About 33 per cent of the world’s sandy beaches have hardened. The Bay of Bengal occupies first position with 84 per cent coastal hardening, a new study has revealed.
Coastal hardening refers to ‘rigid’, semi-impermeable structures created by humans that alter the natural landscape, potentially obstructing the shoreline retreat, and landward translation of sandy beaches, the study stated.
These structures include impervious surfaces or infrastructure such as seawalls, harbours, roads, highways, buildings, railway revetments or other urban structures.
The coastal areas needed protection from erosion and flooding given the rapid increase in population migration towards coasts since the 1950s, the study published in journal Nature said. This had resulted in construction of structures and consequent hardening of beaches.
The Bay of Bengal was followed by western and central Europe, which showed the second-largest coastal hardening with 68 per cent, followed by the Mediterranean with 65 per cent.
Western North America and east Asia showed 61 per cent and 50 per cent respectively. The scientists used Global Impervious Surface Area (GISA) datasets to analyse the extent of hardening.
The study cited examples and stated that the entire sandy beach in front of a retaining wall in Santa Cruz, northern California, was eroded due to waves.
The process of gradual beach loss in front of the seawall or revetment, together with the landward migration of the shoreline, has been well documented along the US Atlantic coast’s barrier islands, as well as along the coasts of Oahu in Hawaii, and the states of California and Washington, the study observed.
“In addition, most of these regions contain high-income and upper-middle-income countries with major seaports where coastal infrastructure investment can be high, necessitating their protection with engineering structures,” the study noted.
It also found that in the Bay of Bengal and the Mediterranean, the coastal population residing within 100 km from the coast was high — estimated to be over 50-75 per cent of the total population, underlining the urgent need of coastal protection and management.
The researchers also analysed as to how much of the global sandy coastline is expected to face severe beach loss at the end of the 21st century.
Sandy beaches could increase by 9-21 per cent considering the immediate scenario where carbon emissions halve by 2050, with interventions. Sandy beach loss is estimated to increase up to 26 per cent in a ‘business as usual’ scenario where emissions continue as present.
A coastline of about 42,080 km is likely to be lost under the immediate scenario while under the ‘business as usual’ scenario, the loss is estimated to be nearly 52,080 km.
“Geographically, most sandy beaches under threat are located in Eastern North America, Northern South America, Mediterranean, Bay of Bengal, Western Africa, and South-East Asia regions,” the study found.
The scientists also ranked regions from lower to highest, based on their median erodible beach width. The artificial structures were found closest to the shores of northern South America, followed by the Caribbean, southern Australia, western Africa, and New Zealand. All the regions averaged a distance of 56 metres from the shoreline.
“The regions with the widest erodible sandy beaches are found in North-Eastern North America, North-Western South America, Central Australia, South Asia, and North-Eastern Africa (lowest to highest),” the study said.
The study also pointed out that the largest share of hardened coastline and sandy beaches facing severe beach loss indicated that high income countries had the resources to invest and maintain coastal hardening structures, leading to more beach losses in the future.
Meanwhile, the study urged acknowledging potential underestimation in the amount of hardened sandy beaches and percentage of sandy beaches facing heavy losses in low and lower middle-income countries. This is mainly due to higher chances of unmapped areas in those regions.
Roxy Koll, climate scientists who was not part of the study, told Down To Earth, “This means that in those coastal areas that are hardened, coastal erosion and encroachment of the sea could be much larger.”
He added that this is concerning because we have a huge coastal population that is vulnerable to rising climate impacts and does not have the capacity to adapt itself (unless external support via policies and government funds is provided).