Figure 17 - uploaded by Michail D. Vrettas
Content may be subject to copyright.
shows the contour map of the research site including the locations of Elder Creek and the wells along the slope. The surface of W01 is close to Elder Creek; with W02 and W03 ∼ 32m upslope, W05, W06 and W07 ∼ 50m upslope, and W10 ∼ 62m upslope. The water table is at its shallowest, approximately ∼ 3m from the surface, at W01 by the creek, and deepest at ∼ 22m at W05. Northern California is in the winter rain regime, with October the 1'st commonly defined as the start of the rainy season, or the water year (WY). Precipitation varied over the six years period of our investigation. The cumulative 12month precipitation was highest, at ∼ 2100mm, for WY2010, and less than half, at ∼ 1000mm, for WY2013, as shown in Figure (18). Moreover, major storms arrived early in the season during WY2010 and WY2012, and did not arrive till February 2014 for WY2013. The differing rain patterns present a challenge for assessing model simulation of the fast and slow penetration of water in the subsurface. Simulation over a fixed time period, say six months, may include the dry season recession of the water table in some years and not others. Therefore, to test the new parameterization's ability to capture the penetration of rainwater to depth, we select a cumulative precipitation threshold of 800mm, for assessing the model parameters. Once the parameters are chosen, we present simulations over the entire six year period. Figure (19) shows the measured precipitation and fluctuations of the water tables, with rapid rise and slow decline repeating at all seven wells through the six years WY2008 to WY2013. At W05 and W10, the rise is most rapid early in the rainy season when the water table is deep, and is much less dramatic for the same storm intensity later in the season. W02 and W03 are at the same elevation but at times exhibit opposite behavior: W02 showed water table rising to 7m from the surface and fluctuating in WY2008 and remained at about 12m with muted fluctuation thereafter; while the opposite obtains for W03. As these wells are at low elevation and close to the Creek, we hypothesize that the base-flow from upslope also contributes to the water table fluctuations.
Source publication
Preferential flow through weathered bedrock leads to rapid rise of the water table after the first rainstorms and significant water storage (also known as "rock moisture") in the fractures. We present a new parameterization of hydraulic conductivity that captures the preferential flow and is easy to implement in global climate models. To mimic the...
Citations
... We hypothesized that the thick layer of weathered bedrock in this region provides conduits for preferential flow and stores moisture accessible by deep roots. To mimic flow through fractures, we developed a new stochastic parameterization of hydraulic conductivity in the vadose zone, one whose variance is inversely proportional to the saturation state itself (Vrettas & Fung 2015). A sensitivity calculation shows that it is only trees with roots >10 m deep that could access the deep moisture and sustain transpiration in the dry summer (Vrettas & Fung 2017). ...
The atmosphere is the synthesizer, transformer, and communicator of exchanges at its boundaries with the land and oceans. These exchanges depend on and, in turn, alter the states of the atmosphere, land, and oceans themselves. To a large extent, the interactions between the carbon cycle and climate have mapped, and will map, the trajectory of the Earth system. My quest to understand climate dynamics and the global carbon cycle has been propelled by new puzzles that emerge from each of the investigations and has led me to study subdisciplines of Earth science beyond my formal training. This article sketches my trek and the lessons I have learned.
... highly variable parameter in the literature (Vrettas and Fung 2015). The high repeatability can be attributed to the controlled compaction and homogeneity of soil samples. ...
Quantification of water infiltrating into the subsurface is mandatory for hydrological modeling of irrigation and drainage projects. Infiltration is influenced primarily by the soil type and initial compaction conditions (dry density and water content). However, few studies have investigated the effect of initial compaction condition on infiltration characteristics of soils and their quantitative relationship. Recent developments such as the portable mini disc infiltrometer (MDI) permit controlled, nondestructive and nonintrusive infiltration measurements in the laboratory, thereby allowing experiments under known initial compaction condition. Based on these measurements, this study developed multiple linear regression (MLR) equations relating near-saturated, near-surface hydraulic conductivity (k), and initial compaction state (dry density, γ; and gravimetric water content, w), with and without consideration of negative pressure head (h) for a cohesive and a noncohesive soil. The developed relationship was found to be statistically significant. For a particular initial w, the infiltration and k decreased with an increase in γ. For a particular γ, the k determined from infiltration measurements decreased with an increase in initial w for both soils. The developed MLR equations were used to study the effect of input variables (w, γ, and h) on k by using the method of difference. It was found that k is more sensitive to initial γ than to w and h, which have comparable influence. The role of sorptivity on the determination of k was investigated by comparing analysis methods from the literature. For lower k values (≤15 mm=h for noncohesive soil and ≤8 mm=h for cohesive soil), the effect of sorptivity on k was found to be negligible. The influence of sorptivity was predominant when initial saturation was less than 30% for which the variation of k was within 10%.
... Shangguan et al. (2017) developed a global DTB by digital soil mapping based on about 1.7 million observations from soil profiles and water wells, which has a much higher accuracy than the dataset by Pelletier et al. (2016). Vrettas and Fung (2016) showed that weathered bedrock stores a significant fraction (more than 30 %) of the total water despite its low porosity. Jordan et al. (2018) estimated the global permeability of the unconsolidated and consolidated Earth for groundwater modelling. ...
Soil is an important regulator of Earth system processes,
but remains one of the least well-described data layers in Earth system
models (ESMs). We reviewed global soil property maps from the perspective of
ESMs, including soil physical and chemical and biological properties, which
can also offer insights to soil data developers and users. These soil
datasets provide model inputs, initial variables, and benchmark datasets. For
modelling use, the dataset should be geographically continuous and scalable and
have uncertainty estimates. The popular soil datasets used in ESMs are often
based on limited soil profiles and coarse-resolution soil-type maps with
various uncertainty sources. Updated and comprehensive soil information
needs to be incorporated into ESMs. New generation soil datasets derived
through digital soil mapping with abundant, harmonized, and quality-controlled soil observations and environmental covariates are preferred to
those derived through the linkage method (i.e. taxotransfer rule-based
method) for ESMs. SoilGrids has the highest accuracy and resolution among
the global soil datasets, while other recently developed datasets offer
useful compensation. Because there is no universal pedotransfer function, an
ensemble of them may be more suitable for providing derived soil properties to
ESMs. Aggregation and upscaling of soil data are needed for model use, but
can be avoided by using a subgrid method in ESMs at the expense of increases
in model complexity. Producing soil property maps in a time series still remains
challenging. The uncertainties in soil data need to be estimated and
incorporated into ESMs.
... Regional groundwater flow and the stream-aquifer interaction strongly depend on hydraulic conductivity (Erdal and Cirpka, 2016). However, it is a spatially variable factor and is related to porosity and aquifer characteristics (Salamon et al., 2007;Vrettas and Fung, 2015). Therefore, hydraulic conductivity is an important factor for groundwater management and should be discerned using different geostatistical techniques and field investigations (pumping tests, etc.) (Zhou et al., 2014). ...
... In addition, some studies have incorporated groundwater models into land surface models to investigate changes in groundwater (Kollet and Maxwell, 2008a;Maxwell and Miller, 2005) and base flow (Kollet and Maxwell, 2008b). However, with the continuous improvement in the description of hydrological processes in land surface models, large-scale hydrological parameterization schemes for climate simulation are emerging, and studies using algorithms in hydrological models to replace parameterization schemes in climate models are gradually decreasing (Niu et al., 2005;Vrettas and Fung, 2015). ...
The terrestrial hydrological process is an essential but weak link in global/regional climate models. In this paper, the development status, research hotspots and trends in coupled atmosphere-hydrology simulations are identified through a bibliometric analysis, and the challenges and opportunities in this field are reviewed and summarized. Most climate models adopt the one-dimensional (vertical) land surface parameterization, which does not include a detailed description of basin-scale hydrological processes, particularly the effects of human activities on the underlying surfaces. To understand the interaction mechanism between hydrological processes and climate change, a large number of studies focused on the climate feedback effects of hydrological processes at different spatio-temporal scales, mainly through the coupling of hydrological and climate models. The improvement of the parameterization of hydrological process and the development of large-scale hydrological model in land surface process model lay a foundation for terrestrial hydrological-climate coupling simulation, based on which, the study of terrestrial hydrological-climate coupling is evolving from the traditional unidirectional coupling research to the two-way coupling study of “climate-hydrology” feedback. However, studies of fully coupled atmosphere-hydrology simulations (also called atmosphere- hydrology two-way coupling) are far from mature. The main challenges associated with these studies are: improving the potential mismatch in hydrological models and climate models; improving the stability of coupled systems; developing an effective scale conversion scheme; perfecting the parameterization scheme; evaluating parameter uncertainties; developing effective methodology for model parameter transplanting; and improving the applicability of models and high/super-resolution simulation. Solving these problems and improving simulation accuracy are directions for future hydro-climate coupling simulation research.
... CZ science is revealing increasing complexities and evermore nuanced insights, particularly regarding moisture availability in the weathered bedrock beneath soil (Rempe & Dietrich, 2018;Salve et al., 2012), subsurface preferential flow paths with multiple perched lateral flows (the fill and spill concept; Tromp- van Meerveld & McDonnell, 2006), and the intermittent hydrologic connectivity that drives plant water use and geochemical releases from catchments (e.g., Brantley, Lebedeva, et al., 2017;Godsey et al., 2009;Hopp & McDonnell, 2009;Lanni et al., 2011;McDonnell, 2014;Rahman & Rosolem, 2017). Indeed, attempts have recently been made to represent the rapid recharge to the deep store via rock fractures in global models (Hartmann et al., 2015Vrettas & Fung, 2015, 2017. However, the state of knowledge and the lack of global subsurface data do not yet allow us to test the importance of these emerging properties. ...
Earth System Models (ESMs) are essential tools for understanding and predicting global change, but they cannot explicitly resolve hillslope‐scale terrain structures that fundamentally organize water, energy, and biogeochemical stores and fluxes at subgrid scales. Here we bring together hydrologists, Critical Zone scientists, and ESM developers, to explore how hillslope structures may modulate ESM grid‐level water, energy, and biogeochemical fluxes. In contrast to the one‐dimensional (1‐D), 2‐ to 3‐m deep, and free‐draining soil hydrology in most ESM land models, we hypothesize that 3‐D, lateral ridge‐to‐valley flow through shallow and deep paths and insolation contrasts between sunny and shady slopes are the top two globally quantifiable organizers of water and energy (and vegetation) within an ESM grid cell. We hypothesize that these two processes are likely to impact ESM predictions where (and when) water and/or energy are limiting. We further hypothesize that, if implemented in ESM land models, these processes will increase simulated continental water storage and residence time, buffering terrestrial ecosystems against seasonal and interannual droughts. We explore efficient ways to capture these mechanisms in ESMs and identify critical knowledge gaps preventing us from scaling up hillslope to global processes. One such gap is our extremely limited knowledge of the subsurface, where water is stored (supporting vegetation) and released to stream baseflow (supporting aquatic ecosystems). We conclude with a set of organizing hypotheses and a call for global syntheses activities and model experiments to assess the impact of hillslope hydrology on global change predictions.
... Drainage of water through the vadose zone below the top few meters of soil has historically been treated as only a function of the slope of the terrain and wetness of the lowest soil layer [3,63]. These results suggest that baseflow parameterizations in LSMs should incorporate the effects of karst; recent research has suggested approaches to such parameterizations [64,65]. ...
Variability and covariability of land properties (soil, vegetation and subsurface geology) and remotely sensed soil moisture over the southeast and south-central U.S. are assessed. The goal is to determine whether satellite soil moisture memory contains information regarding land properties, especially the distribution karst formations below the active soil column that have a bearing on land-atmosphere feedbacks. Local (within a few tens of km) statistics of land states and soil moisture are considered to minimize the impact of climatic variations, and the local statistics are then correlated across the domain to illuminate significant relationships. There is a clear correspondence between soil moisture memory and many land properties including karst distribution. This has implications for distributed land surface modeling, which has not considered preferential water flows through geologic formations. All correspondences are found to be strongest during spring and fall, and weak during summer, when atmospheric moisture demand appears to dominate soil moisture variability. While there are significant relationships between remotely-sensed soil moisture variability and land properties, it will be a challenge to use satellite data for terrestrial parameter estimation as there is often a great deal of correlation among soil, vegetation and karst property distributions.
... For example, incorporation of transport phenomena associated with fracture flow (e.g., film flow; ref. 49) is likely needed to accurately simulate the simultaneous significant storage and rapid transmission of precipitation events after winter wet-up. Novel parameterizations of porous media flow for use in LSMs that account for processes in weathered bedrock are being developed (52)(53)(54). Such models present an opportunity to understand the role of rock moisture on the climate system. ...
Significance
Soil moisture has long been recognized as a key component of the hydrologic cycle. Here, we quantify significant exchangeable water held in weathered bedrock, beneath the soil, that regulates plant-available water and streamflow. We refer to this as rock moisture—a term parallel to soil moisture, but applied to different material. Deep weathered bedrock capable of storing plant-available moisture is common, yet this reservoir of rock moisture—distinct from soil and groundwater—is essentially unquantified. At our study site, the volume of rock moisture exceeds soil moisture and is a critical and stable source of water to plants in drought years. Our observations indicate that rock moisture now needs to be incorporated into hydrologic and climate models.
... At first, much of the synthesis crossed only two disciplines at a time: for example, several papers emphasized how geomorphological concepts related to erosion must be incorporated to understand chemical weathering, and vice versa (Rempe and Dietrich, 2014;Riebe et al., 2016). Likewise, researchers have related tree roots to water cycling (Vrettas and Fung, 2015). Now, researchers are targeting multidisciplinary aspects of CZ entities. ...
... Researchers have likewise developed a energy-balance snowmelt model that is now being used with remotely sensed data for water supply forecasting (Painter et al., 2016). In other integrative efforts, researchers are modeling how hydraulic conductivity, root water uptake efficiency, and hydraulic redistribution by plants sustain evapotranspiration through dry seasons (Quijano et al., 2012(Quijano et al., , 2013Vrettas and Fung, 2015). Work at the Luquillo CZO has supported interpretations of the controls on bed load grain size and channel dimensions for rivers (Phillips and Jerolmack, 2016). ...
The critical zone (CZ), the dynamic living skin of the Earth, extends from
the top of the vegetative canopy through the soil and down to fresh bedrock
and the bottom of the groundwater. All humans live in and depend on the CZ. This zone has three co-evolving surfaces: the top of the vegetative
canopy, the ground surface, and a deep subsurface below which Earth's
materials are unweathered. The network of nine CZ observatories
supported by the US National Science Foundation has made advances in three
broad areas of CZ research relating to the co-evolving surfaces.
First, monitoring has revealed how natural and anthropogenic inputs at the
vegetation canopy and ground surface cause subsurface responses in water,
regolith structure, minerals, and biotic activity to considerable depths.
This response, in turn, impacts aboveground biota and climate. Second,
drilling and geophysical imaging now reveal how the deep subsurface of the CZ
varies across landscapes, which in turn influences aboveground ecosystems.
Third, several new mechanistic models now provide quantitative predictions of
the spatial structure of the subsurface of the CZ.Many countries fund critical zone observatories (CZOs) to measure the fluxes
of solutes, water, energy, gases, and sediments in the CZ and some relate
these observations to the histories of those fluxes recorded in landforms,
biota, soils, sediments, and rocks. Each US observatory has succeeded in
(i) synthesizing research across disciplines into convergent approaches; (ii)
providing long-term measurements to compare across sites; (iii) testing and
developing models; (iv) collecting and measuring baseline data for comparison
to catastrophic events; (v) stimulating new process-based hypotheses; (vi)
catalyzing development of new techniques and instrumentation; (vii) informing
the public about the CZ; (viii) mentoring students and teaching about
emerging multidisciplinary CZ science; and (ix) discovering new insights
about the CZ. Many of these activities can only be accomplished with
observatories. Here we review the CZO enterprise in the United States and identify how
such observatories could operate in the future as a network designed to
generate critical scientific insights. Specifically, we recognize the need
for the network to study network-level questions, expand the environments
under investigation, accommodate both hypothesis testing and monitoring, and
involve more stakeholders. We propose a driving question for future CZ
science and a hubs-and-campaigns model to address that question and
target the CZ as one unit. Only with such integrative efforts will we learn
to steward the life-sustaining critical zone now and into the future.
... To date, much of the synthesis has crossed only two disciplines at a time: for example, several papers have emphasized how geomorphological concepts related to erosion must be incorporated to understand chemical weathering, and vice versa (Rempe and Dietrich, 2014; Riebe 10 et al., 2016). Likewise, researchers have related tree roots to water cycling (Vrettas and Fung, 2015). But many puzzles remain concerning multi-disciplinary aspects of CZ entities, and much effort is currently focusing on such frontiers. ...
... Work at the Luquillo CZO in Puerto Rico has allowed testing of models for stream channel self-organization at many other locations 10 (Phillips and Jerolmack, 2016). In other efforts, researchers are investigating and modelling how hydraulic conductivity, root water uptake efficiency, and hydraulic redistribution by plants combine to sustain evapotranspiration through dry seasons (Quijano et al., 2013;Quijano et al., 2012;Vrettas and Fung, 2015). ...
The critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetation canopy through the soil and down to fresh bedrock and the bottom of groundwater. All humans live in and depend on the critical zone. This zone has three co-evolving surfaces: the top of the vegetation canopy, the ground surface, and a deep subsurface below which Earth’s materials are unweathered. The US National Science Foundation supported network of nine critical zone observatories has made advances in three broad critical zone research areas. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response in turn impacts above-ground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences above-ground ecosystems. Third, several mechanistic models providing quantitative predictions of the spatial structure of the subsurface of the CZ have been proposed.
Many countries now fund networks of critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gas, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each U.S. observatory has succeeded in synthesizing observations across disciplines; providing long-term measurements to compare across sites; testing and developing models; collecting and measuring baseline data for comparison to catastrophic events; stimulating new process-based hypotheses; catalyzing development of new techniques and instrumentation; informing the public about the CZ; mentoring students and teaching about emerging multi-disciplinary CZ science; and discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO experiment in the US and identify how such a network could evolve in the future. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a hubs-and-campaigns model that promotes study of the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.
