Coastal Adaptation Tipping Points 2D: Sea-Level Pathway Model

Sea-Level Scenario

Acceleration what-if 1.0×

Adaptation Strategy

Auto-switch pathway at tipping point

Timeline

Year 2025

Readouts

Sea-level rise

0.00 m

Active strategy

Nature-based

Flood risk score

0.0

Adaptation cost index

0.0

Pathway Log

Simulation starts in 2025.

How it works

A 2D Dynamic Adaptive Policy Pathways (DAPP) model, the framework coastal agencies (e.g. the Dutch Delta Programme) use to plan defenses under deep uncertainty. Sea level follows an accelerating curve, with an optional acceleration multiplier for what-if stress testing:

SLR(t) = R·t + 0.5·(A·mult)·t²     (t = years since 2025)

Each strategy has a fixed design height — the water level it was engineered to withstand, minus a safety freeboard. Nature-based defenses also slowly lose height to erosion. The overtopping probability grows once sea level approaches that design height:

P(overtop) = clamp( (SLR − designHeight) / 0.4 , 0, 1 )
riskScore += P(overtop) · riskWeight · Δt · 10

An adaptation tipping point is the year P(overtop) exceeds 50%. With auto-switching on, crossing it forces an escalation to the next stronger strategy (do nothing → nature-based → hard protection → managed retreat), each carrying a one-off construction cost on top of its yearly upkeep. With auto-switching off, the chosen strategy stays locked in and the flood-risk score keeps climbing after its tipping point — a visual of maladaptation / path lock-in.

Scenario — sets the rate R and acceleration A of sea-level rise.
Acceleration what-if — scales the scenario's acceleration term A to stress-test faster or slower ice-sheet contributions than the base scenario assumes.
Strategy — the starting (or, with auto-switch off, permanent) defense choice; the cross-section's defended row rises or falls with its design height.
Year slider / Play — scrubs or auto-advances time; the whole 75-year run is re-simulated deterministically from 2025 to whatever year is shown, so scrubbing backward is exact, not approximated. The bottom chart can also be click-dragged to scrub the year directly.
Top strip — an along-shore top-down view of the defended row, coloured dry/flooded per along-coast position (the same per-column relief the 3D version renders as a grid).

Dry land Defense structure Flooded Sea level

drag chart to scrub year