The Environment Agency has published the outputs of a project exploring new approaches for examining the impact of droughts on English catchments and water supply systems, with the aim of increasing preparedness and understanding the range of interventions to take in different droughts.

Photo credit: Tom Fisk

Background

This project explored new approaches for examining the impact of droughts on English catchments and water supply systems, with the aim of increasing preparedness and understanding the range of interventions to take in different droughts. Water is essential for the economy, the environment and water supply. Effective drought planning and management reduces the disruption and pressures caused by a temporary reduction in water availability.

Approach

Existing approaches to water resources management and planning tend to concentrate on performance of systems during past droughts such as those experienced in 1933-34 or 1975-76. This is a useful starting point, but the climate is changing, water supply systems and catchments are always in flux, and future droughts will be different from those of the past.

This project is a pilot application of an alternative approach to understanding drought risks, exploring the identification of system vulnerabilities and resilience to low flows in a method known as scenario-neutral stress testing. “Scenario-neutral” means that a wide but plausible range of possible future climate conditions is examined: this contrasts with conventional climate projections to give a much richer understanding of the catchment’s response to droughts of different duration and magnitude. “Stress testing” extends this idea to find the conditions under which different parts of the system fail, allowing decision-makers to test interventions that could lead to better outcomes.

The approach was trialled in two contrasting English catchments: the Warwickshire Avon and the Bure in Norfolk, looking at metrics including the frequency and duration of low river flows and the availability of water for irrigation. Metrics were chosen to help decision-makers understand the impact of different management choices.

Results

The project showed that the stress testing approach was able to consider catchment resilience from different perspectives. This should provide a basis for cross-sectoral discussions and agreement on interventions. Setting out the possible impacts and responses to droughts before an event allows more time for discussion and analysis, and should provide confidence that subsequent drought decisions are evidence-based. However, it remains difficult to predict drought consequences and this can limit the realism of the stress tests. Understanding and balancing the multiple different stressors through hypothetical droughts can also be difficult for decision-makers, and scientists and analysts must work to find ways to explain and visualise the complexities and interactions between different components of the catchment system.  This type of modelling also takes time because every new component multiplies the number of model runs needed.

Conclusions

This pilot study shows the benefits of a stress testing approach for whole-catchment planning for future droughts, and for testing the effectiveness of possible interventions under different drought conditions. Further work is needed to translate hydrological metrics to impacts on ecosystems and crop yields. This approach could complement existing approaches based on historical droughts, offering a richer understanding of drought response and actions.