What is the CLEWs approach?
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CLEWs  stands for ‘Climate, Land, Energy and Water systems’. It is a modelling framework first introduced by the International Atomic Energy Agency in 2009  and later by a multi-United Nations agency application to Mauritius . It takes inspiration from global integrated assessment models made popular in the Limits to Growth study  that tried to assess the integrated nature of development.
Climate, land, energy and water systems are closely linked. An impact in one can affect the other. A (climate induced) change in weather affects water supply. Water is needed for power plant cooling, to generate hydro, to maintain forests etc. At the same time, if we run out of fresh water, it needs to be desalinated. The former affects energy supply, the latter affects energy demand. The compounding impacts happen at the same time and can be disproportionate. For instance, in California there have been droughts that have led to investment in highly energy-intensive desalination. But this is at a time when electricity generation is strained as there is lower hydropower generation. The power system becomes strained at a time when it is needed most. The same is happening in Europe. During recent years power plants across Europe have been at risk of being shut down due to warm temperatures and low river levels. This is either as the water used to cool them becomes dangerously hot to the ecosystems in the rivers to which it is returned, or that (often in the south) there is simply not enough water in the rivers to provide cooling. However, as there is a rise in temperature, at exactly the same time, people start to draw more power as they turn up air-conditioners. This results in power supply shortages. Another example: in a country like Sweden, where summer water restrictions are encouraged, forests have been at risk of fire due to high temperatures and unusually low rain. Further, forests (together with wastes) account for 25% of the country’s total primary energy supply (TPES). Thus, climate impacts water, land, and the energy system, causing re-enforcing stresses that current planning methods do not typically capture.
CLEWs has been developed to understand how these systems work together to deliver the services we need to survive. The ‘delivery chains’ in those systems consist of interlinked activities. They originate from natural resources and ecosystems (such as the rain or forests described above). These are extracted, processed and transported to provide products and services (such as food and water, lighting, cooling, etc.). Those chains are shaped by economics, technology and policies — notably to ensure secure supplies.
The intricate links between energy, water, land use and climate (as well as the broader environment) systems have been well documented for a long time. However, society’s ‘delivery chains’ have traditionally been managed individually (or in related groups). Initially, interactions between many chains were largely inconsequential — their supplies were abundant and our demand was small. For practical reasons, separate management also allows for delineated responsibility and focused planning. Hence, at all governmental levels, we find authorities for energy, water, agriculture and so on, each tasked with their own sectoral mandates. Such mandates often do not include any assessments of the impacts of action in one sector on others. A notable exception is the European Commission’s Strategic Environmental Assessments . These assessments are required for certain types of public plans and programmes (for example, on land use, transport, waste and water management, energy and agriculture).
Although practical, delineation generally discourages coordination. At best, it misses synergies; at worst it creates stresses and conflict. Sectoral interdependencies are increasing. We require increasingly staggering amounts of water to provide food and energy. Water systems require (and can produce) large quantities of energy. At the same time, these sectors affect and are vulnerable to a changing climate.
A CLEWs analysis starts with a clear representation of the interactions between Climate, Land, Energy and Water systems through the following linked delivery chains from ‘resource to service’. I list a few below:
- 1) Energy delivery chains and links
Energy is required for almost all activities. It powers appliances and machinery to provide services such as lighting, cooking, transport, heating, mechanisation and more. It is extracted from renewable or depletable  energy sources – such as fossil or nuclear.
It impacts land, which is needed for wind farms and solar panels and which is scarred by activities such as mining. In the case of biofuels, cultivable land is required, reducing its availability for other crop production or ecosystem support. (Biomass is often collected for fuelwood in poor regions with growing populations, contributing to deforestation and land degradation).
After energy is extracted, it is processed into forms which are easier to use or transport. For hydropower, water is collected in reservoirs – or through-run of river power plants – and electricity generated. (Electricity can be used to power a number of services). This again requires the use of land and the altering or management of water flows. When flooded in dams, vegetation becomes trapped, and decomposing vegetation releases GHGs such as methane. Other transformations take place too. Crude oil and bio-fuel feeds (as well as coal and natural gas) can be transformed into gasoline or diesel for cars and many fuels are used directly (such as coal, gas or fuelwood). Generally, burning fuel to generate electricity (and many other energy transformations) requires large quantities of water for cooling. Or it requires water in its processes, as is the case with oil refining. And where fossil fuels are burned, GHG emissions such as CO2 are released .
Fuels are then transported and distributed and converted into the ‘energy services’ mentioned earlier. This is done by appliances or machinery. In this context we will pay special attention to the use of biofuels for transportation, water pumping for irrigation; chemical processes for fertiliser manufacture and (to cope with climate change induced temperature changes) airconditioning. In most cases GHG (and other) pollutants are emitted directly if non-renewable fuels are burned.
As you will no doubt have picked up – energy (the E in CLEWs) – is closely interwoven with the other systems. Let’s take water next.
- 2) Water delivery chains and links
Water, like energy, is required for life and needed for a number of essential services. Broadly speaking, there are three sources: sea, local precipitation and fossil. Seawater can be desalinated using energy for evaporation or reverse osmosis – this requires large quantities of energy. Local precipitation charges basins, and fossil water is often pumped (or ‘mined’). Where desalinated water or other supplies are far from demand, water is pumped or fed to users via canals or rivers, and is also stored in reservoirs and dams. The pumping can require significant quantities of energy, depending on the context. (India, for example, uses 20-30% of all its electricity just on water pumping!)
In the power sector, users include thermal power plants , which use water for cooling, as well as hydropower plant. Further significant quantities of water are required for other energy processing, such as refining or the manufacture of synthetic fuels.
Water has a particularly important role to play in agriculture. Where local precipitation is insufficient, the land is often irrigated. The availability of irrigation water together with sufficient nutrients can transform marginal lands into cultivable land. (Conversely, overfertilisation and irrigation can damage land). Irrigation can be gravity- or mechanically based, the latter using oil or electricity.
Water has a high potential for purification and recycling, however, the majority of water that is returned to the atmosphere does so via seawater evaporation. Other causes of water loss include transpiration through plant growth as well as evaporation during irrigation, distribution, storage and other uses such as power generation. With excessive evaporation, quantities of water available for direct use can be harmfully reduced.
Again, the links between the W (water) in CLEWs and the other systems are clear.
- 3) Weather and climate
It is understood that the climate is being affected by releases of greenhouse gasses from the burning of fossil fuels and chemical processes. Examples include fossil fuel power production, fertiliser production, crude oil and biomass refining, transport and land cultivation. Thus, there is a significant drive to adopt energy technologies which mitigate or reduce the quantities of CO2 emitted. Examples include renewable energy such as hydropower, wind and biofuels (such as diesel or ethanol produced from crops) as well as nuclear. Another method of reducing CO2 emissions is to capture them in forests or using carbon sequestration and storage technologies.
The climate, as it has done in the past, is changing, and this is associated with changes in weather patterns. When droughts occur, water for electricity generation is limited; demand for irrigation increases, forests become vulnerable and desertification can take place. Conversely, flooding can damage cropland, infrastructure and human settlements.
The link between Climate, the C in CLEWs, and the other systems is again transparent. And that moves us on to the ‘L’ in CLEWs, Land.
- 4) Land delivery chains and links
Very broadly speaking, land (which can be cultivated) falls into four categories: deserts, marginal, cultivable and forests or other natural vegetation such as savannahs. The quantity of cultivable land increases as forests are cleared, or marginal lands and deserts are claimed by irrigation and fertilisation.
The quantity of land available is limited. Thus, depending on the value of its produce, competition for its use can be high. Some typical land uses include livestock, crops for fuel processing, food and other products, wood fuel and infrastructures such as roads, cities, canals and dams. Where practices are poor, land can be damaged as overgrazing, over-cropping, over-fertilisation and fuelwood harvesting takes place. As vegetation changes – e.g. dense forests for crops – significant quantities of GHG emissions can also be released. Land can also be damaged through excessive silting, ground-water removal and erosion relating to agricultural activities and weather patterns.
Clearly the CLEW systems are interwoven – however, to turn this into something we can use, we need to map these systems and delivery chains.
To do so we sketch a RRSS or ‘Reference Resource to Service System’ diagram. The RRSS is useful as a tool to visualise relations which need parametrising as simplified mathematical expressions. Each line represents a ‘flow’ and each ‘box’ an activity – or group of activities - which accounts for some change to that flow. This approach is common, particularly in energy modelling activities (where the RRSS is reduced and known as a Reference Energy System (RES)).
This mapping typically starts a CLEWs analysis. The CLEWs framework can be applied to different cases by defining the flows and activities that are related – and needed for the analysis at hand. The analyst calibrates the levels of: each flow (in terms of physical quantities); activities in terms of their historical production capacities (where systems of equipment are used); costs of operation and investment; as well as mass and energy balance relations  etc. Depending on the price and affordability of the services produced, they are used by the socio-economy. As demands by the socio-economy grow, each system adapts to meet them. While meeting the demands, flows and activities may be limited by physical or financial limits. There may also be interactions between the supply chains for services and the manner in which they are provided. Taken together, the chains of the CLEW system  can be mapped and quantified. After that they are modelled. Representing all of these systems together forms an integrated model which is then used to determine scenarios of how to meet these future needs. This is done while navigating the constraints inherent in and between the systems and chains represented. (Note that the modelling can be done by taking several sector models and passing data between them. It can be done in a single spreadsheet. Often, in our case, we use a free open source model generator with a pre-set generic structure).
The level of detail, complexity, model choice and scenarios investigated are often a function of the policy question that needs to be addressed. And, in my opinion, there are many models that can be used and configured. What is critical is to co-develop the problem description, undertake clear mapping and then apply the most appropriate tools. In a nutshell I would call that the ‘CLEWs’ framework.
What kind of policy questions can be addressed by CLEWs?
There are several that are typically taken on. They include:
- Policy assessments: in the context of limited resources and constraints it is important for the policymaker to ensure that the policies adopted are as effective as possible. If multiple outcomes can be achieved by a single policy, it may be a far more effective development driver than if only a single objective or system was considered in isolation  which shows by combining a number of analyses that multiple benefits can significantly improve the development or counter-development. An aim of the CLEWs framework is to provide a more complete, multi-system policy assessment.
- Facilitating policy harmonisation and integration: there are many instances of contradictory policies throughout governments. The government of India, for example, has provided free electricity to pump irrigation water to grow crops to feed the poor. But those subsidies cause water to be extracted faster than it is replenished, dropping water tables, damaging land and straining the power grid. In time, the very resources needed for the poor will become damaged and unaffordable. An objective, integrated CLEWs tool would help individual policymakers assess the impact of their policies on the goals of other policies. Thus, different policy goals can be traded off transparently.
- Technology assessments: technology options can affect multiple resources at once. Appraising them across policy domains will be an important next step. An example is how nuclear power in the UAE could reduce GHG emissions, increase exports of domestic fuels such as oil, as there is lower domestic demand by the power sector and provide bulk electricity required for desalinating water. As with policies, an aim of the CLEWs framework is to provide a more inclusive assessment of technological options.
- Scenario development: in a sense distinct from the aims above, another goal is to take consistent scenarios development further, to understand future development opportunities. This is important to help understand, for example, whether current development really is sustainable? Are there other development scenarios to consider? And, what kinds of technology improvement might significantly change a development trajectory?
How is the CLEWs framework applied?
The CLEWs framework  has been used in a plethora of projects and in different ways; two are particularly notable. The most comprehensive process for its application has been with the United Nations Economic Commission for Europe (UNECE) in its nexus approach . The other, a similar approach, focuses on national governments . It is applied by the United Nations Division of Economic and Social Affairs (UNDESA) and the United Nations Development Program (UNDP) and recently by the United Nations Economic Commission for Africa (UNECA) .
The approach includes three main tracks: A) stakeholder driven assessment of the interlinkages of key delivery chains and identification of resulting CLEWs linkage or ‘nexus’ challenges; B) development of a quantified CLEWs model or set of CLEWs modelling tools; C) Dissemination and capacity building.
The tracks have varying levels of overlap, depending on the setting. Track A focuses on supporting a group of stakeholders and decision makers by reconstructing  CLEWs delivery chains and identifying critical interactions between them. (Thereafter unearthed key challenges are used to guide the analysis and model development). In track B the model(s) are developed in order to understand the importance of the interlinkages and the implications of inter-sector policy harmonisation. A useful starting point is a simple reconstruction of sector-specific models. The reconstruction can also be particularly helpful in building trust by showing that the results of in-house assessments can be accurately replicated without the interlinkages. After which the impact of the linkages is demonstrated by running the model(s) in a fully integrated mode with consistent scenario parameterisation. Track C focuses on capacity building. This happens during A and B (with the building of chains and their replication) but added to this (and notable in the UNDP/UNDESA approach) is training on the use of the software developed as well as the co-creation (i.e. writing together) of the policy outputs.
These are some concrete examples of applications of the CLEWs framework, spanning local and global application:
CLEWs has been applied at municipal level in a prizewinning  work in New York City  and Oskarshamn (Sweden) . Interesting findings here were that being water efficient resulted in large energy and GHG emissions savings. An example of water efficiency measure is a low-flow shower head. Using them reduces water pumping and treatment needs, both of which require energy.
At the global level, the GLUCOSE toolkit  explored climate change and mitigation strategies by examining the interactions between three modules: the energy sector, land and food production, and material production.
In World Bank Group (WBG)  work, agricultural expansion, irrigation, growing population and hydropower needs were concurrently evaluated within a modelling framework that used an ensemble of models. The objective was to understand the risk posed by climate change to the multi-billion Euro future of planned African hydropower investments. That work was undertaken by the WBG, Stockholm Environment Institute (SEI), the RAND Corporation, Massachusetts Institute of Technology (MIT) and the Royals Institute of Technology (KTH).
Integrated national CLEWs models are used (or to be used) for national planning efforts with support from UNDESA and UNDP in Bolivia, Costa Rica, Ghana, Mexico, Kyrgyz Republic, Paraguay, Mongolia, Vietnam, Uganda and elsewhere. Similar models have been developed with the UNECA for Sierra Leone and Ethiopia. In each case, detailed representation of resources and interactions were made and then optimised in order to inform policy development. Key findings include the identification of ‘hotspots’ where future conflict might arise due to external constraints (such as, for example, climate change) or siloed policy making (for example biofuel production reducing domestic food production security).
The UNECE trans-boundary river basin nexus approach has been implemented on four river basins and is also currently being implemented on a groundwater aquifer in North Africa. An example is the Sava River Basin, which extends over 97,700 km2, is about 3000 km long and is shared between five countries. The study concluded that the development of hydropower should be done sustainably and be developed for power generation as well as so called ‘balancing’. This allows the integration of other renewable energies such as solar and wind. Given the traction, a deep dive study followed into the Drina River Basin (DRB), which is one of the main tributaries of the Sava River. This DRB study underlined the importance of coordinating the operation of the hydropower plants. By coordinating their scheduling, dams could be used as flood control during risky high-rainfall times, with increasing revenue to be had from regional power sales  .
In summary, the challenges are real, and the CLEWs toolkit is being developed to help address them. There is a growing body of analysis. A regular summer school  is open for academics (to support them setting up graduate programs) as well as government analysts. A key model-generator and CLEWs process is free and open source with a growing community. Please do join in and contribute!
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 IAEA, I.A.E.A., 2009. Annex VI: Seeking Sustainable Climate, Land, Energy and Water Strategies (CLEWS), in: Nuclear Technology Review 2009. IAEA, Vienna.
 Howells, M., Hermann, S., Welsch, M., Bazilian, M., Segerström, R., Alfstad, T., Gielen, D., Rogner, H., Fischer, G., Velthuizen, H. van, Wiberg, D., Young, C., Roehrl, R.A., Mueller, A., Steduto, P., Ramma, I., 2013. Integrated analysis of climate change, land-use, energy and water strategies. Nat. Clim. Change 3, 621–626.
 Meadows, D.H., Meadows, D.H., Randers, J., Behrens III, W.W., 1972. The limits to growth: a report to the club of Rome (1972).
 Howells, M., Rogner, H.-H., 2014. Assessing integrated systems. Nat. Clim. Change 4, 246.
 Note that where a renewable resource such as wood-fuel is depleted faster than it is regrown, it is also in a sense depletable – especially where land is damaged due to overuse.
 Note on CCS.
 The US Geological Survey (USGS 2004) estimates that over 50% of freshwater withdrawals were for the cooling of thermal power plant (with the majority of that water returned after use).
 Such as, for example, thermodynamic efficiency, which relates energy flows out of an activity to energy flows coming into it
 Howells, M., Laitner, J., 2003. A Technical Framework for Industrial Greenhouse Gas Mitigation in Developing Countries. Proc. Am.Counc. Energy-Effic. Econ. 2003 Summer Study Ind. Energy Effic.
 Climate, Land (Food), Energy, Water Strategies – CLEWs Framework, n.d.
 This was co-created with KTH-dESA to understand complexities that arise between countries as a result of shared rivers and basins.de Strasser, L., Lipponen, A., Howells, M., Stec, S., Bréthaut, C., de Strasser, L., Lipponen, A., Howells, M., Stec, S., Bréthaut, C., 2016.A Methodology to Assess the Water Energy Food Ecosystems Nexus in Transboundary River Basins. Water 8, 59.
 UN Modelling Tools, n.d.
 Climate, Land, Energy and Water Strategies (CLEWs) to Support the Implementation of Nationally Determined Contributions (NDCs) to Climate Action
 The re-construction helps ensure that the all parties are ‘bought in’ to the reality of the linkages – and missing or additional phenomena are properly captured
 Engström, R.E., Howells, M., Destouni, G., Bhatt, V., Bazilian, M., Rogner, H.-H., 2017. Connecting the resource nexus to basic urban service provision – with a focus on water-energy interactions in New York City. Sustain. Cities Soc. 31, 83–94.
 Urban CLEWs work featured at the first Urban Transitions Global Summit, n.d.
 Glucose is the Global User-friendly CLEWs model. See: Global CLEWS, n.d.
 Cervigni, R., Liden, R., Neumann, J.E., Strzepek, K.M., 2015. Enhancing the climate resilience of Africa’s infrastructure: the power and water sectors. The World Bank