The Importance of Population Forecasts for your Comprehensive Plan

Selecting a population forecast is a critical step for communities beginning the review and update of their comprehensive plan. What are the implications of this decision, what factors should staff and decision-makers consider, and how can a jurisdiction confidently proceed knowing that they have made the right choice? Below is some guidance to help answer these and other questions as you begin the update process.

Know Your Role in the Process

Selecting a population forecast will impact you whether you are a county, city, or other stakeholder in the comprehensive planning process. The forecast is a fundamental step in the periodic update process as it informs Urban Growth Area (UGA) sizing decisions and impacts budget decisions related to capital facilities and transportation infrastructure.

Although counties have the ultimate responsibility to select a population projection and allocate growth targets to UGAs, the process should be collaborative in nature. Countywide planning policies often provide detail on the role of cities and counties, and may identify a process for reaching agreement on population forecasts and growth targets. Early and frequent communication between counties, municipalities, and urban service providers leads to better decisions. Coordination also prevents potential legal challenges that undermine long-term relationships and drain resources from local budgets.

Planning Horizon and Timing of the Forecast

Growth forecasts cover a twenty-year period and begin on the statutory due date identified in RCW 36.70A.130. For example, a jurisdiction scheduled to complete their update on June 30, 2017 would have a planning horizon of 2017 to 2037. Every municipality in a county must use the same timeframe to comply with the GMA’s requirement for consistency. Jurisdictions may choose to adopt a forecast that exceeds the twenty-year horizon, but UGA sizing decisions must be based on the need to accommodate twenty years of growth.

Because growth projections are fundamental assumptions for long-range planning, jurisdictions should attempt to reach consensus on projections at least two years before their update deadline. This provides time to amend comprehensive plan elements based on new population figures and grants an opportunity to develop alternatives if major issues arise, such as the feasibility of providing urban services.

Small and slow-growing jurisdictions are eligible to extend their statutory deadline. Consequently, some counties and cities that must plan together could have different deadlines. Early discussions on countywide projections and allocations help each party move forward with confidence, knowing that growth assumptions are solidified and won’t need to be revisited until the next periodic update.

How the Office of Financial Management (OFM) Develops Its Forecasts

Local population forecasts originate from numbers developed by the State. OFM formulates the GMA projections by starting with a statewide forecast and refining projections at the county level. Both the State and county projections are produced with a cohort component model that projects change based on the three primary factors influencing demographics: births, deaths, and net migration. These three factors are informed by fertility rates, life expectancy, and net migration rates for each county.

OFM provides projections to each county within a range - with a high, medium, and low band. Counties with relatively consistent growth patterns receive a narrower range from OFM. Conversely, OFM selects a wider range for counties with highly variable growth patterns, areas that are more heavily influenced by federal or state programs, or counties with higher concentrations of immigrants.

The high and low bands provide flexibility when selecting a population forecast; however, the OFM medium series is the most likely population projection (see RCW 43.62.035). Therefore, local governments should develop clear written justification before deviating from the OFM medium series. While population growth rates vary, they are always influenced by the three factors discussed above. When developing local projections, refining the assumptions made by OFM for each of these factors provides a rational framework for analyzing options and creates a defensible record. It is particularly important to “show your work” if there is disagreement between municipalities and the county on growth forecasts.

OFM’s website and publications offer a wealth of information on demographic analysis. They provide more specific details on their methodology and assumptions for particular counties.

Implications of Population Forecasts

Selecting a population projection should represent a data-driven decision that is the cornerstone of long-range planning efforts. One of the major pitfalls to avoid is adopting a population projection based on a desired outcome, rather than a projection grounded in reliable data and historical trends.

Planners should recognize that projecting growth is a technical exercise and that policy decisions should be made separately, after finalizing a countywide forecast. Cities and counties should work together to develop the regional projection based on the most likely growth scenario.  Policy discussions should focus on issues local governments can influence directly, such as development patterns and their impact on rural character, trade-offs between increasing density and UGA expansions, and economic development strategies to support and facilitate future growth.

Overly optimistic forecasts can result in long-term infrastructure commitments that run the risk of undermining other local priorities. More conservative forecasts arguably pose less risk. Many decision-makers fear they are locked into a forecast for twenty years, but jurisdictions can (and should) monitor growth as it occurs, and make necessary adjustments during the next periodic review.

Additional Resources from the Department of Commerce

The Department of Commerce updated the UGA guidebook in 2012. It offers great insights into the relationship between population projections, UGA sizing decisions, and infrastructure investments.

If you have questions on population forecasts or other planning issues, the Department of Commerce has staff assigned to your jurisdiction that can provide assistance as you work through your planning process.