Preprints
https://doi.org/10.5194/hess-2022-241
https://doi.org/10.5194/hess-2022-241
 
18 Jul 2022
18 Jul 2022
Status: this preprint is currently under review for the journal HESS.

Recent ground thermo-hydrological changes in a Tibetan endorheic catchment and implications for lake level changes

Léo C. P. Martin1, Sebastian Westermann2,3, Michele Magni1, Fanny Brun1,4, Joel Fiddes5, Yanbin Lei6,7, Philip Kraaijenbrink1, Tamara Mathys8, Moritz Langer9,10, Simon Allen11, and Walter W. Immerzeel1 Léo C. P. Martin et al.
  • 1Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
  • 2Department of Geosciences, University of Oslo, Blindern, 0316 Oslo, Norway
  • 3Center for Biogeochemistry in the Anthropocene, Oslo, Norway
  • 4Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, Grenoble, France
  • 5WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 6Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
  • 7CAS Center for Excellence in Tibetan Plateau Earth System Sciences, Beijing 100101, China
  • 8Department of Geosciences, University of Fribourg, Fribourg, Switzerland
  • 9Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 14473 Potsdam, Germany
  • 10Department of Geography, Humboldt Universität zu Berlin, 12489 Berlin, Germany
  • 11Department of Geography, University of Zurich, Zürich, Switzerland

Abstract. Climate change modifies the water and energy fluxes between the atmosphere and the surface in mountainous regions. This is particularly true over the Qinghai-Tibet Plateau (QTP), a major headwater region of the world, which has shown substantial hydrological changes over the last decades. Among them, the rapid lake level variations observed throughout the plateau remain puzzling and much is still to be understood regarding the spatial distribution of lake level trends (increase/decrease) and paces. The ground across the QTP hosts either permafrost or seasonally frozen ground and both are affected by climate change. In this environment, the ground thermal regime influences liquid water availability, evaporation and runoff. Therefore, climate-driven modifications of the ground thermal regime may contribute to lake level variations. For now, this hypothesis has been overlooked by modelers because of the scarcity of field data and the difficulty to account for the spatial variability of the climate and its influence on the ground thermo-hydrological regime in a numerical framework.

This study focuses on the cryo-hydrology of the catchment of Lake Paiku (Southern Tibet) for the 1980–2019 period. We use TopoSCALE and TopoSUB to downscale ERA5 data and capture the spatial variability of the climate in our forcing data. We use a distributed setup of the CryoGrid community model (version 1.0) to quantify thermo-hydrological changes in the ground during the period. Forcing data and simulation outputs are validated with weather station data, surface temperature logger data and the lake level variations. We show that both seasonal frozen ground and permafrost have warmed (1.7 °C per century 2 m deep), increasing the availability of liquid water in the ground and the duration of seasonal thaw. Both phenomena promote evaporation and runoff but ground warming drives a strong increase in subsurface runoff, so that the runoff/(evaporation + runoff) ratio increases over time. Summer evaporation is an important energy sink and we find active layer deepening only where evaporation is limited. The presence of permafrost is found to promote evaporation at the expense of runoff, consistent with recent studies. Yet, this relationship seems to be climate dependent and we show that a colder and wetter climate produces the opposite effect. This ambivalent influence of permafrost may help to understand the contrasting lake level variations observed between the south and north of the QTP, opening new perspectives for future investigations.

Léo C. P. Martin et al.

Status: open (until 12 Sep 2022)

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Léo C. P. Martin et al.

Léo C. P. Martin et al.

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Short summary
Across the Tibetan plateau, many large lakes have been changing level during the last decades as a response to climate change. In high mountain environments, water fluxes from the land to the lakes are linked to the ground temperature of the land and to the energy fluxes between the ground and the atmosphere, which are modified by climate change. With a numerical model, we test how these water and energy fluxes have changed over the last decades and how they influence the lake level variations.