SUITABILITY ANALYSIS OF ALMOND PRODUCTION

UNDER A CHANGING CLIMATE

A Thesis

Presented to the

Faculty of

California State Polytechnic University, Pomona

In Partial Fulfillment

Of the Requirements for the Degree

Master of Science

In

Regenerative Studies

By

Arpe Kasparian

2015

iii

ACKNOWLEDGEMENTS

I could not have completed this thesis without the mentorship of my thesis

committee for which I am very grateful. I would like to thank Dr. Ed Bobich and Dr.

Denise Lawrence for their insight and support. I would especially like to thank my thesis

chair, Dr. Lin Wu, who provided invaluable knowledge and assistance in completing this

research and did so within my challenging timeline. I thank you all for your time and

dedication.

I would like to thank my family and friends for their support and for

understanding my frequent absence, both physical and mental. A big shout out to my

fellow MSRS comrades; thank you for the communal encouragement and panic.

I would also like to thank Pandora’s “The Lord of the Rings” radio station for

making me believe almond production was an adventure. I’d like to show my

appreciation for the strength and persistence of my car. Lastly, thank you, coffee because

coffee. A great big “No, thank you!” to pharyngitis, cellphone-eating storm water drains,

and hit-and-runs.

This thesis is dedicated to the tree that dedicated its life to all of the copies of this

thesis.

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ABSTRACT

Increasing global temperatures may have negative impacts on agriculture.

California’s most valuable crop, almonds, may be affected by reduced winter chill due to

climate change. This study uses GIS to develop suitability models of potential suitable

locations for growing almonds in California under three emissions scenarios using two

winter chill accumulation calculation methods. Winter chill, elevation, slope, soil type,

and distance from major landmarks, roads, and urban areas were considered when

analyzing suitability of almond production. Insufficient chilling may cause delayed and

improper bud burst resulting in poor flowering, pollination, and almond nut growth.

Therefore, increased winter temperatures may inhibit or stunt the growth of almonds.

Though it is expected that almonds may continue to grow in their current locations, it is

predicted that their crop yields and overall nut quality will decrease.

The suitability maps developed for future potential almond farm locations showed

that areas of suitability shrunk under all emissions scenarios when using the Chilling

Hours (0-7.2oC) Model. The Dynamic Model did not depict any changes in suitability

from current conditions for any of the future scenarios. The Chilling Hours (0-7.2oC)

Model results suggested that for maximum crop yields in Kern County, locations for

almond farming will generally need to shift toward northern areas since winter

temperatures tend to be lower at higher latitudes. Results of this study are limited due to

the extent of the study area, the availability of active weather station data, and the winter

chill accumulation methods used.

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TABLE OF CONTENTS

Signature Page .............................................................................................................. ii

Acknowledgements ....................................................................................................... iii

Abstract ......................................................................................................................... iv

List of Tables ................................................................................................................ viii

List of Figures ............................................................................................................... ix

Chapter 1: Introduction ................................................................................................. 1

Purpose/Problem Statement .............................................................................. 1

Chapter 2: Literature Review ........................................................................................ 3

Almonds ............................................................................................................ 3

History of Almonds............................................................................... 3

Almonds in California .......................................................................... 5

Almond Lifecycle ............................................................................................. 6

Dormancy and Winter Chill .................................................................. 7

Winter Chill Accumulation Models ...................................................... 8

Growth Requirements for Maximum Almond Yields .......................... 12

Global Climate Change .................................................................................... 14

Observed Climate Trends ..................................................................... 14

Projected Climate Trends ...................................................................... 15

Climate Change and Agriculture ...................................................................... 16

Climate Change and Almonds .............................................................. 16

Climate Change Models: Predicting Future Emissions .................................... 20

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Chapter 3: Methodology ............................................................................................... 23

Variables ........................................................................................................... 23

Winter Chill Model Comparison ...................................................................... 25

Date Sources ..................................................................................................... 25

ArcMap Tools ................................................................................................... 26

Creating the Suitability Model .......................................................................... 27

Preparing Independent Input Data Layers ............................................ 27

Combining Independent Input Data Layers .......................................... 33

Preparing Winter Chill Data Layers ..................................................... 35

Current Almond Farm Suitability ......................................................... 37

Future Almond Farm Suitability ........................................................... 37

Model Validation .............................................................................................. 43

Chapter 4: Results and Analysis ................................................................................... 47

Current Suitability of Almond Production ........................................................ 47

Future Suitability of Almond Production ......................................................... 47

Severity of Winter Chill Loss ............................................................... 48

Chapter 5: Discussion ................................................................................................... 65

Suitability Model as a Tool ............................................................................... 66

Limitations ........................................................................................................ 66

Further Research ............................................................................................... 67

Chapter 6: Conclusion .................................................................................................. 70

References ..................................................................................................................... 71

Appendix A: 2014 California Almond Acreage Report ............................................... 75

vii

Appendix B: Weather Station Attribute Table.............................................................. 77

Appendix C: Chill Portions for Fruits and Nuts ........................................................... 78

viii

LIST OF TABLES

Table 1 Projected Globally Averaged Surface Warming and Sea Level Rise at

the End of the 21st Century ......................................................................... 22

Table 2 Means and Standard Deviations of Safe Chill Modeled for Four Regions

in California’s Central Valley for 1950, 2000, 2014-2016 and 2080-2099 39

Table 3 Calculations of Times Tool Input Values ................................................... 39

Table 4 Calculations of Future Chilling Hours ........................................................ 40

Table 5 Calculations of Future Chill Portions ......................................................... 40

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LIST OF FIGURES

Figure 1 Almond kernel inside a shell (left), almond bloom (center), and

unshelled almond in an almond hull (right). ............................................... 3

Figure 2 Current almond production by county. ....................................................... 5

Figure 3 Almond lifecycle. ........................................................................................ 6

Figure 4 Mathematical equation for calculating Chilling Hours ............................... 9

Figure 5 Mathematical equation for calculating Chill Units. .................................... 10

Figure 6 Mathematical equation for calculating Positive Chill Units ....................... 10

Figure 7 Mathematical equation for calculating Chill Portions ................................ 11

Figure 8 Observed U.S. temperature change 1991-2012 compared to average

temperature 1901-1960 ............................................................................... 15

Figure 9 Projected U.S. temperature change by the end of this century under two

emissions scenarios ..................................................................................... 16

Figure 10 Winter chill in California’s Central Valley under the A2 emissions

scenario, calculated using the Chilling Hours (0-7.2oC) Model (top) and

the Dynamic Model (bottom)...................................................................... 19

Figure 11 Climate change scenarios and their future emissions concentrations and

consequent surface warming. ...................................................................... 21

Figure 12 Fuzzy membership map of Kern County elevation and ArcMap model .... 27

Figure 13 Fuzzy membership map of slope and ArcMap model ................................ 28

Figure 14 Fuzzy membership map of landmark areas and ArcMap model ................ 29

Figure 15 Fuzzy membership map of major roads and ArcMap model ...................... 30

Figure 16 Fuzzy membership map of urban areas and ArcMap model ...................... 31

Figure 17 Fuzzy membership map of soils and ArcMap model ................................. 32

Figure 18 Suitability map of almond production without winter chill variable .......... 33

x

Figure 19 ArcMap model of almond production suitability without winter chill

variable… .................................................................................................... 34

Figure 20 Fuzzy membership map of Chilling Hours and ArcMap model ................. 35

Figure 21 Fuzzy membership map of Chilling Portions and ArcMap model ............. 36

Figure 22 ArcMap model of current almond production suitability with

independent and winter chill variables. ...................................................... 37

Figure 23 ArcMap model of future almond production suitability using Chilling

Hours under three emissions scenarios for mid- and end-of-century ......... 41

Figure 24 ArcMap model of future almond production suitability using Chilling

Portions under three emissions scenarios for mid- and end-of-century ...... 42

Figure 25 Current Kern County almond farms correlate with current suitable

areas (CH) ................................................................................................... 44

Figure 26 Current Kern County almond farms correlate with current suitable

areas (CP) .................................................................................................... 45

Figure 27 CH (left) and CP (right) suitability in western region of study area ........... 46

Figure 28 CH (left) and CP (right) suitability in southern region of study area ......... 46

Figure 29 Suitability map of current almond production using the Chilling Hours

(0-7.2oC) Model .......................................................................................... 49

Figure 30 Suitability map of current almond production using the Dynamic

Model (Chill Portions). ............................................................................... 50

Figure 31 Mid-century suitability map of almond production under the B1

emissions scenario using the Chilling Hour (0-7.2oC) Model .................... 51

Figure 32 End-of-century suitability map of almond production under the B1

emissions scenario using the Chilling Hour (0-7.2oC) Model .................... 52

Figure 33 Mid-century suitability map of almond production under the A1B

emissions scenario using the Chilling Hour (0-7.2oC) Model .................... 53

Figure 34 End-of-century suitability map of almond production under the A1B

emissions scenario using the Chilling Hour (0-7.2oC) Model .................... 54

Figure 35 Mid-century suitability map of almond production under the A2

emissions scenario using the Chilling Hour (0-7.2oC) Model .................... 55

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Figure 36 End-of-century suitability map of almond production under the A2

emissions scenario using the Chilling Hour (0-7.2oC) Model .................... 56

Figure 37 Current almond farm locations on mid-century suitability map under

the B1 emissions scenario ........................................................................... 57

Figure 38 Current almond farm locations on end-of-century suitability map under

the B1 emissions scenario. .......................................................................... 58

Figure 39 Current almond farm locations on mid-century suitability map under

the A1B emissions scenario ........................................................................ 59

Figure 40 Current almond farm locations on end-of-century suitability map under

the A1B emissions scenario. ....................................................................... 60

Figure 41 Current almond farm locations on mid-century suitability map under

the A2 emissions scenario ........................................................................... 61

Figure 42 Current almond farm locations on end-of-century suitability map under

the A2 emissions scenario. .......................................................................... 62

Figure 43 Comparison of current Kern County almond farm locations under

future conditions ......................................................................................... 63

Figure 44 Comparison of severity of winter chill loss ................................................ 64

Figure 45 Almond production correlates with California’s drought intensity and

low groundwater levels ............................................................................... 69

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CHAPTER 1

INTRODUCTION

In recent years, almonds have become very popular. It is now really common to

add almond milk to your local, fair-trade coffee, use almond flour for your gluten-free

pizza crust, and almond oil for your organic, homemade, all-natural shampoo. These

products have increased the demand and production of almonds which, for the United

States, solely takes place in California. California’s Mediterranean climate makes the

Central Valley an ideal location for almost all agriculture, especially almonds, which do

not grow as nearly as abundantly in the rest of the world. However, California’s climate

is changing with increasing winter temperatures, threatening the quality of almond

production in California. Higher temperatures are causing almond trees to bloom early,

exposing them to harmful late freezes. Insufficient winter chill during their dormancy

period results in poor flowering, poor pollination, and poor nut development. In addition,

the increased demand for almonds has put a strain on California’s water supply making it

necessary for farmers to re-evaluate where almonds are grown.

Purpose/Problem Statement

The purpose of this study is to create a tool in the form of a GIS model that can

assess the suitability of future crop production in a given location. Though future

suitability of all crops should be monitored, this study focused on almond production in

the southern San Joaquin Valley. For the GIS model, different climate change scenarios

(IPCC, SRES) and different winter chill calculation methods were used. To determine

suitable locations for almond production, which are defined as locations with sufficient

winter chill, well-drained soil, and proper land use. The climate change scenarios, as

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described by the Intergovernmental Panel on Climate Change (IPCC) in their Special

Report on Emissions Scenarios (SRES), were: B1 (low emissions), A1B (moderate

emissions), and A2 (high emissions). Winter chill was calculated using two methods: the

Chilling Hours Model and the Dynamic Model. This GIS suitability analysis was used to

produce maps depicting suitable locations ranging from most suitable to least suitable.

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CHAPTER 2

LITERATURE REVIEW

Almonds

The fruit of an almond tree (Prunus dulcis) is a drupe which consists of an outer

hull and a hard shell with a seed inside (“Almond”). This seed, which is not a true nut, is

the almond we love to eat (Figure 1).

Figure 1. Almond kernel inside a shell (left), almond bloom (center), and unshelled

almond in an almond hull (right). Source: http://science.howstuffworks.com/life/botany

History of Almonds

Almonds are from the deserts and mountain slopes of central and southwest Asia.

They were well adapted to the mild, wet winters and very dry, hot summers at medium

elevations of the region (Micke, 1996, p. 1). There are two types of almonds: bitter and

sweet. Bitter almonds contain cyanide and may be toxic to humans when too much is

consumed; sweet almonds are produced commercially (Duke, 2001, p. 249). Both types

of almonds have been cultivated in the Mediterranean since before recorded history

(Riotte, 1993, p. 110). There were several attempts to bring almonds to the United States,

but because of the risk of frost, rain, and humidity during their growing season in most

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areas, almond trees were not successfully established until they were planted in

California in 1843 (Riotte, 1993, p. 111). California’s Mediterranean climate, with its

rainfall seasons coinciding with those of the native range of almonds, was very suitable

for growing this crop. When almond trees were first introduced in California, it was

found that cross pollination was needed for almond production since few almond

varieties are self-fertile (Micke, 1996, p. 52). A.T. Hatch, a horticultural expert at the

time, selected four varieties of almonds – Nonpareil, IXL, Ne Plus Ultra, and La Prima –

in 1879 that worked well together ("Almond Production", 2015). Nonpareil became the

standard variety in California; Ne Plus Ultra and another variety, Peerless, became the

main pollinizers (Micke, 1996, p. 2). Today, there are more than 2 dozen varieties of

almonds grown in California (Almond Board of California).

Between 1900 and 1925, almond production was established and orchards were

planted on hillsides without irrigation, as was the traditional European method (Micke,

1996, p. 2). Farmers soon discovered that they could substantially increase their almond

yields with irrigation and some fertilization. Between 1925 and 1955, farmers found that

almond trees grew well on fertile, deep, well-drained soil (Micke, 1996, p. 2). In 1950,

the Almond Board of California was established to stabilize the industry and provide

support funds for research for the advancement of almond production (Micke, 1996,

p. 2). With the improvement of harvesting technology and new projects that brought

irrigation to the southern San Joaquin Valley, almond production expanded and acreage

increased threefold. Shifts from other fruit crops to almonds and a decline in the

European almond industry both increased demand for California almonds (Micke, 1996,

p. 2).

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Almonds in California

Almond production reached a new high in 2011 with 760,000 acres of bearing

orchards producing 2.02 billion pounds of almonds (Geisseler, 2014, p. 1). Today,

California produces all of the nation’s almonds and 80% of the world’s almonds. After

the U.S., Spain, Italy and Iran are top almond producing countries in the world. In

California, Kern, Madera, Fresno, Stanislaus, and Merced counties produce the most at

over 100 million pounds of almonds annually (Figure 2; Almond Board of California). In

2014, the almond industry was valued at $11 billion making almonds a leading cash crop

and California’s #1 export (Fujii, 2014). See Appendix A for more information on

almond acreage and value. Growing almonds in California hasn’t been so simple

recently. The increases in temperature coupled with the drought have forced price hikes

and inconsistent crop yields (Kasler, 2014).

Figure 2. Current almond production by county.

Source: Almond Board of California

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Almond Lifecycle

Almond trees take 2-4 years to bear nuts, and will produce nuts for 20-25 years

(Riotte, 1993, p. 17). In winter months, from November to February, almond trees go

through a period of dormancy. During this time, almond trees require adequate winter

chill in order to break dormancy (Micke, 1996, p. 41). Once temperatures are high

enough, sometime between February and early March, almond tree buds burst into

bloom. During this time, populations of bees are brought to almond orchards for

pollination (“Almond Lifecycle”). Almonds continue to mature through June: their shells

begin to harden and their kernels begin to form. Almond hulls begin to split open in July

and early August. At this time the almond shells are exposed and dried. Almonds are

harvested from mid-August through October. Mechanical tree “shakers” vigorously shake

the trees until almonds drop to the ground where they lay for 8-10 days to dry naturally.

Almonds are then swept up by machines and processed through hullers where all debris is

removed. Almond kernels are then separated into bins according to size and either

shipped or processed further (Figure 3; “Almond Lifecycle”).

Figure 3. Almond lifecycle. Source: Almond Board of California

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Dormancy and Winter Chill

During the winter months, deciduous trees enter dormancy and refrain from bud

growth to avoid damage from cold or freezing weather (Niederholzer, 2012). There are

two stages of winter dormancy: endodormancy (the first stage) and ecodormancy (the

second stage).

During endodormancy, growth is limited by an unknown internal factor in the

plant bud and only ends when the tree reaches its chilling requirement. A chilling

requirement is the amount of cool temperatures a tree needs in order to break dormancy

(Luedeling, Zhang, Luedeling, & Girvetz, 2009, p. 23). Chilling requirements vary for

different species of fruit and nut trees, as well as different varieties of the same species;

they may also vary by location. Once the plant has experienced its chilling requirement,

the endodormancy stage ends and the ecodormancy stage begins (Niederholzer, 2012).

The second stage of dormancy is controlled by the temperature just prior to bud

burst. Like the chilling requirement, deciduous trees also require a certain amount of

warm temperatures to trigger growth after endodormancy is complete. Once the heat

requirement is fulfilled, buds burst and ecodormancy ends (Niederholzer, 2012).

The difference between the two stages of dormancy cannot be visually seen.

There have been several studies that have attempted to calculate dates at which almond

trees transfer from one stage to the next (Alonso, Anson, & Espian, 2005); however,

more research is necessary to verify those dates and understand the conditions of transfer.

It has been found that the more chilling accumulated in the winter, the less heat is

required to begin bud break. For many areas with cool winter temperatures, winter

chilling requirements are met well before the winter season is over, but the lack of warm

8

temperatures keep the trees from blooming. To speed up bloom, some farmers spray their

orchards with rest breaking agents, such as hydrogen cyanamide, which cut the first stage

of dormancy short and allow for the accumulation of heat units. However, this only

works if 70% of the chilling requirement has been met. In warmer climates, lower

Chilling Hours can disrupt the dormancy process and result in uneven bud break and poor

flowering (Niederholzer, 2012).

Winter Chill Accumulation Models

The fulfillment of a deciduous tree’s chilling requirement is essential to ensure

even blooming times, proper flowering, and good nut set. Researchers have developed

several ways to calculate how much chill a particular tree needs and have developed

several models including the Chilling Hours Model, the Utah Model, the Positive Utah

Model and the Dynamic Model. This study focuses on two of these: the Chilling Hours

Model and the Dynamic Model. These models provide insight into the chilling

requirements of crops as well as the available chill at a given location. It is important for

farmers to select crop locations with its locational chill in mind and to match the

location’s chill with the chill requirement of their crops (Luedeling, Zhang, Luedeling, &

Girvetz, 2009, p.23).

As previously mentioned, several models have been developed to calculate winter

chill. These models convert temperature records into a metric of coldness (Leudeling,

2009, p. 1). The most basic model used by most farmers is the Chilling Hours Model

developed in the 1930s and 1940s. This model measures winter chill in Chilling Hours

(CH) and assigns one Chilling Hour to every hour below 7.2oC (45oF) during the dormant

season. It was soon discovered that temperatures below freezing do not contribute to chill

9

accumulation. For this reason, the model was revised to assign one Chilling Hour to

every hour between 0 and 7.2oC (32oF-45oF). Figure 4 shows the mathematical equation

for the Chilling Hours (0-7.2oC) Model. Chilling Hours Model is the simplest and most

widely used calculation for winter chill accumulation; however, with this model, all hours

are considered equal and hold the same weight.

Figure 4. Mathematical equation for calculating Chilling Hours.

Source: (Luedeling, Zhang, Luedeling, & Girvetz, 2009, p. 25)

California almond chilling requirements are mostly calculated in Chilling Hours

and different sources claim different ranges. For example, some almond cultivars require

as little as 200-400 CH. The Almond Board of California researchers (UC Davis Nut and

Fruit Information Website) state that almonds require 400-900 CH. None of the sources

specify which version of the Chilling Hours is used to calculate the chilling requirement.

In addition to the fact that freezing temperatures do not contribute to chill

accumulation, warmer temperatures can negatively affect it. The Utah Model, developed

in the 1970s, addresses this issue by assigning a weight for each temperature range

including negative weights for warm temperatures (Leudeling, 2012, p. 219). Figure 5

shows the mathematical equation for the Utah Model, which measures chill in Chill Units

(CU). The weights and temperature ranges for the Utah Model vary depending on the

climate of a certain region.

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Figure 5. Mathematical equation for calculating Chill Units.

Source: (Luedeling, Zhang, Luedeling, & Girvetz, 2009, p. 26)

Many variations of the Utah Model were later introduced including the Positive

Utah Model, which is recommended for use in regions with warmer climates. In this

model, the negative contributions of warm temperatures are removed from the original

model (Figure 6). In California, only the original version of the Utah Model is used

(Luedeling, Zhang, Luedeling, & Grevitz, 2009, p. 26).

Figure 6. Mathematical equation for calculating Positive Chill Units.

Source: (Luedeling, Zhang, Luedeling, & Girvetz, 2009, p. 26)

The most biologically accurate chill accumulation method is the Dynamic Model

which was developed in Israel in the 1980s (Luedeling, Zhang, Luedeling, & Grevitz,

2009, p. 24). The Dynamic Model measures chill in Chill Portions (CP). With this model,

a Chill Portion is accumulated through a two-step process. In the first step, an

intermediate chill product is produced under low temperatures. If conditions remain

favorable, the intermediate product is converted to a Chill Portion. However, this first

stage is reversible and the intermediate product can be destroyed by heat. Once a Chilling

Portion is attained, it is permanent and cannot be reversed. Figure 7 shows the

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mathematical equation for calculating Chill Portions where slp, tetmlt, a0, a1, e0 and e1 are

experimentally derived constants, TK is hourly temperature in Kelvin, t is the time during

the season, and t0 is the starting point of chilling accumulation (Luedeling, Zhang,

Luedeling, & Girvetz, 2009, p. 26). The major difference between the Dynamic Model

and other chill accumulation models is its consideration of the sequence of temperatures

during dormancy (Leudeling 2012, p. 219). Thus, unlike other models, similar

temperatures at different times have different effects on chill accumulation. All hours are

not considered equal and do not hold the same weight.

Figure 7. Mathematical equation for calculating Chill Portions.

Source: (Luedeling, Zhang, Luedeling, & Girvetz, 2009)

Recently, the Chill Portions for the Nonpareil almond variety was determined to

be 22 Chill Portions (Pope, Dose, Silva, Brown, & DeJong, 2014). Even with this new

information, further research is necessary to test and confirm the chilling requirements

for almonds, especially in lieu of climate change. Many researchers agree that the

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Dynamic Model is the most accurate in both measuring current chill accumulation and

predicting future winter chill. However, understanding the Dynamic Model is challenging

and farmers today still use the simpler Chilling Hours (0-7.2oC) Model. It is unclear if

and when freezing temperatures are included in the calculations.

Growth Requirements for Maximum Almond Yields

It takes about 2-4 years for an almond tree to begin to bear almonds. Once

established, almond trees can produce nuts for about 20-25 years (Riotte, 1993, p. 17).

Although almond trees are drought tolerant and do not require much to bear nuts, specific

almond requirements must be met in order to produce maximum yields regularly and to

produce them commercially.

Almond trees grow well in the hot, dry climate of central California, and do

poorly in very wet locations (Duke, 2001, p. 250). Almond trees require a period of cold

during their winter dormancy period in order to properly blossom in the spring. When

plants do not reach their chilling requirement they will flower poorly, if at all, which can

result in less fruit (Kitsteiner, 2011). According to the Almond Board of California,

almond trees require 400-900 cumulative Chilling Hours below 7.2oC (45oF). When

chilling requirements are met, almond trees bloom more evenly and during ideal

pollination periods. When almond trees receive too few or too many Chilling Hours,

Units, or Portions, buds may burst too soon, the blooming period may be shorter, or

flowering may be insufficient (Blake, 2007). Almond trees are known to bloom very

early, some as early as February, which makes almond trees very susceptible to frost

injury or damage caused by late freezes (Riotte, 1993, p. 111).

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Almond trees are not self-fertile, and therefore require the presence of other

almond varieties for pollination in order to produce a crop. Almond trees may also be

fertilized by peach trees that bloom at the same time; however, in an orchard setting, it

can be difficult to coordinate blooming of the two trees (Riotte, 1993, p. 111). Almond

farmers in California rely on bee colonies to pollinate their orchards (Riote, 1993,

p. 111).

Historically, almonds have grown on a variety of soils. Californian almond

farmers have found that for highest crop yields, it is best to grow almond trees in deep,

well-drained loam (Riotte, 1993, p. 112). Although almond trees may grow well in sandy

soils (Duke, 2001, p. 251), loam soils are preferred because they are more fertile, retain

enough water so irrigation is more manageable, and have good root-zone aeration.

Almond tree roots do not do well in heavy soils, such as clay, because they do not drain

well, which may lead to an anoxic environment (Micke, 1996, p. 21), resulting in root rot

in almond trees (Riotte, 1993, p. 112). Almond tree roots can extend to a depth of 12 feet,

but they extract most of their nutrients from the top six feet of soil (Riotte, 1993, p. 112).

For this reason, it is best to have uniform subsoil so that watering and orchard growth and

production can be uniform (Micke, 1996, p. 20). During their first growing season,

almond trees benefit from nitrogen fertilizer (Riotte, 1993, p. 115) and may require

phosphorus fertilizer as well (Duke, 2001, p. 251).

Surprisingly, almond trees are drought-tolerant and naturally, have only used soil-

stored winter rainfall as their main water source. However, since demand for almonds

have increased, almond orchards are now irrigated to produce higher yields and better

quality almonds (Micke, 1996, p. 41). Almond trees need enough water early in their

14

growing season to ensure that the nuts harden in time for harvesting. Not enough water

will slow the enlargements of almonds, reduce shoot growth, result in poor hull split, and

premature leaf drop, all of which will lead to lower almond yields (Micke, 1996, p. 41).

In addition, excess water may be needed in order to maintain a favorable level of salinity

in the root zone (Micke, 1996, p.41). On the other hand, too much irrigated water and

poor soil drainage suffocates roots and can lead to soilborne diseases such as

Phytophthora crown or root rot (Micke, 1996, p. 41).

Global Climate Change

Observed Climate Trends

For the past century, average global temperatures have increased by more than

0.72oC (1.3oF), which has been caused by the unprecedented buildup of greenhouse gases

in our atmosphere and is attributed to human activity (EPA, 2014). According to the U.S.

Global Change Research Program, the average temperature in the United States has

increased by 0.72oC to 1.1oC (1.3 to 1.9oF) (Melillo, 2014, p. 29). Figure 8 shows

observed temperature changes in the U.S. between 1991 and 2012 compared to the

average temperature between 1901 and 1960. Almost all regions in the U.S. have

increased average temperatures by more than 0.85oC (1.5oF).

15

Figure 8. Observed U.S. temperature change 1991-2012 compared to average

temperature 1901-1960. Source: U.S. Global Change Research Program

Projected Climate Trends

Temperatures are expected to continue current rising trends. According to the

IPCC, average global temperatures are expected to increase by 1.1oC to 6.4oC (2oF to

11.5oF) by the end of the century. The exact temperature increase within this range

depends on the level of future greenhouse gas emissions; the more emissions the greater

the temperature increase (Pachauri, 2015). Not only are global temperatures continuously

increasing, they are increasing at a much higher rate. In the United States, surface

temperatures are projected to increase by about 4oF to 11oF depending on future

emissions levels. Figure 9 shows projected temperature changes in the U.S. under high

(A2) and low (B1) emissions scenarios.

Several biological and physical systems are affected by global warming including

marine and terrestrial ecosystems, precipitation patterns, and arctic ice. These, in turn,

impact human systems such as our health, economy, and agriculture (Pachauri, 2015).

16

Figure 9. Projected U.S. temperature change by the end of this century under two

emissions scenarios. Source: www.ipcc.ch

Climate Change and Agriculture

Perhaps the most vulnerable and significant anthropogenic system climate change

threatens is our agricultural system. Climate change causes crop and livestock production

yields to decline due to increased stressors such as precipitation extremes, higher

temperatures, and increases in weeds, diseases and insects. Lack of cold temperatures

may threaten perennial crops that depend on a certain range of winter chill, such as

almonds. Warmer winters can also lead to early bud burst which can result in frost

damage if crops are exposed to a late freeze. Exposure to high temperatures during the

pollination period also increases the risk of low crop yields and crop failures (Hatfield,

2014).

Climate Change and Almonds

Increasing temperatures and greenhouse gas emissions may jeopardize almond

production in California. Almonds have specific growing conditions that must be met in

order to produce maximum and good quality yields. The optimal temperature for their

growth is between 15oC and 30oC (60oF and 85oF). Although higher temperatures and

17

emissions concentrations may increase growth rates, it does not necessarily mean that it

will increase production. An increase in growth rate causes plants to mature more quickly

exposing them to nutrient depletion in the soil during their growing season; also, the risk

of frost damage from a late freeze can result in smaller almond size or crop failure

(Hatfield, 2014). In addition, increase in temperatures causes a decrease in winter chill,

which is a requirement for healthy crop development. According to the IPCC, cumulative

Chilling Hours have decreased over the past few decades and are expected to

continuously decrease (Pachauri, 2015).

Studies have shown that the amount of winter chill in the Central Valley has been

declining due to warming temperatures. This poses a threat to many fruit and nut crops in

California that depend on adequate chilling for proper growth (Baldocchi & Wong,

2007).

Luedeling, Zhang, Luedeling, and Grevitz (2009) first studied the 1950-2000

winter chill patterns of California’s Central Valley and found that overall chill had

declined by at least 30%. In 1950, the Central Valley could expect between 700-1200

Chilling Hours (p. 3). The study continued to model future winter chill under several

climate change scenarios and found that under all scenarios, winter chill declined

substantially by the end of the 21st century (Figure 10) with only 78% of the Central

Valley being suitable for cultivars with 500 Chilling Hours by the end of the 21st century,

under the low and moderate emissions scenarios. Under the high emissions scenario, only

39% of the Central Valley was suitable for production. Luedeling et al (2009) predicted a

similar declining trend when using the Dynamic Model to measure winter chill. However,

the decline in chill was far less severe in all future scenarios. This model projected

18

decreases in winter chill by 30-60% compared to 1950 conditions by the end of the 21st

century.

Almonds bloom early; thus reduced cumulative Chilling Hours coupled with

warmer temperatures may trigger even earlier bud burst. Blooming periods may be

shorter and coordinating pollination during irregular blooms can be difficult and costly.

Lower winter chill may also result in little to no flowering which is vital for pollination.

If pollination is weak or does not occur, the tree will produce smaller, if any, almonds

(Blake, 2007).

Insufficient chilling can result in poor physiological symptoms such as delayed

foliation, reduced fruit set, and reduced fruit quality. In almond trees, uneven and

incomplete flowering can result in poor pollination (Byrne & Bacon, 1992), which can

result in smaller nuts and a reduced crop yield as was exemplified during the 1995-1996

crop year. Kern County experienced record low chilling for the 1995-1996 crop year,

which only accumulated 336 Chilling Hours compared to their average 700 Chilling

Hours. This resulted in a very low crop yield of 960 meat pounds per acre; about half of

what they produced the previous year (Viveros, 2006).

Because orchards remain in production for decades, consideration of future

expected winter chill is necessary for the longevity of an orchard and for proper orchard

management (Luedeling, Zhang, Luedeling, & Grevitz, 2009, p. 1). Even though climates

may be favorable at the time of orchard planting, they may become unfavorable during

the course of an orchard’s productive life.

19

Figure 10. Winter chill in California’s Central Valley under the A2 emissions scenario,

calculated using the Chilling Hours (0-7.2oC) Model (top) and the Dynamic Model

(bottom). Source: Luedeling, Zhang, Luedeling, and Grevitz, 2009.

20

Climate Change Models: Predicting Future Emissions

Climate change models are mathematical, computer-based representations of the

interactions between land, ocean, and atmosphere that help scientists predict future

climate conditions (EPA, 2014). These models divide the earth into a grid. At each grid

point, values of predicted variables, such as temperature, are calculated over time to

predict their future values (EPA, 2014). Current climate change models show that the

global temperature has increased over the past century (EPA, 2014). In order to predict

climate change, future greenhouse gas emissions must be estimated (EPA, 2014). Since,

future greenhouse gas emissions depend on multiple variables, scenarios of future

emissions are developed and predictions are made. Models are based on the

characteristics of these scenarios. Characteristics of scenarios depend on human behavior

and may include factors such as population growth, economic activity, energy

conservation, technological advances, and land use (EPA, 2014).

Some of the most widely used global climate change scenarios are those

developed by the Intergovernmental Panel on Climate Change (IPCC) in their Special

Report on Emissions Scenarios. The IPCC is a group of over 2,000 scientists from all

over the world that operate under the auspices of the United Nations to review and assess

impacts of global climate change as well as mitigation and adaptation options. These

scenarios predict concentration of future greenhouse gas emissions which are eventually

translated to temperature changes and other climate factors such as precipitation. The

report illustrates several scenarios; however, this thesis will focus on the three most

commonly used scenarios: scenario B1, a low emissions scenario; A2, a high emissions

scenario; and A1B, a moderate emissions scenario (Figure 11).

21

Figure 11. Climate change scenarios and their future emissions concentrations and

consequent surface warming. Source: IPCC, 2014

The main characteristics of the B1 (low) scenario include low population growth,

high economic growth, rapid technological innovation, emphasis on renewable energy

sources, and protection of biodiversity. The characteristics of the A2 (high) scenario

include high population growth, low economic growth, slow technological innovation,

emphasis on fossil fuels, and low resource protection. Lastly, the characteristics of the

A1B (moderate) scenario include low population growth, high economic growth, rapid

technological innovation, a balanced emphasis on all energy sources, and active

management of resources (Davidson, 2000).The SRES translates greenhouse gas

emission concentrations to relatable factors such as temperature change and sea level rise

(Table 1). Under the B1 (low) scenario, global average surface temperature is projected

to increase by an estimated 1.8oC or between 1.1 and 2.9oC by the end of the century.

Under the A2 (high) scenario, temperatures are expected to increase by 3.4oC or between

2.0oC and 5.4oC and under the A1B (moderate) scenario, the projected temperature

increase is 2.8oC or between 1.7oC and 4.4oC by the end of the century (Pachauri, 2015).

22

Table 1

Projected Globally Averaged Surface Warming and Sea Level Rise at the End of the 21st

Century

Source: www.ipcc.ch

23

CHAPTER 3

METHODOLOGY

ArcMap 10.2.1 was the GIS program used to develop the suitability models for

almond suitability in California’s Kern County. Kern County is located in the San

Joaquin Valley and produces more almonds than any other California county, with 427.2

million pounds in 2014 and over 150,000 acres (California almond acreage report,

2014). Kern County is also the southernmost county to produce almonds; thus, it was

hypothesized that the almond farms in this county were at greatest risk of climate change

threats than counties to the north.

Variables

To determine which locations are and will be suitable for almond production, the

following variables were taken into consideration: winter chill, elevation, slope, soil type,

and distance from major roads, urban areas, and landmarks with the amount of winter

chill as the dependent variable. Variables such as precipitation, bee colony strength, and

temperatures during the growing season were not considered in this study.

Precipitation was not taken into consideration because almond production

depends heavily on irrigation, not precipitation, for their water source; further, almonds

can produce without irrigation in typical rainfall years. Like most crops farmed in

California, almond orchards must be watered all year long. Almost all precipitation in

California occurs only during winter months and even then does not meet almond water

needs alone. Therefore, precipitation was not considered when analyzing suitable

locations for almond production.

24

Although bee colony strength is vital to the production of almonds, such a

variable would be difficult to define geographically. Also, the strength of bee colonies

depends on several factors such as pesticide use, lack of genetic diversity caused by

monocultural agriculture, and climate change. Since the cause of the decline in bee

colony quality is relatively unknown, it would be difficult to predict its strength under

current conditions and future climate change scenarios. The inclusion of poor quality bee

data would weaken the quality of this study as a whole. Furthermore, the focus of this

study is the effects of declining winter chill; the inclusion of another dependent variable

would result in too many scenarios. It is also important to note that the bee colonies used

in almond production are rented from bee handlers in the Midwest who transport their

bees to almond farms during the pollination season (Almond Board of California). Local

“natural” bees are not used for almond tree pollination.

In this study, it is assumed that California receives enough heat during almond

growing seasons. Increased temperatures due to climate change will not affect the

growing temperature requirement of almond trees; therefore, growing season

temperatures are not included in this study. Almond trees require 15-30oC during their

growing season. Average temperatures in the San Joaquin Valley and the Sacramento

Valley go beyond these requirements and are only expected to continue to increase. The

effects of higher temperatures on almond production have not been studied extensively;

however, increased growing season temperatures caused by global climate change may

increase the rate of almond production (Lobell, 2011, p. 330).

25

Winter Chill Model Comparison

The Chilling Hours (0-7.2oC) Model is the simplest and most widely used method

for calculating winter chill accumulation among farmers in California. However, its

simplistic approach also makes it less accurate, especially when predicting future winter

chill conditions. On the other hand, because the Dynamic Model accounts for the

sequence of winter temperatures, it has been found to be more accurate when predicting

future conditions; though the complexity of it has kept it from being commonly used

among farmers. To compare how these different methods of winter chill calculation differ

when predicting suitability of almond production, two separate models were developed:

one with winter chill calculated using the Chilling Hours (0-7.2oC) Model and the other

with winter chill calculated using the Dynamic Model.

Data Sources

To prepare input data layers, a digital elevation model (DEM) of Kern County

was obtained from the United States Geological Survey (USGS) website. The DEM was

used to create a slope and elevation layer as input data layers in ArcMap. The California

soil data layer was obtained by the U.S. Department of Agriculture and Natural

Resources Conservation Service and obtained from the ArcGIS website. The remaining

input data layers (California urban areas, California major roads, and California

landmarks) were data layers obtained from ESRI Data 10.2.1. These six input data layers

formed the basis of the suitability map.

To determine locational weather information, all active Kern County weather

stations as well as its surrounding weather stations were plotted. These weather stations

are: Shafter, Blackwells Corner, Arvin-Edison, Famoso, Belridge, Kettleman, Alpaugh,

26

Delano, Palmdale Central, and Palmdale. Geographical, elevation, and temperature data

of these weather stations were obtained from the California Irrigation Management

Information System (CIMIS, 2015) website. All calculations of Chilling Hours and Chill

Portions for each weather station were obtained from the University of California Davis

Fruit and Nut Research and Information website. See Appendix B for complete Weather

Station attribute table. NAD 1983 UTM Zone 11N was the coordinate system used.

ArcMap Tools

To depict the suitability of almond locations, the fuzzy membership tool with

different parameter settings was applied to all data layers. This tool rescales the input

data to a 0 – 1 scale “based on the possibility of being a member of a specified set;” in

this case, the scale was based on suitability of almond production (Mitchell, 2012, p.

129). An assignment of 0 to a specific location means it is definitely not a member of the

specified set. In this case, an assignment of 0 means that location is definitely not suitable

for almond production. An assignment of 1 to a specific location means it is definitely a

member of the specified set, or a suitable location for almond production. For all other

points, the closer to 1 the more suitable the location, and the closer to 0 the less suitable

the location (Mitchell, 2012, p. 129).

The assignment of membership is determined by almond growth requirements and

the fuzzy membership function applied. The level of membership (or suitability) is

illustrated with a range of colors. In this study, green depicts most suitable locations,

while red depicts least suitable locations. After all map layers were assigned fuzzy

membership, they were combined using the fuzzy overlay tool. The location of weather

stations delineate the extent of the Kern County suitability map.

27

Creating the Suitability Model

Preparing Independent Input Data Layers

1. Elevation: The elevation requirements for almond production are: 3-91 m (ideal) and

457 m (max). To prepare the elevation data layer, the fuzzy membership tool was

directly applied to the DEM data layer with a negative linear membership type where

the minimum elevation is 3 m and the maximum is 457 m. Lower elevations are

assigned greater suitability (Figure 12).

Figure 12. Fuzzy membership map of Kern County elevation and ArcMap model.

28

2. Slope: Almond orchards, like all orchards, are best managed when they are planted on

flat land. To prepare the slope data layer, the slope tool was applied to the Kern County

DEM layer. Next, fuzzy membership was applied with a negative linear membership type

where the minimum slope was 0 degrees and the maximum was 2 degrees. Lower slope is

assigned greater suitability (Figure 13).

Figure 13. Fuzzy membership map of slope and ArcMap model.

29

3. Distance: Almond farms should be established a safe distance away from major

landmarks, roads, and urban areas since harvesting almonds emits large amounts of

dust into the air making it uncomfortable and unhealthy for locals. Two thousand

meters was the safe distance chosen for suitability. To prepare this layer, first the

Euclidean distance tool was applied to the polygon features of landmarks, roads, and

urban areas. Next, the fuzzy membership tool was applied with a positive linear

membership type where the minimum distance is 2,000 meters with no maximum.

Areas with a distance of at least 2,000 meters from landmarks, roads, and urban areas

were assigned complete suitability (Figures 14, 15, and 16).

Figure 14. Fuzzy membership map of landmark areas and ArcMap model.

30

Figure 15. Fuzzy membership map of major roads and ArcMap model.

31

Figure 16. Fuzzy membership map of urban areas and ArcMap model.

32

4. Soil: Although almond trees do best in loamy soils, they are able to thrive in other well-

draining soils. Thus, the suitability of the soil was determined by its soil drainage type.

Well drained soils were assigned complete suitability and very poorly drained soils were

assigned zero suitability. Before suitability was assigned, the polygon layer was first

converted to a raster layer, after which soil drainage features were reclassified

(Figure 17).

Figure 17. Fuzzy membership map of soils and ArcMap model.

33

Combining Independent Input Data Layers

1. Almond Suitability Input Data Layers: The suitability layers of all six independent

variables (elevation, slope, soil, and distance from landmarks, major roads, and urban

areas) were combined using the fuzzy overlay tool with product overlay type. The

resulting map serves as the input data layer for observing and analyzing differences in

suitability with the two winter chill accumulation models (Figures 18 and 19).

Figure 18. Suitability map of almond production without winter chill variable.

34

Fig

ure

19. A

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35

Preparing Winter Chill Data Layers

1. Chilling Hours: Almond trees require 400-900 Chilling Hours between the months of

November and February. A five-year (2010-2014) average of Chilling Hours

(0-7.2oC) was calculated for each weather station and interpolated using the spline

tool (spline type: tension, weight: 5) to create a Chilling Hours data layer. The fuzzy

membership tool was applied with a positive linear membership type where the

minimum Chilling Hours is 400 and the maximum is 900. Areas with higher Chilling

Hours are considered more suitable (Figure 20).

Figure 20. Fuzzy membership map of Chilling Hours and ArcMap model.

36

2. Chill Portions: The Nonpareil almond variety requires at least 22 Chill Portions

between the months of November and February. Number of Chill Portions were

calculated for each weather station using the Dynamic Model and interpolated using

the spline tool (spline type: tension, weight: 5) to create a Chill Portions data layer.

The fuzzy membership tool was applied with a positive linear membership type

where the maximum Chill Portions is 22. Areas with higher Chill Portions are

considered more suitable (Figure 21).

Figure 21. Fuzzy membership map of Chill Portions and ArcMap model.

37

Current Almond Farm Suitability

To view current suitable locations for almond farms, the independent layers and

winter chill layers were combined using the fuzzy overlay tool with product overlay type.

The layers were combined twice to produce two suitability maps that reflect the different

winter chill calculation methods: Chilling Hours (0 – 7.2oC) Model and Dynamic Model

(Figure 22). The resulting maps illustrate a range of suitable areas for almond production

considering winter chill, soil type, elevation, slope, and distances from major landmarks,

roads and urban areas. Green areas depict suitable locations, while red areas depict

unsuitable locations (Figure 29 and 30).

Figure 22. ArcMap model of current almond production suitability with independent

and winter chill variable.

Future Almond Farm Suitability

To develop maps of future suitability of almond farm locations, the effects of

higher climate on winter chill was considered. According to Luedeling’s study on the

effects of increased temperatures on winter chill, winter chill is expected to decrease in

the future under all emissions scenarios. Specific reductions in winter chill are listed in

Table 2. Luedeling’s values were used to calculate percent reductions of winter chill

38

(Table 3) which were then used to determine future Chilling Hours and Chill Portions

values for all emissions scenarios (Tables 4 and 5).

To depict this change in winter chill on the suitability maps, the times tool was

applied to all winter chill layers. Next, the fuzzy membership tool was applied to the

resulting reduced winter chill layers and combined with the independent input data layers

with the fuzzy overlay tool (Figures 23 and 24). Weather station data shows that current

Chill Portions are well above the 22 CP almond requirement for all emissions scenarios.

With the predicted future chill values, we see that Chill Portions are, again, well above

the CP requirements for all scenarios. When looking at the worst case scenario (end-of-

century, A2 emissions scenario), Chill Portion levels drop to approximately 37.9 CPs.

Although it’s close to the borderline of the CP threshold, it is still sufficient enough to

show complete suitability within the study area.

Chill Portions models for all future scenarios were generated; however, as the

data suggests, future suitable locations remained exactly the same as current suitable

locations. Therefore, although the Chill Portions model was run, only maps of the future

Chilling Hours suitability will be shown. Excluding Chill Portions maps, the resulting six

maps show suitability of almond production using the Chilling Hours (0-7.2oC) Model by

mid-century and by end-of-century under three emissions scenarios: B1 (low), A1B

(moderate), and A2 (high). See Figures 31-36.

39

Table 2

Means and Standard Deviations of Safe Chill Modeled for Four Regions in California’s

Central Valley for 1950, 2000, 2014-2060 and 2080-2099

Source: Luedeling, 2009

Table 3

Calculations of Times Tool Input Values

Beginning

Century

(2000)

Mid-21st Century

(2041-2060)

End-21st Century

(2080-2091)

Current B1 A1B A2 B1 A1B A2

Chilling

Hours 844

697 647 649 587 489 423 Predicted

CH

0.17 0.23 0.23 0.30 0.42 0.50 Percent

Reduction

0.83 0.77 0.77 0.70 0.58 0.50 Times Tool

Value

Chill

Portions 64.3

54.5 50.6 52.2 47.6 41.6 37.9 Predicted

CP

0.15 0.21 0.19 0.26 0.35 0.41 Percent

Reduction

0.85 0.79 0.81 0.74 0.65 0.59 Times Tool

Value

40

Table 4

Calculations of Future Chilling Hours

Table 5

Calculations of Future Chill Portions

41

Figure 23. ArcMap model of future almond production suitability using Chilling Hours

under three emissions scenarios for mid- and end-of-century.

42

Figure 24. ArcMap model of future almond production suitability using Chill Portions

under three emissions scenarios for mid- and end-of-century.

43

Model Validation

The suitability model was generated for both current Chilling Hours and Chill

Portions. Fuzzy membership of the elevation and slope layers show that all eastern and

southern areas are unsuitable; therefore, all current suitability maps also show

unsuitability in those areas.

To validate the model, current Kern County almond farm locations were added to

the current almond suitability maps for both Chilling Hours and Chill Portions (Figures

25 and 26). Most current almond farms are located in the northern parts of the study area

where most of the currently suitable sites occur. There are some almond farms in both

maps that lie on the edges of the suitability area. Although these areas may not appear to

be suitable, there are several factors such as the limitations with elevation and the micro-

climate of the area that may allow for almond production. These farms may also be

located a shorter distance from major roads, landmarks, and urban areas than the

suggested 2,000 meters. As expected, there are no almond farms in the completely

unsuitable areas in the eastern and southern regions.

The Chilling Hours map shows less suitability than the Chill Portions map,

especially in the western and southern parts of the total area of suitability. When looking

at the Chilling Hours map, it appears that some almond farms are located in those

unsuitable areas; however, the Chill Portions map shows that those areas are actually

more suitable. This supports the belief that the Dynamic Model is more tolerant than the

Chilling Hours Model when measuring winter chill accumulation. For both maps,

locations of current farms correlate with current suitability; therefore, we can be

confident that the model results are valid.

44

Figure 25. Current Kern County almond farms correlate with current suitable areas (CH).

45

Figure 26. Current Kern County almond farms correlate with current suitable areas (CP).

46

Figure 27. CH (left) and CP (right) suitability in western region of study area.

Figure 28. CH (left) and CP (right) suitability in southern region of study area.

47

CHAPTER 4

RESULTS AND ANALYSIS

Current Suitability of Almond Production

The eastern and southern areas of Kern County appear to be completely

unsuitable on the resultant maps under all conditions. The location with the most

suitability appears in the northwest area of Kern County. The map depicting the Chilling

Hours (0-7.2oC) model shows the most suitability. The map depicting the Dynamic

Model is similar to the Chilling Hours (0-7.2oC) map though less complete suitability is

illustrated in the center of the suitable area (Figures 29 and 30).

Future Suitability of Almond Production

The future suitability maps using the Chilling Hours (0-7.2oC) Model show a

decline in suitable almond farm locations for all emissions scenarios (Figures 31-36).

Under the low emissions B1 scenario, suitable locations diminish slightly by mid-

century, and become very slim by the end of the century. With a moderate emissions

scenario, there is only a small patch of suitable area which completely disappears by the

end of the century. There are no suitable locations for almonds by the end of the century

under the moderate scenario. With the high emissions scenario, suitable locations in the

mid-century match those of the moderate emissions scenario. However, by the end of the

century, Kern County is completely unsuitable for almond production. Unsuitable land is

located primarily in the southernmost regions early in the century and increases

northward as the century progresses.

Although it is clear that winter chill is declining, winter chill accumulation for

almonds remains sufficient for all emissions scenarios when using the Dynamic Model. It

48

is important to note that the Chill Portions requirement for almonds have not been

extensively studied and confirmed. The Chill Portions requirement used was for one

almond variety and was presented as a threshold; whereas the Chilling Hours requirement

was for almonds in general and was presented as a range creating stricter suitability

membership parameters. Therefore, all areas that received at least 22 Chill Portions were

considered to be completely suitable, while areas that received 400 Chilling Hours (the

minimum) were not considered to be completely suitable, only somewhat suitable.

Further research is necessary to understand the chilling requirements of all almond

varieties.

The results of this study show differing suitability maps for the two winter chill

calculation methods. When almond farms in Kern County are plotted on future almond

suitability maps using Chilling Hours, we see that most almond farms will be growing

under increasingly stressful conditions with decreasing winter chill (Figures 37-42). The

suitability of almond farm locations diminish in the southern areas, but somewhat remain

in the northern areas indicating that suitable locations for future almond production may

be shifting northward to higher latitudes within the study area.

Severity of Winter Chill Loss

Severity of winter chill loss under the Chilling Hours Model can be depicted by

using the minus tool in ArcMap to subtract current and future Chilling Hours (Figure 44).

Areas with the greatest decline in winter chill (though those areas may still remain

suitable for almonds) are shown in red. Illustrating winter chill loss under the Dynamic

Model was not possible since the suitability maps of current and future winter chill were

the same.

49

Figure 29. Suitability map of current almond production using the Chilling Hours

(0-7.2oC) Model.

50

Figure 30. Suitability map of current almond production using the Dynamic Model (Chill

Portions).

51

Figure 31. Mid-century suitability map of almond production under the B1 emissions

scenario using the Chilling Hours (0-7.2oC) Model.

52

Figure 32. End-of-century suitability map of almond production under the B1 emissions

scenario using the Chilling Hours (0-7.2oC) Model.

53

Figure 33. Mid-century suitability map of almond production under the A1B emissions

scenario using the Chilling Hours (0-7.2oC) Model.

54

Figure 34. End-of-century suitability map of almond production under the A1B

emissions scenario using the Chilling Hours (0-7.2oC) Model.

55

Figure 35. Mid-century suitability map of almond production under the A2 emissions

scenario using the Chilling Hours (0-7.2oC) Model.

56

Figure 36. End-of-century suitability map of almond production under the A2 emissions

scenario using the Chilling Hours (0-7.2oC) Model.

57

Figure 37. Current almond farm locations on mid-century suitability map under the B1

emissions scenario.

58

Figure 38. Current almond farm locations on end-of-century suitability map under the B1

emissions scenario.

59

Figure 39. Current almond farm locations on mid-century suitability map under the A1B

emissions scenario.

60

Figure 40. Current almond farm locations on end-of-century suitability map under the

A1B emissions scenario.

61

Figure 41. Current almond farm locations on mid-century suitability map under the A2

emissions scenario.

62

Figure 42. Current almond farm locations on end-of-century suitability map under the A2

emissions scenario.

63

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65

CHAPTER 5

DISCUSSION

If future winter chill conditions are not considered in future orchard management,

it could have dire consequences. The decline in suitability of almond production in the

San Joaquin Valley has many implications for future agriculture in the area. In Kern

County, other crops such as apples, apricots, cherries, and nectarines also have winter

chilling requirements; thus declines in chilling will affect them as well (see Appendix C

for Chill Portions of other crops). In 2014, 19,868 acres of almond trees were planted in

California, with 3,135 acres were planted in Kern County alone (California almond

acreage report, 2014). Almonds are lucrative crops for farmers only if they survive.

This study was conducted with almonds as the main crop; almonds are known to

have relatively low chill requirements. Solving this problem may be as simple as

switching to low-chill almond varieties or, selecting only those crops that will thrive

under the changing climate of California. The rise in popularity of almonds resulted in

farmers ditching their annual crops and planting long-term orchards. Perhaps, the switch

should be made back to yearly crops whose planting will be determined by annual

climate cues. However, there are many more crops grown in the great agricultural lands

of California (deciduous and not) that also have winter chill requirements such as apples

and cherries. Apples, for example, require well over 1000 Chilling Hours and may be

enduring climate stress today.

California’s climate makes it an ideal location for growing crops. Therefore,

planning for the future and adapting to future climate conditions today, would be the best

way to sustain our agricultural system and our environmental resources in California.

66

Suitability Model as a Tool

This project serves as more than a one-time study; it is a tool. The ArcMap model

developed to study the suitability of almond production in the Southern San Joaquin

Valley can be used to study suitability elsewhere using two winter chill calculation

methods. Weather station information of a particular area would need to be added as well

as an adjusted winter chill reduction rate for that particular area. The winter chill

conditions of any county in California can be obtained from weather station data found

on the UC Davis Fruit and Nut Information Website.

Limitations

The limitations of this study include the extent and scale of the study area, the

availability of active weather station data, the scale of the study, and the chill models

used. The Chilling Hours requirements were difficult to confirm. Not only were they

never specified for a particular almond variety, but when displayed, the type of Chilling

Hour calculation method was also not mentioned. Requirements ranged from 250-300

CH (Traynor, 2011), to 200-350 CH (Traynor, 2012) from the same source at a different

time, to 300-600 CH (Niederholzer, 2013), to 500-600 CH (“Chill Hours”), and 400-900

CH (Crisosto, 2011). The last range was chosen to stay consistent with all data sources.

Data on all winter chill calculations and their models were retrieved from the UC Davis

Fruit and Nut Information website. Low-chill almond varieties were not considered since

impacts of reduced winter chill would not have affected them.

In addition, the current average winter chill in the study area was a short 5-year

average. An average of a longer time period would improve precision of the study. Also,

the area surveyed was limited to the active weather stations in it. Five active weather

67

stations in Kern County and five more from surrounding areas were used. The area where

there were more weather stations had more visible suitability displayed. The inclusion of

more weather stations may have produced a more detailed map. Areas that were shown as

unsuitable may have been labeled so because of the lack of a nearby weather station to

more precisely fill in the data of that area.

If more time were available, I would have loved to explore the suitability of all

areas in California to see whether there would be added suitable areas at the northern end

of the Central Valley and other areas in California for almonds and other crops requiring

winter chill.

Further Research

This study opened many unanswered questions that require further research and

study. To begin with, suitability was only defined by a small number of variables. When

determining suitability for almond production one must take spring and growing season

temperatures into consideration. Almonds are an early-blooming tree; some varieties

even bloom in February during winter when they may be susceptible to late winter

freezes. It is essential that temperatures between February and April are monitored for

any tendencies of freezing. Locations that experience late freezes are not suitable.

Growing season temperatures as well as those during pollination should be considered as

well. It is important that there is no rain, and little to no wind during pollination so that

bees are able to pollinate as many trees as possible. Because the Southern San Joaquin

region is usually warm and with favorable temperatures, these variables were not

considered. However, when determining suitability in other locations, such as the

Sacramento Valley, these variables should be considered.

68

The cultivar, or almond variety, used should also be taken into account. There are

over two dozen varieties of almonds grown in California and each have a unique set of

climatic and winter chill requirements. Low-chill almonds can be planted in areas with

lower chill available; however, the quality of these nuts may not be the same and orchard

management will have to be adjusted to accommodate a new lifecycle and production

schedule. The Chill Portions have only been calculated for one almond cultivar:

Nonpareil. Because the Dynamic Model has been observed to be the most accurate of all

models, it would be helpful to develop the Chill Portions requirement for several more

almond varieties grown in California.

Although most of the information on almonds and almond production obtained

for this study come from local sources such as the Almond Board of California and from

farmer blogs, this study did not seek any local knowledge directly. It is well known that

quantitative studies may differ from reality and the only way to confirm their validity

would be to confirm locational conditions with locals directly. In most agriculture, micro-

climate, which is the climate immediately surrounding a particular area, can be controlled

by the farmers. It is unclear if and how these micro-climates are controlled.

Most importantly, this study assumes something that we all know is not true: there

is water in California. The current mega-drought has indicated that water may not always

be available for almond production. The drought has depleted most of California’s

surface water and has forced many farmers to seek water underground. It is difficult to

estimate how much water we have left underground. The lax laws on groundwater

(basically, if you can get it, it’s yours) has farmers scrambling to get their orchard needs

met. Thus, the suitability models may be more optimistic than reality. Though almond

69

production cannot be solely blamed for California’s drought, it would be responsible to

consider its toll on California’s water supply (Figure 45). It can be assumed that locations

at higher latitudes with greater precipitation can be more suitable than those in southern

California where water is scarce. However, even a good amount of precipitation is

probably not enough for the nonstop water needs of an almond orchard. It is important to

remember that almond orchards, like all other fruit and nut crops, require water all year

long for as long as they live. Unlike other crops, almond trees cannot be left fallow

during a dry spell. This will destroy the orchard entirely resulting in lost funds and

resources. It is imperative that the availability of water be considered before any orchard

planning takes place.

Figure 45. Almond production correlates with California’s drought intensity and low

groundwater levels. Source: Mother Jones

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CHAPTER 6

CONCLUSION

The suitability maps developed for future potential almond farm locations show

that areas of suitability for almond farms shrink within the study area under all emissions

scenarios when using the Chilling Hours (0-7.2oC) Model. Areas of suitability are

generally disappearing from the southern agricultural areas of California. In Kern

County, for example, suitable areas remain in the northernmost regions. However, the

same areas remain suitable under all emissions scenarios when using the Dynamic

Model, even though total Chill Portions are also declining. The decline in winter chill is

shown to be more severe and more rapid when using the Chilling Hours (0-7.2oC) Model.

When using the Dynamic Model, it does not appear that future almond farm production

will be threatened by the decline in winter chill.

Farmers must understand the long-time investment of almond orchards, its

climatic requirements (now and during their lifespan), and the availability of all resources

necessary for a good quality crop. If farm management fails to do this, resources that

could have otherwise been used for other crops will be lost. At a time where climate

sensitivity can no longer be ignored, it is imperative that future climate change be

incorporated into farm management. To do so, it is imperative that farmers and

researchers develop a clear understanding for calculating winter chill. More research on

dormancy and vernalization is essential in determining and confirming winter chill

requirements for fruit and nut crops in California.

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APPENDIX A

2014 CALIFORNIA ALMOND ACREAGE REPORT

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77

APPENDIX B

WEATHER STATION ATTRIBUTE TABLE

5-Year Average Winter Chill Calculations

Station Station Name 2014 2013 2012 2011 2010 CP AVG

5 Shafter 68 83 70 74 70 73

54 Blackwells Corner 59 52 69 76 86 68

125 Arvin-Edison 48 57 68 72 77 64

138 Famoso 67 64 73 80 85 74

146 Belridge 54 56 69 72 79 66

21 Kettleman 48 37 47 73 74 56

203 Alpaugh 61 63 70 75 85 71

182 Delano 65 59 67 50 82 65

220 Palmdale Central 56 60 68 72 - 64

197 Palmdale 60 68 72 79 79 72

Station Station Name Elev. Lat. Long. CH CP

5 Shafter 360 35.53256 -119.282 988 73

54 Blackwells Corner 705 35.64986 -119.959 952 68

125 Arvin-Edison 500 35.20558 -118.778 769 64

138 Famoso 415 35.60311 -119.213 966 74

146 Belridge 410 35.50583 -119.691 785 66

21 Kettleman 340 35.86775 -119.895 580 56

203 Alpaugh 210 35.86258 -119.504 1002 71

182 Delano 300 35.833 -119.256 950 65

220 Palmdale Central 2630 34.59222 -118.128 913 64

197 Palmdale 2550 34.61498 -118.032 970 72

Station Station Name 2014 2013 2012 2011 2010 CH AVG

5 Shafter 854 1078 - 1002 1016 988

54 Blackwells Corner 771 819 944 1089 1136 952

125 Arvin-Edison 478 816 821 789 941 769

138 Famoso 708 906 966 1133 1117 966

146 Belridge 578 822 882 703 938 785

21 Kettleman 427 436 439 853 744 580

203 Alpaugh 1048 953 953 928 1126 1002

182 Delano 854 995 944 - 1007 950

220 Palmdale Central 791 945 952 963 - 913

197 Palmdale 939 1004 929 979 997 970

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APPENDIX C

CHILL PORTIONS FOR FRUITS AND NUTS

79