The City of Phoenix Green Infrastructure Cost-Benefit Study is now available online. You can access the report here.
Given the importance of heat stress in Phoenix, instead of using historical temperatures Autocase incorporated future climate change in to its analysis. “More than 155 people died from heat-related causes in the Phoenix area last year, a new record in a place where the number of such deaths has been on the rise” (Phoenix Tries To Reverse Its ‘Silent Storm’ Of Heat Deaths, NPR,
July 9, 2018)
The Triple Bottom Line Cost Benefit Analysis (TBL-CBA) business case was conducted in Autocase – a cloud-based software tool, to provide insights into the value of costs and benefits of the projects to the City, as well as the broader societal and environmental impacts. TBL-CBA is a systematic evidence-based economic business case framework that uses best practice Life Cycle Cost Analysis and Cost Benefit Analysis (CBA) techniques to quantify and attribute monetary values to the Triple Bottom Line (TBL) impacts resulting from an investment. TBL-CBA expands the traditional financial reporting framework (such as capital, and operations and maintenance costs) to also consider social and environmental performance. TBL-CBA provides an objective, transparent and defensible economic business case approach to assess the costs and benefits pertaining to the project being analyzed.
This study provides information for City projects and private development that may want to implement and incorporate GI/LID facilities. The costs and co-benefits of GI/LID features in the Phoenix environment need to be evaluated to identify the benefits and aid in potentially identifying to which stakeholders they accrue.
Apart from the urban heat island, Autocase for Sites was used to value:
What can we learn from this type of analysis?
We also learn where that value comes from and the uncertainty attached to the numbers. Swales, for example, generate an estimated $15,026 (95% confidence interval of -$2,151 to $33,600) in triple bottom line net present value over a 50-year time horizon relative to concrete, with -$2,400 created through financial impacts, $10,000 through social benefits, and $7,500 through environmental benefits. The figure below shows a waterfall chart of the breakdown of these values. On the chart, blue represents value being created, whereas red represents a cost, relative to concrete. We can see that swales have almost no incremental capital expenditure (CapEx) but do have higher operations & maintenance (O&M) costs compared to concrete. We can see that varying amounts of value are created across the social and environmental spectrum of impacts, with the most significant being heat island benefit, flood risk, water quality, and avoided carbon emissions from concrete use. The 95% confidence intervals shown in the report allow us to see the uncertainty in some of these figures. For example, CapEx and replacement costs could be higher or lower than concrete. There is a large spread in heat island benefits as well as water quality, and when all impacts have been assessed it creates a large spread in overall TBL-NPV but reveals only a small chance of generating a negative TBL-NPV as compared to concrete.
Three sites were also analyzed as case studies in the report.
See the report for the results of these case studies.
Multi-account results not only answer the question of “Who benefits?” but equally important, “How much do they benefit?”. By thinking of which stakeholders would benefit from each impact, it allows the City to:
Given the heat stress Phoenix faces, users can utilize these types of results to prioritize projects that have the largest impact on that element. Ultimately, assessing projects across a spectrum of impacts and valuing them in dollar terms allows the City to map benefits and costs to various stakeholders and is an important step toward consensus building and developing a business case in a way that everyone can understand.Back to blog