HYDROGEOPHYSICAL COMPARISON OF HILLSLOPE CRITICAL ZONE ARCHITECTURE FOR DIFFERENT GEOLOGIC SUBSTRATES

Geophysics ◽  
2021 ◽  
pp. 1-84
Author(s):  
Andrew D. Parsekian ◽  
Dario Grana ◽  
Felipe dos Anjos Neves ◽  
Mark S. Pleasants ◽  
Mark Seyfried ◽  
...  
Keyword(s):  
Critical Zone ◽  
Hydrological Models ◽  
Catchment Scale ◽  
Mean Values ◽  
Weathering Processes ◽  
Facies Classification ◽  
Categorical Models ◽  
Hydrological Fluxes ◽  
Landscape Morphology ◽  
Hillslope Scale

The belowground architecture of the Critical Zone consists of soil and rock in various stages of weathering and wetness that acts as a medium for biological growth, mediates chemical reactions, and controls partitioning of hydrological fluxes. Hydrogeophysical imaging provides unique insights into geometries and properties of the earth materials that are present in the Critical Zone and beyond the reach of direct observation besides sparse wellbores. Improved understanding of Critical Zone architecture can be achieved by leveraging geophysical measurements of the subsurface. Creating categorical models of the Critical Zone is valuable for driving hydrological models and comparing belowground architectures between different sites to interpret weathering processes. The Critical Zone architecture is revealed through a novel comparison of hillslopes by applying facies classification in the elastic-electric domain driven by surface-based hydrogeophysical measurements. Three pairs of hillslopes grouped according to common geologic substrates – granite, volcanic extrusive, and glacially altered, are classified by five different hydro-facies classes to reveal relative wetness and weathering states. The hydro-facies classifications are robust to the choice of initial mean values used in the classification and non-contemporaneous timing of geophysical data acquisition. These results will lead to improved interdisciplinary models of Critical Zone processes at various scales, and to an increased ability to predict hydrologic timing and partitioning. Beyond the hillslope scale, this enhanced capability to compare Critical Zone architecture can also be exploited at the catchment scale with implications for improved understanding of the link between rock weathering, hydrochemical fluxes, and landscape morphology.

scholarly journals Designing a suite of measurements to understand the critical zone

2016 ◽  
Vol 4 (1) ◽  
pp. 211-235 ◽  
Author(s):  
Susan L. Brantley ◽  
Roman A. DiBiase ◽  
Tess A. Russo ◽  
Yuning Shi ◽  
Henry Lin ◽  
...  
Keyword(s):  
Land Use ◽  
Critical Zone ◽  
Basic Unit ◽  
Spatial Density ◽  
Earth Surface ◽  
Original Design ◽  
Creek Watershed ◽  
The Individual ◽  
Landscape Morphology ◽  
Shale Hills

Abstract. Many scientists have begun to refer to the earth surface environment from the upper canopy to the depths of bedrock as the critical zone (CZ). Identification of the CZ as an integral object worthy of study implicitly posits that the study of the whole earth surface will provide benefits that do not arise when studying the individual parts. To study the CZ, however, requires prioritizing among the measurements that can be made – and we do not generally agree on the priorities. Currently, the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) is expanding from a small original focus area (0.08 km2, Shale Hills catchment), to a larger watershed (164 km2, Shavers Creek watershed) and is grappling with the prioritization. This effort is an expansion from a monolithologic first-order forested catchment to a watershed that encompasses several lithologies (shale, sandstone, limestone) and land use types (forest, agriculture). The goal of the project remains the same: to understand water, energy, gas, solute, and sediment (WEGSS) fluxes that are occurring today in the context of the record of those fluxes over geologic time as recorded in soil profiles, the sedimentary record, and landscape morphology. Given the small size of the Shale Hills catchment, the original design incorporated measurement of as many parameters as possible at high temporal and spatial density. In the larger Shavers Creek watershed, however, we must focus the measurements. We describe a strategy of data collection and modeling based on a geomorphological and land use framework that builds on the hillslope as the basic unit. Interpolation and extrapolation beyond specific sites relies on geophysical surveying, remote sensing, geomorphic analysis, the study of natural integrators such as streams, groundwaters or air, and application of a suite of CZ models. We hypothesize that measurements of a few important variables at strategic locations within a geomorphological framework will allow development of predictive models of CZ behavior. In turn, the measurements and models will reveal how the larger watershed will respond to perturbations both now and into the future.

scholarly journals Dynamical process upscaling for deriving catchment scale state variables and constitutive relations for meso-scale process models

2006 ◽  
Vol 3 (4) ◽  
pp. 1629-1665 ◽  
Author(s):  
E. Zehe ◽  
H. Lee ◽  
M. Sivapalan
Keyword(s):  
Time Series ◽  
Unsaturated Zone ◽  
Constitutive Relations ◽  
State Variables ◽  
Catchment Scale ◽  
Soil Saturation ◽  
Soil Heterogeneities ◽  
Soil Hydraulic ◽  
Hillslope Scale ◽  
Model Structures

Abstract. In this study we propose an uspcaling approach for the assessment of (a) sub-catchment/REW scale state variables, and (b) of catchment/REW scale soil hydraulic functions which embed/reflect the effects of critical subscale soil heterogeneities in the unsaturated zone on parameterizations of water flow at the next higher scale. The test area for this investigation is the well observed and studied Weiherbach catchment, which is located in a Loess area in south-west Germany. The approach adopted is to use the spatially averaged outputs and internal state variables generated by a highly detailed physically based numerical model that represents the dominant heterogeneities which are typical for this Loess area, and which has been previously shown to closely portray the dynamics of various state variables and fluxes within the study catchment. For these reasons, this detailed numerical model is deemed to be landscape and process compatible. By running this landscape and process compatible model with boundary and initial conditions observed in the Weiherbach catchment, and different assumed structures for soil heterogeneities, we generated time series of catchment-scale average soil saturations in the unsaturated zone by averaging the corresponding distributed model outputs. Due to the differences in assumed spatial patterns of soil heterogeneities and of macropores, the resulting different model structures yield clearly different time series of catchment scale average soil saturation values. The time series of catchment-scale average soil saturation values generated in this way from the landscape and process compatible model structure are, therefore, deemed as best estimates of the actual time series of average catchment scale soil saturation within the study catchment since the model embeds the fingerprints of typical patterns of soils and macropores and is shown to be physically consistent with a distributed set of soil moisture and discharge observations inside the catchment. Finally, we also derive hillslope scale soil hydraulic functions from simulated hillslope scale drainage experiments for the different assumed hillslope model structures. Different patterns of soil and macroporosity within the hillslope yield clearly different hillslope scale soil hydraulic functions, and these differences are consistent with the REV soil pore spectra of the soils. Assuming simple parametric functions for the soil water retention curve and the hydraulic conductivity curve we then obtain different parameters characterizing these soil hydraulic functions for the different assumed model structures. The different parameters obtained for these different model structures thus embed within them fingerprints of the assumed subscale soil patterns and structures on water flow in the unsaturated zone at the next higher scale, in the sense of Vogel and Roth (2003). The ultimate motivation for this analysis is that the so derived, hillslope or sub-catchment scale soil hydraulic functions will become intrinsic components of physically based numerical models, which use subcatchments as building blocks. Lee et al. (2006; this issue) have utilized hillslope scale soil hydraulic functions, derived similarly with the use of the same landscape and process compatible model, for the parameterisation of the CREW model, which is a numerical implementation of the REW approach (Reggiani et al., 1998, 1999), and showed that these lead to successful implementation of the model in the Weiherbach catchment. Their findings show clearly that the presented upscaling approach does indeed yield useful constitutive relations and target state variables for development and validation of meso-scale hydrological models based on the REW approach, embedding within them the fingerprints of the dominant within-catchment heterogeneities on simulated subsurface flow dynamics at the REW-scale.

scholarly journals A comparative analysis of projected impacts of climate change on river runoff from global and catchment-scale hydrological models

2010 ◽  
Vol 7 (5) ◽  
pp. 7191-7229 ◽  
Author(s):  
S. N. Gosling ◽  
R. G. Taylor ◽  
N. W. Arnell ◽  
M. C. Todd
Keyword(s):  
Climate Change ◽  
Hydrological Model ◽  
Climate Model ◽  
Annual Runoff ◽  
Structural Uncertainty ◽  
Hydrological Models ◽  
Catchment Scale ◽  
Monthly Runoff ◽  
Global Mean ◽  
Impacts Of Climate Change

Abstract. We present a comparative analysis of projected impacts of climate change on river runoff from two types of distributed hydrological model, a global hydrological model (GHM) and catchment-scale hydrological models (CHM). Analyses are conducted for six catchments that are global in coverage and feature strong contrasts in spatial scale as well as climatic and developmental conditions. These include the Liard (Canada), Mekong (SE Asia), Okavango (SW Africa), Rio Grande (Brazil), Xiangxi (China) and Harper's Brook (UK). A single GHM (Mac-PDM.09) is applied to all catchments whilst different CHMs are applied for each catchment. The CHMs include SLURP v. 12.2 (Liard), SLURP v. 12.7 (Mekong), Pitman (Okavango), MGB-IPH (Rio Grande), AV-SWAT-X 2005 (Xiangxi) and Cat-PDM (Harper's Brook). Simulations of mean annual runoff, mean monthly runoff and high (Q5) and low (Q95) monthly runoff under baseline (1961–1990) and climate change scenarios are presented. We compare the simulated runoff response of each hydrological model to (1) prescribed increases in global-mean air temperature of 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 °C relative to baseline from the UKMO HadCM3 Global Climate Model (GCM) to explore response to different amounts of climate forcing, and (2) a prescribed increase in global-mean air temperature of 2.0 °C relative to baseline for seven GCMs to explore response to climate model structural uncertainty. We find that the differences in projected changes of mean annual runoff between the two types of hydrological model can be substantial for a given GCM, and they are generally larger for indicators of high and low monthly runoff. However, they are relatively small in comparison to the range of projections across the seven GCMs. Hence, for the six catchments and seven GCMs we considered, climate model structural uncertainty is greater than the uncertainty associated with the type of hydrological model applied. Moreover, shifts in the seasonal cycle of runoff with climate change are represented similarly by both hydrological models, although for some catchments the monthly timing of high and low flows differs. This implies that for studies that seek to quantify and assess the role of climate model uncertainty on catchment-scale runoff, it may be equally as feasible to apply a GHM as it is to apply a CHM, especially when climate modelling uncertainty across the range of available GCMs is as large as it currently is. Whilst the GHM is able to represent the broad climate change signal that is represented by the CHMs, we find however, that for some catchments there are differences between GHMs and CHMs in mean annual runoff due to differences in potential evapotranspiration estimation methods, in the representation of the seasonality of runoff, and in the magnitude of changes in extreme (Q5, Q95) monthly runoff, all of which have implications for future water management issues.

scholarly journals Opinion paper: How to make our models more physically-based

2016 ◽  
Author(s):  
Hubert H. G. Savenije ◽  
Markus Hrachowitz
Keyword(s):  
Conceptual Models ◽  
Storage Capacity ◽  
Root Zone ◽  
Active Agent ◽  
Physical Parameters ◽  
Hydrological Models ◽  
Physical Processes ◽  
Catchment Scale ◽  
Newtonian Theory ◽  
Physically Based

Abstract. Catchment-scale hydrological models that are generally called "physically-based" unfortunately only have a partial view of the physical processes at play in hydrology. Although the coupled partial differential equations in these models generally reflect the water balance equations and the flow descriptors at laboratory scale, they miss essential characteristics of what determines the functioning of catchments. The most important active agent in catchments is the ecosystem (and sometimes people). What these agents do is to manipulate the flow domain in a way that it supports the essential functions of survival and productivity: infiltration of water, retention of moisture, mobilization and retention of nutrients, and drainage. Ecosystems do this in the most efficient way, establishing a continuous, ever-evolving feedback loop with the landscape and climatic drivers. In brief, our hydrological system is alive and has a strong capacity to adjust itself to prevailing and changing environmental conditions. Although most physically based models take Newtonian theory at heart, as best they can, what they generally miss is Darwinian theory on how an ecosystem evolves and adjusts its environment to maintain crucial hydrological functions. If this active agent is not reflected in our models, then they miss essential physics. Through a Darwinian approach, we can determine the root zone storage capacity of ecosystems, as a crucial component of hydrological models, determining the partitioning of fluxes and the conservation of moisture to bridge periods of drought (Gao et al., 2014a). Another crucial element of physical systems is the evolution of drainage patterns, both on and below the surface. On the surface, such patterns facilitate infiltration or surface drainage with minimal erosion; in the unsaturated zone, patterns facilitate efficient replenishment of moisture deficits and preferential drainage when there is excess moisture; in the groundwater, patterns facilitate the efficient and gradual drainage of groundwater, resulting in linear reservoir recession. Models that do not account for these patterns are not physical. The parameters in the equations may be adjusted to compensate for the lack of patterns, but this involves scale-dependent calibration. In contrast to what is widely believed, relatively simple conceptual models can accommodate these physical processes very efficiently. Of course the parameters of catchment-scale conceptual models, even if they represent physical parameters, such a time scales, thresholds and reservoir sizes, require calibration or estimation on the basis of observations. Fortunately, we see the emergence of new observation systems from space that become more and more accurate and detailed as we go along. Recent products estimating precipitation and evaporation from space have shown to allow the estimation of the root zone storage capacity of ecosystems globally (Lan-Erlandsson et al., 2016), DEMs allow the identification of heterogeneity in the landscape, providing information on the heterogeneity of dominant runoff generating mechanisms (Gharari et al., 2011, Gao et al., 2014b), and gravity observations from space can be used to estimate sub-surface storage fluctuation and groundwater recession (Winsemius et al., 2009). As a result, it will become more and more practical to calibrate well-structured conceptual models, even in poorly gauged catchments. These insights and developments will contribute to the revaluation of conceptual models as physics-based representations of hydrological systems.

scholarly journals Climate, landscape and vegetation controls of behavioral catchments on dominant runoff response and catchment travel time distribution

2021 ◽  
Author(s):  
Chatchai Jothityangkoon ◽  
Haruetai Maskong
Keyword(s):  
Travel Time ◽  
Overland Flow ◽  
Theoretical Perspective ◽  
Hydrologic Model ◽  
Runoff Generation ◽  
Catchment Scale ◽  
Physical Relationship ◽  
Relative Contribution ◽  
Hillslope Scale ◽  
The Impact

The three dominant processes contributing to runoff as proposed by the Dunne diagram are Hortonian overland flow (HOF), Dunne overland flow (DOF) and subsurface storm flow (SSF). Using a theoretical perspective, we investigate the impact of climate, soil, topography and vegetation on catchment water balance and the probability distribution of the travel times of each runoff generation component in respect of the connected instantaneous response function (CIRF) including the interaction of a partial contributing area connecting to the outlet. A simple distributed hydrologic model is used to capture the effect of the catchment response and to estimate the CIRFs under different possible integration of combined effect of climate, soil, topography and vegetation. A set of dimensionless similarity parameters represent catchment functions and provide a quantitative explanation of the conceptual Dunne diagram. Behavioral catchments are defined from the empirical range of the Budyko curve and mainly compatible to the physical relationship as illustrated in the Dunne diagram. The results consistent with the Dunne diagram are: (1) DOF and SSF dominates in humid for behavioral sand and silt catchments, (2) HOF dominates in arid for behavioral silt and clay catchments. Inconsistent results are: (1) SSF dominates in arid for behavioral sand, silt and clay catchments, (2) HOF dominates in humid for behavioral clay catchment and (3) no dominant HOF for behavioral sand catchment. For HOF and DOF dominates, the distribution of CIRFs can be grouped into similar shapes, which depend on the relative contribution of hillslope scale and catchment scale. For SSF behavioral catchments, the shape of the CIRFs depends on the dryness index. The combined catchment CIRFs of mean travel time for runoff responses consists with the higher first peak from the HOF and/or DOF and the second peak from the SSF.

scholarly journals Stable isotopes reveal evaporation dynamics at the soil-plant-atmosphere interface of the critical zone

2017 ◽  
Author(s):  
Matthias Sprenger ◽  
Doerthe Tetzlaff ◽  
Chris Soulsby
Keyword(s):  
Stable Isotopes ◽  
Isotopic Composition ◽  
Scots Pine ◽  
Soil Depth ◽  
Critical Zone ◽  
Soil Evaporation ◽  
Pore Waters ◽  
Catchment Scale ◽  
Scottish Highlands ◽  
Northern Latitudes

Abstract. Understanding the influence of vegetation on water storage and flux in the upper soil is crucial in assessing the consequences of climate and land use change. We sampled the upper 20 cm of podzolic soils at 5 cm intervals in four sites differing in their vegetation (Scots Pine (Pinus sylvestris) and heather (Calluna sp. and Erica Sp)) and aspect. The sites were located within the Bruntland Burn long-term experimental catchment in the Scottish Highlands; a low energy, wet environment. Sampling took place on 11 occasions between September 2015 and September 2016 to capture seasonal variability in isotope dynamics. The pore waters of soil samples were analysed for their isotopic composition (δ2H and δ18H) with the direct equilibration method. Our results show that the soil waters in the top soil are, despite the low potential evaporation rates in such northern latitudes, kinetically fractionated compared to the precipitation input throughout the year. This fractionation signal decreases within the upper 15 cm resulting in the top 5 cm being isotopically differentiated to the soil at 15–20 cm soil depth. There are significant differences in the fractionation signal between soils beneath heather and soils beneath Scots pine, with the latter being more pronounced. But again, this difference diminishes within the upper 15 cm of soil. The enrichment in heavy isotopes in the topsoil follows a seasonal hysteresis pattern, indicating a lag time between the fractionation signal in the soil and the increase/decrease of soil evaporation in spring/autumn. Based on the kinetic enrichment of the soil water isotopes, we estimated the soil evaporation losses to be about 5 and 10 % of the infiltrating water for soils beneath heather and Scots pine, respectively. The high sampling frequency in time (monthly) and depth (5 cm intervals) revealed high temporal and spatial variability of the isotopic composition of soil waters, which can be critical, when using stable isotopes as tracers to assess plant water uptake patterns within the critical zone or applying them to calibrate tracer-aided hydrological models either at the plot to the catchment scale.

WATZON: the Italian network of ecohydrology and critical zone observatories 

2021 ◽  
Author(s):  
Marco Borga ◽  
Daniele Penna ◽  
Nasta Paolo ◽  
Comiti Francesco ◽  
Stefano Ferraris ◽  
...  
Keyword(s):  
High Resolution ◽  
Spatial Scales ◽  
Critical Zone ◽  
Catchment Scale ◽  
Data Set ◽  
Near Surface ◽  
High Resolution Data ◽  
Water Mixing ◽  
Study Sites ◽  
Scientific Questions

<p>The Italian initiative WATZON (WATer mixing in the critical ZONe) is a network of instrumented sites, bringing together six pre-existing long-term research observatories monitoring different compartments of the Critical Zone - the Earth's permeable near-surface layer from the tops of the trees to the bottom of the groundwater.  These observatories cover different climatic and physiographic characteristics over the country, providing information over a climate and eco-hydrologic transect connecting the Mediterranean to the Alps. With specific initial scientific questions, monitoring strategies, databases, and modeling activities, the WATZON observatories and sites is well representative of the heterogeneity of the critical zone and of the scientific communities studying it. Despite this diversity, all WATZON sites share a common eco-hydrologic monitoring and modelling program with three main objectives:</p><p>1) assessing the description of water mixing process across the critical zone by using integrated high-resolution isotopic, geophysical and hydrometeorological measurements from point to catchment scale, under different physiographic conditions and climate forcing;</p><p>2) testing water exchange mechanisms between subsurface reservoirs and vegetation, and assessing ecohydrological dynamics in different environments by coupling the high-resolution data set from different critical zone study sites of the initiative with advanced ecohydrological models at multiple spatial scales;</p><p>3) developing a process-based conceptual framework of ecohydrological processes in the critical zone to translate scientific knowledge into evidence to support policy and management decisions concerning water and land use in forested and agricultural ecosystems.</p><p>This work provides an overview of the WATZON network, its objectives, scientific questions, and data management, with a specific focus on existing initiatives for linking data and models based on WATZON data.</p><p> </p>

Characterizing Hydrological Fluxes of Lesser Himalayan hillslopes

2020 ◽  
Author(s):  
Aliva Nanda ◽  
Sumit Sen
Keyword(s):  
Soil Moisture ◽  
Hydraulic Conductivity ◽  
Soil Temperature ◽  
Soil Properties ◽  
Negative Correlation ◽  
Soil Hydraulic Conductivity ◽  
Hydrological Fluxes ◽  
Soil Hydraulic ◽  
Hillslope Scale ◽  
Hillslope Processes

<p>Hillslope-scale studies play a vital role in understanding the spatial and temporal dynamics of hydrological fluxes of an ungauged watershed. The linkage between static (i.e. topography, soil properties and landuse) and dynamic (i.e. runoff, soil moisture and temperature) characteristics of a hillslope provides a new insight towards hillslope processes. Thus, two Lesser Himalayan hillslopes of Aglar watershed have been selected in two different landuses (grass-covered and agro-forested) and aspects (south and north). In this study, we analyzed the different hydrological fluxes i.e. rainfall, runoff, soil moisture and soil temperature along with the soil properties to get a holistic understanding of hillslope processes. We used the soil moisture dynamics and soil hydraulic conductivity as the major components to derive the hillslope hydrological connectivity. It was observed that the grassed (GA) hillslope generates less runoff than the agro-forested (AgF) hillslope as the upslope runoff of GA hillslope re-infiltrated in the middle portion due to higher soil hydraulic conductivity and surface resistance. Further, this explains that the runoff contributing areas are located at the lower and upper portions of hillslopes due to the presence of low soil hydraulic conductivity zones.  As both the hillslopes are dominated with Hortonian overland flow, the negative correlation was found between topographic indices (TWI) and soil moisture and positive correlation was noticed between soil hydraulic conductivity. Higher runoff (less infiltration) from AgF hillslope results in a higher negative correlation between TWI and soil moisture in comparison to GA hillslope. This results in a higher rate of change in soil temperature of GA hillslope than the AgF hillslope. After analyzing 40 rainfall events, it was concluded that a temperature drop of more than 2<sup>o</sup>C was recorded when the average rainfall intensity and event duration exceeds 7.5mm/hr and 7.5hr, respectively. The understanding of covariance of these hydrological fluxes will be used in the future to develop a hillslope-scale conceptual model.</p>

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