Accelerating growth of human coastal populations at the global and continent levels: 2000–2018

The rapid growth of human populations along coastlines is increasingly at odds with the growing number of natural and human-induced hazards in these regions.
Accelerating growth of human coastal populations at the global and continent levels: 2000–2018
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The Problem

Despite the critical importance of understanding population patterns in coastal regions, reliable, high-resolution data on the scale, distribution, and changes in these populations is surprisingly limited. Accurate and comprehensive data is essential for effective coastal monitoring, especially in light of the risks associated with climate change and other environmental challenges. Unfortunately, previous studies have yielded inconsistent estimates, making it difficult to grasp the full extent of human presence along coastlines.

What We Did

To address this gap, we applied a novel approach, utilizing the latest LandScan Global population distribution data to estimate and characterize high-resolution coastal populations over the early years of the 21st century. Our methodology involved several key stepsEstimating Global and Continental Coastal Populations: We focused on populations within 50 kilometers of the shore, analyzing data from 2000 to 2018. This allowed us to capture broad patterns of population concentration along coastlines across the globe.

Modeling Population Buildup by Distance from Shore: We examined how population densities vary with proximity to the coast, identifying trends in population "buildup" as we moved farther inland.

Calculating Growth Rates: We tracked the rate of population growth within 5-kilometer bands from the shoreline, covering the period from 2000 to 2018. This provided insights into how rapidly coastal populations are expanding compared to inland areas.

Developing Coastal Population Metrics: To assist with long-term coastal monitoring, we devised several cross-sectional and temporal metrics to characterize macro-level population patterns in coastal regions.

Key Findings

Our analysis revealed several important trends:

Concentrated Coastal Populations: Nearly 2 billion people live within 50 kilometers of the coast, with approximately 1 billion residing within just 10 kilometers. These findings underscore the significant human presence in these narrow coastal zones, which are particularly vulnerable to environmental hazards.

Faster Coastal Population Growth: Coastal populations are growing at a faster rate than inland populations. Between 2000 and 2018, the population within 50 kilometers of the coast increased by 463 million, while the population within 10 kilometers grew by 233 million. This suggests that coastal regions are experiencing disproportionately high population pressures.

Influence of Proximity to the Coast: Our analysis confirmed that proximity to the coast is a strong predictor of population distribution (Figure 1). The closer to the coast, the denser the population, creating a pattern that can be modeled effectively using mathematical functions.

Power Function for Population Patterns: We discovered that a power function could describe not only the distribution of coastal populations but also their growth rates at global and continental levels. This finding may have broader applications, as it suggests a useful mathematical model for understanding the dynamics of Earth's systems, including the impact of coastal populations on the environment.

These findings highlight the growing anthropogenic effects on coastal ecosystems and human populations, with significant implications for environmental risks, including sea-level rise, land subsidence, extreme weather events, and public health.

The Broader Impact

High-resolution estimates of coastal population growth have far-reaching implications for a variety of global issues. Coastal regions are hubs of economic activity and infrastructure development, often playing critical roles in national and global economies. However, the rapid population growth in these areas is exacerbating environmental risks. As coastal populations expand, so do the anthropogenic effects, particularly in regions experiencing high economic growth.

The coastal population boom also poses significant risks to the people living in these areas. Coastal regions are highly susceptible to the impacts of climate change, including rising sea levels, land erosion, and extreme weather events such as hurricanes, tsunamis, and floods. These hazards are well-documented, and the increasing concentration of people in high-risk coastal zones only amplifies the dangers. The more people who reside in vulnerable areas, the greater their exposure to these risks.

Our analysis shows that the patterns of human population growth along the coast coincide with increasing risk exposure. As coastal populations grow, the magnitude of risk increases, creating a situation where the potential for harm to both human and natural systems is greatly amplified.

Emerging Questions

While our study has provided valuable insights into the growth and distribution of coastal populations, it also raises important questions. One such question is whether the growth of coastal populations should be conceptualized as a demographic trend similar to urbanization. If so, what factors contribute most to this growth—natural increase, rural-to-coastal migration, or urban-to-coastal migration? Furthermore, recent research suggests that populations in low elevation coastal zones (LECZ) are becoming more urbanized, with urban populations in these areas growing faster than urban populations elsewhere. This trend suggests that urbanization in coastal areas may be an important driver of coastal population growth, further complicating efforts to manage the associated risks.

Final Thoughts

Our findings indicate that coastal populations are not only growing rapidly but also following distinct patterns that can be mathematically modeled. The discovery that a power function describes not only the distribution but also growth of coastal populations offers a potential new tool for understanding how human activities are influencing Earth's systems. For example, this power function could be adapted into a "coastal gravity model," analogous to the gravity models used to estimate urban influence. However, instead of focusing on a central urban point, this model would track the influence along the coastline itself.

As the world continues to grapple with the challenges posed by climate change and environmental degradation, understanding coastal population dynamics will be increasingly important. Our study provides a foundation for future research, offering both a methodology for tracking population changes and a framework for exploring the complex interactions between human populations and coastal environments.

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