Model applications

Hydro-economic modelling (HEM) is a water management tool that can help researchers, water practitioners and policymakers address critical questions about the socioeconomic and biophysical perspectives of current and future water demand and supply. In the past it has been used to evaluate the impacts of climate change and adaptations, assess hydropower and reservoir operations, weather forecasting and the water-energy-food nexus. And although HEM has become a valuable tool for analysing water-human systems, forecasting water management scenarios, developing policy and optimising infrastructure operations, some of its limitations can produce unreliable predictions.

With the management of water resources becoming increasingly complex due to greater demand and competition across different economic sectors, researchers from the University of California, the International Institute for Applied Systems Analysis and the Union of Concerned Scientists, recently undertook a review of more than 150 scientific papers that addressed water-related topics. They say that the ‘overarching objectives’ of their review was to:

• Identify how existing HEMs have innovated in integrating sectoral models such as climate, hydrological, energy, agricultural, environmental and economy-wide models.
• Assess the scope of the impact and water policy issues that HEMs have addressed.

As lead author José Pablo Ortiz Partida says, such models “shine a light on these challenges, helping us to navigate the intricate challenges of water management in an increasingly thirsty world”. The research he worked on with colleagues, called Hydro-Economic Modelling of Water Resources Management Challenges: Current Applications and Future Directions, was recently published in the journal Water Economics and Policy, and highlighted five distinct themes. 

1.Water is better managed through partnership and collaboration. 

Models showed more sustainable water resource management and better outcomes for stakeholders as levels of cooperation increased. This becomes even more important as the impacts of climate change become more apparent, but the authors warn there is still much work to be done to ensure that all relevant factors and stakeholders are integrated to make informed decisions. Furthermore, it was noted that basin-wide cooperation optimises benefits, and that comprehensive water management requires interdisciplinary teams.

2. Equity and sustainability in water allocation

As demand for water resources grows, so does the need for solutions that address resilience and reliability through equitable water (re)allocation. While rethinking water management at the water-food-energy-ecosystems level may prove to be one of the most significant areas to improve water sustainability.

3. Climate change adaptation and uncertain management

Water policies should consider the role of water in stakeholders’ activities while it is crucial that extreme scenarios are considered when developing adaptation strategies. Addressing and integrating uncertainty is a crucial feature of water management and in allowing stakeholders to understand the risks associated with different water management options and the costs of inaction. In addition, climate change is severely impacting agricultural systems, reducing the availability of water resources and crop yields, and increasing irrigation water requirements. 

4. Groundwater needs to be sustainably managed at all costs. 

Sustainable management of groundwater is imperative, given its crucial role in buffering municipal and agricultural systems and mitigating price spikes. The current costs associated with responsible groundwater usage, though significant, pale in comparison to the potential consequences of depleting this vital resource in the future. To address situations where overexploitation leads to private gains at the expense of public costs, economic sanctions have proven effective. Implementing measures such as raising irrigation water and energy prices can contribute to curbing excessive groundwater exploitation.

5. Water Policy and governance

The cost of inaction will be ‘unbearable’, the authors stress, adding that in the absence of adequate policies protecting water resources and natural ecosystems, water users will deplete reservoirs, aquifers, and river flows for short-term adaptation to climate change, disregarding the impacts on the environment and future human activities. Furthermore, although local control is important, there still needs to be some minimal central guidelines. The authors give the example of countries in the EU that have ‘a more cohesive approach to dealing with transboundary water policy’ than the US. While the EU uses transboundary models that account for climate change and other topics that are ‘controversial’ for certain politicians, some US states don’t even acknowledge climate change as a reality, hindering the country’s efforts to improve water use and plan sustainably. 

In conclusion Ortiz-Partida et al state that despite the multiple applications of hydro-economic models, which are undoubtedly useful, there are still many challenges that these water management tools need to overcome to be more effective. 

For example, hydro-economic studies largely focus on biophysical and economic indicators and often overlook stakeholders’ preferences and perspectives, partly explained by the large-scale and technical nature of HEMs. However, the authors say that more robust integration of social components may increase trust in and adoption of HEMs by local stakeholders. While social aspects intrinsic to water systems, such as health and equity, are still a relevant gap in knowledge.

As Ortiz-Partida adds: “The real-world impact of these models is significantly amplified when they are used in collaboration and involve all relevant stakeholders.”

Looking to the future, HEMs should incorporate additional ecosystem-related metrics (such as floodplain inundation time, peak streamflow, or consecutive days without precipitation during rainy seasons) which have implications for ecosystem restoration, and precision agriculture, among others.

Finally, the authors add that their analysis shows that multiple studies encourage international cooperation and coordination to increase water and economic security, even under future water scarcity scenarios. They describe cooperation in water resources as “the most equitable and most economically feasible options”. While transboundary partnerships and stakeholder participation in decision-making and local solutions can help prompt a better response “to the broader global issues of natural resource trade-offs and sharing”.

Modelling sedimentation

In their research published in Scientific Reports, Kilian Mouris et al introduce an interdisciplinary model chain to quantify the footprint of global change on reservoir sedimentation. 

Although large artificial reservoirs may effectively alleviate hydro-climatic extremes, their storage capacities are threatened by sedimentation processes which in turn are exacerbated by land use change. Envisioning strategies for sustainable reservoir management, the authors say, requires interdisciplinary model chains to emulate key processes driving sedimentation under global change scenarios. 

A fundamental challenge, Mouris et al go on to claim, is that most of the currently available modelling tools to assess global change impacts lack the necessary level of detail and capacity. Only a few existing models are capable of accounting for combined land use and hydro-climatic change impacts on sediment dynamics, and while more simplistic reservoir models can still approximate the storage loss of a reservoir, they cannot account for spatially explicit morphological processes and do not consider recirculation zones, lateral inflows, the influence of the outflows (eg turbine operation), and other complex 3D hydrodynamics.

To address these challenges, Mouris et al’s research focussed on a novel model chain that uses information on catchment physics, including hydro-climatic state and land use to predict long-term sediment dynamics and multi-dimensional reservoir sedimentation processes. The process-based model chain accounts for changes in temperature, precipitation, discharge, sediment yield, and reservoir sedimentation, by also considering the geometry and operating scheme of the reservoir. The centrepiece of the model chain is a 3D numerical model which predicts flow dynamics and sediment transport, showing how different global change scenarios impinge on reservoir sedimentation processes. 

The model was applied to the Devoll catchment, a typical Mediterranean mountainous region with high sediment production.

According to the research, a low emission scenario sustains higher discharges by 2100, while mid to high greenhouse gas emissions and unequal development or fossil-fuelled development scenarios amplify water scarcity. Specifically, increased winter rainfall, reduced snowfall, and decreased summer precipitation contribute to limited water availability during hot and dry Mediterranean summers, emphasising the need for artificial water storage in reservoirs.

In the low-emissions scenarios, higher discharges lead to elevated sediment yields but lower sediment concentrations compared to less sustainable emissions scenarios. In particular, the sediment concentration decreases with the implementation of sustainable land use. In contrast, less sustainable land use leads to higher sediment concentrations and sediment yields due to decreased forest and grassland areas. The scenarios with higher sediment yields experience the most substantial loss of storage volume and the delta moves further downstream, resulting also in a decrease in trapping efficiency.

Ultimately, the interdisciplinary model chain highlights that land use change outweighs climate change effects in Mediterranean regions. Therefore, localised management actions for land use change in the catchment, such as policy-enforced crop adaptations and afforestation, can reduce soil loss and sediment production. In addition, the long-term prediction strength of the model and the spatially explicit deposition patterns enable the implementation of targeted reservoir management strategies.

In conclusion, the authors say that such a complex interdisciplinary and physics-informed model chain demonstrates the considerable impacts of hydro-climatic and land use changes on water availability, sediment production, and reservoir sedimentation in a Mediterranean region. Ultimately the model chain shows that global change leads to increased sediment yields and decreased river discharge, with seasonal shifts for most of the climate and land use change projections considered.

Modelling reverse osmosis

Reverse osmosis (RO) desalination plants are viewed as being one solution to the impending crisis where demand for fresh water is expected to grow by over 40% by 2050. Converting saline water, such as seawater, into drinking water will help increase freshwater supplies but, as Matthew Haefner and Maha Haji explain in a recent paper published in Applied Energy, the energy requirement for the RO process would only exacerbate the lack of fresh water due to the effects of global warming, if sourced from fossil fuels. 

In comparison to the treatment of surface water for drinking water, the treatment of seawater for drinking water requires significantly more energy. Thus the ability to incorporate renewable energy sources into the RO process would be ideal for eliminating such a trade-off between freshwater production from RO and carbon emissions from burning fossil fuels. 

And this is where pumped hydro can play a role – the fact that RO desalination plants and pumped hydropower plants utilise and require elevated reservoirs, respectively, presents an opportunity for the co-location of these two systems as an Integrated Pumped Hydro Reverse Osmosis System (IPHROS). Combined with the fact that many drought-stricken coastal areas have nearby mountains at the necessary elevation for these upper reservoirs, a symbiotic relationship can be ascertained through the co-location of a pumped storage hydropower (PSH) system with a reverse osmosis (RO) desalination system. 

The authors say that merging PSH and RO into one IPHROS instead of implementing each individually could result in a number of benefits, including reduced capital investment, lower maintenance costs, and a natural mechanism for diluting the highly saline brine discharge generated from the RO process.

For this multi-objective optimisation, the authors explain how a new reverse osmosis model was created that utilises a blend of empirical and fundamental equations based on the solution–diffusion model of membrane transport, and the boundary layer effects that naturally occur along reverse osmosis membranes. 

In their paper, Haefner and Haji say they take a much deeper dive into modelling the element-level performance of the RO system, considering factors such as the development of surrogate models for predicting membrane performance and including concentration polarisation.

Developing a new RO model for the IPHROS model represents an initial venture into increasing the accuracy of the model in representing real-life phenomena. As the authors conclude, enhanced modelling and optimisation, as initiated in their paper, will eventually aid in IPHROS’ large-scale adoption into energy and freshwater infrastructure.

Design models

According to Tsuanyo et al in their paper published in Energy Research, run-of-river hydropower plants are often viewed as being more attractive than conventional hydroelectric plants from an economic and environmental point of view. However, their expected energy production pattern heavily depends on several construction variables that need an appropriate design using specific models. 

Here the authors analyse several existing models used for the calculation of penstock diameter and thickness and the optimal selection and implantation (admissible suction head) of a turbine, to estimate the energy produced and expected cost of small hydropower projects for grid-connected and off-grid/micro-grid applications. 

They say their review can be used as a guide in the design and simulation of run-of-river hydropower plants, thus helping in the assessment of the economic feasibility of projects. It also proposes a classification of reviewed models that could be used as a reference by scholars and practitioners in the field. Furthermore, scholars and developers interested in developing run-of-river feasibility studies and further research activity, especially in the context of Sub-Saharan Africa could find the study to be of use, while study results could also be used to develop a tool for the preliminary studies of run-of-river hydropower projects.