Impacts of climate change on groundwater flooding and ecohydrology in lowland karst

Abstract. Lowland karst aquifers can generate unique wetland habitats which are caused by groundwater fluctuations that result in extensive groundwater-surface water interactions (i.e. flooding). However, the complex hydrogeological attributes of these systems often present difficulty in predicting how they will respond to changing climatological conditions. Extremely fast aquifer recharge processes and flow through well-connected conduit networks in such karst systems make them very susceptible to surcharge conditions – i.e. groundwater-surface water interaction (flooding) – and therefore vulnerable to changes in the sequence and intensity of precipitation patterns. This study investigates the predicted impacts of climate change on a lowland karst catchment by employing a semi-distributed karst model populated with output from high-resolution regional climate models for Ireland. The lowland karst catchment is located on the west coast of Ireland and is characterised by a well-developed karstified limestone aquifer which discharges to the sea via intertidal and submarine springs. Annual above ground flooding associated with this complex karst system has led to the development of unique wetland habitats in the form of ephemeral lakes known as turloughs, however extreme flooding of these features causes widespread damage and disruption in the catchment. This analysis has shown that mean, 95th and 99th percentile flood levels are expected to increase by significant proportions for all future emission scenarios. The frequency of events currently considered to be extreme is predicted to increase, indicating that more significant groundwater flooding events seem likely to become far more common. The seasonality of annual flooding is also predicted to shift later in the flooding season which could have far reaching consequences in terms of ecology and land use in the catchment. The impacts of increasing mean sea levels were also investigated, however it was found that anticipated rises had very little impact on groundwater flooding due to the marginal impact on ebb tide outflow volumes. Overall, this study highlights the vulnerability of lowland karst systems to future changing climate conditions mainly due to the extremely fast recharge which can occur in such systems. The study presents a novel and highly effective methodology for quantifying the potential impact of climate change in lowland karst systems by coupling karst hydrogeological models with the output from high resolution climate simulations.