Flooded Rivers, Drying Wetlands, Vanishing Tributaries: Hydrological Paradox of the East Ganga Plains

Manudeo Singh , SK Tandon

The East Ganga Plains (EGP) present a striking hydrological paradox: while embanked rivers flood with increasing magnitude, adjacent wetlands and groundwater-fed streams are desiccating, and aquifer storage is declining. Using satellite remote sensing and gravimetry, we document that: (i) wetlands exhibit significant water-cover loss despite stable monsoon rainfall; (ii) small rivers and tributaries are seasonally desiccating; (iii) vegetation greenness has increased significantly, reflecting irrigation intensification rather than wetter conditions; (iv) GLDAS Noah component separation confirms that 91.8% of the variance in GRACE terrestrial water storage is attributable to groundwater storage change (ΔGW), validating satellite gravimetry as a groundwater proxy and documenting a sustained negative ΔGW anomaly; and (v) Height Above Nearest Drainage (HAND) analysis of trajectory-classified wetland pixels reveals a median elevation of 0.00 m above nearest drainage, with almost three-quarters within 0.25 m, demonstrating that desiccation is embankment-imposed rather than topographically determined. All three cross-variable Pearson correlations between ΔGW, wetness index (MNDWI), and vegetation index (NDVI) (n = 20) are significant at p ≤ 0.004 and fall in the direction predicted by connectivity loss, indicating that irrigation intensification is drawing down aquifer storage and eliminating wetland water cover. The ΔGW–MNDWI coupling is concentrated in the lowest-lying wetland pixels, consistent with direct surface connectivity as the primary mechanism. The Kosi–Gandak interfan provides the most spatially coherent expression of this paradox. This study presents the first basin-scale, multi-proxy synthesis with explicit GLDAS-based groundwater validation for the EGP. We propose a monitoring framework and four research priorities to support hydrologically secure development in this densely populated, underrepresented region.