Rabi H. Mohtar

Water–energy–food (WEF) Nexus Tool 2.0: guiding integrative resource planning and decision-making

The paper introduces a framework and set of methodologies that define the linkages between the interconnected resources of water, energy and food, and enable explicit corresponding quantifications. The paper presents a new water–energy–food (WEF) Nexus modelling tool (WEF Nexus Tool 2.0) based on that framework which offers a common platform for scientists and policy-makers to evaluate scenarios and identify sustainable national resource allocation strategies. The tool is applied to a case study focusing on Qatar, a hyper-arid Gulf country.

Sustainability in the water-energy-food nexus

Today we are more than ever convinced that security in food, energy and water is interwoven with human, economic and environmental sustainability, and that this interplay is strengthening under growing natural resource scarcity and climate change. This recognition suggests that policy making and decision making for sustainability could benefit from a holistic nexus approach that reduces trade-offs and builds synergies across sectors, and thus helps reduce costs and increase benefits for humans and nature, as compared to independent approaches to the management of water, energy and food, without compromising the resource basis on which humanity relies. In the past, research and policy work related to the nexus has looked at the interactions between water and food or water and energy, but given political and institutional realities there has been a reluctance to bring forward a broader systemic perspective to capture the dependencies across multiple sectors and resources. At the same time, the cost to the environment of neglecting these linkages has increased. The players in the nexus approach are public, private and civil society at local and broader human scales. Recognizing the urgent need to focus on sustainability in the water–energy–food nexus (WEF nexus) together with tools to analyze and approaches to govern the linkages at different scales, the Global Water System Project, the United Nations Environment Programme, the Deutsches Institut für Entwicklungspolitik, the Center for Development Research (ZEF), University of Bonn, and the CGIAR Research Program on Water Land and Ecosystems organized an international conference, Sustainability in the WaterEnergy-Food Nexus, in Bonn, Germany, in 2014. The conference addressed sustainability in the WEF nexus as a key research-for-action initiative, and included an international policy consultation process to inform, influence and catalyze action of policy makers, nongovernmental organizations, the private sector, educators and researchers towards a nexus approach that both draws on and supports the environment. The conference brought together available information, identified knowledge and action gaps, shared lessons on viable instruments and approaches, facilitated networks, and contributed to consensus on priorities for appropriate investment and action by different actors and stakeholders for moving towards action on the WEF nexus. This special issue is an outcome of that conference, and contains significant pieces of work on the WEF nexus that were presented at the conference focusing on relevant tools, solutions and governance at different scales. Together, the articles in this special issue

Heuristic space–time design of monitoring wells for contaminant plume characterization in stochastic flow fields

An optimization methodology for designing groundwater quality monitoring networks applicable to stochastic flow fields is presented and evaluated. The approach sets itself apart from previous techniques by incorporating the time dimension directly into the objective function. This function is extremized using a directed partial enumeration strategy guided by physical considerations related to transport processes. The result is a set of monitoring well locations and a sampling schedule that minimizes plume characterization error while satisfying constraints on the maximum number of wells and allowable number of active wells. The method is evaluated using hypothetical plumes with varying degrees of heterogeneity. Results indicate that the proposed approach is successful in generating near-optimal sampling networks that satisfy all imposed constraints. Monitoring networks with as little as three active wells and a total of 12 wells are found to provide adequate plume characterization for low toxicity contaminants.

Stability and accuracy of two-dimensional kinematic wave overland flow modeling

Abstract A two-dimensional finite element based overland flow model was developed and used to study the accuracy and stability of three numerical schemes and watershed parameter aggregation error. The conventional consistent finite element scheme results in oscillations for certain time step ranges. The lumped and the upwind finite element schemes are tested as alternatives to the consistent scheme. The upwind scheme did not improve on the stability or the accuracy of the solution, while the lumped scheme provided stable and accurate solutions for time steps twice the size of time steps needed for the consistent scheme. A new accuracy based dynamic time step estimate for the two-dimensional overland flow kinematic wave solution is developed for the lumped scheme. The newly developed dynamic time step estimates are functions of the mesh size, and time of concentration of the watershed hydrograph. Due to lack of analytical solutions, the time step was developed by comparing numerical solutions of various levels of discretization to a reference solution using a very fine mesh and a very small time step. The time step criteria were tested on a different set of problems and proved to be adequate for accurate and stable solutions. A sensitivity analysis for the watershed slope, Manning’s roughness coefficient and excess rainfall rate was conducted in order to test the effect of parameter aggregation on the stability and accuracy of the solution. The results of this analysis show that aggregation of the slope data resulted in the highest error. The roughness coefficient had a smaller effect on the solution while the rainfall intensity did not show any significant effect on the flow rate solution for the range of rainfall intensity used. This work pioneers the challenge of providing guidelines for accurate and stable numerical solutions of the two-dimensional kinematic wave equations for overland flow.

Water-Energy-Food Nexus Framework for facilitating multi-stakeholder dialogue

Water, energy and food are deeply interlinked resources. Food and energy production require over 90% of our global water resources. In this time of climate change and rapid population growth, water is increasingly the limiting factor for economic development and future security of both energy and food. Present policy making often lacks the necessary mechanisms to incorporate the interlinkages between water, energy and food. The different institutions governing resource allocation often do not communicate with one another, creating a lack of integrated planning, allocation and management of these key resources. Although the scientific community has made serious efforts to identify and quantify the interlinkages between resource systems, there continues to be a wide gap between science and policy making in effectively communicating those findings for proper incorporation in planning agendas. This science-to-policy gap could be reduced through improved exchange and the integration of scientific data and policy considerations into inclusive tools that address policy objectives and are technically viable from the perspective of sustainable resource utilization. Global debates have placed economic security, in which water, energy and food security are the main constituent pillars, on a par with physical security threats, such as terrorism and disease. Water, energy and food security are high on the agendas of global think tanks – identified as critical, interconnected risks that need to be addressed. The InterAction Council (Axworthy & Adeel, 2014) identified the water-energy-food nexus as one of the major risks facing our global community, alongside religious divides and nuclear proliferation. Moreover, Global Risk reports from 2007 through 2015 (World Economic Forum, 2015) highlight food crises, water scarcity and energy shocks among the top five risks to the modern world in terms of likelihood and impact. Awareness of the volume of present and expected challenges has grown in multiple circles, including academic, policy, business, and civil society. Nevertheless, the tools and mechanisms to ensure that these challenges are properly addressed have yet to be developed.

Present and future of the water-energy-food nexus and the role of the community of practice

The paper discusses an integrated approach to the management of three primary resources: water, energy, and food (WEF), as these increasingly represent the greatest global risks because they are expected to be highly impacted by climate change, demographics, aging infrastructure, and other challenges in the twenty-first century. As background, the WEF nexus is defined; significant historical developments of nexus thinking noted; and important connections to systems-science theory presented. An interdisciplinary WEF nexus platform is defined and proposed to support scholarship and to be a bridge between science, policy, and the general community of stakeholders. The interdisciplinary nexus platform is then differentiated from more common discipline-specific approaches. A review of the WEF nexus history, important benchmarks, and the foundation in system-science theory are presented. The paper concludes with a call for a WEF nexus community of practice (NCoP) to promote and enable an integrative approach to develop and employ tools with the purpose of strengthening sustainable food security, increasing energy production, and bridging water supply gaps that have arisen in demands for both food and energy. The transdisciplinary platform created by the NCoP will carry strong societal impact while addressing the scarcity and sustainable management of these primary resources.

A world wide web-based grazing simulation model (GRASIM)

This paper introduces the Web-based GRAzing SImulation Model (GRASIM). It describes the models core algorithms, the multi-paddock grazing and scheduling capabilities, and presents the Web interface structure and its execution mechanism. GRASIM estimates daily forage dry matter, daily soil water content and drainage, and daily soil nitrate content and leaching. The Web interface for GRASIM was developed to better deliver this useful computing resource to general users with access to a Web browser, regardless of their computer platform. With this Web interface, users can setup and modify GRASIM input files, run the model and obtain immediate responses to questions of interest with great ease. WWW-GRASIM also includes a help manual developed to give users instant help on all the model-input variables, components in GRASIMs Web interface and model execution procedures.

Stability and accuracy of finite element schemes for the one-dimensional kinematic wave solution

Solving the kinematic wave equations for overland flow using the conventional consistent Galerkin finite element scheme is known to result in numerical oscillations due to the non-symmetric first spatial derivative terms in the kinematic wave equations. In this paper the lumped and the upwind finite element schemes are evaluated as alternatives to the consistent Galerkin finite element scheme. Stability analysis of the upwind scheme shows that the damping effect, that could reduce the oscillations, is small for the high Courant numbers encountered in overland flow problems. The upwind scheme, using upwind factors of 0.1 and 1.0, did not provide any improvement to the stability of the lumped and the consistent schemes. The lumped scheme considerably reduces oscillations without significant reduction in the overall solution accuracy. No analytical guidelines for time-step criteria that will insure stability and accuracy were provided by the stability analysis performed for the three schemes. Problem specific accuracy-based dynamic time-step criteria was developed and evaluated for the lumped scheme. These time-steps were found to be on average, double the size of the dynamic time-steps for the consistent scheme.

Field method for separating the contribution of surface‐connected preferential flow pathways from flow through the soil matrix

[1] Liquid latex was used as a method to seal visible surface-connected preferential flow pathways (PFPs) in the field in an effort to block large surface-connected preferential flow and force water to move through the soil matrix. The proposed approach allows for the quantification of the contribution of large surface-connected cracks and biological pores to infiltration at various soil moisture states. Experiments were conducted in a silty clay loam soil in a field under a no-till corn-soybean rotation planted to corn. Surface intake rates under ponding were measured using a simplified falling head technique under two scenarios: (1) natural soil conditions with unaltered PFPs and (2) similar soil conditions with latex-sealed large macropores at the surface. Results indicated that the contribution of flow from large surface-connected macropores to overall surface intake rates varied from approximately 34% to 99% depending on the initial moisture content and macroporosity present. However, evidence of preferential flow continued to appear in latex-sealed plots, suggesting significant contributions to preferential flow from smaller structural macropores, particularly in two out of four tests where no significant differences were observed between control and latex-sealed plots. Citation: Sanders, E. C., M. R. Abou Najm, R. H. Mohtar, E. Kladivko, and D. Schulze (2012), Field method for separating the contribution of surface-connected preferential flow pathways from flow through the soil matrix, Water Resour. Res., 48, W04534,

Field and numerical analysis of in-situ air sparging: a case study

An in-situ air sparging operation was used to remediate the sandy subsurface soils and shallow groundwater under a drum storage site near Chicago, IL, where either periodic or random spillage of a light non-aqueous phase liquid (LNAPL) occurred between 1980 and 1987. Both field measurements and model simulations using commercially available computer software suggested that microbial degradation was the most significant contributor to the removal of contaminant mass. Toluene, ethylbenzene and total xylenes (TEX), which were of major concern with regards to reaching clean-up criteria at the site, were observed to decline by 88% in concentration. Furthermore, up to 97% of the total mass removed through microbial degradation consisted of TEX. Of the total contaminant spill, up to 23% of initial organic chemical mass was removed through microbial degradation compared to less than 6% by physical stripping. Greater loss to microbial degradation is most likely attributed to the relatively low air injection rate used during the course of the air sparging remediation. Evaluation of air sparging at the site using model simulations supported this analysis by estimating 140 and 620 kg of total contaminant mass being removed through volatilization and biodegradation, respectively. An evaluation of several system design parameters using model simulations suggested that only the type of sparging operation (i.e. pulsed or continuous) was significant in terms of total contaminant removal time, while both the sparging operation and air injection rate were significant in terms of removal of a critical species, total xylenes.