Rapid seaward expansion of seaport footprints worldwide

Global maritime traffic is increasing, demanding greater seaport infrastructure and capacity. Seaports, vital for global trade (approximately half by value is maritime), are vulnerable to coastal hazards, and this risk is projected to increase due to sea-level rise and escalating trade volumes. Current risk assessments often treat seaport footprints as static, neglecting the significant seaward expansion occurring through coastal land reclamation. This expansion impacts global trade routes, climate risk dynamics, coastal environments, and ecological health. The lack of readily available spatiotemporal data on seaport areas has hindered previous efforts to quantify this growth. This paper addresses this gap by analyzing satellite imagery to measure the extent of seaward expansion in major container ports.

Existing research highlights the heterogeneous geographical distribution of seaport exposure to climate-driven hazards, with risk hotspots concentrated in cyclone corridors. Studies have shown that functional risk to seaport infrastructure will intensify before 2050 due to sea-level rise and increased trade volume. While regional and global analyses of seaport risk are improving, they generally treat seaport footprints as static. The lack of spatiotemporal data on seaport area change has prevented a comprehensive understanding of the patterns and impacts of seaward expansion. Previous reports on coastal land reclamation related to port expansion have tended to focus on specific geographical locations, lacking a global perspective. This study builds upon this existing work by providing a comprehensive, globally distributed analysis of seaport expansion using readily available satellite data.

The study analyzed annual patterns of seaward expansion in 65 of the world's top 100 container ports (ranked by 2020 throughput) using a recently published method for quantifying coastal land reclamation from satellite imagery in Google Earth Engine. The method uses a 1990 composite coastline as a baseline, identifying seaward shifts in the coastline as land reclamation. To differentiate seaports from ports in riverine or inshore settings, the Lloyd's List of the 100 largest container ports was used. Seaports with less than 1 km² of seaward expansion since 1990 were excluded. The analysis utilized the 30m resolution Global Surface Water (JRC-GSW) dataset from 1990 to 2020. Annual patterns of seaport reclamation were measured as changes in water surface area at the coastline, registering as "lost permanent water surfaces." Bounding polygons for each seaport were manually defined using OpenStreetMap data and Google Earth Engine outputs. The method does not differentiate among specific uses of reclaimed space; the measured seaward extents are interpreted as a partial gauge of gross port area. Time series variability was estimated using a three-year sliding window to detrend sub-series and calculate standard deviations, accounting for missing data and nonlinearity. Container throughput data from 2011-2020 were compiled from archived Lloyd's List reports for a subset of the ports.

The study found that the 65 analyzed seaports expanded their footprints seaward by a total of 978 km² between 1990 and 2020, a significant portion (approximately 22%) relative to the estimated current area of port terminals worldwide. Two-thirds of this expansion occurred in Asia, with China accounting for 63% of the total. The port of Tianjin alone reclaimed over 183 km², more than triple the expansion of Singapore. While approximately half of the seaports expanded less than 5 km², all but seven at least doubled their seaward area since 1990. Time series analysis revealed diverse patterns of seaward expansion, including asymptotic, exponential, sigmoidal, and cubic curves. The regional distribution of expansion aligns with global trade dominance, with Asia (especially China) leading the way, though Northern Europe and the Middle East also exhibited significant growth. While a general positive relationship exists between seaward reclamation and container throughput, the relationship is not straightforward at the individual port level. A significant number of seaports showed disproportionately large reclamation relative to their throughput. Time series analysis (2011-2020 for 43 ports) showed various trajectories, some indicating that reclamation facilitates increased trade volume, while others reveal exceptions to this trend, possibly due to lags between reclamation and infrastructure development. The study cautions against applying simple scaling relationships between seaport area and trade volume.

The study's findings highlight the widespread and substantial seaward expansion of major container ports worldwide. This pattern transcends national policy differences, underscoring the ubiquitous nature of this phenomenon. While a positive correlation between expansion and throughput exists, the relationship is complex and varies across individual seaports. Seaport expansion acts as a ratchet mechanism, potentially enabling increased market share even if trade volumes fluctuate. Global maritime traffic growth is a key driver of this expansion, but factors such as limited coastal real estate in urban centers likely play a role. The findings contribute to a broader understanding of coastal risk and ocean sprawl, highlighting the environmental consequences of coastal hardening and the potential challenges in adapting to future climate change. The study underscores the need for case-specific assessments of the logistical, policy, ecological, and hazard-exposure implications of seaport expansion.

This research provides a comprehensive quantification of the rapid seaward expansion of global container ports, revealing a globally distributed pattern of coastal land reclamation exceeding previous estimates. While generally correlating with trade volume, the relationship between port expansion and throughput is complex. Future research should explore case-specific factors influencing expansion, assess the impact on coastal ecosystems, and analyze the implications for climate adaptation strategies. Improving the global understanding of seaport dynamics as dynamic sites of coastal modification is crucial for mitigating associated risks and fostering sustainable port development.

The analysis focuses on seaward expansion, neglecting landward growth and specific land-use within the seaport complex. The method relies on satellite imagery, potentially leading to inaccuracies in measuring areas of seaward changes, especially in areas with complex shoreline features or limitations in image resolution. The use of reported container throughput data might not fully capture all aspects of port activity and capacity. The analysis does not explicitly consider the various political, policy, and market factors driving port expansion, nor does it model future impacts.