Abstract
Arctic warming is leading to substantial changes to permafrost including rapid degradation of ice and ice-rich coasts and riverbanks. In this study, we present and evaluate a high spatiotemporal resolution three-year time series of X-Band microwave satellite data from the TerraSAR-X (TSX) satellite to quantify cliff-top erosion (CTE) of an ice-rich permafrost riverbank in the central Lena Delta. We apply a threshold on TSX backscatter images and automatically extract cliff-top lines to derive intra- and inter-annual CTE. In order to examine the drivers of erosion we statistically compare CTE with climatic baseline data using linear mixed models and analysis of variance (ANOVA). Our evaluation of TSX-derived CTE against annual optical-derived CTE and seasonal in situ measurements showed good agreement between all three datasets. We observed continuous erosion from June to September in 2014 and 2015 with no significant seasonality across the thawing season. We found the highest net annual cliff-top erosion of 6.9 m in 2014, in accordance with above-average mean temperatures and thawing degree days as well as low precipitation. We found high net annual erosion and erosion variability in 2015 associated with moderate mean temperatures but above average precipitation. According to linear mixed models, climate parameters alone could not explain intra-seasonal erosional patterns and additional factors such as ground ice content likely drive the observed erosion. Finally, mean backscatter intensity on the cliff surface decreased from −5.29 to −6.69 dB from 2013 to 2015, respectively, likely resulting from changes in surface geometry and properties that could be connected to partial slope stabilization. Overall, we conclude that X-Band backscatter time series can successfully be used to complement optical remote sensing and in situ monitoring of rapid tundra permafrost erosion at riverbanks and coasts by reliably providing information about intra-seasonal dynamics.
Highlights
The Arctic is warming almost twice as fast as the global mean [1]
Thermokarst and thermal erosion are prominent processes associated with permafrost degradation
Remote Sens. 2018, 10, 51 characteristic landforms result from the thawing of ice-rich permafrost or the melting of massive ice [6], such as thaw slumps [7] and thermokarst lakes or basins [8]
Summary
The Arctic is warming almost twice as fast as the global mean [1]. This phenomenon contributes to the rapid degradation of permafrost landscapes which has far-reaching implications for ecological and social systems at local and global scales [2,3,4,5]. Thermal erosion is the removal of ice-bearing permafrost by the combined thermal and mechanical action of moving water [6,9], and is the most effective process of permafrost degradation [10,11]. It dominates the reshaping of permafrost landscapes by the erosion of ice-bearing riverbanks [12,13], coastlines [9,14] and lake shores [15] and leads to the formation of retrogressive thaw slumps [7], as well as gullies and valleys [16]. Thermo-denudation is the combined influence of solar insulation and heat advection on the energy balance of the ground surface causing erosion above the water level [9]
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