The Sea Level Affecting Marshes Model (SLAMM) is a widely adopted computer model used to predict long term change in shoreline habitats and flooding frequencies as a function of land elevation, tide range, sea level rise (SLR), and other environmental factors.
The model is capable of generating results in two ways. The first is by using specific model input values. The second employs SLAMMs uncertainty module, which generates results in terms of their likelihood of occurring using alternative model input values. For example, one key model input factor is SLR. Instead of selecting a specific SLR scenario value, SLAMM’s uncertainty module generates results that consider all five possible scenarios with mid-range SLR values having greater influence over model results than low or high scenarios. For more on SLAMM’s uncertainty module, see Warren Pinnacle Consulting’s Advancing Existing Assessment of Connecticut Marshes’ Response to SLR-Final Report (Section 2.13 Uncertainty Analysis Setup).
The viewer displays instances of both types of SLAMM results.
The model used the best available data at the time of its development. It inherently considers uncertainty in key model input factors such as marsh surface sediment accretion rates, tide range variation, SLR, etc. To calculate and include uncertainty, the model is run several hundred times using alternative model input values randomly drawn from data input distributions tables. Each modeling result represents one possible future state for the studied area. All model results were then assembled into probability distributions of wetland coverage to reflect the effects of data uncertainty on prediction results. Model results were then statistically analyzed to show the likelihood of occurrence of different outcomes. This viewer displays the ‘likelihood’ of areas of new marsh, high marsh and marsh loss expressed in terms of their occurring in the future.
To predict future road flooding frequencies, the viewer uses SLAMM’s High-Medium SLR rate of about 4.2 feet by 2100, depicted by the orange line in the following graph. This line includes a point approximating the Connecticut Institute Resilience of Climate Adaptation’s upper bound SLR planning threshold recommendation of approximately 20 inches of SLR by 2050 recently adopted by the State of Connecticut.
Scenarios based upon New York City Panel on Climate Change, 2013: Climate Risk Information 2013: Observations, Climate Change Projections, and Maps. Prepared for use by the City of New York Special Initiative on Rebuilding and Resiliency, New York, New York. Mayor’s Office of Long-Term Planning & Sustainability.