The imprint of climate and geology on the residence times of groundwater

Surface and subsurface flow dynamics govern residence time or water age until discharge, which is a key metric of storage and water availability for human use and ecosystem function. Although observations in small catchments have shown a fractal distribution of ages, residence times are difficult to directly quantify or measure in large basins. Here we use a simulation of major watersheds across North America to compute distributions of residence times. This simulation results in peak ages from 1.5 to 10.5 years, in agreement with isotopic observations from bomb-derived radioisotopes, and a wide range of residence times—from 0.1 to 10,000 years. This simulation suggests that peak residence times are controlled by the mean hydraulic conductivity, a function of the prevailing geology. The shape of the residence time distribution is dependent on aridity, which in turn determines water table depth and the frequency of shorter flow paths. These model results underscore the need for additional studies to characterize water ages in larger systems

Integrated surface–groundwater flow modeling: A freesurface overland flow boundary condition in a parallel groundwater flow model

free-surface overland flow boundary condition in a parallel groundwater flow mode

Potential impacts of human water management on the European heat wave 2003 using fully integrated bedrock-to-atmosphere simulations

Potential impacts of human water management on the European heatwave 2003 using fully integrated bedrock-to-atmosphere simulationsJessica Keune (1,2,3), Mauro Sulis (2), Stefan Kollet (1,3), Yoshihide Wada (4,5,6)(1) Institute for Bio- and Geosciences, Agrosphere (IBG-3), Research Centre Jülich, Jülich, Germany ([email protected]),(2) University Bonn, Meteorological Institute, Bonn, Germany, (3) Centre for High-Performance Scientific Computing inTerrestrial Systems, Geoverbund ABC/J, Jülich, Germany, (4) International Institute for Applied Systems Analysis,Laxenburg, Austria, (5) Department of Physical Geography, Utrecht University, Utrecht, The Netherlands, (6) NASA GoddardInstitute for Space Studies, NY, USARecent studies indicate that anthropogenic impacts on the terrestrial water cycle lead to a redistribution of waterresources in space and time, can trigger land-atmosphere feedbacks, such as the soil moisture-precipitationfeedback, and potentially enhance convection and precipitation. Yet, these studies do not consider the fullhydrologic cycle from the bedrock to the atmosphere or apply simplified hydrologic models, neglecting theconnection of irrigation to water withdrawal and groundwater depletion. Thus, there is a need to incorporate waterresource management in 3D hydrologic models coupled to earth system models.This study addresses the impact of water resource management, i.e. irrigation and groundwater abstraction, onland-atmosphere feedbacks through the terrestrial hydrologic cycle in a physics-based soil-vegetation-atmospheresystem simulating 3D groundwater dynamics at the continental scale. The integrated Terrestrial Systems ModelingPlatform, TerrSysMP, consisting of the three-dimensional subsurface and overland flow model ParFlow, theCommunity Land Model CLM3.5 and the numerical weather prediction model COSMO of the German WeatherService, is set up over the European CORDEX domain in 0.11resolution. The model closes the terrestrial waterand energy cycles from aquifers into the atmosphere. Anthropogenic impacts are considered by applying actualdaily estimates of irrigation and groundwater abstraction from Wada et al. (2012, 2016), as a source at the landsurface and explicit removal of groundwater from aquifer storage, respectively. Simulations of the fully coupledsystem are performed over the 2003 European heat wave and compared to a reference simulation, which doesnot consider human interactions in the terrestrial water cycle. We study the space and time characteristics andevolution of temperature extremes, and soil moisture and precipitation anomalies influenced by human watermanagement during the heat wave. A first set of simulations utilizes the spectral nudging technique to keepthe large-scale circulation consistent to the driving ERA-Interim reanalysis and examines the direct and localfeedback pathway, along which irrigation cools the land surface, enhances evapotranspiration and increases thetotal atmospheric water vapor, which may induce local precipitation. A second set of simulations without spectralnudging addresses the indirect feedback, where the atmospheric circulation is modified indirectly by irrigation.Simulations are evaluated over a range of spatial and temporal scales, i.e. from daily to seasonal variations.Results indicate systematic responses at the land surface, but a strong non-linearity of the local feedback affectingtropospheric processes and the occurrence of precipitation, and hence emphasize the need to integrate humanwater management in regional climate simulations.References:Wada, Y., L. P. H van Beek, and M. F. P. Bierkens (2012), Nonsustainable groundwater sustaining irrigation: Aglobal assessment, Water Resources Research, 48, W00L06, doi: 10.1029/2011WR010562.Wada, Y., I. E. M. de Graaf, and L. P. H. van Beek (2016), High-resolution modeling of human and climateimpacts on global water resources, J. Adv. Model. Earth Syst., 8, 735–763, doi: 10.1002/2015MS000618

Proof of concept of regional scale hydrologic simulations at hydrologic resolution utilizing massively parallel computer resources

We present the results of a unique, parallel scaling study using a 3-D variably saturated flow problem including land surface processes that ranges from a single processor to a maximum number of 16,384 processors. In the applied finite difference framework and for a fixed problem size per processor, this results in a maximum number of approximately 8 x 10(9) grid cells (unknowns). Detailed timing information shows that the applied simulation platform ParFlow exhibits excellent parallel efficiency. This study demonstrates that regional scale hydrologic simulations on the order of 10(3) km(2) are feasible at hydrologic resolution (similar to 10(0)-10(1) m laterally, 10(-2)-10(-1) m vertically) with reasonable computation times, which has been previously assumed to be an intractable computational problem

Multicriteria land cover design via coupled hydrologic and multi-sector water management models

We investigate how hydrologic-land feedbacks and a hydrologic-water management linkage impact land cover arrangements optimized within a multiobjective land cover design framework. The framework integrates a spatially-distributed and physically-based hydrologic model, for simulating surface and subsurface flow and land processes, with a network-based multi-sector water resources management and allocation model. Both models used (Parflow, Pywr) are open-source. The framework is applied to a hillslope problem to identify land cover patterns that optimize trade-offs between water, food, energy and environment objectives. Results show trade-offs depend on land cover composition and the spatial arrangement of land covers within the catchment. Total runoff volume and peak flow of runoff was found to change 3 and 2-fold, respectively, between optimized solutions as land cover composition and spatial patterns were altered to satisfy different combinations of objectives. At the same time, up to a 15% reduction in the total runoff volume and an 8% reduction in the peak flow of runoff were observed within optimized land cover patterns having equal composition but different spatial arrangements. This emphasizes the impact on hydrologic behavior of the spatial location of land covers within a catchment. The emergence of patterns in land cover distribution for different trade-offs between objectives is driven by feedback mechanisms between subsurface hydrology and land processes, which are implicitly linked to the properties of each land cover and the interactions between neighboring land covers through lateral groundwater flow. The study demonstrates the added benefits of coupling distributed hydrologic models with water management simulation for multisector multicriteria land cover planning.</p

Scalable Algorithms for Adaptive Mesh Refinement: Extension to General Element Types and Application to Fluid Dynamics

We discuss the development of parallel algorithms for adaptive mesh refinement (AMR) and their application to large-scale problems in simulating fluid dynamics. Our approach to AMR can be described as using a forest of octrees (or quadtrees in 2D) that are adaptively refined. The storage of elements is distributed in parallel, and fast and scalable algorithms exist for dynamic refinement/coarsening and other important tasks, such as partitioning and the extraction of one layer of off-process (ghost) neighbours. Our contributions are twofold: (a) We use the p4est software as a basis to create numerical applications to simulate the flow of gas in the atmosphere (advection equations), variably saturated subsurface flow (Richards), and the free flow of liquid (Navier-Stokes). (b) In addition to using quadrilateral/cubic elements, we are developing space filling curves and high-level AMR algorithms for triangles and tetrahedra. We include scalability results and simulation snapshots obtained on the JUQUEEN supercomputer

Initial results of fully coupled water cycle EURO-CORDEX evaluation simulations with TerrSysMP from 1989-2008

Initial results of fully coupled water cycle EURO-CORDEX evaluationsimulations with TerrSysMP from 1989-2008Ketan Kulkarni (1,4), Jessica Keune (2,3,4), Fabian Gasper (2,4), Wendy Sharples (1,4), Bibi Naz (2,4), KlausGoergen (2,4), Stefan Kollet (2,4)(1) SimLab Terrestrial Systems, Jülich Supercomputing Centre, Research Centre Jülich, Jülich, Germany, (2) Institute of Bio-and Geosciences, Agrosphere (IBG-3), Research Centre Jülich, Jülich, Germany, (3) Meteorological Institute, BonnUniversity, Bonn, Germany, (4) Centre for High-Performance Scientific Computing in Terrestrial Systems, GeoverbundABC/J, Jülich, GermanyInteractions and feedbacks between the sub-surface including groundwater, the land surface and the atmosphereare highly relevant for weather and the climate system. However, many state of the art global and regional earthsystem models do not consider the impacts of groundwater dynamics, which are critical for the closure of thehydrological cycle on different spatial and temporal scales. In this study we implement the coupled Terrestrial Sys-tems Modelling Platform over the EURO-CORDEX domain for evaluation experiments in line with the CORDEXexperiment design in order to study how the explicit treatment of groundwater affects states and fluxes of theterrestrial water and energy cycle over a continental domain on longer simulation time spans and in relation to ex-isting uncoupled EURO-CORDEX RCM simulations. The Terrestrial Systems Modelling Platform (TerrSysMP) isa fully coupled scale-consistent numerical modelling system, currently consisting of the COSMO NWP model, theCommunity Land Model (CLM) and the ParFlow variably saturated surface and subsurface hydrological model,coupled with the external coupler OASIS3(-MCT). TerrSysMP allows for a physically-based representation oftransport processes across scales down to sub-km resolution with explicit feedbacks between the individual com-partments, including 3D groundwater dynamics and a full representation of the terrestrial hydrological cycle. Theland surface-groundwater subsystem is spun up with a 1979-1989 cyclic climatological forcing derived from ERA-Interim reanalysis until an equilibrated groundwater state is achieved. Using this as the initial conditions, the fullycoupled simulation for the period from 1989 to 2008 are carried out over the EURO-CORDEX domain at 12 kmresolution using ERA-Interim as lateral boundary forcing. COSMO physics settings are in line with the CCLMconsortium runs done for EURO-CORDEX to allow for a better comparison. The JUBE2 (Juelich BenchmarkingEnvironment) workflow engine is used to manage the complex operation of the simulations. In the analysis, wediscuss the impact of groundwater on land atmosphere feedbacks and atmospheric boundary layer properties todemonstrate the added value of the coupled simulations. Several climate indices and performance metrics are usedover PRUDENCE analysis regions in a comparison with observational data