The Spatial Structure of Land Use from 1970â€“2000 in the Phoenix

The Spatial Structure of Land Use from 1970–2000 in thePhoenix, Arizona, Metropolitan Area

Eric KeysThe University of Florida

Elizabeth A. Wentz and Charles L. RedmanArizona State University

This article explores the dimensions of rapid urbanization in the Phoenix Standard Metropolitan Statistical Area(SMSA) over the past thirty years with respect to land use change. We devote primary attention to developing anunderstanding of what land transformations took place, the extent to which they occurred, and where theyoccurred. Our findings indicate that 32 percent of the Phoenix SMSA changed between 1970 and 2000. Morethan half of the overall change was from agriculture to some form of urban land use, and although a largepercentage of the region remains open desert the parcels of desert are increasingly fragmented. This hassignificant implications for urban ecology and biodiversity. The growth indicates that rather than a pattern thatreflects the agglomeration effects of a polycentric metropolis, the central business district of the City of Phoenixdominates the region. This has implications with respect to employment patterns, traffic congestion, and urbanair quality and climate. Key Words: land use/land cover change, Phoenix, urbanization.

The Phoenix-Mesa Standard MetropolitanStatistical Area (SMSA; hereinafter

Phoenix1) is a rapidly growing, spatially expan-sive metropolitan area in the American West.For some, it exemplifies automobile-orientedurbanization mirrored in places such as LasVegas, Albuquerque, and Salt Lake City (Tea-ford 1993; Gober and Burns 2002). To others,Phoenix represents some of the direst problemsfacing urban growth: increasing water demands,billowing smog creation, and intensifying socialisolation (Gober, McHugh, and Reid 1991; Ko-erner and Klopatek 2002; Hawkins et al. 2004).Phoenix grew to a population nearing 3.5 mil-lion people mainly over the past fifty years(Gammage 1999). This article describes landtransformations since 1970 and the impact ofthose transformations on the urban structure.We anticipate that better understanding of thetypes of urban growth sheds light on othertransformations in periurban regions beyondPhoenix (Fink et al. 2003). The growth patternsand environmental stresses that Phoenix nowexperiences may reflect those of rapidly growingcities in other arid parts of the world (Blowers

1993; McDonald 1998; Blowers and Pain 1999;Stefanov, Ramsey, and Christensen 2001;Goudie 2004; IHDP 2005). Recent meetingsand science plans indicate that urbanization (interms of both the drivers and the consequences)is one of the central issues of interest to globalchange science, both for the potential impacts ofthis change on urban areas and for the ways thatcities contribute to global change (IHDP 2005).

Urban growth in Phoenix features low-densityurban development that moves into surroundingagricultural and desert land (Gober et al. 1998;Waits 2000; Jenerette and Wu 2001). Land con-version generally shifts from semiarid desertvegetation and agricultural land to residentialand commercial urban land uses. This article firstidentifies and quantifies the types of land trans-formations occurring since 1970. We expect thatmost land-use changes represent transitionstoward residential urban land use and itssupporting infrastructure (e.g., transportation,commercial) given the dominance of residentialland use in cities. Where residential land usesgrow, however, is of importance to economicand ecological planning; therefore this article

The authors acknowledge the input of many colleagues without whom this article never would have been written. Keys especially appreciates thecomments of the anonymous reviewers. Any errors and omissions are the responsibility of the authors. Funding for this research was provided by theNational Science Foundation (#DEB-9714833), Central Arizona Project—Long Term Ecological Research. Gratitude also goes to Barbara Trapido-Lurie (Arizona State University) for producing the graphics.

The Professional Geographer, 59(1) 2007, pages 131–147 r Copyright 2007 by Association of American Geographers.Initial submission, May 2005; revised submissions, March and June 2006; final acceptance, June 2006.

Published by Blackwell Publishing, 350 Main Street, Malden, MA 02148, and 9600 Garsington Road, Oxford OX4 2DQ, U.K.

explores from what and to what land useschanged. In Phoenix the conversion of the sur-rounding Sonoran desert and agriculture forurban use attains special significance as bothwater and natural vegetation are considered to beof paramount importance (MAG 2003, 2006).This article explores where urban developmentoccured in terms of what types of lands wereconverted and at what distance from the citycenter.

Urban geography examines the physicalstructure of the urban landscape and how thatstructure changes over time. Social science ex-planations of urban morphology and land userefer to theories from Alonso (1964), Christaller(1966), Von Thunen (1966), and Muth (1969),which recognize that, all things being equal, theleast valuable land use lies the most distant fromthe urban core. Athough Von Thunen’s IsolatedState and Christaller’s Central Place Theoryheld sway in urban geography for the first half ofthe twentieth century, contemporary urbangeography enriches economic-based land usediscussions describing why a particular land uselies where it does by recognizing the importanceof local and regional politics, social and culturalchoices, and transportation advances.

Therefore, the second focus of this article isevaluation of the neoclassical economic bid-rent theory by looking at the intensity of landuse types at different distances from the urbancore and how this pattern changes over time.The broad assumptions of bid-rent theory arethat the city is located on a flat plain, transportcosts are relative to distance, the city has onecentral business district (CBD), and the peopleliving in the city make economically rationaldecisions with respect to residential and em-ployment location (Thrall 1987). We usedPhoenix to test the general idea that land valuesdecrease as distance from city center declines.The bid-rent focus presents an interestingproblem in Phoenix since it is a conglomerateof approximately twenty-one incorporatedareas, suggesting that a polycentric metropolismay better reflect the land use pattern. We hy-pothesize, however, that the City of Phoenixcontinues to drive urban development over theother incorporated areas and that the represen-tative patterns of bid-rent relationships areevident with the Phoenix CBD as thecore. Understanding how Phoenix, and byextension other rapidly developing cities, has

grown portends important consequences foranalyzing traffic flows, employment patterns,air quality, and other challenges associatedwith metropolitan areas (Waits 2000; IHDP2005).

Urban Land Use

Almost universally, urban land-use change stud-ies document human impact on the natural en-vironment through urbanization (Leung 1974;Sisk 1998; Fagan et al. 2001; Grimm and Red-man 2004; IHDP 2005; Seto and Fragkias 2005;Tan, Li, and Lu 2005). Documenting land usechange supports numerous human impact in-vestigations on topics such as biodiversity andecological changes (Martin 2001; Hope et al.2003; Berling-Wolff and Wu 2004; Miltner,White, and Yoder 2004; Long and Schorr 2005),air pollution and climate (Bolin et al. 2000;Grossman-Clarke et al. 2005; Mennis and Jor-dan 2005), and the spread of diseases (Barbieri,Sawyer, and Soares 2005). Understandingmore than just the extent of change furtheraids such investigations. For example, Seto andFragkias (2005) quantified the patterns of landuse change in four Chinese cities, demonstrat-ing that geographic and geometric descriptorsof urban growth provide more informationrelevant to ecology than do simple growthdescriptions. Like Seto and Fragkias (2005), weanalyze the structure of the urban landscape,providing understanding of the urban growthby discussing the geographic location of landuse change beyond the extent of cumulativegrowth using distance from a center point as ageographic descriptor.

Understanding the extent of land transfor-mation and the urban structure of Phoenix pro-vides a basis of comparison and insight intogrowth in other rapidly growing arid cities inthe Southwest and globally. As an urbanizingregion, Phoenix represents the second wave ofU.S. urbanization; its rapid growth occurredduring the past fifty years rather than duringthe industrial revolution. Phoenix moreresembles Los Angeles and Las Vegas—and indeed much of urban growth world-wide—in terms of its rapid urbanization andsuburbanization associated with the automo-bile. Designed with automobile owners inmind, Phoenix features wide streets, expansive

132 Volume 59, Number 1, February 2007

residential lots, and quickly built commercialdevelopments (Sisk 1998).

Phoenix, located in Maricopa County, Ari-zona, was first occupied by Native Americans,Hohokam people, in the third century BCE andending around 1400 CE, representing the firstsuccessful urbanization in the American South-west (Redman 1999; Dean 2001). After the de-cline in Hohokam populations the Phoenix arearemained sparsely populated until the late nine-teenth century when settlers arrived from east-ern portions of the United States (Sheridan1995; Gammage 1999; Gober 2005). Rapid ur-banization in this area encouraged economicactors to convert nonurban lands such as desertand agriculture to residences, commercialspace, and other urban land uses.

Our description of land use change expandson previous studies of land use in Phoenix byemploying finer categories and more temporalresolution. Stefanov and others (Stefanov,Ramsey, and Christensen 2001; Stefanov 2002)employed an expert system to classify land coverfor 1998 in the Phoenix SMSA with LandsatThematic Mapper imagery. They identifiedtwelve distinct land cover categories, includingdistinctions between mesic residential (irrigatedlandscaping) and xeric residential (desertlandscaping). In a number of studies Jeneretteand Wu (2001) and Wu, David, and Jenerette(2003) studied land cover change from 1912 to1995 using Markov cellular automata simula-tions to backcast and forecast three land cov-ers—urban, agriculture, and desert—with afourth class, ‘‘no data,’’ describing nonclassifiedareas. Our research builds on these studies byemploying datasets with more time periods thanthe Stefanov (2002) study and more categoriesthan the Jenerette and Wu study (2001).

Our research contributes methodologicallyto challenges associated with transdisciplinaryresearch. Urban-based research enjoys a longtradition in geography, planning, sociology, andrelated disciplines; now other disciplines studycities as well. Among those disciplines thatthis article contributes to are biology, geology,climatology, and ecology. These traditionallynatural science disciplines now recognizethat the human impact on the biosphere andatmosphere is indelible and also recognize theimportance of comprehending coupled human-environment systems (Sisk 1998; Grimm et al.2000; IHDP 2005).

Methods

Study Area

The Phoenix–Mesa SMSA consists of the city ofPhoenix and fourteen other incorporated cities.We restricted the present study to the boundaryof the Central Arizona Project–Long TermEcological Research (CAP-LTER) study areathat includes the City of Phoenix, surroundingcities, and near-urban desert (Figure 1). Duringthe twentieth century, the area grew to be one ofthe largest urban areas in the United States. At agrowth rate of 45.3 percent per decade, thePhoenix area grew to 3.25 million people be-tween 1990 and 2000. This elevated metropol-itan Phoenix’s national ranking from 19 in 1990to 14 in 2000 (United States Census Bureau2000), and Phoenix proper to be the sixth largestcity in the United States by 2004 (City Mayors2006). It is projected that over the next twentyyears the resident population will increase al-most 70 percent, regional transportation willrise nearly 80 percent, and congestion levels areexpected to rise alongside them (MAG 2006).

The area’s climate combines warm tempera-ture (261C annual mean maximum) and low pre-cipitation (20 cm annually) to make an attractivedestination for both part-time winter dwellersand full-time new residents (Gammage 1999).Influenced by climate, the area was previouslydominated by stands of creosote bush (Larreatridentate L.) and burrsage (Ambrosia deltoidea L.).Human hydrological alterations in the form oftransported water increase the amount of wateravailable for vegetation and animal life. Hopeet al. (2003) report that urban portions of the cityhave higher levels of plant biodiversity than theneighboring open desert as householders opt forvaried landscape choices.

Data

We restricted land use and land cover data toapproximately 200 one-mile-square block re-gions (Figure 2). These blocks represent theland-area surrounding each ecological censuspoint from the CAP-LTER biological survey/inventory. Most of the individual blocks dem-onstrate a variety of land use/cover classes (cf.Figure 3 in the Results section). Ideally, therewould have been complete spatial coverage ofland use but resources required to interpret aer-ial photography for the entire Phoenix area(�7,650 km2) for four time periods were

The Spatial Structure of Land Use from 1970–2000 in the Phoenix Metropolitan Area 133

unavailable. Instead, the 200 regions represent aweighted random sample from the study areaso there are representatives from urban,agricultural, and natural land use/land covertypes (Hope et al. 2003). Sample designersweighted the sample to highlight plots in thehigh urban density area ringed by a partiallycompleted Loop 101-202-303 highway system.

The CAP-LTER project digitized land use/land cover data from aerial photographs. For1970, 1980, and 1990, hardcopy photographswere obtained from Landiscor Aerial Informa-tions (Phoenix, AZ) at a scale of 100 ¼ 1,2000 andscanned. For 2000, digital images with a reso-lution of 0.5 m/pixel were acquired from KennyAerial Mappings. Land use/land cover datawere interpreted and digitized from the digitalimages into Arc Views shape files in the Arizonastate plane coordinate system in zone¼ 3176.Since the hardcopy maps were scanned intodigital form, the operators experience little dif-ference between the early years and the year

2000 set. There were five operators, threesupervisors and technical support, and one per-son who guided the development at monthlymeetings. When difficulties arose in interpret-ing land use, the lead supervisor made the finaldecision. The final data sets contain twenty-eight unique categories, based on a modifiedAnderson Level 2 classification scheme, withshort definitions of each land use, listed in col-umn 3 of Table 1.

To understand the impact of the samplingstrategy on analysis, we compared the CAP-LTER sampled data to land use developed bythe Maricopa Association of Governments(MAG), a council of local governments that in-fluence county politics and decision making.The MAG data cover the full spatial extent ofthe study area for the year 2000. We comparedMAG and CAP-LTER datasets to evaluatewhether or not the continuous coverage ofMAG agreed with the sampled coverage ofCAP-LTER. MAG data are classified into

Figure 1 The Phoenix metropolitan area with Loop 101-202-303 boundary indicating high-density sam-

pling areas.


forty-four categories (Table 1, column 2). Thedata are used for a variety of planning purposesincluding socioeconomic forecasting and airquality modeling. The original MAG data werein the Arizona State plane coordinate system, inzone¼ 3176 in feet.

Analysis

The CAP-LTER dataset has twenty-eight cat-egories and the MAG dataset has forty-fourcategories. MAG’s emphasis on transportationplanning and economic development is reflect-ed in its categories that focus on commercial andemployment sectors. To use MAG and CAP-LTER as confirmatory data sets, we generated acommon classification system (Table 1, column1). We compared the new classification systemfor significant variations in terms of the per-centage of land in given uses to verify thesampling strategy of the CAP-LTER with thecontinuous MAG dataset. The LTER from theyear 2000 and the MAG data, also year 2000,were converted into a new system with twentycategories. We calculated the percentage area

for each class and compared their relative per-centages. We also calculated the differencebetween the two percentages. In general, thesample and the MAG data compared well toeach other, allowing us to carry out our analysis.

The second step of the analysis involved cal-culating transition matrices on both the Level 1(the more general land use/land cover classifi-cation system) and Level 2 (the more detailedsystem) using the CAP-LTER data. The tran-sition matrices calculated the amount of landuse change that occurred on a particular parcelover a particular period. For the Level 2 anal-ysis, in which we employed a more detailedclassification system, we calculated the percent-age area in given land uses. From this calcula-tion, we ranked the top ten categories for eachin terms of area percentage. To calculatetrajectories, we used 1970 as the base year forcomparisons with subsequent years. Upon com-pleting the transition descriptions, we builttransition matrices that aided in the identifica-tion of current land use types and the stagesthat that parcel went through to arrive at the

Figure 2 Location of the 200-point CAP-LTER biological census, used as sample plots for this study.

CAP-LTER¼Central Arizona Project—Long Term Ecological Research.


current state. Transition matrices enable abetter understanding of how urban land chang-es in conditions of rapid growth.

In addition to transition matrices, we ana-lyzed land use by distance from the center ofPhoenix both relative to the same land use andrelative to other land uses at a given distance.We compared land uses during the four times(1970, 1980, 1990, and 2000) and graphedwhere the land uses were most intensive usingtwo different methods. We calculated the in-tensity of land use types in concentric rings fromthe Phoenix urban core to test central placetheory. We used the intersection of the maincross streets in the City of Phoenix as the centrallocation (Central Avenue and Van Buren Street,with the coordinates 400261, 3701667 in Ari-zona State Plane coordinates). From that loca-tion, concentric rings at 7, 14, 21, 28, 35, 42, 49,and 63 km were identified. The percentage ofeach land use type at each distance was calcu-lated. We repeated the analysis for each of ourfour periods, 1970, 1980, 1990, and 2000. Wealso analyzed how the percentages of a land usetype at certain distances compared over time.These data analyses allow us to understand how

land use has changed in the Phoenix-MesaSMSA over space and time.

Results

The CAP-LTER data for the four periods rep-resent a sample of land uses in MaricopaCounty. The MAG dataset is a continuous cov-erage of land uses and land covers. Table 2compares the revised land use categories be-tween the two datasets for the year 2000. Wenote that although most categories exhibitagreement, significant differences in samplingof agriculture and open space exist between thetwo datasets (Table 2). Categories that fell with-in one standard deviation of this difference wereconsidered to represent the same overall per-centage, but categories that fell outside onestandard deviation were not. Of the existingdisagreements, we see that the CAP-LTERshows more active open space/parks than theMAG dataset outside of the Loop 101-202-303dataset, most likely the result of classificationdifferences from the two teams assessing landuse. The weighted sampling method employedselected urban areas more than unoccupied

Figure 3 Example of the land use as represented in one of the 200-point sample locations.


desert yet we found general agreement betweenthe CAP-LTER and MAG datasets in terms ofthe percentage of land devoted to urban uses.Without the weighted methods, the 200-pointsurvey of the CAP-LTER would demonstratethat most of the land in the research region is

desert and unchanged over the past thirty years.Similar explanations hold true regarding thelower representation of desert and open space inthe CAP-LTER; these areas received a lowerpreference in the weighted random samplingstrategy employed. Given the overall agree-

Table 1 New classification system for comparing MAG and CAP-LTER land use classes

New category codes MAG codesa CAP-LTER codes

Small lot residential High density residential Small lot residential

Small lot residential

Very small lot residential

Medium density

Medium lot residential Medium lot residential Medium lot residential

Large lot residential Large lot Large lot residential

Very large lot

Rural residential Rural residential Rural residential

Very high density Very high density High density

Educational/institutional Educational Institutional

Institutional

Commercial General Commercial

Specialty

Neighborhood

Community

Regional

Superregional commercial

Office general

Office low rise

Office mid rise

Office high rise

General employment

Tourist and visitor accommodations

Business park

Industrial Industrial Industrial

Public facilities

General industrial

Warehouse/distribution centers

Mining No MAG Mining

Large assembly area Special events Large assembly areas

Cemeteries Cemeteries No LTER

Other employment Other employment (low) No LTER

Other employment (medium)

Other employment (high)

Under construction No MAG code Graded, under construction

Golf courses Golf courses Golf courses

Active open space/parks Active open space Parks

Vacant/desert General open space General open space

Passive open space Desert

Vacant Vacant

Agriculture Agriculture Active cropland

Fallow cropland

Active pasture

Orchard

Feeding operations

Water Water Streams, rivers, canals

Lakes

Transportation General transportation Highway

Roads Major roads

Streets

Railroad

Airport Airport Airport

Note: MAG ¼ Maricopa Association of Governments; CAP-LTER ¼ Central Arizona Project—Long Term Ecological Research.aThe original MAG classification included a category ‘‘General residential’’ that referred to unclassified or unclassifiable residential

lands. This is omitted from the present analysis as all residential land has been classified.


ment, we felt confident using the CAP-LTERdata to examine urban land use change.

We present the Level 1 transition matrixbased on the CAP-LTER data in Table 3. Thetable shows the change in total area of each cat-egory and the change in average parcel size foreach category. With an overall increase in resi-dential and commercial and decrease in agri-culture and desert/vacant, the data conveyurbanization processes for spatially expandingurban areas. Even as the overall area in residen-tial and commercial area has changed, parcelsizes have remained essentially unchanged—with the exception of open desert, which has

experienced decreasing parcel size. Althoughdesert remains the most abundant land use inthe sample, its absolute coverage is declining, asis the size of desert patches. Fragmentation ofdesert portends important ecological implica-tions for species that traverse that desert as wellas for invasive species that take advantage ofedges. The Level 1 analysis confirms that agri-culture and desert in the Phoenix area transformto urban land uses, findings reported in Jene-rette and Wu (2001). Of the years examined inthis study, 1970 witnessed the top four land usesin the Phoenix SMSA as extensive land uses orcovers (agriculture, desert, open space, and

Table 2 Comparison of the percentage of total area for each of the land use classes in the MAG andCAP-LTER databases for 2000 as reflected by the new categories of land use classes

Land use classes Inside Outside

MAG (%) CAP-LTER (%) Differencea MAG (%) CAP-LTER (%) Differencea

Small lot residential 32.42 29.08 3.34 2.57 2.19 0.38

Medium lot residential 5.08 7.70 �2.62 1.42 2.44 �1.02

Large lot residential 7.28 6.06 1.22 3.22 0.27 2.95

Rural residential 0.10 4.27 �4.17 1.01 3.83 �2.82

Very high density 1.55 3.19 �1.64 0.03 0.10 �0.07

Educational/institutional 3.33 4.22 �0.90 0.25 0.27 �0.02

Commercial 7.44 8.72 �1.28 0.43 0.35 0.08

Industrial 5.96 3.12 2.83 0.86 0.18 0.68

Mining 0.00 0.00 0.00 0.00 0.08 �0.08

Large assembly area 0.11 0.21 �0.10 0.04 0.00 0.04

Cemeteries 0.09 0.00 0.09 0.01 0.00 0.01

Other employment 0.08 0.00 0.08 0.92 0.00 0.92

Under construction 0.00 1.75 �1.75 0.00 2.08 �2.08

Golf courses 1.99 0.00 1.99 0.86 1.07 �0.21

Active open space/parks 8.08 1.71 6.37 5.49 0.27 5.23Vacant/desert 13.29 16.03 �2.75 64.07 65.64 �1.57

Agricultural 9.27 9.87 �0.59 13.80 18.12 �4.32Water 1.69 1.59 0.10 4.16 2.25 1.91

Transportation 1.62 1.50 0.12 0.23 0.48 �0.24

Airport 0.63 0.98 �0.35 0.62 0.40 0.22

Note: MAG¼Maricopa Association of Governments; CAP-LTER¼Central Arizona Project—Long Term Ecological Research.aBold numbers indicate that the percentage difference for the class fell outside one standard deviation.

Table 3 Comparison of land use conversions in the CAP-LTER sample, in km2

1970 1980 1900 2000

Totalarea

Averageparcel size

Totalarea

Averageparcel size

Totalarea

Averageparcel size

Totalarea

Averageparcel size

Agricultural 1880.83 5.951995 1418.179 5.836129 1183.085 4.868663 935.0523 4.561231

Commercial 157.0997 0.801529 227.5558 0.776641 294.8136 0.790385 340.8019 0.831224

Graded, under

construction

119.244 1.611405 181.5876 1.815876 153.9473 1.729745 130.3184 1.94505

Industrial 21.77674 1.146144 48.64689 1.569255 84.26025 1.87245 94.81559 1.896312

Institutional 142.1049 1.52801 178.6679 1.285381 134.5141 0.755697 164.1501 0.752982

Open 2973.885 7.93036 2798.436 5.360989 2906.336 4.64271 2634.574 3.851717

Residential 799.5669 2.284477 1296.351 2.81204 1731.77 2.735813 2098.569 2.862987

Transportation 69.47148 1.828197 74.91188 1.628519 89.75056 1.693407 114.9596 1.796244

Water 121.5569 1.870107 135.3057 1.4549 153.2692 1.197416 143.4825 1.024875

Note: CAP-LTER¼Central Arizona Project—Long Term Ecological Research.


rural); the later stages demonstrate an intensi-fication of land uses (residential, institutional,and commercial classes), especially as repre-sented by the absolute and relative increase ofresidential lands.

Figure 3 shows that in addition to overallchanges in land use over the past thirty years, theplot level complexity of changes in the area alsochanged. Figure 3 is an example of a plot thatfollowed a transition from agriculture and opendesert to a fragmented combination of desert,

agriculture, residential, and commercial landuse classes. As the Phoenix-Mesa SMSA under-goes infill and increased population densities,we can expect these types of changes to intensify.

Figure 4 illustrates the rank position of eachland use category through the four periods. Thetop ten categories represent approximately 90percent of the total database in each year.2 Thisdiagram illustrates that desert remains the high-est overall in total land area and that agriculturallands are losing ground to residential and other

Figure 4 Relative rank position of the top ten land use categories from 1970 to 2000.

Figure 5 Change in percent of several of the top land use categories from 1970 to 2000.


urban uses. Figure 5 shows changes in totalpercentages for each individual category. Deserthas ranked first in all four periods (Figure 4) buthas decreased in terms of total area. Likewise,some of the lower ranked categories such ascommercial have more than doubled.

The Level 2 analysis indicates that the lossesare occurring primarily in the agricultural landinstead of the desert and the gains are occurringin the small lot residential. To investigate theserelationships further, we created change trajec-tories in which we identified the conversion ofactual parcels. Between 1970 and 2000, 29.1 per-cent of the land changed from one type of landuse to another according to the CAP-LTER da-taset (Table 3). Of this, more than half of the totalland use (16.1 percent) changed from agricultureto some type of urban land use, with residentialbeing the highest ranked endpoint (11.1 percentof the total changed land). Figure 6 illustratesthose land uses that changed and what they be-came. Of the 54 percent that was agriculture in

1970, 38.1 percent of that became residential; ofthe 40 percent that was open in 1970, 30 percentbecame residential, and of the graded, underconstruction 4.6 percent became residential.

Bid-rent curves and ring maps show the in-tensity of land use types at varying distancesfrom the urban core (Figures 7 and 8). In all fouryears, we see the expected pattern of increasingopen desert farther from the city and residen-tial/commercial activities closer toward thecore. One of the striking differences betweenthe different years is the distance at which the‘‘under construction’’ category is the highest. In1970, ‘‘under construction’’ is positioned moreclosely to the urban core and this distance in-creases by 2000.

Discussion

Land Use Change

Between 1970 and 2000 no change was experi-enced in 68 percent of the land; however, there

Figure 6 Landusechangetrajectoriesshowingconversion fromagricultureanddesert toprimarily residential.


was change in 32 percent. We note that the rankordering and total area of land under certainland uses does change during the period be-

tween 1970 and 2000. Not counting desert,which remains the most prevalent land coverthroughout the area, the top four land uses in

Figure 7 Land use at differing distances from central Phoenix for the four time periods by type.


1970 were, in order: active cropland, vacant,fallow cropland, and small lot residential. Thus,three of the top four land uses in 1970 wereextensive—that is, they represent spatiallybroad land uses. By 2000, however the orderof land uses shifted considerably. In 2000 (againdiscounting desert), the four most prominentland uses were, in order: small lot residential,

active cropland, medium lot residential, andcommercial. The 2000 pattern demonstrates aregion that is shifting from one based on agrar-ian livelihoods to one increasingly based onurban livelihoods. On the lower end of land userankings, we see in Figure 4 that the relativeamount of fallow cropland and vacant spacedeclined dramatically.

Figure 8 Land use at differing distances from central Phoenix for the four time periods by time.


We note that areas classified as rural residen-tial increased from tenth to seventh between1980 and 2000. More residences that are ruralmay seem counterintuitive to the general pat-tern of increased urban settlement. These resi-dences, however, may be the vanguard ofexpanding urbanization. Phoenix is noted forits ‘‘leapfrog’’ pattern of development in which ahandful of residences are built and filled in astime passes. Rural residential growth influencesthe patch size and shape of the desert surround-ing the Phoenix SMSA. Leapfrog growth fol-lowed by infill allows patches of desert to remainfor a time until urban development moves out-ward and creates a larger urban field.

Agriculture in the Phoenix SMSA transitionmatrices shows an overall shift to residentialland uses, although significant portions of agri-cultural shifts into other urban uses such ascommercial, industrial, and institutional use.Indeed more than half of the land devoted toagriculture in 1970 now represents an urbanuse. That agriculture represents the most likelycandidate for shifting into urban land uses mostlikely owes to the fact that agricultural landspossess guaranteed water rights from irrigationschemes developed in the early twentieth cen-tury, not always the case with desert or openspace. Nonetheless, open space (including des-ert) did demonstrate significant conversionrates toward urban land uses, with residentialagain representing the single largest land useconversion between 1970 and 2000. Of the landunder construction—labeled as graded—mostland converted to residential land uses, againfollowed by other supporting urban land uses.We observed land shifts from agricultural ratherthan open desert, with little evidence of desertconverting to agricultural uses due to economicshifts and, most important, because the Phoe-nix-Mesa SMSA is an active management areafor water conservation that does not allow newagricultural colonization. Thus, as urban landuses take over agricultural areas, the agriculturallands are not replaced.

In total, agriculture declined by more than 50percent over the preceding thirty years and thesize of the average agricultural plot declined,further evidence of subdivision and urban de-velopment. Open space declined by 12 percentover the same period, and parcel size declineddramatically from an average of 7.93 km2 in1970 to an of 3.85 km2 in 2000. Even as the

overall size of open space declined to less thanagricultural land, the shape of that open landbecame increasingly fragmented ( from ‘‘leap-frog’’ development). Residential land use rep-resents the most significant source of growthfrom open and agricultural land uses, growingby more than 250 percent during the studyperiod. Commercial space more than doubledduring the same period, to support the growingurban population in terms of consumptionneeds and job growth. Land classified as indus-trial quadrupled, with possible implications forindustrial emissions. Finally, we note that trans-portation zones nearly doubled in the sampledpoints, the result of increased traffic and ve-hicular emissions. As the Phoenix SMSA con-tinues to grow, we predict that future changeswill mirror the changes of the past thirty years.With these growth rates, however, we predictthat open or desert space will increasingly con-vert to urban land uses as agricultural lands dis-appear almost completely. From ecological andsocial perspectives the implications of movinginto desert are significant given the consequentincreased need for as-yet-unavailable waterand given the consequent habitat disruptionfor native Sonoran desert species.

Government policy on water rights providesthe most significant explanation for the agri-culture to residential land transformation. Earlywater policy in Arizona was based on the doc-trine of prior appropriation: ‘‘first in time, firstin right.’’ This means that the person who putswater to its first beneficial use acquires the rightsto the water, where ‘‘beneficial use’’ is broadlydefined in the Public Water Code enacted on 12June 1919. This law mandates that a personmust apply for and obtain a permit in order toappropriate surface water. New residential de-velopments must provide proof of assured oradequate water supply for 100 years. Agricul-tural parcels already have that documentation.In fact, it is assumed that agricultural land usesmore water annually than residential uses, so thetransfer of water rights is relatively straightfor-ward and certainly much easier than document-ing assured and adequate water supply for desertparcels.

Urban Morphology

Geographic attributes—including shape, dens-ity, and pattern of land use categories—all re-flect the outcome of the urbanization process


(Longley et al. 1992; Longley and Mesev 2002).To understand how urban growth occurred inthe Phoenix area we tested the pattern of landuse categories against classic bid-rent theory.We examined the intensity of land use types atvarying distances from the urban core and howthese patterns changed over time. Althoughsome argue that the Phoenix area is polycentric,the City of Phoenix dominates in many of thepolitical, social, economic, and cultural aspectsof metropolitan life. We therefore hypothesizedthat the presence of Phoenix influences otherurban areas and that the area’s geographic pat-terns develop with Phoenix as the core.

The geographic patterns seen in Phoenixtend to confirm classical bid-rent ideas (Figure8A–D). In the 1970s (Figure 8A), commercialdominates at the urban core, followed by trans-portation. Industrial and residential land usespeak at 21 km from the core followed by under-construction at 28 km, an indication of growthin that area. By 21 km, industrial land use dis-appears. Agriculture peaks at 49 km and opendesert dominates at 60 km.Transportation re-mains consistent throughout all distances, in-dicating relatively even access to transportation.A similar pattern emerges for 1980 and 1990(Figure 8B). The difference is the intensity ofgraded has decreased and residential has in-creased at 28 km, suggesting that developmenthas occurred. By 2000 (Figure 8C), graded, un-der construction has migrated to 35 km andresidential and commercial dominate at 21 kmand 28 km, respectively. Industrial developmenthas reappeared at 28–35 km. Agriculture hasvirtually disappeared close to the CBD andsome open space does still exist—most likelyurban parks.

This dramatic outward shift of high valueland uses suggests that the growth of Phoenixresembles a spreading out of land values andthus conforms to the bid-rent model of urbanmorphology, at least to the most basic extent. InPhoenix, the rapid adoption of the automobileas the primary mode of transportation in partdrove this development. The automobile pro-vides the freedom for individuals to pick homelocations at greater distances from their work.As a result, it has made the extent of the sprawlpossible. Despite efforts to reduce automobileuse in the area (e.g., high occupancy vehicle[HOV] lanes on freeways, the bus system, and arecently funded light rail system), the automo-

bile remains the primary mode of transportationin the area (MAG 2006). Continued reliance onthe automobile in urban areas is problematicbecause of traffic congestion and air pollution(Waits 2000). Nevertheless, the convenience ofautonomous transportation is attractive and ne-cessary for many urban dwellers in the Phoenixarea. The presence of the automobile allowedthe CBD of Phoenix to dominate the region ra-ther than reflecting the agglomeration effects ofthe polycentric metropolis. While the pattern ofcommercial land use has mirrored the residen-tial land uses, employment and industry haveremained relatively centralized.

The physical environment is a secondary fac-tor explaining the pattern of land use in Phoe-nix. The Phoenix metropolitan area is a flatplain without the constraint of an ocean or othernondevelopable feature. There are severalmountain ranges to the east and north but theyare approximately 35 and 40 miles, respectively,from the CBD, leaving ample space for urbanexpansion. The basin and range character of thevalley creates a few mountain features, makingthese locations more challenging to massdevelopment but certainly very attractive toexpensive homes and large estates.

Conclusions

The land conversions we examined are a resultof the process of urbanization. This processlinks to more factors than just populationgrowth and sprawl. These driving factors in-clude local politics, development regulations,social and cultural choices, and economic fac-tors. Each plays a role in how and why a regionchanges. Examining these drivers of urbaniza-tion is important; however, they extend beyondthe scope of our data and research. We choseinstead to reflect on the dimensions of urban-ization with respect to land use change—describing what occurred and where it occurred.

We can speculate on the impact that primarilyagricultural to residential land transformationshave on local climate change. Scientists havedocumented evidence of the urban heat islandeffect in Phoenix. This effect has increasedsummer nighttime temperatures by as much as6.671C in the past fifty years. Scientists reportthat it is strongest in the central core of themetropolitan area; that xeric (nonirrigated)landscaping styles have higher temperatures;


and that a 1 percent increase in temperature re-sults in a 2 percent increase in urban water use.

The spread of residential land uses away fromthe urban core will certainly affect greenhouseemissions as automobile usage expands withsuch development. Studies of CO2 levels (e.g.,Wentz et al. 2002) have shown that elevated at-mospheric CO2 could be predicted in Phoenixwith measures of human activity, such as auto-mobile usage, because CO2 surfaces mirror de-clining densities of human activity with distancefrom the city center. For example, on weekends,when automobile travel is less predicable andmore spatially dispersed, the CO2 pattern is alsospatially diffuse. Considerable research remainson the impact of urban atmospheric CO2 onglobal environmental change but lacunae stillexist in terms of the temporal and spatial natureof emissions.

The Phoenix SMSA grew rapidly during thethirty years of the study period and most pre-dictions suggest that it will continue to grow inthe near and medium term. The impacts of thatgrowth are beginning to appear as researchdemonstrates higher levels of carbon emissions,a marked heat island, and the fragmentation ofdesert and open space. Although the total areaof the desert has decreased less than agriculture,its increasing fragmentation indicates that hu-man activities in this part of the Sonoran desertmay be leading to significant alterations of therelationships between native species and localbiophysical variables. Further research shouldinvestigate whether or not the growth experi-enced in Phoenix resembles that of other rapidlygrowing, young cities.’

Notes

1 In this article ‘‘Phoenix’’ represents the Phoenix-Mesa SMSA. We use ‘‘City of Phoenix’’ to representthe city of Phoenix proper.

2 Actual values are 89.9 percent for 1970, 87.9 percentfor 1980, 90.6 percent for 1990, and 88.2 percent for2000.

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CHARLES L. REDMAN is Professor of Anthropol-ogy and Director of the Global Institute of Sustain-ability at Arizona State University, Tempe, AZ 85287.E-mail: [email protected]. His research inter-ests include archaeology, urban ecology, and globalenvironmental change.


Documents

The Spatial Structure of Land Use from 1970â€“2000 in the Phoenix