Reply to comment by H. Lough, Department of Civil Engineering, University of Canterbury, Christchurch, New Zealand, on the paper “Stream depletion predictions using pumping test data from a heterogeneous stream–aquifer system (a case study from the Great Plains, USA)”

1. General remark 2. The study by Kollet and Zlotnik (2003) 3. Remark on the explanation of the drawdown behavior 4. Remark on the re-analysis of the data from piezometer C2d 5. Summar

Causal deep learning models for studying the Earth system

Earth is a complex non-linear dynamical system. Despite decades of research and considerable scientific and methodological progress, many processes and relations between Earth system variables remain poorly understood. Current approaches for studying relations in the Earth system rely either on numerical simulations or statistical approaches. However, there are several inherent limitations to existing approaches, including high computational costs, uncertainties in numerical models, strong assumptions about linearity or locality, and the fallacy of correlation and causality. Here, we propose a novel methodology combining deep learning (DL) and principles of causality research in an attempt to overcome these limitations. On the one hand, we employ the recent idea of training and analyzing DL models to gain new scientific insights into relations between input and target variables. On the other hand, we use the fact that a statistical model learns the causal effect of an input variable on a target variable if suitable additional input variables are included. As an illustrative example, we apply the methodology to study soil-moisture–precipitation coupling in ERA5 climate reanalysis data across Europe. We demonstrate that, harnessing the great power and flexibility of DL models, the proposed methodology may yield new scientific insights into complex non-linear and non-local coupling mechanisms in the Earth system.</p

Quantifying the effects of three-dimensional subsurface heterogeneity on Hortonian runoff processes using a fully-coupled numerical, stochastic approach.

The impact of three-dimensional subsurface heterogeneity on hillslope runoff generated by excess infiltration (so called Hortonian runoff) is examined. A fully-coupled, parallel subsurface overland flow model is used to simulate runoff from an idealized hillslope. Ensembles of correlated, Gaussian random fields of saturated hydraulic conductivity are used to create uncertainty and variability (i.e. structure) due to subsurface heterogeneity. A large number of cases are simulated in a parametric manner with variance of the hydraulic conductivity varied over two orders of magnitude. These cases include rainfall rates above, equal and below the geometric mean of the hydraulic conductivity distribution. These cases are also compared to theoretical considerations of runoff production based on simple assumptions regarding (1) the rainfall rate and the value of hydraulic conductivity in the surface cell using a spatially-indiscriminant approach; and (2) a percolation-theory type approach to incorporate so-called runon. Simulations to test the ergodicity of hydraulic conductivity on hillslope runoff are also performed. Results show three-dimensional features (particularly in the vertical dimension) in the hydraulic conductivity distributions that create shallow perching, which has an important effect on runoff behavior that is fundamentally different in character than previous two dimensional analyses. The simple theories are shown to be very poor predictors of the saturated area that might runoff due to excess infiltration. It is also shown that ergodicity is reached only for a large number of integral scales ({approx}30) and not for cases where the rainfall rate is less than the geometric mean of the saturated hydraulic conductivity

Implementation and scaling of the fully coupled Terrestrial Systems Modeling Platform (TerrSysMP) in a massively parallel supercomputing environment – a case study on JUQUEEN (IBM Blue Gene/Q)

Continental-scale hyper-resolution simulations constitute a grand challenge in characterizing non-linear feedbacks of states and fluxes of the coupled water, energy, and biogeochemical cycles of terrestrial systems. Tackling this challenge requires advanced coupling and supercomputing technologies for earth system models that are discussed in this study, utilizing the example of the implementation of the newly developed Terrestrial Systems Modeling Platform (TerrSysMP) on JUQUEEN (IBM Blue Gene/Q) of the Jülich Supercomputing Centre, Germany. The applied coupling strategies rely on the Multiple Program Multiple Data (MPMD) paradigm and require memory and load balancing considerations in the exchange of the coupling fields between different component models and allocation of computational resources, respectively. These considerations can be reached with advanced profiling and tracing tools leading to the efficient use of massively parallel computing environments, which is then mainly determined by the parallel performance of individual component models. However, the problem of model I/O and initialization in the peta-scale range requires major attention, because this constitutes a true big data challenge in the perspective of future exa-scale capabilities, which is unsolved

Modeling Interactions of Surface-Subsurface Flow Using a Free-Surface Overland Flow Boundary Condition in a Parallel Flow Simulator

Models incorporating interactions between surface and subsurface flow are commonly based on the conductance concept that presumes a distinct interface at the land surface, separating the surface from the subsurface domain. In these models the subsurface and surface domains are linked via an exchange flux that depends upon the magnitude and direction of the hydraulic gradient across the interface and a proportionality constant (a measure of the hydraulic connectivity). Because experimental evidence of such a distinct interface is often lacking in the field, a more general coupled modeling approach would be preferable. We present a more general approach that incorporates a two-dimensional overland flow simulator into the parallel three-dimensional variably saturated subsurface flow code ParFlow developed at LLNL. This overland flow simulator takes the form of an upper, free-surface boundary condition and is, thus, fully integrated without relying on the conductance concept. Another advantage of this approach is the efficient parallelism of ParFlow, which is exploited by the overland flow simulator. Several verification and simulation examples are presented that focus on the two main processes of runoff production: excess infiltration and saturation. The usefulness of our approach is demonstrated in an application of the model to an urban watershed. The influence of heterogeneity of the shallow subsurface on overland flow and transport is also examined. The results show the uncertainty in flow and transport predictions due to heterogeneity. This is important in determining, for example, total maximum daily loads of surface water systems

Demonstrating fractal scaling of residence time distributions on the catchment scale using a fully-coupled, variably-saturated groundwater and land surface model and a Lagrangian particle tracking approach

The influence of the vadose zone, land surface processes, and macrodispersion on scaling behavior of residence time distributions (RTDs) is studied using a fully coupled watershed model in conjunction with a Lagrangian, particle-tracking approach. Numerical experiments are used to simulate groundwater flow paths from recharge locations along the hillslope to the streambed. These experiments are designed to isolate the influences of topography, vadose zone/land surface processes, and macrodispersion on subsurface RTDs of tagged parcels of water. The results of these simulations agree with previous observations that RTDs exhibit fractal behavior, which can be identified from the power spectra. For cases incorporating residence times that are influenced by vadose zone/land surface processes, increasing macrodispersion increases the slope of the power spectra. In general the opposite effect is demonstrated if the vadose zone/land surface processes are neglected. The concept of the spectral slope being a measure of stationarity is raised and discussed

Haematopoietic stem cell migration to the ischemic damaged kidney is not altered by manipulating the SDF-1/CXCR4-axis

Background. Haematopoietic stem cells (HSC) have been shown to migrate to the ischemic kidney. The factors that regulate the trafficking of HSC to the ischemic damaged kidney are not fully understood. The stromal cell-derived factor-1 (SDF-1)/CXCR4-axis has been identified as the central signalling axis regulating trafficking of HSC to the bone marrow. Therefore, we hypothesized that SDF-1/CXCR4 interactions are implicated in the migration of HSC to the injured kidney

The groundwater-land-surface-atmosphere connection: soil moisture effects on the atmospheric boundary layer in fully-coupled simulations

This study combines a variably-saturated groundwater flow model and a mesoscale atmospheric model to examine the effects of soil moisture heterogeneity on atmospheric boundary layer processes. This parallel, integrated model can represent spatial variations in land-surface forcing driven by three-dimensional (3D) atmospheric and subsurface components. The development of atmospheric flow is studied in a series of idealized test cases with different initial soil moisture distributions generated by an offline spin-up procedure or interpolated from a coarse-resolution dataset. These test cases are performed with both the fully-coupled model (which includes 3D groundwater flow and surface water routing) and the uncoupled atmospheric model. The effects of the different soil moisture initializations and lateral subsurface and surface water flow are seen in the differences in atmospheric evolution over a 36-hour period. The fully-coupled model maintains a realistic topographically-driven soil moisture distribution, while the uncoupled atmospheric model does not. Furthermore, the coupled model shows spatial and temporal correlations between surface and lower atmospheric variables and water table depth. These correlations are particularly strong during times when the land surface temperatures trigger shifts in wind behavior, such as during early morning surface heating

Groundwater Availability Within the Salton Sea Basin Final Report

It is widely recognized that increasing demands for water in Southern California are being affected by actions to reduce and redirect the amount of water imported from the Colorado River. In the Imperial Valley region, for example, import reductions will not only affect agricultural users but also could produce significant collateral impacts on the level and quality of water in the Salton Sea, its regional ecology, or even the long term air quality in the greater basin. The notion of using groundwater in the Imperial Valley as an additional source for agricultural or domestic needs, energy production, or Salton Sea restoration efforts, so as to offset reductions in imported water, is not a new concept. Even though it has been discussed recently (e.g., LLNL, 2002), the idea goes back, in part, to several studies performed by the US Department of Interior and other agencies that have indicated that there may be substantial, usable amounts of groundwater in some portions of the Imperial Valley. It has been estimated, for example, that between 1.1 and 3 billion acre-feet (AF) of groundwater lie within the extended, deep basin underlying the valley and Salton Sea region, even though much of it may be unrecoverable or too poor in its quality (Imperial County, 1997). This is a significant volume with respect to the total annual precipitation volume received in California, whose average is close to 200 million (or 0.2 billion) AF per year (DWR, 1998), and especially with respect to the total annual precipitation received in the Salton Sea watershed itself, which we estimate (Appendix A) to be approximately 2.5 million acre feet (MAF) per year. Clearly, a thorough appraisal of the groundwater resources in the Imperial Valley and Salton Sea region--i.e., an assessment of their overall physical availability--will be needed to determine how they can be used and managed to suit new or redirected demands in the region. Development of an improved or updated groundwater assessment in the Salton Sea Basin is the subject of the project described in this report. Much of the project work was done in cooperation with the US Bureau of Reclamation, Lower Colorado Region Office ('Reclamation'), which manages the Salton Sea Restoration project for the US Department of the Interior, and complements other recent assessment efforts (e.g., Imperial County, 1995). In this context, the notion of groundwater availability is defined by four separate, but interrelated concepts or components: (1) Volume and Capacity--This refers to the volume of groundwater available in storage in (or the related storage capacity of) the sediments and geologic media that comprise a groundwater basin. The volume of groundwater in a basin will vary in time as a function of recharge, well production, and land subsidence. (2) Producibility--This refers to the ease or difficulty of extracting groundwater in a basin from wells. Groundwater producibility will be affected by well depth and the formation permeability surrounding the open intervals in wells. (3) Quality--This refers to the extent that water produced from wells is potable or otherwise suitable for domestic or other uses. It may also refer to the chemical compositions of groundwater that are unrelated to potability or suitability issues. Groundwater quality will be affected by its residence time and flow pathway in the formation and will also be influenced by the quality of its original source before entering the groundwater regime. (4) Renewability and Recharge--This refers to the extent that groundwater is recharged to the basin as part of the natural hydrologic cycle or other artificial means. Groundwater renewability is normally a function of recharge derived from precipitation (and thus a function of regional climate), but may also be affected in local areas by irrigation, leaking canals, aquifer storage and recovery operations, and so forth. Along with the other factors, renewability will strongly affect how much water can be safely produced from a basin from one year to the next. In this report, we specifically consider two categories of information that comprise, are pertinent to, or facilitate such a groundwater assessment. The first category includes the vast assortment of descriptive geologic, hydrologic, chemical, and climatic data related to the regional groundwater aquifers in the Salton Sea area and the occurrence, movement, production, and quality of groundwater. We will refer to these as Hard Data. They may include, for example, spatially distributed geologic or lithologic information, operational wells, water level monitoring data, and well production reports, groundwater quality information, other land use information, historical precipitation and climatic records, and so forth. The second category includes more interpretive or analytic information based upon, or derived from these data and knowledge of related geologic, hydrologic, chemical, or climatic processes