Sensitivity of Estuaries to Climate Hazards (SEARCH)

Twenty million people living near UK estuaries are at risk from compound flooding hazards. Recent near-miss flooding in UK catchments and estuaries (Dec-2013, Jan-2017) could have been much worse with subtle changes in surge-precipitation timings, although still caused extensive damage costing £500M. Estuary communities are especially vulnerable to future changes in flood risk; via sea-level rise combined with increases in storm surge heights - and changing precipitation and temperature patterns that will have profound impacts on fluvial behaviour. The SEARCH project will address this important issue directly by developing a new method to evaluate climate flooding hazards in UK estuaries. For the first time this method will be fit-for-purpose for compound flooding events across different spatial and temporal scales, and for different catchment and estuary types. This method will accurately resolve all hydrological and marine processes and their joint-probabilities. It will evaluate how climate predictions from UKCP18 downscale to flooding impact; hence, providing unique and crucial inundation and likelihood data for the EA, NRW and SEPA to identify the most vulnerable communities to compound flooding and to manage their resources effectively during incidence response. Importantly, we will show how compound flooding occurs and how sensitive different systems are to the different drivers of climate change.

Global sea levels are expected to rise up to 1 m this century and for some regions like the UK, precipitation and temperature distributions are likely to change, with extreme events such as storms, heatwaves and droughts becoming more intense and seasonal with altered timings. Changes in the intensity of flood drivers are expected to affect the hazard and risk. However, we hypothesise that changes in their timings relative to one another will also be vital for flood risk. For example, the timings of fluvial events will likely change due to changes in precipitation and temperature affecting soil moisture and groundwater flow. As a proof of concept in the NERC project CHEST, the investigators established the sensitivity of estuaries to tide-surge-fluvial events acting in combination, isolating distinct zones within estuaries of increased risk depending on catchment size relative to the estuary, estuary shape and the timing of surge and fluvial events relative to each other. Changes in flood risk due to climate change will therefore be site specific, with the relative roles of hazard drivers varying spatially. Long-term changes in extreme events are often unforeseeable because our understanding of the integrated system is incomplete. Considering the high socio-economic and environmental value of estuaries, the complexity of compound hazards, the projected changes in drivers, and unregulated landuse management, it is timely to develop new strategies for mitigating against compound flooding and to develop improved risk assessment tools for flood protection.

Working with the UK regulators of flooding, SEARCH will use past and new observations with UKCP18 projections of precipitation, temperature, fluvial flows, storm surge and sea level applied to a fast, tested and open-source hydrodynamic-groundwater model to simulate flooding hazards. We will simulate 14 systems that cover the range of locations and estuaries within the UK. Our results are urgently needed, as probabilistic methods of determining flood risk are obsolete because they do not capture the non-linear dynamics and do not include future changes. This two year project brings together world-leading researchers in catchment-to-coast environmental science (with PDRAs at Bangor and Hull Universities) to tackle this computationally challenging and under-investigated issue. This team have worked together successfully, with the involvement and support of key policy and industrial partners, establishing a new paradigm in flood risk and accumulating a vast amount of data.