Spatial Multi-Objective Optimisation of Catchment-Scale Nature-based Solutions Strategies

The UK has ambitions to face a host of challenges exacerbated by a changing climate. This includes managing growing drought and flood risk, abating carbon emissions to meet legal obligations, and tackling its biodiversity decline. In the past two decades, research and uptake of Nature-based Solutions (NbS) have intensified. These interventions are designed to enhance and restore the capacity of landscape features to provide multiple co-benefits, such as slowing storm runoff, intercepting pollutants, and creating habitat. There is a recognition that incorporating local knowledge and empowering community leadership is crucial to the delivery and long-term success of these schemes. This co-design principle should be tied into new projects to achieve transformative adaptation to climate change, but it also introduces more objectives and preferences, which complicates the challenge of identifying appropriate NbS designs.

Whilst there is an ever-growing evidence base, much guidance remains qualitative and further upscaling of schemes from the plot scale to the catchment scale is hindered by funding and uncertainty in performance. A key area of uncertainty is the interplay between different NbS interventions and whether they may have positive or negative feedback on each other. This has motivated further research into modelling and systematically exploring trade-offs across a large design space of different intervention options, and evaluating their effectiveness against multiple stakeholder objectives.

Even for a small catchment, evaluating all possible combinations is intractable, so the model is incorporated into a multi-objective optimisation framework for decision support. This research uses a genetic algorithm to explore intervention parameters and placement, and then simulates the performance for different intervention arrangements with a physically-based hydrological model to capture vertical as well as lateral surface flows. This seeks to form the basis for a catchment-scale planning tool which allows catchment stakeholders to interrogate the details between alternative strategies and evaluate if high-level needs are being met. A case study in the Wansbeck catchment will be presented, quantifying trade-offs between attenuating peak flow, habitat creation, carbon sequestration, and the cost of implementation.