Rahman, A S M Mostaquimur: Influence of Subsurface Hydrodynamics on the Lower Atmosphere at the Catchment Scale. - Bonn, 2015. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-42091
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-42091,
author = {{A S M Mostaquimur Rahman}},
title = {Influence of Subsurface Hydrodynamics on the Lower Atmosphere at the Catchment Scale},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2015,
month = dec,

volume = 70,
note = {Processes (e.g., groundwater flow, evapotranspiration, precipitation) in different compartments of the hydrological cycle (e.g., subsurface, land surface, and atmosphere) show characteristic variability at different space-time scales and interact with each other through complex non-linear feedback mechanisms. In the hydrologic cycle, subsurface hydrodynamics that may be expressed through the presence of a free water table, interact with land surface mass and energy balance components (e.g., shallow soil moisture and evapotranspiration), which may significantly affect atmospheric processes (e.g., atmospheric boundary layer height and convective precipitation). This thesis aims to understand and quantify the feedback mechanisms between groundwater dynamics and the atmosphere via land surface processes at the catchment scale by analyzing the space-time variability of the fluxes and states of the coupled water and energy cycles. Both modeling and observations of various mass and energy balance components of the hydrological cycle are applied in order to achieve this goal. A coupled simulation platform consisting of a subsurface model (ParFlow), a land surface model (CLM3.5), and an atmospheric model (COSMO-DE) is applied over a model domain encompassing the Rur catchment, Germany, to simulate the fluxes from the subsurface across land surface into the atmosphere over multiple years. The coupled model continuously simulates the mass and energy fluxes over space and time for all three compartments of the hydrological cycle. A comprehensive comparison between the model results and observations demonstrates the model’s capability to reproduce the dynamics as well as the absolute values of the mass and energy fluxes (e.g., shallow soil moisture, groundwater table depth, latent heat flux, sensible heat flux, near-surface temperature). Statistical, geostatistical, and spectral analysis techniques are used to explore the inherent variability of the compartmental mass and energy fluxes, which reveals the interconnections of the compartmental processes at various space-time scales. In this thesis, a novel concept of a dual-boundary forcing is introduced to represent and quantify the interactions between the compartmental mass and energy balance components at the relevant space and time scales. According to this concept, atmosphere and groundwater act as the upper and lower boundary conditions, respectively, for the land surface. The dominating boundary condition controlling the variability of land surface processes is determined by space and time localized moisture and energy availability. This concept states that the space-time patterns of land surface processes can be explained by the variability of the dominating boundary condition, which is corroborated by applying continuous wavelet transform and variogram techniques on the model results and observations. In the ensuing step, the proposed dual-boundary forcing concept is tested considering different lower boundary conditions based on groundwater dynamics in a coupled subsurface-land surface model. The results show that there are significant and predictable differences in the variability of land surface processes at monthly to multi-month time scales from the model configurations with different lower boundary conditions, which indicates that the representation of groundwater dynamics in a numerical simulation platform affects the temporal variability of land surface processes. For example, it was demonstrated that the temporal variability of evapotranspiration simulated by a coupled subsurface-land surface model is reduced at monthly to multi-month time scales in case of a simplified representation of groundwater dynamics. Finally, fully integrated simulations of the terrestrial hydrological cycle are performed considering different groundwater dynamics in a subsurface-land surface-atmosphere model of the larger Rur catchment to study the influence of subsurface hydrodynamics on local weather generating processes. The results show that differences in groundwater dynamics in the model affect shallow soil moisture, evapotranspiration, and sensible heat transfer, which influences atmospheric boundary layer height, convective available potential energy, and precipitation especially under strong convective conditions. These results suggest that groundwater dynamics may generate systematic uncertainties in atmospheric simulations in a fully-coupled model. This thesis reveals that the presence of groundwater dynamics is important to take into account in atmospheric simulations and water resources assessments, such as, drought prediction.},
url = {https://hdl.handle.net/20.500.11811/6576}

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