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Desert Preserve Acquisition Strategic Analysis
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Ray Quay
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In December of 1995, the Phoenix City Council Approved a Desert Preserve Preliminary Plan. This plan identified the type of lands appropriate for inclusion in the Desert Preserve; primary and secondary washes, utility and view corridors, bajadas and transition lands, and scenic corridors. The plan was very general in terms of identifying parcels of lands and did not specify a strategy for the desired acquisition, nor does it identify the cost of these lands.
To begin to explore these acquisition issues the City initiated a Desert Preserve Acquisition Strategic Analysis (DPASA). The purpose of the Desert Preserve Acquisition Strategic Analysis (DPASA) was to provide decision-makers with a framework from which decisions regarding the acquisition of land for desert preserves can be made. The initial Desert Preserve Acquisition Strategic Analysis report discussed the various methods of acquiring or protecting land for Desert Preserves, potential funding sources, estimated amounts available and the timing of funding sources. The report also provided a strategic analysis of these techniques. Using acquisition and growth scenarios, implications of different acquisition strategies were analyzed based on their success in acquiring lands and the cost to acquire the lands.
The results of this analysis were then later incorporated into the final Sonoran Preserve Master Plan adopted by the City on 1998 and are now being used to further refine an acquisition strategy.
The fact is that 20,000 acres is a lot of land. Mix that with....
The result is a very complex environment with dozens of issues to be addressed.
One of the goals of DPASA was to help refine these issues and provide an outline for what will likely be a complex process of acquiring property for preservation.
These issues included:
State Ownership. Though 2/3 the land the proposed preserved are owned by the state, these lands are held for the State's School Trust, which is used to fund public education. These lands are either leased or sold to generate funds for the Trust. Given the need for education funds, the management of the lands to generate top dollar is highly scrutinized. State land sales, which are usually for urban development are often criticized if they do not appear to be for "market value". Setting a market value of vacant land that is miles from any infrastructure and to be sold in blocks of thousands of acres will be very difficult.
Urban Development. The Preserve Plan consists of land that today is many years away from being developable. For most of these lands very little public street access no water or sewer infrastructure. However, the Preserve is bounded on the east and wraps around two of Phoenix' recognized growth areas. Much of the private land identified in the plan lies within these corridors. This means that in these areas, preservation interest will be competing with development interests.
Funding techniques. Currently, the City has no dedicated funding source for acquisition of desert preserves. And it is unlikely, given the size of the potential price tag, that a single source of funds will be not be practical. As has been the case in other areas of the country, residents with the Valley have expressed through surveys in Phoenix and at the voting booth in Scottsdale support for sales tax initiatives dedicated to open space and desert preserve acquisition. However, exactly how much they would be willing to support for Phoenix' Plan is uncertain. Other funding sources such as bonding may be available in the near future, but the amount that could be dedicated to preservation is likely to be limited. Development based techniques are also available. The City has and impact fee program that could be used, but it is not likely this could generate more than 10% of the funds required. Further it would be spread out over many years and dependent on the growth rate. Some type of Transfer of Development Rights approach could be used, and has been used in the past for preservation of hillside areas. This technique may be useful in acquiring lands that are not developable such as hillsides and floodplains, but would be difficult to implement on lands that would be highly desirable for development.
Growth Rates: Though Phoenix is currently experiencing a growth boom, over the life of an acquisition program such rates are likely to vary. How these affect funding and competition for land over the life of the program may affect what strategies are used to acquire lands.
Given the complexity of the issues, it was clear that there was a need to find some way to simplify the so that decision makers could understand them and take some action towards an acquisition strategy. It was decided that the best way to do this would be to analyze a series of acquisition strategies and report which ones best met the City's preserve goals and why the did so. It was also anticipated that during process of discussing these scenarios, the City Council or public would suggest other scenarios that should be tested. And of course it had to be done quickly and cheaply.
To accomplish this a GIS based model was developed which utilizing data on land characteristics, funding sources, acquisition techniques, and growth rates could evaluate how much land could potentially be acquired for preservation and urban development. The model was then used to test a variety of acquisition strategies, using different techniques, funding amounts, and growth rates.
The goal of the model is simple. Given as input specific funding techniques and limits, specific parcels of land desirable for acquisition, and a specified growth rate; which parcels of land will be acquired for preservation, for development, or not acquired. To accomplish this several basic models were developed to determine:
There are a number of methods that could be used to acquire land for desert preserve. Techniques for desert acquisition and funding sources to "fuel" these techniques were investigated. Particularly attention was paid to when each technique could be used, what types of properties it could be used on, and what limitations may exist as a result of ownership or land form characteristics. These techniques included:
Various funding sources that could be used to generate cash need were also identified and studied. In addition to the limitations under which each funding source could be used, estimates of cash flow each source could generate and the factors which may affect this cash flow were estimated. These included:
Based on an this analysis the techniques that would be the most effective for land acquisition were narrowed to:
The funding sources were similarly narrowed to:
Since in the analysis land is the ultimate commodity being acquired, a study was also done on what the market value of vacant land was within the region that was located in areas similar to the City proposed preserve. The key factor to this value appeared to be the time frame in which infrastructure would be available for development. Based on this study a heuristic model was developed that would estimate the market value of a parcel of land at any given time based on the time till infrastructure would reach the parcel, and natural land characteristics of the parcel.
For each acquisition technique a heuristic model was created that could be used to determine at any given time period if a particular parcel could be acquired by that technique. Variables to the model included a funding source and the availability of funds from that source at any given time, ownership, General Plan Designation, and natural land features of the parcel.
To determine the desirability of individual parcels for desert preservation and development, a generalized heuristic model was created to assign parcel a weight based on factors related to preservation and development. Table 1 summarizes the factors and their weights. The rank on each parcel is determined by adding the weights applicable for each feature. Figures 1 and 2 shows the results of the base models used for preservation and development desirability. |
Figure 1: Development Priority |
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Table 1: LAND FEATURE WEIGHTS
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Figure 2: Preservation Priority |
The final component of the model was a database of parcels to be acquired. Utilizing GIS based data collected by other City planning efforts and work done by Arizona State University and database of all the parcels in the northern area of Phoenix was created. Natural and political features in the database included :
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Figure 3: Slope |
Figure 4: General Plan Land Uses |
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All of the components were combined into a single model coined The Preservation Acquisition Model (PAM). At the heart of this model was a simple goal-seeking allocation model based on a modified desirability rating and resource allocation model. PAM's basic goal is to acquire as much land that is highly desirable for desert preservation as possible given specific resource constraints, competing demands for land, the rules of land acquisition.
The models rating/allocation/analysis process has four basic steps:
Output from the allocation model is a summary of acquisition results and a list of parcels acquired for preservation and development. Information on each parcel includes what it was acquired for (development or preservation), year it was acquired, what was the cost, and what technique was used.
Twelve scenarios were created based on different combinations of funding amounts, acquisition techniques and growth rates. The scenarios were crafted to both reflect the proposals being publicly discussed as well as to test combinations that represented "themes" such as "low public support" and "high public support". The model was run for each scenario and the result saved in a database. The results were analyzed based on the number of acres acquired, the type if lands acquired, cost of the total program, the number of acres and type of land acquired by each technique and how well desert preservation goals were met. In addition to analyzing each of the model results, a risk analysis was preformed.
The purpose of the risk analysis was to try and determine the level of risk of not meeting the Sonoran Preserve Master Plan's goals. The analysis essentially identified properties that had high desirability of being acquired and a low probability of being acquired. Probability of acquisition was estimated by assuming that each of the scenarios tested had some probability of occurring. Properties not acquired in each scenario were assigned a weight based on the probability of each scenario. This represents the probability of not being acquired, 100% being the highest probability. This value for each parcel was then averaged over all the scenarios. Finally this value was multiplied by a normalized desert preserve desirability value. The properties with the highest final values were properties of high desirability and low probability of being acquired.
Analysis of the model results provided a great deal of insight into the balance between growth and preservation, the funds likely to be required, how critical different techniques will be to acquire different types of properties, and the importance of timing. Table 2 summarizes the acres acquired and the estimated costs for each of the four types of acquisition techniques/funding sources studied in this analysis.
Table 2: Acquisition Technique Analysis
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Technique/Fund |
Cost, Range (000,000) |
Acres, Range (000) |
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Infrastructure Fee |
$16-$31 |
1.0-2.0 |
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Bonds |
$27- $36 |
1.8-3.3 |
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TDR |
$40-$120 |
2.0-6.0 |
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Sales Tax |
$190-$380 |
9.0-24.0 |
Figures 5 and 6 show the results of the High Support Slow Growth and High Support High growth scenarios. By example, these two maps show how growth can play a major role in the process not only in the amount of preserves acquired but the type of land acquired. The Slow Growth option shows a substantial portion of the preserve acquired, but not all the 20,000 acres is acquired. The high growth scenario shows a significant portion of the 20,000 acres is acquired, however a closer inspection will reveal that portions of the preserve acquired under the slow growth option, are lost to development under the high growth option. Figure 7 shows the risk analysis results. Most of the high risk properties are located within the North Black Canyon Corridor, one of Phoenix's recognized growth corridors.
Figure 6: Model Results
The following summarizes some of the strategic analysis results:
Before the acquisition study was done, many people were looking for a single silver bullet option and were under estimating the funds that would be required to acquire the preserve. Now most people have accepted that many techniques will need to be utilized and significant commitments to funding will be required to meet preservation goals. Much attention had been and is still focused on the state lands because they own the majority, however it is the study has begun to make people realize that it is the private lands that are at the greatest immediate risk of being lost to development. The study has also increased attention to the lands at the edges of washes and mountains. These are the most desirable lands for development, yet are being identified as critical to maintaining an ecological balance within the preserves.
It is anticipated that as the City moves forward towards an acquisition policy, the options will be narrowed and the model will be utilized to understand the implications of these refined strategies.
One aspect of the model that proved particularly useful was the interactive nature of the model. Since the purpose of the model was to run many scenarios, the model was designed to easily change the model parameters through a GUI interface. The process of interactively changing funding amounts, techniques and even the heuristic allocation models and quickly seeing a map of the results was very useful. The ease of this process actually encouraged experimentation to see how techniques could be applied in different ways to get better acquisition results. Given the technology and software available on the desktop today, such as desk top GIS, such interaction likely could be applied to other models such as growth and transportation models to allow planners to easily test different policies.
The concept of risk analysis would likely be particularly useful to other natural resource management situations where funding resources are limited. Using such a technique of testing different strategies and estimating the probability of each strategy can help to narrow in on the critical aspects of the issue in general.
This approach may also be useful in optimizing programs where multiple and overlapping funding sources are available. Such a model could be used to optimize goal achievement by helping to decide how the funding sources should be used.
Ray Quay, AICP
Assistant Director
Planning Department
City of Phoenix
Email rquay@ci.phoenix.az.us