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Introduction

Scenario-based planning enables users to conduct selected analyses given combinations of climate futures and growth management options. For this study and report, three climate futures and three management options were considered, yielding nine separate scenarios. This section briefly describes the key assumptions underlying each of these scenarios.

 

Scenario Planning Grid

 

Climate Futures

Lucky Climate Future

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, zones: A & AE from the effective FIRMs). Other climactic conditions (e.g., storm frequency and intensity, heat waves) will remain consistent with patterns in recent history.

Expected Climate Future

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 “100-year” storm event will create waves that will encroach upon coastal properties, with areas subject to wave action such as might be delineated by FEMA for coastal high velocity (VE) zones (methods for approximating VE zones on Great Lakes shores are provided below), areas subject to sheet flow as delineated by FEMA proposed AO zones, and nearshore areas subject to inundation as delineated by FEMA proposed AE zones. Riverine flooding at a “100-year” storm event level will also be present. During the “100-year” storm, areas located within the 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

Great Lakes water levels will continue to fluctuate according long-term decadal patterns, consistent with assumptions made for the Expected future. As a difference, Great Lakes still water elevation will be higher than the long-term average and closer to the long-term high. In addition to that assumption, because of increased frequency and intensity of storms, the shoreland areas subject to VE zones, as well as coastal and riverine inundation as delineated by the FEMA proposed “500-year” storm event (shaded-x zones), will essentially become the “100-year” storm event (i.e., much more likely to occur). Properties within these areas, in addition to properties in the proposed AE and AO zones, will be severely damaged by inundation. Similar to the Expected future, during the “100-year” storm, areas located within the VE zone will be completely destroyed.

Growth Management Options

Current Conditions

This management option reflects the infrastructure (buildings, roads, critical facilities, etc.) that is currently in place in communities. This option assumes no changes in the built environment and allows the planning analyst to examine the impact of climate futures on the community’s current state.

Full Build-Out

This management option extrapolates from the current zoning ordinance and simulates what a full build-out would look like should the current zoning guidelines remain unchanged. A full build-out does not necessarily
mean that 100% of a community’s land will be built on, but rather reflects a level of build-out that could be reasonable given the current zoning and basic assumptions about land reserved for roadways, parks, and so on. In this report, a full build-out represents a 60% build-out efficiency of developable land to account for inherent natural space within lots, as well as additional roads, sidewalks, and other infrastructure enhancements. In simulating what the future might look like under a full build-out, this management option would allow the planning analyst to assess potential impacts to building inventory under the three different climate futures, should a community continue to develop under current zoning practices.

Best Management Practice (BMP) Build-Out

This management option simulates what future development might look like if communities implement certain zoning practices based on best management practices (BMPs). Instead of strictly adhering to the current zoning ordinances of the communities, this option applies basic, spatially restrictive BMPs to the simulation for this type of build-out. Such BMPs include: 50-foot buffers around inland water features (rivers, lakes, streams) and wetlands of 5 acres or more in size (as defined by Michigan’s Final Wetland Inventory), and a restriction of development altogether within wetlands 5 acres or more in size (as defined by Michigan’s Final Wetland Inventory). Using a scenario that involves BMPs would allow the community to assess how implementing these BMPs would alter potential development futures and assess the different impacts that the climate futures would have on future development.