Estimation of stream water components and residence time in a permafrost catchment in the central Tibetan Plateau using long-term water stable isotopic data

Abstract. Global warming has significantly impacted the
hydrological processes and ecological environment in permafrost regions.
Mean residence time (MRT) is a fundamental catchment descriptor that
provides hydrological information regarding storage, flow pathways, and water
source within a particular catchment. However, water stable isotopes and MRT
have rarely been investigated due to limited data collection in the
high-altitude permafrost regions. This study uses the long-term stable
isotopic observations to identify runoff components and applied the
sine-wave exponential model to estimate water MRT in a high-altitude
permafrost catchment (5300 m a.s.l.) in the central Tibetan Plateau (TP).
We found that the isotope composition in precipitation, stream, and
supra-permafrost water exhibited obvious seasonal variability. The freeze–thaw
process of the permafrost active layer and direct input of precipitation
significantly modified the stable isotope compositions in supra-permafrost
and stream water. The hydrograph separation revealed that precipitation and
supra-permafrost water accounted for 35 ± 2 % and 65 ± 2 %
of the total discharge of stream water, respectively. MRT for stream and
supra-permafrost water was estimated at 100 and 255 d, respectively. Such
shorter MRTs of supra-permafrost and stream water (compared to the
non-permafrost catchments) might reflect the unique characteristics of
the hydrological process in permafrost catchments. Moreover, the MRT of
supra-permafrost water was more sensitive to environmental change than that
of stream water. Climate and vegetation factors affected the MRT of stream
and supra-permafrost water mainly by changing the thickness of the permafrost
active layer. Our results suggest that climate warming might retard the rate
of water cycle in permafrost regions. Overall, our study expands our
understanding of hydrological processes in high-altitude permafrost
catchments under global warming.
