- A recent study revealed that Bali’s coastline shrank from 668.64 kilometers (415.47 miles) to 662.59 km (411.71 mi) between 2016 and 2021 due to human activities and wave circulation, at an average rate of -1.21 meters (3.97 feet) annually.
- The erosion, combined with rising sea levels, threatens the island’s ecosystems, infrastructure and communities, which are economically and culturally significant.
- Despite the erosion, there was a net land increase of 1.25 km2 (0.48 mi2) due to land reclamation and infrastructure development, though these efforts also posed environmental risks.
- The study highlights the need for integrated coastal management to balance environmental protection with the needs of coastal communities.
JAKARTA — Indonesia’s Bali island is shrinking at a faster rate than most coastal areas in the world due to human activities and wave circulation, according to a recently published study.
Bali’s shoreline decreased to 662.59 kilometers (411.71 miles) from 668.64 km (415.47 mi) between 2016 and 2021 at an average rate of -1.21 meters (3.97 feet) annually, said a group of researchers from Indonesia, Japan and Turkiye (Turkey) in their paper published on May 29 in the journal Regional Studies in Marine Science. Globally, 24% of the world’s sandy beaches have faced erosion at rates more than 0.5 m (1.6 ft) per year. Coastal erosion in the U.S. causes an estimated $500 million in property loss and damage annually.
They warned that the continuous erosion coupled with the ongoing rise in sea level might exacerbate coastal flooding and further retreatment, threatening surrounding ecosystems, infrastructure and communities. Bali’s coastal zone is vital for its socioeconomic and cultural heritage, serving as a settlement center for most of the population, driving the economy through tourism and holding deep cultural, traditional and religious significance.
“Asia’s coasts are under threat from increasing sea levels and rapid development,” the paper read. “These problems frequently result from inadequate planning and funding for managing erosion.”
Shoreline is a crucial indicator for monitoring coastal changes, essential for spatial planning and sustainable development due to its importance to coastal ecosystems and marine environments. The paper said that many studies have been conducted in Bali’s coastal zone, but none has used the latest high-resolution imagery data to monitor the coastline.
The researchers, led by Amandangi Wahyuning Hastuti from Yamaguchi University’s Graduate School of Science and Technology for Innovation, analyzed advanced geospatial methods and data covering six years from 2016-22 and in March 2023 conducted a field survey along the shoreline of Bali province, collecting a total of 75 sampling points.
They found that most sandy shore erosion happened on the southern coast of Bali, including the southwest and southeast coasts, namely the districts of Jembrana, Tabanan, Badung, Denpasar, Gianyar, Klungkung and Karangasem.
Bali province is bordered by the Bali Sea (north), the Bali Strait (west), the Lombok Strait (east) and the Indian Ocean (south), with a mountain chain stretching from west to east dividing the island into north and south parts. The topography, characterized by volcanic alluvial deposits on most beaches and limestone formations in the south, has significantly influenced coastal evolution, present-day coastal morphologies and the formation of mangrove-lined beaches in areas such as Benoa Bay, Gilimanuk Bay and northern Nusa Lembongan Island.
However, rapid development to support tourism, such as airport extensions, freeway construction and seaside hotels, has led to environmental challenges such as pollution, coastal erosion and significant land use changes, threatening the natural environment. A 2022 research paper showed that 22% of Bali’s coast was categorized as very highly vulnerable to the effects of climate change, such as erosion, flooding and storms, including sea level rise. Sea levels have risen by an average of 2.5 millimeters (0.09 inches) per year in the last 25 years, according to the Intergovernmental Panel on Climate Change (IPCC).
The newly published study also found that Bali saw significant coastal growth with a net land increase of 1.25 km2 (0.48 mi2), notably exceeding the erosion rate in the island province during the study period. The researchers said land reclamation and infrastructure development contributed to the shoreline increase, while natural processes combined with human intervention have eroded Bali’s coasts.
They pointed out that coastal structures — such as seawalls, sandbags, breakwaters or groins — might provide some protection against erosion, but these additional artificial shorelines could cause unavoidable negative consequences, including downdrift coastal erosion, declining water quality, sedimentation and subsequent socioeconomic implications among coastal communities — rendering careful engineering estimation a necessity.
“Seawalls can effectively defend against flooding and erosion, immobilizing the adjacent beach sand,” the paper read. “However, the cost and effectiveness of seawalls depend on their shape and size.”
The study’s findings have offered much-needed, albeit concerning, data and analysis about coastal management on small islands like Bali, said Ketut Sarjana Putra, senior adviser at Conservation International, who was not involved in the research but reviewed it per Mongabay’s request.
“This is very crucial for decision-makers, leaders and the people of Bali in general — even all of Indonesia,” Ketut told Mongabay in an interview. “Because, as the study suggests, and also based on my knowledge, coastal management of a small island like Bali needs an all-around modeling, including coastline change and ocean dynamics associated with climate change, so that the most effective way can be decided to manage the coastline and that the shores can fully sustain its equilibrium.”
Ketut said further studies must be conducted to expand the time frame in order to capture broader and deeper insight of Bali’s coastline changes and potentially become a model to estimate future changes and anticipate the estimated vulnerabilities.
“It means a study like this provides us some input that if we think about the impacts for the next 10 or 20 years, maybe now is the time to stop, pause for a while in increasing the coastline or, in other words, conducting land reclamation,” he said. “Because we must realize that an island and wave movement are dynamic and we don’t have the dataset to predict when they are going to stabilize and what the patterns look like, and therefore, we can’t yet decide how much is the risk in the future and what the best intervention looks like.”
Ketut said that the Bali government, unfortunately, has yet to produce a master plan with a holistic, integrated and interdisciplinary approach for managing the island’s coasts.
The paper’s researchers suggested that focusing solely on environmental protection wouldn’t be sufficient, as a healthy coast requires a balance between protecting coastal communities and ecosystems.
“Bali Province can mitigate and prevent further coastal erosion by implementing site-specific strategies and protecting valuable coastal ecosystems and vital infrastructure,” the paper read.
Basten Gokkon is a senior staff writer for Indonesia at Mongabay. Find him on 𝕏 @bgokkon.
See related story:
As Bali reclamation project dies, activists seek conservation status
Citations:
Hastuti, A. W., Nagai, M., Ismail, N. P., Priyono, B., Suniada, K. I., & Wijaya, A. (2024). Spatiotemporal analysis of shoreline change trends and adaptation in Bali Province, Indonesia. Regional Studies in Marine Sciences, 76. doi:10.1016/j.rsma.2024.103598
Luijendijk, A., Hagenaars, G., Ranasinghe, R., Baart, F., Donchyts, G., & Aarninkhof, S. (2018). The state of the world’s beaches. Scientific Reports, 8(1). doi:10.1038/s41598-018-24630-6
Hastuti, A. W., Nagai, M., & Suniada, K. I. (2022). Coastal vulnerability assessment of Bali province, Indonesia using remote sensing and GIS approaches. Remote Sensing, 14(17), 4409. doi:10.3390/rs14174409
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