📄 earth_science

Spatio-Temporal Analysis of Urban Encroachment at the Sakumono Ramsar Site, Ghana (2005-2026)

This study utilizes multi-temporal satellite imagery and classification analysis to reveal that urban encroachment at Ghana's Sakumono Ramsar Site accelerated dramatically between 2015 and 2026, with built-up areas expanding from 0.04% to nearly 50% of the site, primarily by converting bare and degraded land.

Original authors: Kelvin Fafanyo, Jesslyn Akrokoh, Benjamin Edinam Cofie, Aishatu Abdul Rahman Agyeman, Akua Amankwaa Acheampong, Audrey Korsah Asubonteng

Published 2026-07-10

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Kelvin Fafanyo, Jesslyn Akrokoh, Benjamin Edinam Cofie, Aishatu Abdul Rahman Agyeman, Akua Amankwaa Acheampong, Audrey Korsah Asubonteng

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the Sakumono Ramsar Site as a giant, breathing sponge sitting right next to the bustling cities of Accra and Tema in Ghana. This sponge isn't just any sponge; it's a protected wetland, a special zone recognized by the whole world (the Ramsar Convention) to keep water clean, stop floods, and give over 30,000 birds a safe place to eat and sleep. But between 2005 and 2026, something dramatic happened: the city started eating the sponge.

The Great City Takeover
Think of the wetland as a 1,362.42-hectare pie. In 2005, the "city" slice of that pie was microscopic—just 0.54 hectares, or about 0.04% of the whole thing. It was barely a crumb. But fast forward to 2026, and that crumb has exploded into a massive slice covering 675.99 hectares. That's nearly half the entire pie (49.62%) now covered in concrete and buildings instead of water and plants.

The paper shows that this wasn't a slow, steady nibble. It was more like a sudden, ravenous gulp. Between 2005 and 2015, the city grew by about 64 hectares. But between 2015 and 2026, the growth rate skyrocketed. The city gained 611.1 hectares in that second decade—roughly nine times more than it gained in the previous ten years. The authors measured this using satellite photos (like taking pictures from space) and found that the city didn't just expand; it accelerated wildly.

How the City Ate the Sponge
You might wonder, "Did the city just jump straight onto the bird nests?" Not exactly. The study found a specific pattern, like a game of dominoes.

First, the city ate the "Bare/Degraded Land." In the second decade alone, 547.11 hectares of this damaged, empty land turned directly into buildings.
Then, the city started eating the healthy "Wetland Vegetation." About 68.94 hectares of green plants were converted to buildings.
The paper suggests that the damaged land acted as a "stepping stone." Once the city took over the empty, degraded spots, it became much easier for construction to push deeper into the healthy, green parts of the wetland.

Once a piece of land became a building, it almost never went back. The study found that 92.4% of the buildings that existed in 2015 were still there in 2026. The authors note that under current rules, turning a building back into a wetland is practically impossible.

What Was Lost?
As the city grew, the other parts of the pie shrank.

Open Water: Dropped from 59.31 hectares in 2005 to 43.38 hectares in 2026.
Wetland Vegetation: Shrank significantly, losing 123.66 hectares between 2015 and 2026 alone.
Bare Land: Interestingly, this category actually grew in the first decade (as vegetation died off) but then shrank rapidly in the second decade as the city paved over it.

How Sure Are We?
The researchers didn't just guess; they checked their work carefully. They used a method called "Maximum Likelihood Classification" to sort the satellite pixels into categories like water, plants, or buildings. They tested their maps against real-world photos and found they were right more than 80% of the time for all three years (2005, 2015, and 2026). The numbers are solid measurements, not just simulations or ideas.

The Big Picture
The paper argues that even though Sakumono is officially a protected international site, the protection hasn't been strong enough to stop the city. The authors suggest that without active enforcement, a "protected" label alone isn't enough to save a wetland in a fast-growing city. The data shows that the wetland is being transformed from a functioning ecosystem into an urban landscape, and this change is happening faster than ever before. The authors warn that this loss means the area is losing its ability to filter water, stop floods, and support the 70+ bird species that call it home.

Technical Summary: Spatio-Temporal Analysis of Urban Encroachment at the Sakumono Ramsar Site, Ghana (2005-2026)

Problem Statement
The Sakumono Ramsar Site, a critical coastal wetland in Ghana's Greater Accra Region, faces severe pressure from rapid urbanization. Despite its designation as a Ramsar Site in 1992 and the enactment of the Wetlands Management Regulations Act in 1999, the site has experienced sustained encroachment driven by the demographic expansion of the Accra–Tema metropolitan area. While previous studies have documented land use and land cover (LULC) changes at national and regional scales, there is a lack of site-specific quantification regarding the dynamics of encroachment at Sakumono over the most recent two decades. Specifically, the rate at which degradation in peripheral zones transitions to permanent built-up conversion remains under-explored, limiting the development of spatially targeted enforcement and management strategies.

Methodology
The study employs a spatio-temporal analysis of LULC changes across three epochs: 2005, 2015, and 2026.

Data Sources: Multi-temporal Landsat surface reflectance imagery was acquired from the USGS Earth Explorer portal. Images were selected from the dry season (December–February) to minimize cloud cover and ensure comparability of open-water extents. The dataset includes Landsat 7 ETM+ (SLC-off) for 2005, Landsat 8 OLI/TIRS for 2015, and Landsat 9 OLI/TIRS for 2026.
Pre-processing: Imagery was processed in ArcGIS Pro 3.1. False Colour Composites (FCCs) were generated to enhance feature discrimination. All rasters were clipped to the official Ramsar Site boundary (1,362.42 ha) using a WGS 1984 UTM Zone 30N projection.
Classification: A supervised Maximum Likelihood Classification (MLC) was applied to map four distinct LULC classes: Open Water, Wetland Vegetation, Bare/Degraded Land, and Built-up/Urban. Training samples (50 per class) were digitized on-screen and verified against historical Google Earth Pro imagery.
Change Detection: Post-classification change detection matrices were generated to quantify transitions between epochs (2005–2015 and 2015–2026).
Accuracy Assessment: Independent validation was conducted using 100 random points per epoch, verified against time-series imagery. Metrics included Overall Accuracy (OA), Producer's Accuracy (PA), User's Accuracy (UA), and the Kappa Coefficient ( $\kappa$ ). The study established minimum acceptance thresholds of OA $\ge$ 80% and $\kappa$ $\ge$ 0.70.

Key Results
The analysis reveals a dramatic acceleration in urban encroachment, particularly in the second decade of the study period.

Built-up Expansion: The built-up area expanded from a negligible 0.54 ha (0.04%) in 2005 to 675.99 ha (49.62%) by 2026.
Acceleration of Change: The net gain in built-up area during the 2015–2026 period (611.1 ha) was approximately nine times greater than the gain recorded during 2005–2015 (64.35 ha).
Transition Dynamics:
- 2005–2015: The dominant transition was Bare/Degraded Land converting to Wetland Vegetation (+151.38 ha), suggesting partial vegetative recovery, alongside a modest conversion of Bare Land to Built-up (63.99 ha).
- 2015–2026: The primary driver of urban expansion was the direct conversion of Bare/Degraded Land to Built-up areas (547.11 ha). Additionally, 68.94 ha of Wetland Vegetation was converted to Built-up.
Wetland Loss: Open Water declined from 59.31 ha (4.35%) in 2005 to 43.38 ha (3.18%) in 2026. Wetland Vegetation peaked in 2015 (383.4 ha) before declining to 259.74 ha (19.06%) in 2026.
Persistence: Built-up areas exhibited a high persistence rate of 92.4% from 2015 to 2026, indicating the near-irreversibility of urban conversion under current governance conditions.
Accuracy: All classifications met the study's acceptance criteria. The 2005 classification achieved an OA of 80% and $\kappa$ of 0.73; 2015 achieved 82% OA and $\kappa$ of 0.76; and 2026 achieved the highest accuracy with 88% OA and $\kappa$ of 0.84.

Significance and Claims
The paper claims to provide an updated, quantitative baseline for wetland conservation planning within Ghana's Ramsar network. The findings demonstrate that despite international protected status, the Sakumono Ramsar Site has undergone a fundamental transformation from a functioning coastal wetland complex to an increasingly urbanized landscape, with nearly half of the designated area converted to built-up use by 2026.

The study posits that the observed trajectory reflects a systemic governance failure rather than a site-specific anomaly, consistent with patterns observed in other West African coastal wetlands. The results highlight that Ramsar designation alone, without commensurate institutional capacity and active enforcement, offers limited protection against rapid urban expansion. The documented change trajectories serve as a foundation for spatial prioritization of conservation investments and establish a baseline against which future restoration efforts can be evaluated. The authors emphasize that the near-perfect persistence of built-up pixels underscores the critical importance of prevention over remediation as a conservation strategy.

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