Urban Green Cover & Built-up Analysis — Chennai-region

This month's digest for the Chennai region reveals a nuanced landscape through the lens of Sentinel-2A satellite imagery captured on September 8, 2025. We've analyzed the Normalized Difference Vegetation Index (NDVI) to gauge vegetation health and the Normalized Difference Built-up Index (NDBI) to assess built-up areas. Only images with cloud cover below 50% are considered, ensuring clarity in our monthly updates. This digest, curated by I Hug Trees and sourced from the Microsoft Planetary Computer, highlights the interplay between urban expansion and green spaces in the region.

The NDVI values for the Chennai region range from a minimum of 0.010 to a maximum of 0.850, with a mean of 0.325 and a median of 0.310. This indicates a moderate level of vegetation cover across the region, with some areas showing dense vegetation. The NDBI values show a minimum of -0.300, a maximum of 0.600, a mean of 0.150, and a median of 0.140. This suggests a significant presence of built-up areas, though not overwhelmingly so. The mean difference between NDBI and NDVI is 0.175, indicating that built-up surfaces predominate in the region. The NDVI–NDBI difference map (see ndvi_ndbi_diff_color.png) shows areas where built-up surfaces exceed vegetation, flagging these zones as higher heat-risk on the heat-risk map (see heat-risk.png).

• Areas with NDVI values above 0.500 are likely lush, green zones that contribute to cooling.
• Regions where NDBI exceeds 0.300 may experience increased urban heat due to dense construction.
• Transitional zones with mixed NDVI and NDBI values could benefit from targeted greening efforts.

To explore the Chennai region's landscape in greater detail, use the interactive overlay available at ndvi_map.html. You can zoom in on specific areas, adjust the transparency slider to compare layers, and validate features against high-resolution basemaps. Remember that the cloud cover for this observation was 2.41%, which might affect the clarity of some areas. We recommend field validation to confirm satellite observations and suggest a monthly monitoring cadence to track changes over time.

Urban heat island effect

Our analysis indicates that built-up surfaces predominate in the Chennai region, with a mean difference of 0.175 between NDBI and NDVI. This suggests increased urban heat risk in areas where construction is dense. We recommend a monthly monitoring cadence to observe changes, prioritize greening efforts in transitional zones, and engage the community in urban cooling initiatives.

Disclaimer: this analysis refers to the satellite crop / geo-bounds stored under the 'Chennai-region' folder (may include extended suburbs) and does not represent the full administrative limits of Chennai.

    @misc{ihugtrees_ndvi_2025,
      author    = {I Hug Trees},
      title     = {NDVI and NDBI Analysis Data - Chennai region 2025},
      year      = 2025,
      note      = {GeoTIFF and images provided for scientific purposes},
      url       = {https://ihugtrees.org}
    }
      

    @software{microsoft_open_source_2022_7261897,
      author       = {Microsoft Open Source and
                      Matt McFarland and
                      Rob Emanuele and
                      Dan Morris and
                      Tom Augspurger},
      title        = {microsoft/PlanetaryComputer: October 2022},
      month        = oct,
      year         = 2022,
      publisher    = {Zenodo},
      version      = {2022.10.28},
      doi          = {10.5281/zenodo.7261897},
      url          = {https://doi.org/10.5281/zenodo.7261897}
    }