Satellite-Based Early-Warning Framework for Cultural Heritage Protection Across Diverse Environmental Landscapes in India

Introduction
Regular on-ground monitoring of geographically distributed cultural heritage sites is challenging due to financial and logistical constraints. As a result, gradual environmental changes may remain unnoticed until they become clearly visible and difficult to address. Satellite remote sensing provides a remote, non-contact and scalable approach for regularly assessing environmental conditions around heritage sites. Monitoring changes in environmental indicators can help us to identify emerging pressures and support targeted field investigations for preventive conservation.

Methods
This study develops a remote-sensing-based monitoring framework for thirty-six UNESCO-listed cultural heritage sites in India using multi-temporal Landsat 8 imagery from 2016, 2021 and 2025 processed through Google Earth Engine. Four environmental indicators—Normalised Difference Vegetation Index (NDVI), Normalised Difference Water Index (NDWI), Normalised Difference Built-up Index (NDBI) and Land Surface Temperature (LST)—were extracted within five kilometres around each heritage site. The sites were grouped into five landscape categories to establish landscape-specific environmental baselines.

Results
The analysis revealed distinct environmental patterns across the five heritage categories: urban, coastal, mountainous, arid/semi-arid and inland plain landscapes. Urban heritage landscapes showed greater built-up influence with the lowest median vegetation condition (NDVI = 0.181) and elevated thermal conditions (LST = 37.81 °C). Arid/semi-arid landscapes recorded the highest median surface temperature (LST = 39.31 °C), while mountainous landscapes showed the strongest trend of vegetation improvement (median δNDVI = +0.048). These landscape-specific baselines provide a reference for identifying heritage sites that are experiencing significant environmental changes and require further assessment.

Conclusion
The integration of multi-temporal satellite indicators provides an effective approach for supporting preventive cultural heritage conservation. Remote-sensing-based screening can help conservation authorities prioritise field surveys, optimise monitoring resources and identify vulnerable heritage landscapes before environmental pressure becomes severe. This approach provides a foundation for landscape-specific risk assessment and enables targeted conservation interventions by directing on-ground efforts toward sites that require detailed evaluation.