Question: Can freely available satellite vegetation trends serve as an annual spatial indicator of groundwater extraction intensity between CGWB assessment cycles?
Approach:
- Computed the “intensifier fraction” — the fraction of cropland pixels with strongly positive Sentinel-2 peak-NDVI trends (2018–2024)
- Evaluated consistency with CGWB extraction percentages across 6 over-exploited blocks (102–118% of annual recharge)
- Used Arunachala Hill (Tiruvannamalai) as geographic anchor for stratified sampling, controlling for broad-scale climate and topographic gradients
- Ran Sentinel-1 VV detectability analysis to explain why single-pixel SAR trend detection fails where block-level optical detection succeeds
Key Results:
- Intensifier fraction positively associated with extraction percentage: Pearson r = 0.814, p = 0.049, permutation p = 0.061
- Rainfall trends show no evidence of confounding
- Block-level aggregation necessary — per-pixel NDVI changes fall below the single-pixel detection bound
Scope: Proof-of-concept for one district; requires multi-district validation before operational use. Intended as a supplement to well monitoring, not a replacement.
Status: Manuscript prepared; independent work outside institutional affiliation.