About the Global Water Body Surface Area Atlas

Status: Educational/Research Project in Active Development
Last Updated: October 12, 2025
Lead: Nguyen Truong An

⚠️ Important Disclaimer

This is an educational research project created with AI assistance (GitHub Copilot). It demonstrates modern geospatial data processing techniques but is NOT peer-reviewed scientific work. Do not cite this as authoritative research.

🎯 Project Objectives

Primary Goal

Create the world’s first comprehensive, polygon-based global water body surface area atlas using direct measurement rather than statistical extrapolation. This enables precise calculations for biogeochemical modeling (GHG emissions, carbon fluxes, nutrient budgets).

Why This Matters

Previous Approach (Laruelle et al. 2025):

• Manually measured 735 estuaries
• Extrapolated to global estimate
• Result: ~734,000 km² ± 39,892 km²

Our Approach (2025):

• Direct measurement of 20.5 million river reaches globally
• Polygon-based calculation (not extrapolation)
• Higher spatial resolution and accuracy

Specific Objectives

1. Calculate precise surface areas for all aquatic system types:
   • Rivers (non-tidal, tidal freshwater zone, saline reaches)
   • Estuaries (by geomorphology type: Delta, Fjord, Lagoon, etc.)
   • Lakes and reservoirs
   • Wetlands

2. Implement O’Connor et al. (2022) Tidal Freshwater Zone framework globally

3. Provide open-access, reproducible methodology - all code and data sources documented

4. Enable next-generation biogeochemical models with precise spatial data

5. Compare results with Laruelle 2025 to validate methodology

🔬 Scientific Background

What is an Estuary?

“A semi-enclosed coastal body of water that has a free connection with the open sea and within which sea water is measurably diluted with freshwater derived from land drainage.”
— Pritchard (1967)

Why Classify Estuaries?

Different estuary types have fundamentally different characteristics that affect their biogeochemical function:

• Sediment dynamics: Deltas trap sediment, fjords export little
• Mixing patterns: Shallow vs stratified water columns
• Residence time: Hours (tidal channels) to months (lagoons)
• Productivity: Nutrient availability and light penetration

The O’Connor et al. (2022) Framework

The Tidal Freshwater Zone (TFZ) is a distinct biogeochemical reactor:

• Salinity: 0-0.5 PSU (parts per thousand)
• Experiences tidal influence but remains freshwater
• High methane emissions (anaerobic sediments + organic matter)
• Critical for global GHG budgets

🛠️ Technology Stack

Data Processing

• Python 3.10+ with GeoPandas, Pyogrio, Pandas
• GDAL/OGR for format conversion
• Spatial analysis with Shapely, RTree

Web Visualization

• Leaflet.js for interactive mapping
• Chart.js for statistics
• GitHub Pages for hosting

Development Tools

• VS Code with Copilot AI assistance
• Git/GitHub for version control
• Markdown for documentation

📊 Dataset Overview

Current Data Coverage

Type Distribution (Dürr Dataset)

• Delta: 1,768 estuaries (29%)
• Fjord: 2,303 estuaries (38%)
• Lagoon: 510 estuaries (8%)
• Coastal Plain: 1,645 estuaries (27%)
• Others: Karst, tectonic, etc.

🎓 Intended Use Cases

✅ Appropriate Uses

• Educational purposes: Learning geospatial data processing
• Methodology development: Testing analytical workflows
• Preliminary exploration: Understanding global patterns
• Code examples: Reference for similar projects
• Discussion starter: Informing research proposals

❌ Inappropriate Uses

• Policy decisions: Not validated for regulatory use
• Scientific publications: Not peer-reviewed data
• Engineering projects: Requires professional validation
• Commercial applications: See license restrictions

🔍 Transparency & Limitations

Known Limitations

1. Not peer-reviewed: Methodologies need scientific validation
2. AI-assisted development: Code may contain errors requiring expert review
3. Data quality varies: Depends on source dataset accuracy
4. Processing incomplete: Still calculating final global areas
5. Simplified assumptions: Real-world complexity not fully captured

What We’re Doing About It

• Complete provenance tracking: Every data source documented
• Open-source code: All processing scripts available for review
• Validation against literature: Comparing with Laruelle 2025, Dürr 2011
• Continuous improvement: Fixing issues as discovered (e.g., GRIT data integrity)
• Clear documentation: Honest about uncertainties and limitations

Recent Fixes

October 12, 2025: Discovered and fixed critical GRIT v0.6 data integrity issue where coastal catchments were disconnected from river segments. Implemented spatial join workaround. See full analysis.

📚 Key References

1. Dürr et al. (2011): “Worldwide Typology of Nearshore Coastal Systems” - Estuaries and Coasts
2. Laruelle et al. (2025): “Continental shelves as a source of CO₂” - Estuaries and Coasts
3. O’Connor et al. (2022): “The Tidal Freshwater Zone” - Estuarine, Coastal and Shelf Science
4. Baum et al. (2024): “Structural estuaries” - Marine dataset
5. GRIT v0.6 (2025): Global River Topology - Michel et al.