquin River.

Regulatory Delta outflows to support native ecosystems were

also reduced during the drought by the State Water Board, allowing

the salinity zone to move eastward. This reduced environmental

outflows by about 1.4billion m3(1.1 million acre-ft, MAF) over

the drought, but did not greatly reduce in-Delta water quality

for export, agriculture, and urban use (Gartrell et al. 2017a,b).

Much of this saved outflow was retained in reservoirs for potential

additional dry years. At market prices for water south of the Delta

(over $0.8=m3,$1,000=acre-ft), this amounted to approximately

$1 billion worth of environmental water made available for water

users and storage. Populations of native fish in the Delta continued

to decline during the drought. Considerable controversy resulted

from the uncompensated reductions in environmental flows to

favor other water users (State Water Resource Control Board

2015;Lund et al. 2014;Lund and Moyle 2014). State and federal

regulations specify Delta water quality standards, export limita-

tions, and salinity gradient location.

Aquatic Ecosystems

The benefits of organization and preparation for drought are evident

in comparing drought management for urban and agricultural uses

with fish and waterfowl in the drought (Hanak et al. 2015b;Moyle

and Qui˜nones 2014;Jeffries et al. 2016). From 2013 to 2016,

Table 3. Hydropower production in California during drought

Year

Net production

(GWH)

Average

hydropower

(%)

Hydropower percentage

of 2015 state electricity use

2011 42,731 124 16

2012 27,459 80 11

2013 24,097 70 9

2014 16,476 48 6

2015 13,992 41 5

2016 28,977 84 11

2017 43,333 126 16

1983–2016

Average

34,338 100 13

Source: Data from California Energy Commission (2017a,b).

Table 4. Delta export pumping during drought

Water year Delta export pumping, 109m3(maf)

1986–2010 average 6.2 (5.0)

2011 8.0 (6.5)

2012 5.8 (4.7)

2013 4.9 (4.0)

2014 2.3 (1.9)

2015 2.2 (1.8)

2016 4.0 (3.3)

2017 7.6 (6.2)

Source: Data from California Department of Water Resources (2018b).

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

drought emergency ecosystem support spending totaled $66 million

and $67 million from the state and federal governments. Lack of

drought preparation for the environment increased the severity of

the effects on ecosystems (Hanak et al. 2015b).

California supports 129 species of freshwater fish. Approxi-

mately two-thirds of these species are found only in California.

Most of these species are either currently endangered or at risk

of becoming endangered (Moyle et al. 2011;Hanak et al. 2015b).

Low flows and high temperature from the drought reduced water

quality and impaired habitat for native fish species. Additionally,

the drought’s lower flows, longer water residence times, and higher

temperatures supported expansions of some invasive species, par-

ticularly aquatic vegetation (Durand et al. 2018). Intervention by

the State Water Resources Control Board required some to reduce

surface-water diversions or groundwater pumping, which affects

flows in some salmon and steelhead streams. However, the State

Water Resources Control Board also temporarily voided at least

35 environmental flow regulations during the drought (Hanak

et al. 2015b;Mount et al. 2017).

Salmon populations suffered from higher temperatures and re-

ductions of flow during the drought. The hardest-hit was the winter

run of Chinook salmon, which historically spawned in cold water,

high in the upper Sacramento River watershed. They are now dis-

placed and reduced to habitat below Shasta Dam, where spawning

is supported by cold water from the bottom of the reservoir. During

the previous long drought (1991), cold water from the reservoir be-

came depleted and caused high egg and juvenile mortality, leading

to their official listing as an endangered species, construction of a

temperature-mixing control device on Shasta Dam, and regulatory

and operational changes for Shasta Dam. During the first years of

the 2012–2016 drought, the cold water available behind Shasta Dam

was enough to maintain spawning and rearing habitat. However, by

2014, lower reservoir levels, higher temperatures, and various man-

agement problems depleted cold water behind Shasta Dam before

the outmigration of juveniles, leading to substantial elimination of

that year’s cohort of winter-run salmon. Despite the attention from

this failure, a similar result occurred in 2015, the drought’s deepest

year. Juvenile salmon populations in these 2 years were supported

mostly by refuge hatchery releases (Durand et al. 2018).

Regarding waterfowl, California is a primary stop on the Pacific

Flyway (Hanak et al. 2015b;Mount et al. 2017). However, draining

of most natural wetlands in California has limited waterfowl to

wetlands managed as state and federal refuges, private land, duck

hunting clubs, and flooded farmland. Decreased drought water

allocations for managed wetlands reduced fall and winter habitats

for waterfowl. Wildlife refuges throughout the state collaborated to

identify where water supply should be allocated to best support

waterfowl habitat (Hanak et al. 2015b;Mount et al. 2017).

Isolated Cities

Cities isolated from California’s intertied water system had fewer

options to prepare for and adapt to drought. Santa Cruz in 2014

required a 30% mandatory use reduction as local water supplies

became depleted without other recourse (City of Santa Cruz

Water Dept. 2016). This was the first sizable city forced to man-

datory rationing by the absence of water during the drought. Late in

the drought, Lake Cachuma, the primary water source for Santa

Barbara County, was expected to empty, despite increased supplies

acquired from a small connection to the State Water Project. In

2016, the City of Santa Barbara required a 30% water-use reduction

and restrictions on residential and commercial water uses (City of

Santa Barbara 2017). The city banned all residential lawn irrigation

in January 2017 (McPhate and Medina 2016), lifting the ban in

March 2017 as Lake Cachuma began to refill.

Cities better connected to other supplies were more able to

prepare and adapt to drought. Urban utilities in the San Francisco

Bay Area and southern California served by the State Water Project

and Central Valley Project faced 80%–95% reductions in water

allocations for 2014–2015. These cities responded with sizable

voluntary water conservation actions, withdrawals from water

stored in reservoirs and banked in local and distant groundwater

basins, water purchased from more senior agricultural water users,

and purchases or exchanges from neighboring water systems

(Alameda Zone 7 2015;SCVWD 2016;ACWD 2016;MWDSC

2015;CCWD 2016). Water banked with agricultural water districts

in the Tulare basin provided particularly important replacement ur-

ban water supplies. These preparations and interties to neighboring

areas greatly reduced drought impacts, largely from agreements

and interties developed since the 1988–1992 drought.

Water Accounting and Water Rights Administration

The 2012–2016 drought highlighted California’s lack of a coherent

water accounting system (Hanak et al. 2014;Escriva-Bou et al.

2016). Although water systems are connected by conveyance

networks and hydrologic processes, these water systems are

governed and regulated independently with separate water account-

ing systems. During the drought, legislators and state regulators

directed several efforts to incrementally improve water accounting

policies (Escriva-Bou et al. 2016).

The 2014–2015 water years were the first since the 1976–1977

drought when junior water rights were formally curtailed by the State

Water Board. The 2014–2015 curtailments were made easier by

2009 legislation requiring all water-right holders, not just those hold-

ing post-1914 state permits, to report monthly water use. By 2014,

the first years of these new data were becoming available. In 2015,

Senate Bill 88 required surface-water-right holders to measure and

report their monthly diversions annually (Escriva-Bou et al. 2016).

The 2014 Sustainable Groundwater Management Act (SGMA) also

created a timeline for local groundwater accounting and regulation,

with potential state agency enforcement. Similarly, government

agencies began expanding environmental flow regulations.

Although some water accounting policy improvements occurred

during the drought, further actions are needed to establish broadly

effective water accounting in California. These actions include de-

termining water availability, water rights and use quantities, and

creating transparent and coherent water balance and information

systems (Escriva-Bou et al. 2016).

Some of the biggest impacts of the 2012–2016 California

drought were similar to those of the 1976–1977 drought, a shorter

drought containing the driest year on record. An excellent assess-

ment of the 1976–1977 drought found that the biggest economic

impacts were for agriculture, forests, and hydropower production

(DWR 1978). These sectors are inherently water-intensive and

can react to water losses almost exclusively by reducing produc-

tion. In the case of forest impacts, little can be done to substantially

manage or compensate for drought impacts (Butsic et al. 2017).

Water-based recreational losses are also direct and often difficult

to manage. Most problematic areas tended to be less well organized

institutionally and less well funded, such as the environment.

Why So Little Economic Impact from Drought in

California?

Perhaps the biggest lesson from the drought is how small the

economic impacts of drought were relative to the size of the

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

hydrologic event. Total economic losses, on the order of $10 billion

over 5 years, were less than 0.09% of the state’s $2.3 trillion/year

economy. The drought’s statewide economic impact was less than

the effects from business cycles, federal policies, and international

exchange rates. California’s statewide economy was substantially

adaptable and robust for a temporary loss of approximately one-

third of normal water supplies. Modeling studies show substantial

economic adaptability and robustness to still longer and deeper

droughts (Harou et al. 2010).

Preparation

This was not California’s first drought. California’s long history of

drought has led to the accumulation of infrastructure, institutions,

and changes in water demands adapted to droughts (Pisani 1984;

Lund 2016c).

Perhaps the best illustration of successful preparation is the con-

trast of urban drought impacts from California’s 1988–1992

drought and the most recent drought. The 1988–1992 drought

brought deep widespread impacts to urban areas, often with man-

datory cutbacks of 20–30%. Following the 1988–1992 drought,

cities individually, regionally, and with state support instituted

more effective and permanent water conservation, regional intertie

pipelines, local water storage projects, groundwater storage, waste-

water reuse, water market arrangements, and contingency plans

(Lund 2014b,2015e,2016c). As a result, of major cities, only Santa

Cruz and Santa Barbara were forced to implement mandatory water

conservation by lack of water.

For all other cities and years, urban conservation efforts were

voluntary, except for 2015, the drought’s fourth and deepest year,

when the Governor required 25% urban use reductions, given

prospects for additional dry years. These state-required cutbacks

varied locally by per-capita water-use rates from 8 to 40%. Given

the high proportion of urban water use for landscape irrigation

(discussed subsequently), the overall economic impact of this

1-year 25% urban water-use reduction was very small (Lund

2015a,b,c,d).

Groundwater Supplies for Agriculture

Most agriculture in California is blessed with large underlying

freshwater aquifers, particularly in the Central Valley, which pro-

vides substantial drought water storage. Statewide surface reservoir

storage capacity is approximately 52 billion m3(42 MAF), but

total groundwater storage is approximately 500 billion m3(400

MAF), making groundwater the main stored water source for long

droughts. Additional groundwater pumping supplied more than

70% of the drought reductions to agriculture’s water supply.

However, long-term overdraft of approximately 2.5billion

m3=year (2MAF=year) undermines the availability of ground-

water for future droughts. In the San Joaquin Valley, groundwater

overdraft is about 17% of the total water supply (Arnold et al.

2017). The 2012–2016 drought highlighted groundwater’s impor-

tance as a long-term and drought source, and the need to protect

groundwater availability. This spurred passage of California’s

Sustainable Groundwater Management Act of 2014, which requires

reaching basin groundwater sustainability by 2040. An average net

reduction of consumptive use of approximately 2.2billion m3=year

(1.8MAF=year) in the San Joaquin Valley will be needed to main-

tain groundwater for future droughts. Permanent fallowing of some

irrigated areas, additional groundwater recharge in wetter years,

and pressure to import additional water can be expected (Hanak

et al. 2017;Nelson et al. 2016).

Economic Structure

California’s economic structure tremendously reduces drought vul-

nerability. Growth in California’s economy has been greatest in less

water-consuming sectors for many decades. In the 1920s, agricul-

ture was about 30% of California’s employment, and is less than 4%

today. Manufacturing has shifted to less water-consuming methods,

and the service sector, where most growth has occurred, requires

relatively little water. These changes make California’s economy

overall much less dependent on abundant water supplies and less

affected by drought water shortages. This shift has been driven by

technological modernization, as well as economic globalization.

Globalization of California’s agricultural sector was particularly

effective in reducing drought impacts (Lund 2016c;Sumner 2015;

York and Sumner 2015;Lund 2015b). Although the drought idled

hundreds of thousands of crop acres and markedly reduced farm

revenues, the drought’s effect on the statewide agricultural

economy was relatively small. During the drought, farmers reduced

economic losses by allocating water to higher-valued crops, where

California has a large share of national and global production

(Sumner 2015;York and Sumner 2015). Production and market

prices for these specialty crops (particularly almonds) were strong

during the drought, which bolstered agricultural revenues and em-

ployment (Medellín-Azuara et al. 2015b). California’s food staples,

which are marketed more globally, saw no higher prices due to

drought.

Sizable Lower-Valued Water Uses

Although California has a globalized economy, in which primary

agricultural production is a small share of GDP, agriculture is a

major source of income and employment in rural areas and the

Central Valley. Agricultural water use is approximately 80% of

all human water use statewide; the rest goes to cities and towns.

Within agriculture, about 85% of employment and gross revenues

from crops is from fruits, nuts, and vegetables, which use less than

half of all irrigated area and agricultural water use (Fig. 1). The

remaining agricultural land and water use support grains and

feed crops. Dairy and beef cattle production are about a fourth

of all agricultural value and relies on feed from out of state and

local silage production. Challenges for agriculture include labor

Fig. 1. Crop shares of agricultural crop revenues and employment.

(Data from California Employment and Development Department

2018;IMPLAN 2015.)

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

shortages, droughts, permanent cutbacks to protect groundwater,

and competing economic land uses. Another challenge is the con-

tinued expansion of permanent crops, orchards and vines, which

are more difficult to fallow in dry years, encouraging more attention

to groundwater management.

Urban water use has a similar economic structure, with about

half of California’s urban water use being for landscape irrigation

providing relatively little economic contribution. In 2015, the State

mandated an average 25% reduction in urban water use, varying

from 8% to 36% locally, with cities having higher per-capita water

use being required to reduce use more. Reductions were accommo-

dated mostly in landscape irrigation, with little economic impact,

despite some inconvenience and loss of urban trees, sometimes

referred to as the “war on lawns.”

Energy System Flexibility and Market

Hydropower is a highly variable source of California’s electricity

from year to year, ranging from 7% to 21% of statewide electricity

production since 2002 (CEC 2017a,b). Market flexibility, cheap

natural gas thermoelectric power, growing electricity production

from wind and solar sources, and long-term declining overall

electricity use dampened the impact of hydropower losses (CEC

2017a). Still, many power retailers added drought surcharges to

cover higher generation costs.

Water System Flexibility and Water Markets

In past droughts, even modest water trading among willing sellers

and buyers dampened economic impacts to agriculture and cities

(Israel and Lund 1995). Water markets and exchanges were particu-

larly important for shorted agricultural areas lacking access to

surface water. Urban water systems in southern California and

the San Francisco Bay area activated long-term water market con-

tracts for stored water and agricultural land fallowing. Irrigation

districts and farmers lacking sufficient groundwater sought to pur-

chase water from others, driving agricultural water prices as high as

$1.7=m3($2,000=acre-ft), but often over $0.8=m3($1,000=acre-ft),

approximately triple the recent non-drought-water market prices

(Hanak et al. 2015b;Hanak et al. 2017).

Cooperative operations, aided by greater availability of interties

and anticipatory agreements, further supported water markets and

exchanges to make fuller use of available water across California’s

extensive conveyance and storage network. Institutional flexibility

and capability allowed deep and abrupt disruptions in water deliv-

eries to Sacramento Valley farmers from endangered species

operations to be rapidly, if inconveniently, accommodated with

little economic loss. San Francisco Bay area utilities faced with

80–95% reductions in State Water Project deliveries used markets

and system flexibility to accommodate such cuts without severe

water rationing.

Water markets face both infrastructure and institutional barriers.

Many ideas for improving market effectiveness are discussed

(Hanak et al. 2011). Although regulations and agency oversight

impede or delay some transfers, within-district resistance due to

future water security and other issues is also common. Cooperative

agreements among water users, system operators, and government

agencies might help smooth low-environmental-impact transfers.

Waterfowl Institutional Preparation and Response

Waterfowl in California benefitted during the drought from a com-

bination of preparation, luck, and creative management (Hanak

et al. 2015b). First, waterfowl are more mobile than fish and

can therefore better adapt and move with drought conditions.

Waterfowl require ponds with a small volume of standing shallow

water, in contrast to native fish in streams or the Delta, which

require constant fresh water flow. Luckily timed winter storms

during the drought helped ease impacts to migrating waterfowl.

Beyond this, California has a long-established system of federal,

state, and private wetland wildlife refuges, with some coordination.

This refuge and institutional infrastructure was well employed to

identify and address foreseeable gaps in waterfowl habitat at critical

times. Such actions involved many groups. Perhaps the most

creative action was the Nature Conservancy’s Bird Returns pro-

gram, in which farmers bid for payments to water fields at particu-

lar times and places to support migrating waterfowl (Hallstein and

Miller 2014).

The 2012–2016 years were not California’s first multiyear

drought, and the cumulative lessons of past droughts did much

to shape the adaptive capacity and responses for the more recent

drought. Although statewide economic impacts were modest, some

areas were more acutely and chronically affected. Impacts were

mostly in areas least prepared or organized or inherently difficult

to organize (forests, fish, and rural water systems).

Benefits from Previous Droughts

The fear, impacts, and controversies of drought bring professional,

popular, and political focus needed to make strategic water man-

agement improvements. Historically, major droughts have led to

major innovations. This is also true for California, as summarized

in Table 5. Early droughts alerted immigrants from the humid

eastern United States that California’s seasonally dry climate could

be even drier. As the state’s agricultural economy grew, droughts in

the 1920s and 1930s led to extensive water infrastructure construc-

tion from the 1940s through the 1970s (Pisani 1984). The short,

deep 1976–1977 drought surprised many agencies and led to

widespread urban conservation programs and early water-market

activity (DWR 1978). The prolonged 1988–1992 drought also

caught many urban and agricultural areas underprepared, leading

to greatly improved urban interties, conjunctive use, and much

more extensive water markets. This drought also led to pivotal

changes in environmental management with the follow-up listing

of several endangered fish species. The short 2007–2009 drought

precipitated new institutions for the Delta and improved collection

of surface-water-use data.

California’s economy, society, and climate are dynamic. Each

historical drought has been different hydrologically and impacted

a different human economy with a substantially different water

management and infrastructure. A region’s economic structure

drives drought management and impacts. In addition, California’s

economic structure has always been driven by its changing global

economic roles, from shipping hides globally in the early 1800s,

gold in the late 1800s, grain in the early 1900s, and markets for

higher valued crops, wine, electronics, manufacturing, software,

and tourism in the last century.

Changes in California’s economic structure drive changes in

economic demands for water management (Pisani 1984). Improv-

ing technology and changing political institutions and social

expectations also change what is possible and desired in water

management (Kelley 1989). However, institutional arrangements

can be slow to evolve, and droughts (like floods and major lawsuits)

provide the attention and sense of urgency often needed for stra-

tegic changes. Droughts, floods, and lawsuits help water systems

adjust to accumulating historical changes (Hanak et al. 2011).

Adjustments are usually both technological and institutional,

and typically build on existing institutions and infrastructure.

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

The development of large regional and statewide water projects,

responding to droughts in the early twentieth century, did not elimi-

nate local water utilities and irrigation districts. Existing local dis-

tricts continued to manage local supplies and merely contracted

with regional wholesale projects. Existing and new local districts

could then benefit from economies of scale with newer regional

water management technologies (large dams and aqueducts) and

financing institutions (Metropolitan Water District, CVP, SWP),

with little loss of local advantages and sovereignty (Maass and

Anderson 1978).

In examining the swings of technologies and innovations, often

accelerated by droughts, changes in the most economical techno-

logical innovations are often accompanied by rebalancing of the

portfolio of managing and regulating local, regional, state, and

federal institutions. Large-scale regional water infrastructure devel-

opment shifted initiatives in water management to federal, state,

and regional governments. Before this time, water systems were

almost entirely local. Now that large reservoir and conveyance

systems are largely completed, today’s newer water management

innovations, such as water conservation, wastewater reuse, con-

junctive use of ground and surface waters, and water markets, are

often better led and financed locally, requiring adjustments in state

and federal regulations and regional system operations. These ad-

justments challenge routine finance and regulatory structures, and

often depend on droughts to accelerate change.

Environmental Susceptibility

The general drought robustness of California’s urban, agricultural,

energy, and recreation sectors contrast starkly with weaknesses

seen in environmental and ecosystem management. In part, the

drought management successes of California’s economic sectors

come from water delivery systems, levees, storage and conveyance

infrastructure, management, and water allocations that disrupt con-

ditions for native ecosystems in droughts and in wetter years.

Drought buffering for the economy in part has been paid for by

native ecosystems.

Many of California’s aquatic ecosystems remain chronically

starved for habitat and water in all years, but especially in droughts.

Therefore, native species enter droughts with diminished and geo-

graphically limited populations, only to encounter greater stresses

during drought (Moyle et al. 2017). Chronic problems of water de-

velopment for aquatic ecosystems include dams that block fish mi-

gration to upper watershed habitats, elimination of wetland and

floodplain spawning and rearing habitat by levees, entrainment

of juvenile fish by water export pumping, and poor water quality.

Most of California’s endemic species’populations were at histori-

cal lows at the 2012–2016 drought onset. By entering the drought

with such low stocks, several species were pushed to the brink of

extinction by higher water temperatures and lower flows.

As species approach extinction, federal and state agencies

charged with species protection have become more deeply in-

volved. Droughts have often accelerated the listing of endangered

species and regulatory agency involvement due to rapid reductions

in native fish populations. For winter-run salmon and Delta smelt,

this process began after the 1988–1992 drought, after long declines.

Droughts have long-term environmental effects that may take

many years and management changes to repair. Without the time,

water, and habitat needed to rebuild fish stocks, droughts ratchet

down native fish populations, with little recovery between

droughts. The Delta smelt was listed as threatened in 1993, state

endangered in 2010, and nearly disappeared from detection by

2016. Droughts also facilitate invasive organisms, beginning in

the early 1900s with the invasive teredo’s spread into the Delta

in drier years (Means 1928). More recently, invasive clams and veg-

etation have been aided by drought, disrupting food webs, stressing

native populations, and disturbing infrastructure and passage

(Jeffries et al. 2016;Lehman et al. 2017).

Successful environmental and ecosystem management will re-

quire a more proactive approach, involving planning, organization,

and financing of effective actions, including drought planning. Pro-

active drought-management approach has been effective for urban

and agricultural sectors, and for managing wetlands for waterfowl.

Innovations and Future Benefits from This Drought

The 2012–2016 California drought brought a range of innovations

likely to improve preparations for future droughts.

The 2014 SGMA, the first forceful state effort to make ground-

water use sustainable, passed because of the drought, approxi-

mately 100 years after California legislation first regulated surface

water. A thoughtfully implemented SMGA will not only improve

Table 5. Historical droughts in California, their impacts, innovations, and leading innovators

Drought Impacts Innovations

Leading

innovators

1800s Herds and crops devastated Local irrigation, 1873 Federal Central

Valley study

Local, private

1924 Crop devastation Local reservoir projects, major regional/state

water project plans

Local, public, and private diverters

1928–1932 Delta salinity, crop losses Major statewide dam and canal plans and

projects (CVP, SWP)

Regional, statewide water

agencies and project users

1976–1977 Major urban and agricultural

shortages

Urban conservation; early markets Urban water utilities, water buyers and sellers

1988–1992 Urban and agricultural shortages;

endangered fish

Interties, conjunctive use; water markets;

conservation;

new storage

Local and regional urban water agencies,

irrigation districts

2007–2009 Water shortages for

agriculture and fish

New water use reporting requirements,

Delta planning institutions, and urban

water conservation mandates

State agencies, new Delta planning

institutions, urban water agencies

2012–2016 Warm drought, little Delta

water, major agricultural

shortages, damage to fish and forests

Groundwater sustainability legislation;

Delta barrier; state urban conservation mandates;

more water use reporting; local responsiveness

Local water agencies; water project operators;

state agencies

Source: Data from Lund (2014a).

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

prospects for dealing with future droughts by improving ground-

water reserves but will also foster broader coordination, account-

ing, and tighter water management at local and regional scales

(Hanak et al. 2017).

The drought brought local and state government pressure to

reduce per-capita urban water use, which remains higher that most

of the country and most other developed economies in dry regions

(Cahill and Lund 2013). Urban areas face long-term state pressure

to reduce per-capita, mostly outdoor, water use from drought-

driven legislation in 2009 and more recent drought legislation,

executive orders, and regulations.

In 2014 and 2015, low inflows and depleted upstream storage

raised concerns about seawater intrusion into the Delta and led to

consideration of several temporary flow barriers to reduce salinity

intrusion and the construction in 2015 of a temporary salinity

barrier in the western Delta. Future droughts will also likely use

salinity barriers, perhaps with greater planning and preparation.

Another benefit of the drought was additional state and federal

spending on drought-related water problems in California (Hanak

et al. 2015a). Much of these funds were merely redirected or retitled

from other water and environmental programs, and some helped

to directly relieve drought impacts to small communities and farm-

ers, but some also led to longer-term infrastructure improvements

and other long-lasting benefits.

The drought did not immediately result in broad improvements

to environmental management. Some notable innovations occurred

for coordinating water-bird management (Hallstein and Miller

2014). California’s WaterFix and EcoRestore mandate over 8,000

acres of tidal habitat restoration in the Delta, which may help buffer

some threatened populations. Much attention was paid to potential

innovations from Australia (Mount et al. 2016). Perhaps the diffi-

culties of managing forest and aquatic ecosystems from drought

will motivate more effective efforts to come. Discussion of an envi-

ronmental water right has begun, which may be one way to allow

environmental flows to support postdrought recovery of vulnerable

fish species and end drought ratcheting of ecosystems (Mount

et al. 2017).

One of the most important benefits of the drought is the

reminder to the broader society and political discourse that

California is a dry place overall, where water must be carefully

managed. This lesson is particularly poignant for the southern

Central Valley, which has extensive and high-valued agricultural

water demands in one of California’s drier regions, prone to

groundwater overdraft, and particularly vulnerable to shortages

of Delta water imports.

A final optimistic lesson is that if water is well managed,

damages from drought (and floods) will usually be quite modest

in the context of California’s overall society and economy. The

combination of California’s global economy, urban and substantial

agricultural preparation for drought, relatively abundant ground-

water reserves, and substantial institutional flexibility greatly

dampened the impacts of one of history’s most severe and lengthy

droughts in California (Lund 2016b). Important problems and op-

portunities are also pointed out that should be addressed to both

prepare for future droughts and improve the water system overall.

Having demonstrated substantial economic robustness to severe

drought allows California the opportunity to more aggressively

counter environmental damages. California has considerable

wealth and flexibility to solve its environmental and water quality

crises. Much of the resources needed to effectively manage the

environment (e.g., water, money, habitat restoration) are needed

during interdrought periods, when resources should be more avail-

able. Investments in environmental preparation for drought could

be as successful as they are for economic sectors.

Use and Organization of Science

The behavior of systems under unusual stress is an important op-

portunity to learn and improve, despite undesired impacts. The

drought provided opportunities for “natural”ecological and institu-

tional experiments that would otherwise be impossible to permit or

be impractically expensive. Drought-related reductions in flows

and rises in temperatures were widespread. Major emergency

changes to infrastructure, such as the Delta emergency salinity

barrier, provided opportunities to examine effects of major Delta

changes on water quality, flow, and ecological conditions.

State and federal agencies and science programs were largely

unprepared to take advantage of these scientific opportunities.

Some important scientific work did occur (Durand et al. 2018;

Jeffries et al. 2016;Lehman et al. 2017;Medellín-Azuara et al.

2018;Lord et al. 2018), although often less systematically. Scien-

tific syntheses that assemble data, analyses, and lessons from the

drought likely have great value.

Historically, major droughts in California have occurred at a rate

of each generation experiencing approximately one major drought

in a career. This often means that each drought is greeted by a new

generation of professionals, lacking direct drought management

experience. This infrequency of drought dampens personal incen-

tives for institutions to learn from past droughts and prepare for the

next drought. If climate warming and tighter water demands make

drought more frequent, with two or more droughts expected in a

career, agencies might make deeper drought preparations. More

frequent droughts appear likely to affect environmental protection

agencies especially, with noted weaknesses in drought preparation.

The development and use of water-use data and estimates saw

particular advances during the drought. Drought legislation in 2009

required all surface-water right holders to report monthly use to the

State Water Board every 3 years—for the first time applying to

riparian and pre-1914 appropriative water right holders. The

2010–2013 water-right use data became available in 2013. Although

these data were often incomplete, they greatly improved water-use

estimates for declarations of water unavailability by the state.

Errors in models and field data also became apparent during the

drought. Models of stream and reservoir temperatures were forced

to operate outside their normal and calibrated ranges. Field mea-

surements of reservoir temperature took on new significance and

were sometimes found to be gravely inaccurate for the salmon they

were intended to protect (Durand et al. 2018).

Droughts always heighten public, political, and agency interest

in drought forecasting. This drought greatly increased funding and

publicity for real-time predictions of drought and floods (often

based on El Nino conditions). Such efforts have improved insights

into atmospheric processes, but long-term forecasting remains

substantially unsuccessful (Cayan and Mount 2015;Schonher

and Nicholson 1989).

Conclusions

Water management in California was unusually effective for the

2012–2016 drought, with the exception of ecosystems and rural

drinking water supplies. However, the drought highlighted several

moderate to severe problems, and helped bring attention and

innovations—following a common pattern of droughts bringing

innovation.

Success in water management for California has always been

dynamic. California’s semi-arid Mediterranean climate and ever-

changing economy, society, and ecosystems require that water

management constantly adapt, as it has for over 150 years. Such

adaptations are always imperfect and controversial, involving a

J. Water Resour. Plann. Manage., 2018, 144(10): 04018067

messy awkward mix of convenient past practices, present exigen-

cies, and preparing for an imagined future.

Several overall conclusions arise from California’s most recent

drought:

1. Droughts focus attention and encourage improvements in water

management. Each major drought in California’s history has

motivated improvements in water management, often respond-

ing to long-term problems and opportunities. The current

drought highlighted the dependence of California’s agriculture

on groundwater in dry periods, and led to substantial legislation

requiring more effective local groundwater management. Some

improvements in water accounting, urban water conservation,

and other areas were accelerated by the drought;

2. A diversified economy with deep global connections signifi-

cantly buffers economic effects of drought. California and most

modern economies depend less on abundant water supplies than

in the past. Agriculture is California’s most water-dependent

industry, about 80% of human water use, but despite its growth

and prosperity, provides less than 4% of California’s jobs. High

values for major export crops greatly reduced the impacts of

fallowing about 6% of the least-profitable irrigated land during

this drought. Despite local problems, the effect of major drought

on California’s statewide economy was quite small (Howitt et al.

2014,2015a,b). Urban areas, supporting most of the people

and economic activity, have developed diversified portfolios

of water supply and conservation activities that were quite

successful during the California drought;

3. Major drought and climate change have much less impact on

irrigated water systems with diversified supply sources, particu-

larly groundwater, and flexibility in operations with water net-

works and markets. California’s extensive and diverse water

infrastructure allowed more than 70% of lost water supplies

to be replaced by pumped groundwater for agriculture, requiring

greater recharge of groundwater in the long term. Although

costly compared with dryland agriculture, California’s irrigation

infrastructure and network of reservoirs and canals greatly mute

the effects of drought, and are particularly effective for protect-

ing the most economically valuable crops and economic

activities. With reductions in the least-profitable irrigated area,

this system can be sustainable for many decades if properly

managed;

4. Ecosystems were most affected by the drought, given the weak

condition of many native species, even in wet years, due to dec-

ades of losses of habitat and water and the growing abundance

of invasive species. With each drought, humans become better at

weathering drought, but effective institutions and funding are

lacking to improve ecosystem management and preparation

for drought. Forests are particularly vulnerable and difficult

to protect from droughts. Dedicated environmental water rights

and restoration and migration programs can help support eco-

systems. Such actions are needed to break the cycle of cumu-

lative drought impacts to ecosystems and the environment;

5. Small rural water systems are especially vulnerable to drought.

Small systems often struggle in normal years, lack economies of

scale, typically have only a single vulnerable water source, and

commonly lack sufficient organization and finance; and

6. Every drought is different. Droughts are hydrologically unique

events that occur under different historical, economic, and

ecosystem conditions, and increasingly with different climate

conditions. But all droughts provide opportunities and incentives

to improve and adjust water management to changing economic

and environmental conditions and priorities. In well-managed

systems, each drought is greeted with improved preparations

from previous droughts.

Acknowledgments

This paper benefitted from work and conversations with many

diverse stakeholders, agencies, researchers, and journalists during

the drought, as well as insightful reviewer comments. This work

was partially funded by the California Department of Food and

Agriculture, the US Environmental Protection Agency (Assistance

Agreement 83586701), and the S.D. Bechtel, Jr. Foundation. None

of these funders reviewed, approved, or endorsed this product.

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Feb 2025
ESTUAR COAST

Anthropogenic climate change on local to global scales has transformed the cycling of particulate organic carbon (POC) in river deltas. Understanding the biogeochemical processing of POC across deltas is key to developing a predictive framework for disruptions in carbon cycling within vulnerable ecosystems. This study examined the spatial and temporal variations in POC, particulate nitrogen (PN), and total suspended sediments (TSS) concentrations across the Sacramento-San Joaquin Delta (Delta) over three water years (2021–2023), covering drought-like conditions observed in spring, summer, and fall. Comprehensive Delta-wide surveys were conducted, employing a mass balance model to estimate total POC flux and constrain POC influx/efflux. Limited seasonal variability in POC and PN concentrations reflected a constrained particle supply under hydrologic conditions increasingly representative of the Delta’s future. Results revealed an 81% decrease in annual total suspended sediment concentration inputs to the Sacramento River from the 1957 water year compared to the average of 2021–2022, with levels during the study period much lower than previous decades. POC influx ranged from 39 to 79% of total efflux during spring to fall of low water years, with 8 to 37% of daily POC flux diverted to southern water pumping stations, limiting opportunities for particle deposition and internal production within the Delta. This was reflected in average Delta POC concentrations: 0.77 mg/L (2021), 0.54 mg/L (2022), and 0.42 mg/L (2023). The sustained reduction in sediment and POC levels in the Delta, driven by human activities, hinders wetland accretion, carbon sequestration, and overall ecosystem stability.

Forecasting Drought Using Machine Learning in California

Preprint

Feb 2025

Drought is a frequent and costly natural disaster in California, with major negative impacts on agricultural production and water resource availability, particularly groundwater. This study investigated the performance of applying different machine learning approaches to predicting the U.S. Drought Monitor classification in California. Four approaches were used: a convolutional neural network (CNN), random forest, XGBoost, and long short term memory (LSTM) recurrent neural network, and compared to a baseline persistence model. We evaluated the models' performance in predicting severe drought (USDM drought category D2 or higher) using a macro F1 binary classification metric. The LSTM model emerged as the top performer, followed by XGBoost, CNN, and random forest. Further evaluation of our results at the county level suggested that the LSTM model would perform best in counties with more consistent drought patterns and where severe drought was more common, and the LSTM model would perform worse where drought scores increased rapidly. Utilizing 30 weeks of historical data, the LSTM model successfully forecasted drought scores for a 12-week period with a Mean Absolute Error (MAE) of 0.33, equivalent to less than half a drought category on a scale of 0 to 5. Additionally, the LSTM achieved a macro F1 score of 0.9, indicating high accuracy in binary classification for severe drought conditions. Evaluation of different window and future horizon sizes in weeks suggested that at least 24 weeks of data would result in the best performance, with best performance for shorter horizon sizes, particularly less than eight weeks.

Drought has varying impacts on the national economy

Article

Full-text available

Feb 2025
STOCH ENV RES RISK A

Droughts can significantly impact the water, energy, and agriculture sectors, leading to substantial effects on the national economy. This study examines the potential influence of drought on the national economy, using Gross Domestic Product (GDP) as a measure of economic performance. It explores the linear relationship between a country’s GDP and the Palmer Drought Severity Index (PDSI). The study employs detrended GDP, processed using the logarithmic trend-free pre-whitening (TFPW) method, to account for the exponential growth in GDP. Findings show a varying relationship between drought and national GDP but do not speak on how drastic that effect will be. The correlation values presented in this study do not reflect the magnitude of drought’s effect on economic strength but rather the consistency of the effects. The economic impact of drought is multifaceted, influencing sectors such as agriculture, industry, and beyond. Drought's impact on GDP varies across sectors, with agriculture being the most directly affected. However, factors such as irrigation, technological advancements, and levels of economic development shape these effects differently in developed and developing nations. This study provides a preliminary assessment, emphasizing the need for more robust evidence and detailed analyses that incorporate socio-economic factors, technological advancements, and diverse drought metrics.

Spatio-temporal monitoring of compound droughts over global land areas

Article

Apr 2025
ENVIRON MODELL SOFTW

Does drought management care for nature? Identifying gaps in the consideration of freshwater ecosystems

Article

Full-text available

Apr 2025
ENVIRON RES LETT

Growing evidence suggests that freshwater ecosystems incur exacerbated impacts during drought due to anthropogenic activities. This has prompted calls for the development of drought management strategies that more effectively incorporate these ecosystems. Efforts to examine how drought management instruments care for freshwater ecosystems are scarce, limited to a few geographic regions, and do not systematically analyse each of the elements of the drought management process. In this study, we review drought management instruments in 26 countries or regions within countries to assess the extent and the manner with which freshwater ecosystems are considered. We apply an analytical framework integrating knowledge from drought management, ecological risk assessment and ecological drought to extract data from these instruments and identify patterns and gaps. Results indicate that care for freshwater ecosystems in drought management is as yet at an early stage. This is reflected in the limited inclusion of freshwater ecosystems across critical elements of the drought management process, as well as significant shortcomings in how these ecosystems are considered. We synthesise these shortcomings in four gaps. First, the socio-ecological perspective of ecological drought, particularly regarding the combined natural-human causes of drought impacts on freshwater ecosystems, is often lacking in drought definitions, exposure and vulnerability assessments. Second, despite their importance to ecosystems, there is limited consideration of variables related to groundwater, water quality, and aquatic habitats in freshwater ecosystem indicators, exposure assessments and measures. Third, the duration, frequency and timing of drought, which are relevant to the ecology of freshwater ecosystems, are rarely considered in drought indicators and measures. Finally, exposure and vulnerability assessments often lack a comprehensive understanding of ecological drought risk in freshwater ecosystems. We discuss these gaps and provide an outlook towards more integrated and sustainable drought policy and management.

Foundations of Smart Water and Artificial Intelligence Technologies

Chapter

Feb 2025

The increasing global demand for water, compounded by the challenges posed by climate change, urbanisation, and population growth, necessitates the adoption of innovative solutions for water management. Smart Water technologies, which encompass the integration of advanced sensors, data analysis, and automated systems, offer a promising approach to optimising water use and enhancing sustainability. While challenges remain, the benefits of adopting these technologies are substantial, warranting further investment and research. As global water challenges intensify, the role of Smart Water systems will become increasingly critical in ensuring the sustainable management of this vital resource. This chapter explores the components, benefits, and challenges of Smart Water systems, providing a comprehensive overview of their role in modern water management.

Progress Report: Subsidence in California, March 2015 – September 2016

Technical Report

Full-text available

Jan 2017

Subsidence in California as measured by InSAR

Improving the Health of California’s Headwater Forests

Technical Report

Full-text available

Sep 2017

California’s headwater forests are not thriving under current management practices, and changes are needed to make them more resilient to periodic drought and long-term climate change. More active management of these lands is needed to improve forest health, reduce the risk of major wildfires and pest infestations, and maintain the flow of benefits provided by this critical natural infrastructure. Decades of fire suppression, an emphasis on short-term management priorities, weather extremes, and a warming climate have set the stage for the decline in forest resilience. Two-thirds of the state’s surface water supply originates in these mountainous forests. California stands to lose timber production, wildlife habitat, recreational opportunities, and water supply if this vital natural infrastructure continues to decline. Management options exist— prescribed fire, managed wildfire, mechanical thinning, and forest pest treatments—that can help rebuild resilience in these forests and prepare them for a challenging future. California needs to increase the pace and scale of efforts to improve forest health. The strategic removal of high-density smaller trees and fuels is essential to increasing long-term resilience of headwater forests. This will require management, regulatory, and legal reforms. We suggest changes in three areas: - Make long-term forest health the top priority for guiding agency rules, policy, and management practices. - Define forest treatment needs and make the most of available funds. - Make greater use of tools that create opportunities for collaboration. Within each of these broad themes, we suggest specific reforms and actions to implement them. Many of these actions can take place without major legislation or large increases in funding, relying instead on changes in rules or administrative decisions. Taken together, implementing these reforms will improve the health of California’s headwaters and ensure the environmental, social, and economic benefits they provide.

Remote Linkages to Anomalous Winter Atmospheric Ridging Over the Northeastern Pacific

Article

Full-text available

Nov 2017

Severe drought in California between 2013 and 2016 has been linked to the multi-year persistence of anomalously high atmospheric pressure over the Northeastern Pacific Ocean, which deflected the Pacific storm track northward and suppressed regional precipitation during California's winter “rainy season.” Multiple hypotheses have emerged regarding why this high pressure ridge near the west coast of North America was so resilient—including unusual sea surface temperature patterns in the Pacific Ocean, reductions in Arctic sea ice, random atmospheric variability, or some combination thereof. Here we explore relationships between previously documented atmospheric conditions over the North Pacific and several potential remote oceanic and cryospheric influences using both observational data and a large ensemble of climate model simulations. Our results suggest that persistent wintertime atmospheric ridging similar to that implicated in California's 2013-2016 drought can at least partially be linked to unusual Pacific sea surface temperatures, and that Pacific Ocean conditions may offer some degree of cool-season foresight in this region despite the presence of substantial internal variability.

State of the Salmonids: Status of California's Emblematic Fishes 2017

Technical Report

Full-text available

Aug 2017

California has, or had, 32 distinct kinds of salmonid fishes. They are either endemic to California or at the southern end of their ranges. Most are in serious decline: 45% and 74% of all salmonids will likely become extirpated from California in the next 50 and 100 years, respectively, if present trends continue. Our results suggest that California will lose more than half (52%) of its native anadromous salmonids and nearly a third (30%) of its inland taxa in just 50 years under current conditions. Climate change is a major overarching threat driving population declines throughout California and strongly affects the status of 84% of all salmonids reviewed. In addition, dams, agricultural operations, estuary alteration, non-native species, production hatcheries, and myriad other human-induced threats have contributed to declines. 81% of salmonids in California are now worse off than they were in 2007, when the previous version of this report was prepared. The changes in species status are the result of the 2012-2016 historic drought, improved data collection and review, and an improved understanding of climate change impacts. Returning these iconic species to sustainable levels requires access to productive and diverse habitats which promote the full range of life history diversity necessary to weather change. We recommend (i) protecting and investing in fully functioning watersheds such as the Smith River and Blue Creek, (ii) protecting and restoring source waters such as Sierra meadow systems, groundwater, and springs so that the impacts of climate change are reduced, (iii) restoring function and access to once productive and diverse habitats such as Central Valley floodplains, coastal lagoons, and estuaries, (iv) adopting reconciliation ecology as a basis for management in human dominated landscapes, (v) improving habitat connectivity and passage to historical spawning and rearing habitat, and (vi) improving salmonid genetic management throughout California.

Water stress and a changing San Joaquin Valley

Technical Report

Full-text available

Mar 2017

The San Joaquin Valley—California’s largest agricultural region, and an important contributor to the nation’s food supply—is in a time of great change and growing water stress. Agriculture is a leading economic driver and the predominant water user. The region’s farms and related manufacturing businesses account for 25 percent of the valley’s revenues and 16 percent of local jobs—and 89 percent of annual net water use. The latest drought underscored valley agriculture’s vulnerability to water scarcity and long-term declines in groundwater reserves. The region has a greater abundance of productive farmland than local water supplies for irrigation. In most years since the mid-1980s, groundwater has been used faster than it is being replenished (“groundwater overdraft”). Over the past three decades, overdraft has averaged nearly 2 million acre-feet per year, or 13 percent of net water use. This has contributed to increased pumping costs, dry wells, sinking lands, and declining reliability of this vital drought reserve. The Sustainable Groundwater Management Act of 2014 (SGMA) requires valley farms and communities to bring their groundwater basins into balance by 2040. Farms must also respond to a variety of related resource and environmental challenges. Notable issues include nitrate contamination of groundwater—a special challenge in poor, rural communities—as well as accumulating salinity in soils, local air pollution, and the broad decline in aquatic, wetland, and terrestrial ecosystems. With so many changes underway, major questions loom about the future of the valley’s agriculture and the wider consequences for the region’s economy, society, and environment. Several broad strategies can help address the valley’s water imbalance and related problems:  Manage groundwater reserves: Groundwater sustainability agencies being formed under SGMA will need solid water accounting tools to understand how much water is available and how much is being withdrawn. They will also need the ability to incentivize both recharge and reductions in pumping to attain long-term groundwater balance.  Expand usable supplies: Capturing and storing more local runoff in groundwater basins and reusing water would help reduce the current deficit in the near term. Longer term, larger infrastructure investments such as improved water conveyance from the Delta could help.  Reduce demand: Although farmers can save some water through crop choice and management, idling some farmland is also likely in basins that cannot close the groundwater deficit with new supplies. Water trading—both within and across basins—can lessen the costs of shortages.  Explore multi-benefit strategies: Opportunities exist to manage groundwater recharge in ways that improve water supply and quality—for example, by tailoring irrigation systems and crop choices to maximize clean recharge in prime areas. Similarly, with the right incentives and regulatory assurances, idled lands can be managed to reduce impacts on air quality while improving wildlife habitat. Valley farmers and residents have a history of creatively adapting to changing conditions. In meeting today’s challenges, there are numerous opportunities to tackle problems cooperatively. But the valley also has a complex mix of entities and institutions managing water and land. Perhaps one of the region’s greatest challenges is developing new cooperative approaches to seize these opportunities. The entire region—and California as a whole—will benefit if solutions to the valley’s problems support the economy while improving public health and environmental conditions.

Battling the Inland Sea

Book

Dec 1998

Robert Kelley

From the Family Farm to Agribusiness: The Irrigation Crusade in California and the West, 1850–1931

Book

Dec 1984

Donald J. Pisani

Drought Water Right Curtailment Analysis for California’s Eel River

Article

Feb 2018

Water users in California's hybrid water rights system have different legal priorities to available surface water in times of water scarcity. A set of two linear programming models was developed to determine curtailments of water use under drought conditions according to riparian and appropriative water right doctrines with spatially varying water availability and water rights within a basin. The models were implemented in spreadsheets and extended to estimate water right reliability and factors of safety in water rights administration. Alternate methods for calculating water use curtailments are discussed. Curtailments from the models are compared with actual water shortage notices issued by the state for the Eel River, California for June 30, 2014. Analyzing water use curtailments with an algorithm in spreadsheet software offers a mechanistic, transparent, accessible, and precise approach derived from legal doctrines to support water rights administration during drought.

What if California's drought continues?

Article

Jan 2015

Hydroeconomic modeling of sustainable groundwater management

Article

Mar 2017
WATER RESOUR RES

In 2014 California passed legislation requiring the sustainable management of critically overdrafted groundwater basins, located primarily in the Central Valley agricultural region. Hydroeconomic modeling of the agricultural economy, groundwater, and surface water systems is critically important to simulate potential transition paths to sustainable management of the basins. The requirement for sustainable groundwater use by 2040 is mandated specifically for overdrafted groundwater basins that are decoupled from environmental and river flow effects. We argue that, for such cases, a modeling approach that integrates a biophysical response function from a hydrologic model into an economic model of groundwater use is preferable to embedding an economic response function in a complex hydrologic model as is more commonly done. Using this preferred approach, we develop a dynamic hydroeconomic model for the Kings and Tulare Lake sub-basins of California and evaluate three groundwater management institutions–open access, perfect foresight, and managed pumping. We quantify the costs and benefits of sustainable groundwater management, including energy pumping savings, drought reserve values, and avoided capital costs. Our analysis finds that, for basins that are severely depleted, losses in crop net revenue are offset by the benefits of energy savings, drought reserve value, and avoided capital costs. This finding provides an empirical counter-example to the Gisser and Sanchez Effect. This article is protected by copyright. All rights reserved.