Drought in California

"Even a single dry year can pose problemsfor activities that are wholly dependent onunmanaged water supplies, such as drylandfarming or livestock grazing."
About Jack Berlin

California Department of Water Resources - Natural Resources Agency - State of California
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Water Drought Water supply California YEAR system Drought Impact Groundwater Water system conditions Southern California single dry YEAR State manage area Groundwater Basin Water manage Plan Central valley Project small Water YEAR
<p>F A L L  2 0 1 2
Cali fornia Depar tment of  Water Resources
1416 ninth St reet ,  Sacramento ,  C A 95814
w w w.water. ca . gov/droug ht
Drought in California
California Depar tment of  Water Resources
Natural  Resources Agenc y 
State of  California
Definition
California  
Drought
Cause &  
Prediction
Impact
Groundwater
Preparation
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10
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YEAR
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Red line Denotes 11-year running mean
Western Regional
Climate Center
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Defining Drought
2 0 1 2  D R O U G H T  B R O C H U R E
2
There are many ways that drought can be defined. Some ways can 
be quantified, such as meteorological drought (period of below 
normal precipitation) or hydrologic drought (period of below average 
runoff), others are more qualitative in nature (shortage of water 
for a particular purpose). There is no universal definition of when a 
drought begins or ends. Drought is a gradual phenomenon. 
Impacts of drought are typically felt first by those most dependent on annual 
rainfall, such as ranchers engaged in dryland grazing or rural residents relying on 
wells in low-yield rock formations. Drought impacts increase with the length of 
a drought, as carry-over supplies in reservoirs are depleted and water levels in 
CALIFORNIA STATEWIDE PRECIPITATION 
OCTâ€“SEPT (WATER YEAR)
CONTENTS
Defining Drought
 2 
Definition
 4 
Droughts in California
 6 
Drought Causation and Prediction
 8 
Drought Impacts from a Water  
 
Use Perspective
10 
Droughts and groundwater
11 
Preparing for Droughts and  
 
Mitigating Drought Impacts
Defining Drought
2 0 1 2  D R O U G H T  B R O C H U R E
3
Through water year 2012, Colorado River inflow into Lake 
Powell has been below average in 10 of the past 13 years, 
resulting in reduced storage levels in Lakes Mead and Powell. 
The Colorado has historically been a highly reliable water 
supply for Southern California despite long-term drought, 
thanks to its large reservoir storage capacity. Interim 
guidelines adopted in 2007 for Lower Basin shortages and 
coordinated operations of Lakes Mead and Powell help reduce 
the risk of shortages to California.
ground water basins decline. Hydrologic impacts of drought 
to water agencies may be exacerbated by other factors 
such as regulatory requirements to protect environmental 
resources or to satisfy the rights of senior water right holders.
from a water use 
perspective, drought is 
best defined by its impacts 
to a particular class of 
water users in a particular 
location. In this sense, 
drought is a very local 
circumstance. Hydrologic 
conditions constituting a 
drought for water users 
in one location may not 
constitute a drought for water users in a different part of the 
state or with a different water supply. Californiaâ€™s extensive 
system of water supply infrastructureâ€” reservoirs, managed 
groundwater basins, and inter-regional conveyance 
facilitiesâ€”mitigates the effect of short-term (single year) 
dry periods. Individual water suppliers may use criteria 
such as rainfall/runoff, amount of water in storage, decline 
in groundwater levels, or expected supply from a water 
wholesaler to define their water supply conditions.  
Criteria used to identify statewide drought conditionsâ€”
such as statewide runoff and reservoir storageâ€”do not 
address these localized circumstances. And although 
Californiaâ€™s water supply infrastructure provides a means 
to mitigate impacts for some water users, other types of 
impacts (increased wildfire risk, stress on vegetation  
and wildlife) remain. 
 
Californiaâ€™s extensive 
system of water supply 
infrastructureâ€” 
reservoirs, managed 
groundwater basins, and 
inter-regional conveyance 
facilitiesâ€”mitigates the 
effect of short-term  
(single year) dry periods. 
DroUgHTS In CAlIfornIA
2 0 1 2  D R O U G H T  B R O C H U R E
4
Drought played a role in shaping Californiaâ€™s early 
history, as the so-called great Drought in 1863-
64 contributed to the demise of the cattle rancho 
system, especially in Southern California. 
Subsequently, a notable period 
of extended dry conditions was 
experienced during most of the 1920s 
and well into the 1930s, with the latter 
time including the Dustbowl drought 
that gripped much of the United States. 
three twentieth century droughts were 
of particular importance from a water 
supply standpoint â€“ the droughts of 
1928-35, 1976-77, and 1987-92. 
The 1928-35 Dustbowl drought 
established hydrologic criteria widely 
used in used in designing storage 
capacity and yield of large northern 
California reservoirs. The 1976-77 
drought, when statewide runoff in 1977 
hit an all-time, low served as a wake-
up call for California water agencies 
that were unprepared for major cut-
backs in their supplies. forty-seven of 
the Stateâ€™s 58 counties declared local 
drought-related emergencies at that 
time. Probably the most iconic symbol 
of the 1976-77 drought was construction of an emergency 
pipeline across the San rafael Bridge to bring water obtained 
through a complex system of exchanges to Marin Municipal 
Water District in southern Marin County. The 1987-92 
drought was notable for its six-year duration. Twenty three 
counties declared local drought emergencies. Santa Barbara 
experienced the greatest water supply reductions among the 
larger urban areas. In addition to adoption of measures such 
as a 14-month ban on all lawn watering, the city installed a 
temporary emergency desalination plant and an emergency 
pipeline was constructed to make State Water Project 
supplies available to southern Santa Barbara County. 
It is important to recognize that a period of historically 
recorded hydrology of little more than a century does not 
represent the full range of the climate systemâ€™s natural 
variability. Paleoclimate information, such as streamflow 
reconstructions based on tree-ring data, shows that natural 
variability can be far greater than that observed in the historical 
record. These reconstructions have identified droughts 
prior to the historical record that were far more severe than 
todayâ€™s water institutions 
and infrastructure were 
designed to manage.  
The Colorado river Basin, 
an important source of 
Southern Californiaâ€™s 
water supply, has been 
particularly well studied; 
its streamflow reconstructions show multidecadal periods 
when flows were below the long-term average. 
MULTI-YEAR 
DROUGHTS OF 
LARGE-SCALE 
EXTENT SINCE 
1900
(Based on statewide 
runoff )
 
1918â€“1920
 
1923â€“1926
 
1928â€“1935
 
1947â€“1950
 
1959â€“1962 
1976â€“1977
 
1987â€“1992
 
2000â€“2002
 
2007â€“2009
Droughts in California
The 1928-35 Dustbowl 
drought established 
hydrologic criteria widely 
used in used in designing 
storage capacity and 
yield of large Northern 
California reservoirs.
Emergency pipeline constructed during 1976-77 drought 
to bring water to southern Marin County.
Fl
ow
, M
ill
io
n 
A
cr
e-
Fe
et
YEAR
Long-term Streamï¬‚ow Reconstruction from Tree-ring Data Observed Flow
Annual Flow
10 Running Year Mean
20 Running year Mean
25
20
800
1000
900
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2005
15
15
5
0
762
DroUgHTS In CAlIfornIA
2 0 1 2  D R O U G H T  B R O C H U R E
5
Some 5,000-6,000 years ago these trees were growing on lands 
now submerged by Lake Tahoe, illustrating centuries-long periods 
drier than present conditions.  National Geographic submersible 
shown inspecting tree stumps still rooted in place on the lakebed.  
Photo courtesy of National Geographic.
RECONSTRUCTED COLORADO RIVER  
STREAMFLOW AT LEE FERRY
Most of Californiaâ€™s moisture originates in the 
Pacific ocean. During the wet season, the 
atmospheric high pressure belt that sits off 
western north America shifts southward, allowing 
Pacific storms to bring moisture to California. 
on average, 75 percent of the stateâ€™s average annual 
precipitation occurs between november and March, with half 
of it occurring between December and february. A few major 
storms more or less shift the balance between a wet year and 
a dry one. A persistent high pressure zone over California 
during the peak winter water production months predisposes 
the water year to be dry.
Drought Causation  
and Prediction
On average, 75 percent of the stateâ€™s average 
annual precipitation occurs between November 
and March, with half of it occurring between 
December and February.
Mount Shasta in 2008 at the end of the water year. 
The impacts of climate change, such as the shift 
in timing of spring runoff in the Sierra Nevada, are 
becoming increasingly discernible in analysis of 
hydroclimate data.  Efforts to predict drought must 
evaluate the natural climate variability seen in 
historical and paleoclimate records, together with 
changed conditions such as increased warming.
The ability to reliably predict drought conditions at 
seasonal or annual timescales is very limited. The status of 
El niÃ±o-Southern oscillation (EnSo) conditions is presently 
the only factor that offers a hint of predictive capability 
for precipitation in California. EnSo is a periodic shifting 
of ocean-atmosphere conditions in the tropical Pacific that 
ranges from El niÃ±o (warm phase) to neutral to la niÃ±a (cold 
phase). la niÃ±a conditions tend to favor a drier outlook for 
Southern California, but do not typically show significant 
correlation with water year type for northern and Central 
California. The predictive capabilities provided by EnSo 
events are related to the strength of an event; stronger 
events yield better predictive signals. In any individual year, 
interactions with other climate patterns or forcings may affect 
the outcome that would otherwise be expected from EnSo 
conditions alone. How other factors such as the Madden-
Julian oscillation, Pacific Decadal oscillation, north Atlantic 
oscillation, or Arctic oscillation modulate the expression of 
EnSo conditions remains a subject for research. 
GLOBAL-LEVEL TOP 10 WARMEST 
YEARS SINCE 1880
Source:  National Climate Data Center
 
 1 
2005
 
 2 
2010
 
 3 
1998
 
 4 
2003
 
 5 
2002 
  
 6 
2006
 
 7 
2009
 
 8 
2007
 
 9 
2004
 
10 
2001
0
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5
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ES
7
9
Jan.
Feb.
Mar.
Apr.
May
June
MONTHS
July
Aug.
Sept.
Oct.
Nov.
Dec.
0
2
5
7
9
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DroUgHT CAUSATIon AnD PrEDICTIon
2 0 1 2  D R O U G H T  B R O C H U R E
7
 MONTHLY DISTRIBUTION OF STATEWIDE PRECIPITATION, 
SHOWING WET, AVERAGE, AND DRY YEARS
KEY
1923â€“1924
1982â€“1983
Average
Satellite image of atmospheric river reaching West Coast. 
Atmospheric river storms â€“ storms fueled by concentrated 
streams of water vapor from the Pacific Ocean â€“ are big 
contributors to annual water supply conditions. 
A few major storms more or less shift the balance between 
a wet year and a dry one. 
 
Image courtesy NOAA Hydrometeorology Testbed.
DroUgHT IMPACTS froM A WATEr USE PErSPECTIvE
2 0 1 2  D R O U G H T  B R O C H U R E
8
Even a single dry year can pose problems 
for activities that are wholly dependent on 
unmanaged water supplies, such as dryland 
farming or livestock grazing. 
Some unmanaged recreational uses can also be affected, 
such as rafting in rivers where flows are not controlled  
by reservoir releases. Single dry year impacts to the natural 
environment can often be seen in the form of increased 
wildfire risk, a risk that increases in multiple dry years. 
Damages associated with wildfires and loss of timber 
resources can be one of the largest economic impacts of 
drought, and California faces increasing risk of damages 
as urban development encroaches on the urban/wildland 
interface. Californiaâ€™s most devastating urban/wildland  
fire episodes (oakland hills in 1991, Southern California  
in 2003, Southern California in 2007) occurred during a drought 
or in a year immediately following a multi-year drought,  
when dry vegetation created conditions favorable for 
massive fire outbreaks.
Multiple dry years predictably create problems for 
small water systems in at-risk areas. Urban water suppliers, 
particularly those serving larger metropolitan areas, normally 
provide highly reliable supplies for their customers, as they 
have the resources and the revenue base to prepare for and 
respond to drought impacts. The majority of serious water 
Drought Impacts from a 
Water Use Perspective
SIZE DISTRIBUTION OF  
CALIFORNIA PUBLIC WATER SYSTEMS
California Department of Public Health data
Transient nCWS
CWS, large  
   
(3300+/Wholesaler) 
CWS, large  
(1000 â€“ 3300) 
CWS, large  
(500 â€“ 999) 
CWS, Small  
(100 â€“ 499) 
CWS, Small  
(25 â€“ 99) 
CWS, Small  
(<25) 
non-Transient nCWS
KEY
CWS = Community Water System
NCWS = non-community Water System
Non-transient NCWS = serves 25 or more of 
the same non-resident individuals, at least 
6-month out of the year; e.g. schools, 
places of employment, etc.
Transient NCWS = serves 25 or 
transient individuals per day, for  
any 60-days out of the year; e.g  
rest stops, campgrounds, etc.
DroUgHT IMPACTS froM A WATEr USE PErSPECTIvE
2 0 1 2  D R O U G H T  B R O C H U R E
9
supply problems during droughts (e.g. inability to maintain  
fire flows, need for truck haulage of water) are experienced 
by small water systems. Although small systems serve 
a low percentage of Californiaâ€™s total population, they 
constitute the majority of the stateâ€™s public water systems. 
Small systems tend to be located outside the stateâ€™s major 
metropolitan areas, often in lightly populated rural areas 
where opportunities for interconnections with another 
system or water transfers are nonexistent. Small systems 
also have limited financial resources and rate bases 
that constrain their ability to undertake major capital 
improvements. Most small system drought problems stem 
from dependence on an 
unreliable water source, 
commonly groundwater 
in fractured rock systems 
or in small coastal terrace 
groundwater basins. 
Historically, particularly 
at-risk geographic areas 
have been foothill areas of the Sierra nevada, Coast range, 
and inland Southern California mountains, and the north 
and Central Coast regions. 
In the irrigated agriculture sector, the largest at-risk 
area has been the west side of the San Joaquin valley, 
particularly the area supplied by Central valley Project 
south-of-Delta exports. Central valley Project contractors 
in this area received 100 percent of their supplies in  
only three years during the 23-year period from 1990 
through 2012, and 75 percent or better of their supplies  
in only eight of those years, due to combined impacts 
of dry conditions and environmental regulatory 
requirements. The impacts of reduced supplies were 
evident in the 2007-09 drought, when growers abandoned 
permanent plantings such as orchards and vineyards due 
to water shortages. 
Some avocado growers in Southern California stumped 
orchards as a short-term measure to reduce water use 
while keeping the trees alive, in hopes of improved 
future water supplies after the 2007-09 drought.
 
Orchard on Westside of San Joaquin Valley 
abandoned during 2007-09 drought .
Even a single dry year  
can pose problems for 
activities that are wholly 
dependent on unmanaged 
water supplies, such 
as dryland farming or 
livestock grazing.
DroUgHTS AnD groUnDWATEr
2 0 1 2  D R O U G H T  B R O C H U R E
10
Some users of managed surface water supplies have the 
ability to increase their use of groundwater when those 
surface supplies are reduced. 
An increase in the number of new wells being drilled or of existing 
wells being deepened is typical during droughts; private residential 
wells represent the single largest category of new or deepened wells. 
As with small water systems, residential well problems are common in 
fractured rock groundwater production areas. 
Increased groundwater use is reflected in declining groundwater 
levels; in groundwater basins not experiencing overdraft, a pattern 
of water level drawdown during dry conditions and recovery during 
wet conditions is typically seen. groundwater level decline in 
overdrafted basins is typically exacerbated by drought. 
Data availability limitations make it difficult to 
assess drought impacts on groundwater at 
statewide or large regional scales in a 
near real-time manner, as can be 
done for surface water. 
Groundwater basins as defined by DWR are shown  
in blue. Areas outside these basins are often fractured 
rock groundwater zones, where groundwater production 
capability is uncertain.
Droughts and 
Groundwater
GROUNDWATER BASINS
Guidebook to Assist Urban Water  
Suppliers to Prepare a 2010 Urban  
Water Management Plan
California  
Department of Water Resources
PrEPArIng for DroUgHTS & MITIgATIng DroUgHT IMPACTS
2 0 1 2  D R O U G H T  B R O C H U R E
11
Californiaâ€™s extensive system of statewide and  
regional-scale water infrastructure greatly enhances 
the stateâ€™s drought resilience by providing the  
capacity for facilitating water transfers and exchanges. 
lessons learned from past droughts and from 
disasters such as earthquakes and wildfires have 
fostered system interconnections among the stateâ€™s 
major water utilities, helping enable 
mitigative measure such as transfers. 
over more than three decades, Californiaâ€™s 
voters have authorized substantial amounts 
of state financial assistance to local urban 
and agricultural water agencies, funding 
projects â€” such as water conservation, 
water recycling, or groundwater storage â€“ 
that are tools for drought preparedness. In 
recent years, the 2002 Integrated regional 
Water Management Act established state 
policy of encouraging local agencies to work 
cooperatively to manage local and imported 
water supplies to improve their quantity, 
quality, and reliability. In 2002 and 2006  
the voters approved two bond measures 
which specifically authorized a combined 
$1.5 billion for water supply-related 
integrated regional water management 
planning and projects. 
Drinking water supplies are additionally 
covered by statutory and administrative 
provisions. California Water Code Sections 10610 et seq. 
require that public water systems providing water for 
municipal purposes to more than 3,000 customers or serving 
more than 3,000 acre-feet annually prepare an urban water 
management plan and update it every five years. The plans 
Preparing for Droughts 
& Mitigating Drought 
Impacts
The Urban Water 
Management Planning 
Act was adopted in 
1983, setting in motion 
a process of continuing 
refinements and updates 
to local plans for 
ensuring service area 
water supply reliability. 
must include a water shortage contingency analysis that 
addresses how systems would respond to supply reductions 
of up to 50 percent, and must estimate supplies available  
in a single dry year and in multiple dry years. The plans 
must also address systemsâ€™ responses to catastrophic 
supply interruptions. Although smaller water systems are 
not covered by these requirements, state 
drinking water regulations require that the 
systems demonstrate technical, financial, 
and managerial capacity (including having 
an emergency response plan) as part of 
being eligible for financial assistance. 
In the agricultural sector, individual 
water users (i.e., growers) are eligible for 
a variety of programs authorized by the 
farm Bill and administered through the U.S. 
Department of Agriculture. Programs range 
from risk management programs (crop 
insurance) to disaster financial assistance 
for drought impacts or prevented planting. 
Many managed water supplies have 
associated environmental regulatory 
requirements that provide dry year 
protections such as mandated instream 
flows for fishery purposes. operations 
of the State Water Project and federal 
Central valley Project in the Sacramento-
San Joaquin river Delta, for example, are 
intensively managed to meet water quantity and quality 
requirements for fish species of special concern. Major 
wildlife refuges in the Central valley have been guaranteed 
specific quantities of water since the 1990 passage of the 
Central valley Project Improvement Act. 
Even a single dry year can pose problems  
for activities that are wholly dependent  
on unmanaged water supplies, such as dryland 
farming or livestock grazing.
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