Urban Green Cover & Heat Risk Assessment: Osaka-region

Yaragarla, Ramkumar

Observation Metadata

Satellite Platform	Sentinel-2A (Sentinel 2)
Observation Date	2025-11-30
Cloud Cover	0.203683%
Spectral Bands Used	B04 (Red), B08 (NIR), B11 (SWIR1), B12 (SWIR2)
Processing Date	2025-12-07

Sentinel-2 satellite preview of Osaka-region, captured on 2025-11-30 from an altitude of approximately 786 km.

Statement of Problem

Rapid urbanization and climate change are placing unprecedented stress on cities worldwide. As built-up areas expand and green spaces decline, urban heat islands intensify, air quality deteriorates, and residents face increased health risks. Understanding the spatial distribution of vegetation and development is essential for evidence-based urban planning, climate adaptation, and public health protection. This analysis quantifies the current balance between green cover and built-up surfaces in Osaka-region, identifies thermal vulnerability hotspots, and provides actionable recommendations for enhancing urban forestry and green infrastructure.

1. Urban Forestry Assessment: Current Vegetation & Built-Up Status

1.1 Vegetation Distribution (NDVI Analysis)

The current state of vegetation distribution in the Osaka-region, as assessed by the Normalized Difference Vegetation Index (NDVI), presents a concerning picture. The mean NDVI value of 0.038 suggests minimal green cover across the region. This is further corroborated by the median NDVI value of 0.022, indicating that more than half of the region has even lower vegetation density. The standard deviation of 0.065 highlights a relatively uniform distribution of low vegetation cover, with few areas showing significantly higher values. Spatially, the NDVI color and greyscale maps reveal sparse patches of green, primarily concentrated in peripheral areas, while the central urban zones show almost no vegetation. This pattern is indicative of the challenges Osaka-region faces in maintaining urban green spaces.

1.2 Built-Up Intensity (NDBI Analysis)

The Built-Up Intensity in the Osaka-region, as measured by the Normalized Difference Built-Up Index (NDBI), shows a stark contrast to the vegetation cover. With a mean NDBI value of -0.017, the region exhibits a low level of built-up areas. However, this average is skewed by the extensive green and water areas. The minimum NDBI value of -1.0 and a maximum of 0.71 indicate a wide range of urbanization levels. The NDBI maps highlight the central urban core as the most intensely built-up area, with a clear demarcation from the surrounding less developed regions. This pattern suggests a concentrated development pressure in the urban center, which could have implications for future urban planning and expansion.

NDVI Color Visualization

NDVI Greyscale (Index Values)

NDBI Color Visualization

NDBI Greyscale (Index Values)

Additional Vegetation & Water Indices

Beyond NDVI and NDBI, three complementary indices provide deeper insights into vegetation health and water presence:

EVI (Enhanced Vegetation Index)

EVI improves on NDVI by correcting for atmospheric conditions and canopy background noise. It is more sensitive in areas with dense vegetation, making it useful for monitoring forest health and identifying vegetation stress that NDVI might miss.

EVI Color Visualization

EVI Greyscale (Index Values)

MNDWI (Modified Normalized Difference Water Index)

MNDWI enhances water body detection by using green and shortwave infrared bands. It is more effective than NDWI at separating water features from built-up areas, making it ideal for mapping urban water bodies like lakes, rivers, and reservoirs.

MNDWI Color Visualization

MNDWI Greyscale (Index Values)

NDMI (Normalized Difference Moisture Index)

NDMI measures vegetation water content by comparing near-infrared and shortwave infrared reflectance. Higher values indicate well-hydrated vegetation, while lower values suggest drought stress. This index is valuable for assessing irrigation effectiveness and identifying areas at risk of vegetation die-off.

NDMI Color Visualization

NDMI Greyscale (Index Values)

2. Vegetation-Development Balance Analysis

2.1 NDVI-NDBI Difference Analysis

Analyzing the NDVI-NDBI difference bins provides a clearer understanding of the balance between vegetation and built-up areas in the Osaka-region. The majority of the region (60.84%) falls into the bin ranging from -0.456 to -0.005, indicating a dominance of built-up areas over vegetation. Only a small fraction (1.56%) shows a positive NDVI-NDBI difference, suggesting areas where vegetation slightly outweighs built-up structures. The difference map and legend illustrate this imbalance, with most of the region shaded in colors representing built-up dominance. This analysis underscores the need for a more balanced approach to urban development and green space preservation.

2.2 Overlay Interpretation

The combined NDVI-NDBI overlay image reveals a complex interplay between vegetation and built-up areas. Patterns emerge where green spaces are interspersed with built-up zones, particularly around the urban periphery. This overlay helps in identifying areas where green cover is either complementing or conflicting with urban development, providing valuable insights for future planning and policy-making.

NDVI-NDBI Difference Map (Green = vegetation-dominated; Red = built-up-dominated)

Combined NDVI-NDBI Overlay

3. Urban Heat Island Risk & Thermal Vulnerability

3.1 Heat Risk Distribution

The heat risk distribution in the Osaka-region, as indicated by the Urban Heat Index bins, presents a worrying scenario. A significant portion of the region (60.84%) falls into the bin ranging from -0.447 to 0.005, suggesting moderate heat risk. High-risk zones, where NDBI exceeds NDVI, are less prevalent but still notable, representing 0.47% of the region. These high-risk zones are primarily located in the urban core, as shown in the heat index map. The implications for the urban heat island effect are significant, with potential adverse effects on public health and urban livability. The heat index legend aids in understanding the severity of these zones.

3.2 Key Findings & Implications

Total green cover percentage stands at a mere 1.19%, indicating a critical lack of urban green spaces.
Healthy vegetation constitutes only 0.04% of the total, highlighting the poor quality of existing green cover.
The ecological balance score of 119.336 suggests a significant imbalance between urban development and natural ecosystems.
Water bodies cover 34.5% of the region, providing a potential cooling effect but also indicating limited space for green initiatives.

Urban Heat Index Map (Red = high risk zones)

4. Strategic Recommendations for Green Infrastructure

4.1 What's Working Well

The presence of water bodies covering 34.5% of the region offers a natural cooling effect, mitigating some of the urban heat island effects.
Areas with higher NDVI values, though limited, indicate successful green spaces that could serve as models for future initiatives.

4.2 Critical Challenges

The low total green cover percentage of 1.19% poses a significant challenge for urban sustainability and livability.
The minimal healthy vegetation percentage (0.04%) suggests a need for better maintenance and quality improvement of existing green spaces.
High-risk heat zones in the urban core require immediate attention to prevent adverse health impacts and improve urban comfort.

4.3 Evidence-Based Recommendations

Implement targeted greening initiatives in high-risk heat zones to mitigate the urban heat island effect.
Enhance the quality and maintenance of existing green spaces to increase the percentage of healthy vegetation.
Integrate green infrastructure into urban planning to create a more balanced and sustainable urban environment.

Analysis Coverage Area

The interactive map below shows the exact geographical bounds of this satellite analysis. The colored overlay represents the NDVI coverage area overlaid on OpenStreetMap. You can zoom and pan to explore how the analysis boundaries align with streets, neighborhoods, and landmarks in Osaka-region.

Interactive map: Use mouse/touch to zoom and pan. The overlay shows the satellite image bounds used for NDVI/NDBI calculations.

Note: The analysis boundaries may extend beyond administrative city limits as they represent the satellite image crop captured on 2025-11-30. This ensures complete coverage of the urban area and surrounding regions for comprehensive vegetation and heat risk assessment.

Why Urban Green Cover Matters

Urban forests and green spaces are critical infrastructure for healthy, livable cities. Trees and vegetation reduce air pollution, lower urban temperatures through shade and evapotranspiration, manage stormwater, support biodiversity, and improve mental health and well-being. As cities grow denser and climate change intensifies heat events, monitoring and protecting urban green cover becomes essential for public health and environmental resilience.

Satellite remote sensing provides objective, repeatable measurements of vegetation health and urban development patterns across entire metropolitan areas. The Normalized Difference Vegetation Index (NDVI) quantifies photosynthetic activity and green cover, while the Normalized Difference Built-up Index (NDBI) identifies impervious surfaces and development intensity. Together, these indices reveal the changing balance between nature and urban growth—and highlight where intervention is most needed.

Understanding NDVI and NDBI

NDVI (Normalized Difference Vegetation Index) measures the difference between near-infrared light (strongly reflected by healthy vegetation) and red light (absorbed by chlorophyll). Values range from -1 to +1, with higher values indicating denser, healthier vegetation. Typical ranges: 0.6-0.9 = dense forest; 0.3-0.6 = moderate vegetation; 0.1-0.3 = sparse vegetation; <0.1 = bare soil or built-up areas.

NDBI (Normalized Difference Built-up Index) uses shortwave infrared and near-infrared bands to identify constructed surfaces. Positive values indicate built-up areas (roads, buildings, concrete), while negative values suggest natural or vegetated land. When NDBI exceeds NDVI in an area, it signals high development intensity and elevated urban heat island risk.

README Note

Our Mission: We want this research dataset brief to be Simple, Authentic, and Repeatable.

1. Title of the Dataset

Urban Green Cover and Heat Risk Assessment

2. What This Dataset Is About

This dataset was created to help anyone understand how vegetation and green cover in this region is changing over time. It brings together processed satellite data, simple calculations, and a few observations that give the bigger picture.

3. Why This Dataset Matters

At I Hug Trees, we believe that Geospatial Satellite imagery and processed data should be accessible to everyone. While grounded in scientific principles, outputs are presented in accessible formats so that technical imagery and calculations resonate with ordinary people and communities. Because only when it is relatable, can it tell clear stories about our greenery and urban life: shaping how we live, how we breathe, and how we cope with rising heat.

This dataset tries to make that easier. Whether you are a researcher, policy maker, student or just curious about the environment, these numbers and images help you see trends that are not obvious at first glance.

4. Source of the Data

Satellite: Sentinel-2
Provider: Microsoft Planetary Computer
Acquisition Window: Past 60 days (filtered by cloud cover)
Cloud Cover Threshold: < 30%
Initial Tile Discovery: Copernicus Data Space Ecosystem browser

5. How the Data Was Processed

Basic Preprocessing:

It is important to get the right tile from the Sentinel-2 database for imagery processing. The browser feature from the Copernicus Data Space Ecosystem helped us identify the correct tile, its bounds, and the subset coordinates needed for extraction. It is always essential to double-check the preview image to verify that the fetched tile truly corresponds to the target region.

Next, we used an AWS Lambda environment for the bounds-discovery phase. This step involved fetching band data from the Microsoft Planetary Computer for dates where cloud cover was below 30% within the past 60 days. Once the acquisition date met this condition, we moved to AWS EC2 server scripts written in Python to download raw band data and process them into COGs (Cloud Optimised GeoTIFFs) along with additional indices.

These processed COGs and index outputs are then used for image displays, NDVI interpretation, and HTML digest features published on our platform. All indices raw value outputs are in JSON files for easy repeatable processing. We currently run this workflow on a quarterly schedule for each identified region.

Cloud Masking:

This dataset uses Sentinel-2's Scene Classification Layer (SCL) to remove pixels affected by clouds, shadows, haze, and saturation. Only surface-clear classes are kept, ensuring that the vegetation indices are calculated from clean, reliable pixels. The masking is applied at the pixel level, meaning every index (NDVI, EVI, etc.) is computed only on valid areas after stripping away noisy regions. This results in more trustworthy COGs, cleaner previews, and more meaningful temporal comparisons.

Calculation Formulas Used:

NDVI = (NIR − Red) ÷ (NIR + Red)
EVI = 2.5 × (NIR − Red) ÷ (NIR + 6×Red − 7.5×Blue + 1)
NDWI = (Green − NIR) ÷ (Green + NIR)
NDBI = (SWIR1 − NIR) ÷ (SWIR1 + NIR)

Tools Used:

Data Source: Microsoft Planetary Computer (Sentinel-2 L2A), rasterio, GDAL
Computation: Python 3, NumPy, SciPy, Pillow, Rasterio, rio-cogeo
AWS Pipeline: Lambda (triggers), EC2 (processing), S3 (storage), Bedrock (AI summaries)
Mapping: Leaflet.js, tile layers served from S3
Automation: Python boto3, Cron (EC2 quarterly jobs)

6. File Contents

The dataset includes metadata.json with satellite tile information, various index outputs (NDVI, EVI, NDWI, NDBI, MNDWI, NDMI), and statistical summaries. Please find the detailed list of files available for download in the Download Data & Maps section below.

7. How to Use This Dataset

You can explore the NDVI trends, plug the json file into your favourite tool, build visualisations, or compare it with earlier datasets. It's created to be flexible.

8. Leveraging AI

AI helped speed up some parts of the work, like spotting unusual patterns, creating brief insights, and checking for inconsistencies. All metadata and bin-statistics JSON files were loaded and parsed into structured dictionaries, ensuring the AI receives clean, context-rich inputs for stable summarisation and interpretation.

9. Limitations & Things to Keep in Mind

Cloud cover may affect accuracy
NDVI has known limitations
Spatial resolution is 10 meters
Some patterns may need ground truth validation

10. License / Permissions

Please refer to the How to Cite This Analysis section below for citation guidelines. This dataset is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).

11. Contact

For any questions, collaborations, or clarifications, feel free to reach out at: nature@ihugtrees.org

Data & Methods

Data Sources

Satellite: Sentinel-2A Level-2A (atmospherically corrected)
Provider: Microsoft Planetary Computer
Observation Date: 2025-11-30
Cloud Cover: 0.203683%
Spatial Resolution: 10 meters (NDVI), 20 meters (NDBI, resampled to 10m)

Index Calculations

NDVI = (NIR - Red) / (NIR + Red) using Bands 8 and 4
NDBI = (SWIR1 - NIR) / (SWIR1 + NIR) using Bands 11 and 8
Difference Index = NDVI - NDBI (positive = vegetation-dominated; negative = built-up-dominated)
Urban Heat Index = Composite metric flagging areas where NDBI > NDVI (high heat risk)

Processing Workflow

Images were processed using Python with the pystac-client and rasterio libraries. Cloud masking was applied using the QA60 scene classification layer. Statistics were computed using rasterio zonal statistics and exported as JSON for analysis. All geospatial outputs are provided as Cloud-Optimized GeoTIFFs (COGs) for efficient web access and GIS integration.

Limitations

Analysis represents a single-day snapshot; seasonal and temporal trends require time-series analysis
Cloud cover and atmospheric conditions affect image quality
10-meter resolution may not capture individual trees or small green spaces
Study area boundaries reflect the satellite image crop, not administrative city limits
Heat risk is inferred from spectral indices; ground validation recommended for mitigation planning

Download Data & Maps

Images & Visualizations

Geospatial Data (Cloud-Optimized GeoTIFFs)

Statistical Data

How to Cite This Analysis

Recommended Citation

Yaragarla, R. (2025). Urban Green Cover & Heat Risk Assessment: Osaka-region. I Hug Trees. Retrieved from https://ihugtrees.org/data-analytics/sentinel-ndvi/Osaka-region/2025/12/04/digest.html

Satellite data: Copernicus Sentinel-2 (ESA), processed via Microsoft Planetary Computer.

BibTeX Entry

@misc{ihugtrees_urban_osaka-region_2025,
  author = {Yaragarla, Ramkumar},
  title = {Urban Green Cover \& Heat Risk Assessment: Osaka-region},
  year = {2025},
  publisher = {I Hug Trees},
  url = {https://ihugtrees.org/data-analytics/sentinel-ndvi/Osaka-region/2025/12/04/digest.html},
  note = {Satellite data: Copernicus Sentinel-2}
}

License

This analysis and associated datasets are licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). You are free to share and adapt this work with appropriate attribution.

Planetary Computer Citation

If using Microsoft Planetary Computer data, please cite: microsoft/PlanetaryComputer (2022)

Urban Green Cover & Heat Risk Assessment: Osaka-region A Research Brief on Urban Forestry Data