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1. Tucson-the city and the desert
At an introductory evening session, members of the Department of Geography of the University of Arizona described the physical setting of Tucson, the growth of the settlement and the changing attitudes of the inhabitants to their desert environment.
Development of Tucson: Andrew W. Wilson
The Spanish walled presidio of Tucson was founded in 1775 on the east bank of the Santa Cruz River near the site of several American Indian villages of the Sobaipuri tribe, which are now merged into the more numerous Papago. The name Tucson comes from the village San Cosme del Tucson and is derived from two native words: schuk or "black" and son or "talus," and refers to the black volcanic talus slopes of Sentinel Peak ("A" Mountain), at the foot of which the village was located.
Set in a structural basin at about 760 m elevation, Tucson is surrounded by mountains which attain 2800 m on three sides, but which are much lower on the west (Fig. 1). The higher mountains are granitic, but those west of the city contain many volcanic rocks. The coalesced alluvial fans that fill the down-faulted basin are derived largely from the high surrounding mountains, and the basin fill attains thicknesses of 900 or 1000 m.
The Tucson Basin is drained by the Santa Cruz River which enters at its south-west corner and exits to the northwest, passing close to the foot of pediments of the Tucson Mountains west of the city centre. Until a century ago the river was perennial and contained fish. It was used to run a waterpowered grain mill south of the city from about 1860 to 1880. With the pumping of groundwater, the cueing of galeria forest south of Tucson and intensive grazing on the surrounding slopes, all around 1880, the watertable began to fall and the river became intermittent, as it is today.
Fig. 1. Tucson and its physical setting (land above 900 m shaded)
More than 100 years of climatic records for Tucson show that extreme temperatures have ranged from-14°C to 45°C, that frosts occur every year, and that relative humidities are very low (less than 10 per cent) when temperatures are high. Precipitation comes in a winter and in a summer rainy season, and autumn and spring are dry. Mean annual precipitation is 292 mm, including 25 mm of snow, with 43 per cent falling in the cooler six months and 57 per cent in the warmer half of the year. As one goes west from Tucson, precipitation decreases and winter precipitation becomes relatively more important, whilst eastwards from Tucson the reverse is found.
Vegetation around Tucson is mostly desert shrubland, but as one ascends the mountain slopes one finds Pinon pine with more grassland, followed at higher and moister elevations by Ponderosa pine, Douglas fir and, finally, subarctic conifers. Vegetation on the slopes south of Tucson has changed in the last century, from desert bunch grassland to mesquite scrub. The cause is in dispute, but the change is in effect an example of desertification.
Groundwater is available at 5 m depth along stream channels with high rates of infiltration, but is regionally much deeper (usually below 100 m) and watertables are falling. Groundwater presently being used has been dated to several thousand years before the present. Large amounts of groundwater still remain to depths as great as 500 m, enough to supply the city for a century, but pumping leads to surface subsidence and damage to buildings and has been restricted in built-up areas.
In its early years Tucson was an agricultural community and a supply base for ranchers and miners. In the early nineteenth century the Mexican Revolution freed the area from Spanish control and in 1848 the United States annexed the area north of the Gila River. In 1853 the United States bought the southern part of Arizona in the Gadsden Purchase to provide a low-level rail route eastwards from southern California. The railroad from Los Angeles reached Tucson in 1880 and continued eastwards. This led to a great increase in cattle grazing, which was one cause of the change in vegetation mentioned earlier. Mining also became of considerable relative importance in the following years and Tucson served as a supply and shipping point for miners and ranchers. The population of Tucson in 1900 was 7,500, while Pima County totalled 14,700.
In the first half of this century the economy of Arizona was popularly characterized as consisting of the "four Cs": cattle, copper, cotton and climate (tourism), and this applied equally to Tucson. By 1940 Tucson had a population of 35,750, and Pima County, of which Tucson is the county seat of government, one of 72,838. In 1950 the population of Tucson had increased to 45,500 and Pima County had 141,200 residents, with manufacturing increasing and US governmental activities adding to the economy. In 1979 Tucson had about 325,000 citizens and the population of Pima County had reached half a million. Government at all levels is the major employer (26 per cent), trade follows (23 per cent), then services (21 per cent), manufacturing (9 per cent), construction (8 per cent), mining ( 5 per cent), agriculture (1 per cent), and others (10 per cent). This indicates a very diverse and changing economic base, with manufacturing now being the most active growth element and mining and agriculture of relatively low importance.
In adapting a modern, technologically advanced city to a desert landscape, adjustments have not come easily. Although the desert environment has been the essential attraction for many of the new residents, they have been slow to give up folkways brought from the humid midwest and northeast of the United States. The midwestern small town with its single-family houses set in green lawns has been a model for many, and it is only in recent years that desert landscaping has become popular. This has been encouraged by recent large increases in water rates. Summer cooling of homes and buildings is another high cost, and better insulation is being adopted for homes and other buildings. Most homes in Tucson are cooled by the relatively cheap evaporative coolers, but in July and August these are only marginally acceptable; accordingly, refrigerated cooling has been increasing in spite of its expense, and now many homes have both systems.
Public Perception of the Desert in Tucson: Thomas F. Saarinen Dr. Saarinen pointed out that perception of the desert environment is a necessary preliminary to perception of desertification, whence the relevance of his topic to the meeting. He traced the changing perception of the desert by the inhabitants of Tucson with a review of historical evidence and from results of recent social surveys.
As shown by the history of the Great Plains, a critical factor in bringing changed perception of a semi-arid environment by settlers from more humid regions is the dependency of their livelihood on local rainfall patterns, through a drought-induced learning process. However, in Tucson, a predominance of urban settlement from the early years and the relative importance of livelihoods less dependent on rainfall, such as mining and ranching, hindered this learning process.
Early settlers adopted Hispano-Mexican forms, such as thick. walled, flat-roofed adobe houses with high ceilings and breezeways and shaded interior courts, partly out of necessity and partly through cultural assimilation. However, later arriving Anglos brought with them their eastern image of what a city should be and, as opportunity allowed, imported the trappings of their former lifestyles in humid environments. The desert was alien and ugly to them, since it differed from their ideal of the pastoral English landscape with ploughed fields and village skylines. The "frontier" was seen as a challenge to the creation of these ideal landscapes.
First attempts to attract tourists in the post-railroad period from 1870 to 1880 were based on the attraction of large resort hotels in the Eastern mould, and the visitors gained little appreciation of the land or people of the West.
A change in the attitude towards the desert began in the 1890s, as the pioneer phase receded into the past, but it was very slow to gain general acceptance. Among the innovators were anthropologists and prehistorians who tended to romanticize the Southwest Indian. Artists and writers were also attracted, and desert country motifs began to gain acceptance at the turn of the century as Indian crafts became appreciated and mission architecture became popular. The dude ranch movement in the 1920s was another expression of changing attitudes.
It was not until the 1950s, however, that the grass-lawn tradition was seriously challenged, as newcomers began to see the desert as a weekend playground rather than a hostile environment. Desert shrubs and stone began to be used in landscaping, and by the mid-1970s half the homes in Tucson had adopted this style. It had taken a century for a positive approval of the desert landscape to become apparent, although there was an earlier appreciation of the advantage of the sunny desert climate, as aridity came to be seen as an asset rather than a problem by the urban settler.
Surveys indicate a continuing high awareness of the climatic amenities through the 1970s and also a growing appreciation of the problem of falling watertables, perhaps the primary symptom of desertification in Tucson. A 1970 survey showed that the climate was the major advantage perceived by Tucson residents, while the desert appeared as an advantage in only 1 per cent of the sample interviews (Table 1). At that time less than half those interviewed perceived the problem of a falling watertable as serious, and there was even less awareness of other symptoms of desertification such as deteriorating rangelands, soil erosion and arroyo cutting.
A replication of the survey in 1977 revealed an increasing awareness of problems associated with desertification, for by then a majority of the sample considered a falling watertable as a very or somewhat serious problem, and there was a growing awareness of other related environmental problems as shown by the responses. The interesting thing is the recency of this development, perhaps part of the growing national awareness of environmental problems, aided by media attention, rather than an independent local development.
In conclusion, Dr. Saarinen stressed a growing awareness and appreciation of the desert environment, a shift towards desert landscaping and a growing public perception of the seriousness of problems associated with desertification, but noted that the most striking features of these developments are the slowness with which they took place and the strong influence of national norms on the inhabitants of this southwestern desert region.
Table 1: Perception by Tucson Residents in 1970 and 1977 of Problem Associated with Desertification
|Very and Somewhat Serious (%)||Not Serious (%)||Don't Know(%)|
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