General Introduction

The CLEWs-EU model is developed within the OSeMOSYS (Open-Source Energy Systems Model) modelling framework. OSeMOSYS is a long-term cost-optimisation energy system model (Howells et al., 2011). OSeMOSYS has been used in numerous studies with a focus ranging from a global, regional and national scale (Gardumi et al., 2018; Peña Balderrama et al., 2018; Sridharan et al., 2019). It is a bottom-up technoeconomic model that is demand-driven, meaning the exogenously defined demand must be met, regardless of the cost. The choice of technologies and energy mix is based on the adopted technoeconomic assumptions (e.g., fuel costs, technology costs, resource availability, emission limits). The model’s objective function is the minimisation of the total discounted system cost over the entire modelling horizon. The CLEWs-EU model builds on the structure of the Global CLEWs model (Beltramo et al., 2021), with several enhancements being implemented. Two separate main modules, namely i) energy; and ii) land with water, have been developed with several interlinkages between them. Greenhouse gas emissions are tracked across the modules, which in turn are affected by climate assumptions. For instance, temperature affects water demand in agriculture, while precipitation affects hydropower output and crop yield. In the energy module, a large set of technologies are used to represent primary energy supply, electricity generation, transport, buildings and industry. In addition, the suite of technologies has been expanded to include a broader range of decarbonisation options. For instance, use of hydrogen – either imported or locally produced – is an option that was not available in the Global CLEWs but is included in the CLEWs-EU model. In the land module, the available land resources for crop production, livestock grazing and other uses are being defined at the EU level and for each country individually, assessing the impact of policies and climate on water and energy. Furthermore, whereas the Global CLEWs model employs a simple accounting approach to calculate water requirements throughout the system, the CLEWs-EU model has a more explicit representation of water demand and supply. More information on the structure of each module is provided in the subsequent sections.

Two levels of geographical resolution are adopted:

  1. Aggregated regional model, in which the EU is represented as a single node, serving as an engagement model, upon which capacity development activities on EU climate policy can be developed due to its simplified structure and low computational effort. Coupled with the adoption of a user-friendly interface, enabling direct changes in model parameters and visualisation of the system dynamics, it allows the exploration of climate change mitigation pathways by a broad range of stakeholders. This ensures consistency with the philosophy behind the initial development of the Global CLEWs model.

  2. Disaggregated model, in which the level of spatial resolution has been extended to the national level, to be used for the more extensive analyses foreseen within DIAMOND (e.g., through soft links in WP4). Unlike the high-level focus of the aggregated model, the disaggregated model provides more focused insights and can be used to support the development of national policies within the context of mutual EU obligations/targets. As expected, the development of the disaggregated model has entailed a larger volume of input data compared to the aggregated model. For the land and water module, mostly country-specific data has been incorporated in this version. However, in certain cases, like groundwater usage shares, livestock numbers, EU-27 averages have been used for countries which do not report explicit numbers. These assumptions can be revisited in future model developments, and country-specific data will be updated wherever possible.