Achieving Net Zero: Understanding the Potential Hydrological Impacts of Changing Climate and Land Cover in the UK

Climate change is set to increase the magnitude and frequency of fluvial flooding in many regions across the world, making it a growing risk to billions of people living near rivers. Changing drainage basin land cover and hydrological connectivity further complicates how these streamflow extremes may evolve. Engineered solutions to mitigate the risk of future high magnitude runoff events to populations may no longer be suitable to meet these needs due to these changes in climate and land cover.

By reducing the level of global CO₂ emissions, climate models predict that we can reduce the severity of climate change impacts upon communities. To achieve the goals set by the Paris Agreement to limit global warming, the UK has proposed a range of policies to reach net zero carbon emissions by 2050. One of these proposals includes widespread afforestation across the UK. Where to plant this woodland and the scale of impact it may have on the future hydrological cycle is currently unquantified. This project seeks to investigate three aspects of how future streamflow trends my change due to afforestation in respect to: woodland location, differing afforestation rates, and the hydrological responsiveness of drainage basins to land cover changes.

Physics-based models provide the possibility to explore the relative importance of climate and land cover on future streamflow trends, both together and separately. The Joint UK Land Environment Simulator (JULES) is used to explore catchment responses across the UK to potential extreme weather events with theoretical changes in land cover at a 1 km resolution. Theoretical land cover scenarios of afforestation were generated according to proximity to existing land cover, drainage basin structure and proposed afforestation sites. An extreme precipitation scenario (the winter of 2013/14) is explored to comprehend streamflow regime response to high magnitude precipitation events caused by changing climate and land cover using the Weather@home perturbed model ensembles and CHESS-met datasets. This approach provides the potential to explore how increasing afforestation could change the discharge dynamics of landscapes across the UK and thus its potential benefits and drawbacks to flood risk management. 

Results show how potential land cover changes will impact streamflow response to storms across the UK. These results help provide a clearer picture of how changing landscape systems impact river response to external climatic forcing and may provide evidence for management and policy strategies tailored to the requirements of individual drainage basins to reduce the risk of flooding upon downstream populations.