Quantification of Water Released by Thawing Permafrost in the Source Region of the Yangtze River on the Tibetan Plateau by InSAR Monitoring

The source region of the Yangtze River (SRYR, 1.4 x 10(5) km(2) above Zhimenda station) on the Tibetan Plateau (TP) has 78% permafrost coverage. The streamflow depth increased at a rate of 2.5 mm/a since 2000. Quantification of the water contribution brought by permafrost thawing is a difficult task. In this study, we used Sentinel-1 data and the SBAS-InSAR technique to monitor terrain deformation from September 2016 to December 2021, and then utilized the long-term deformation rate to assess ground ice meltwater release and the seasonal deformation to evaluate water storage in the active layer. Results reveal that 55.3% of the terrain in the SRYR has subsidence >2.5 mm/a, indicating widespread ground ice melting. The release rate of ground ice meltwater is 4.3 mm/a in the entire SRYR, above 6 mm/a at the Dangqu and Tuotuo River subbasins. The water release rate is relatively small (similar to 3%) in comparison to the streamflow depth of 151 mm per year during the investigation period of 2017-2021. We did not detect a strong increasing or decreasing trend among the 5-year seasonal deformation, which reflects that the total soil water content in the active layer did not change significantly during the short investigation period. The results provide a data basis for ground ice richness and loss information in the SRYR and help to understand the impact of permafrost thawing on the regional water cycle in the permafrost environment.

Automated summary

This study used remote sensing and SAR techniques to monitor terrain deformation in the source region of the Yangtze River, assess the release of ground ice meltwater, and evaluate water storage in the active layer. The results indicate widespread ground ice melting in the region, but the water release rate is relatively small. The findings provide a data basis for understanding the impact of permafrost thawing on the water cycle in the region.