To fully capture the potential for risks to a community from coastal hazards, the scenario planning method presented here employs three distinct climate futures and three management options, yielding nine separate scenarios for comparison. This section briefly describes the key assumptions underlying each of these scenarios.
Climate Futures
“Climate futures” are not themselves scenarios; rather, they represent potential physical conditions that might be experienced by a coastal community in the future, particularly within its coastal shoreland areas. Great Lakes water levels are not continually rising as are sea levels. Instead, Great Lakes standing water levels fluctuate up and down semi-regularly over the course of seasons, years, and decades. On a Great Lakes shoreline, therefore, the key coastal dynamics that determine the level and kind of risks a community might experience at any given time include the standing lake water level combined with the extent of wave run-up and flooding that might be experienced should a severe storm hit. Both of those conditions can change over both space and time in unpredictable ways.
To describe the potential range of coastal hazards a community might experience from “best case” to “worst,” three climate futures are presented here, each of which represents a combination of standing water level and storm severity. These climate futures are referred to as: “lucky,” “expected,” and “perfect storm.” The key assumptions for each of these climate futures are described in this section. Figure 3 summarizes the differences between each flood scenario.
Lucky Climate Future
Key assumptions: Great Lakes water levels will continue to stay relatively low. Although there will be wave and wind action, major storm events and wave impacts will not encroach on properties landward of current beaches. Potentially flooded inland areas, including riverine flooding, will remain as currently delineated by FEMA under effective Flood Insurance Rate Maps (FIRMs). Specifically, the 1% storm flood zones (A & AE) from the effective FIRMs will be impacted. Other climatic conditions (i.e., storm frequency and intensity, heat waves) will remain consistent with recent historical patterns.
Expected Climate Future
Key assumptions: Great Lakes water levels will continue to fluctuate according to long-term decadal patterns, including recent extreme storm events. There will be periods of high water levels similar to the long-term highs recorded in 1986, with Great Lakes still water elevations closer to that of long-term average. Large storm events will also occur more frequently. During these high water periods, a 1% storm event (sometimes referred to as the “100-year storm”) will create waves that will encroach upon coastal properties, with the following FEMA-delineated areas subject to wave action:
- Coastal high hazard areas (“Estimated VE Zones”) *;
- Areas subject to sheet flow (“AO zones”); and
- Nearshore areas subject to inundation ( “AE zones”).
* At the time when these methods were developed, a significant portion of Michigan’s coastline had not been evaluated by FEMA for VE zones. As a result, our research team outlined a method for approximating VE zones on Great Lakes shores in Section 4 of this manual. These zones are noted as “Estimated VE Zones” throughout this manual.
Riverine flooding associated with a 1% storm event level will also be present. During the 1% storm, areas located within the Estimated VE zone will be completely destroyed while areas of the community within the AO and AE zones will be severely damaged by inundation.
Perfect Storm Climate Future
Key assumptions: Great Lakes water levels will continue to fluctuate according to long-term decadal patterns, consistent with assumptions made for the “Expected” climate future. However, Great Lakes standing water elevations will be higher than the long-term average and closer to the long-term high. Additionally, due to increased frequency and intensity of storms caused by climate change, the 0.2% storm (sometimes referred to as the “500-year storm“) will effectively become the new 1% storm. As a result, the Estimated VE zones and coastal and riverine inundation areas FEMA has associated with the 0.2% storm event (“Shaded-X zones”) will be impacted. Specifically, properties within these areas, in addition to properties in the proposed AE and AO zones, will be severely damaged by inundation, while areas located within the Estimated VE Zone will be completely destroyed.
Shoreland Management Options
Having determined the different kinds of risks a community faces in its coastal areas given different potential climate futures, the next step for creating scenarios for comparative analysis is to frame out an array of options the community might employ to manage the current and future use of its shoreland areas. As with the use of three potential climate futures, the scenario planning method presented here involves three potential land management options, including a “Current Conditions” option, a “Full Buildout – Current Zoning” option, and a “Full Buildout – Best Management Practices Zoning” option. The key assumptions for each of these management options are summarized here.
Current Conditions
Key assumptions: The “Current Conditions” management option reflects the infrastructure (buildings, roads, critical facilities, etc.) that is currently in place within a municipality. This option assumes no changes in the built environment, providing a baseline that allows the analyst to examine the various potential impacts of different climate futures relative to the community’s current state.
Full Buildout – Current Zoning
Key assumptions: The “Full Buildout – Current Zoning” (FB-CZ) management option allows the analyst to assess potential impacts to the built environment should a community continue to develop under its current zoning scheme. This option extrapolates development based on the municipality’s current zoning code and other relevant land ordinances, simulating the “most” development that could theoretically occur should the current zoning and development regulations remain unchanged.
This projection reflects a level of development that could reasonably occur given the current zoning, other active municipal ordinances, and basic assumptions about land reserved for roadways, parks, sidewalks, and other infrastructure. However, this is not a forecast of will necessarily – or even likely – occur. For this analysis, the FB-CZ zoning option depicts a 60% build-out efficiency level of developable land to account for a variety of factors, such as land set aside for rights-of-way.
Full Buildout – Best Management Practice (BMP) Zoning
Key assumptions: The “Full Buildout – Current Zoning” (FB-CZ) management option allows the analyst to assess potential impacts to the built environment should a community continue to develop under its current zoning scheme. This option extrapolates development based on the municipality’s current zoning code and other relevant land ordinances, simulating the “most” development that could theoretically occur should the current zoning and development regulations remain unchanged.
- 50-foot buffers around inland water features (rivers, lakes, streams);
- 50-foot buffers around wetlands of 5 acres or more in size (as defined by Michigan’s Final Wetland Inventory); and
- No development within any designated wetlands, as defined by Michigan’s Wetland Inventory.
The FB – BMP zoning option allows a community to assess how implementing these restrictions would change development projections, as well as to evaluate the different impacts that the climate futures would have on future development under those modified conditions.
Scenarios for Planning Analysis
In sum, combining the three climate futures with the three shoreland management options yields nine distinct scenarios, as summarized in Figure 4 below. These scenarios can then be further analyzed for comparison as part of coastal community resilience planning effort, as detailed in the sections that follow.
Figure 4. Matrix of the nine scenarios developed for further comparative analysis.