Elevation-Dependent Glacier Velocity and X-Band SAR Backscatter Indicate Seasonal and Topographic Controls on Tropical Glacier Dynamics in the Central and Southern Cordillera Blanca, Peru

Abstract

Tropical glacier dynamics are influenced by topography, near-surface thermodynamic conditions, basal processes indirectly reflected in surface motion, and climate variability, yet the regional-scale relationship between radar backscatter and glacier motion remains poorly constrained. We present a regional analysis of ice surface velocity and X-band synthetic aperture radar (SAR) backscatter across the central and southern Cordillera Blanca, Peru, using 72 high-resolution TerraSAR-X StripMap scenes acquired between December 2016 and May 2021. Ice surface velocities were derived from SAR intensity offset tracking, yielding a continuous 4.42-year record for 195 glaciers at an effective ground resolution of ∼60 m, with mean velocities ranging from 0.01 to 0.69 m d−1. Radiometrically calibrated γ0 backscatter shows strong seasonal and elevation-dependent variability, with pronounced annual amplitudes at mid-elevations (∼5000–5500 m a.s.l.) and nearly invariant signals above ∼5800 m a.s.l. While γ0 decreases during the wet season, glacier velocities show recurrent dry-season accelerations. Correlations between detrended velocity residuals and precipitation are weak to moderate and spatially heterogeneous, whereas correlations with the Niño 3.4 index are spatially heterogeneous. In contrast, γ0-precipitation correlations are predominantly negative, consistent with the sensitivity of X-band SAR to near-surface snow/firn moisture conditions. Cumulative displacement is predominantly linear over the 4.42-year observation period, with departures from linearity confined to dynamically complex sectors such as glacier tongues, crevassed basins, and areas adjacent to proglacial lakes. Overall, the results provide spatially distributed evidence for a vertically and seasonally stratified glacier response in the analyzed sectors: radar backscatter primarily reflects elevation- and season-dependent near-surface snow/firn conditions, whereas glacier surface velocity appears to be more strongly associated with glacier geometry and broader glacier-dynamic processes.