Coupled water-heat carbon exchange processes in cold environments: Observation and numerical modeling

Lianyu Yu

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Abstract

Recent climate changes have accelerated the coupled water, heat, and carbon exchanges in cold regions, which can further exert the positive feedbacks to climate changes, leading to the increasingly vulnerable ecosystem, warming climate, and unsustainable Earth system. The current ESMs, however, usually adopted the single-phase flow physics with the omission of soil vapor flow and dry airflow. This results in the model discrepancies and may lead to large uncertainties in the future projection of Earth system under climate changes. With such knowledge gaps in mind, this thesis is aiming to understand the underlying physics of water, heat, and carbon exchange processes and links it to the surface/subsurface hydrothermal, biogeochemical, ecohydrological regimes, with the focus on the freeze-thaw processes, snowpack associated processes, soil water and groundwater interactions, and cold-region ecosystem functioning.
This thesis starts with the first quantification of the role of vapor flow and airflow, and its interaction with soil ice in frozen soils using the developed STEMMUS–FT model.
We then translated the difference in soil physical processes into the modelling results of soil hydrothermal regimes via the detailed analysis of the heat transport processes. It is suggested to consider the vapor flow, thermal effect on water flow, and airflow for better portraying soil hydrothermal dynamics, especially during freezing-thawing transition periods.
Moreover, we investigated the effect of snowpack on soil mass transfer considering the coupled soil water-heat-air transfer mechanisms and indicated the underlying physics for the enhanced LE after winter precipitation events.
Furthermore, we built up soil water-groundwater (SW–GW) coupling framework STEMMUS–MODFLOW, physically considering the heterogeneous water exchange between the SW–GW interface, and demonstrated its application in a cold region environment.
Lastly, the linkage between soil hydrothermal regimes and water and carbon cycle was elaborated on a cold region ecosystem.
In conclusion, this thesis highlights the needs to understand the water, heat, and carbon exchange processes across the groundwater-soil-plant-atmosphere interfaces in an integrated and feedback coupling manner. Both the observation and numerical modelling tools are required to reconcile and advance our understanding of the Earth system at different spatiotemporal scales under current and future climate conditions.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Faculty of Geo-Information Science and Earth Observation
  • University of Twente
Supervisors/Advisors
  • Su, Bob, Supervisor
  • Zeng, Yijian, Co-Supervisor
Award date12 Jan 2022
Place of PublicationEnschede
Publisher
Print ISBNs978-90-365-5311-7
DOIs
Publication statusPublished - 12 Jan 2022

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