The global flood protection savings provided by coral reefs

Abstract

Coral reefs can provide significant coastal protection benefits to people and property. Here we show that the annual expected damages from flooding would double, and costs from frequent storms would triple without reefs. For 100-year storm events, flood damages would increase by 91% to $US 272 billion without reefs. The countries with the most to gain from reef management are Indonesia, Philippines, Malaysia, Mexico, and Cuba; annual expected flood savings exceed $400 M for each of these nations. Sea-level rise will increase flood risk, but substantial impacts could happen from reef loss alone without better near-term management. We provide a global, process-based valuation of an ecosystem service across an entire marine biome at (sub)national levels. These spatially explicit benefits inform critical risk and environmental management decisions, and the expected benefits can be directly considered by governments (e.g., national accounts, recovery plans) and businesses (e.g., insurance).

Fig. 1

Key steps and data for estimating the flood protection benefits provided by reefs. a Stage 1: Oceanographic data are combined to assess offshore sea states (waves and sea level). Stage 2: Waves are modified by nearshore hydrodynamics. Stage 3: Effects of habitat on wave run-up are estimated. Stage 4: Flood heights are extended inland along profiles (every 2 km) for four locally generated, storm events (10, 25, 50, 100-yr events) with and without coral reefs. Stage 5: The land, people and built capital damaged under the flooded areas are estimated. Image © TNC. b The scenarios for reef loss only assume a loss of the top 1-m in height and roughness across the reef profile. c Example results for Mayan Riviera in Mexico; blue polygons are expected flooding in 25-yr event and green polygons are added flooding without the top 1 m of reefs. Map Data © 2018 Google. d Inset photo shows coral reef bleaching of top most branching corals in 2015 El Nino event in Guam. ©The Ocean Agency/XL Catlin Seaview Survey

Fig. 2

Annual expected benefits from coral reefs for flood protection. Estimates of the effects of reefs on avoided flooding to land, people, exposed capital and damaged capital. The differences between scenarios with and without reefs are avoided damages or present benefits of reefs

Fig. 3

The expected economic benefits of coral reefs for flood protection in avoided damages. The values are the expected damages to global built capital from flooding with and without reefs by storm return period. The difference between the curves represents the avoided damages or benefits provided by reefs at present

Fig. 4

The expected land protection benefit of coral reefs at present and with sea level rise. The values are the land areas (km²) flooded globally with reefs at present, without the top 1 m of coral reefs and with relative sea level rise under a high emissions scenario (RCP 8.5 in 2100) by storm return period

Fig. 5

The value of coral reefs for flood protection. Circles represent the annual expected benefit from coral reefs for flood protection ($US millions). The values are the difference in annual expected damages with and without (the top 1 m) of reefs for the 20 km coastal study units