Mangroves shelter coastal economic activity from cyclones

Abstract

Mangroves shelter coastlines during hazardous storm events with coastal communities experiencing mangrove deforestation are increasingly vulnerable to economic damages resulting from cyclones. To date, the benefits of mangroves in terms of protecting coastal areas have been estimated only through individual case studies of specific regions or countries. Using spatially referenced data and statistical methods, we track from 2000 to 2012 the impact of cyclones on economic activity in coastal regions inhabited by nearly 2,000 tropical and subtropical communities across 23 major mangrove-holding countries. We use nighttime luminosity to represent temporal trends in coastal economic activity and find that direct cyclone exposure typically results in permanent loss of 5.4-6.7 mo for a community with an average mangrove extent (6.3 m per meter of coastline); whereas, a community with more extensive mangroves (25.6 m per meter of coastline) experiences a loss equivalent to 2.6-5.5 mo. These results suggest that mangrove restoration efforts for protective benefits may be more cost effective, and mangrove deforestation more damaging, than previously thought.

Keywords: ecosystem services; global spatial analysis; mangroves; natural disaster; storm protection.

Fig. 1.

Economic impact of cyclone exposure (6.3 m of mangroves per meter of coastline). Cyclone exposure occurs in year 0. Shaded areas represent 95% confidence intervals around the cumulative impact of cyclone exposure on the trend in economic activity growth rate. The solid line represents estimates from the ordinary least squares (OLS) specification and the line with asterisks represents two-stage least squares estimates instrumented using the width of mangroves located in protected areas, which are less likely to be converted during postdisaster recovery. Both estimates are evaluated at the sample mean mangrove width (6.3 m per meter of coastline).

Fig. 2.

Economic impact of cyclone exposure (25.6 m of mangroves per meter of coastline). Cyclone exposure occurs in year 0. Shaded areas represent 95% confidence intervals around the cumulative impact of cyclone exposure on the trend in economic activity growth rate. The solid line represents estimates from the OLS specification and the line with asterisks represents two-stage least squares estimates instrumented using the width of mangroves located in protected areas, which are less likely to be converted during postdisaster recovery. Both estimates are evaluated at the sample mean mangrove width + 1 sample SD (25.6 m per meter of coastline).

Fig. 3.

Storm events and mangrove deforestation rates for sample LLAs with 95% confidence intervals. The annual rate of deforestation is calculated as the percentage of mangrove coverage loss annually. Cyclone exposure occurs in year 0. Here, sample deforestation rates are presented before, during, and after direct storm exposure with 95% confidence bands.