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

Abstract

Abstract. Lowland karst aquifers can generate unique wetland ecosystems 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, linked to extremely fast aquifer recharge processes and flow through well-connected conduit networks, often present difficulty in predicting how they will respond to changing climatological conditions. This study investigates the predicted impacts of climate change on a lowland karst catchment by using a semi-distributed pipe network model of the karst aquifer populated with output from the high spatial resolution (4 km) Consortium for Small-scale Modelling Climate Lokalmodell (COSMO-CLM) regional climate model simulations for Ireland. An ensemble of projections for the future Irish climate were generated by downscaling from five different global climate models (GCMs), each based on four Representative Concentration Pathways (RCPs; RCP2.6, RCP4.5, RCP6.0 and RCP8.5) to account for the uncertainty in the estimation of future global emissions of greenhouse gases. The one-dimensional hydraulic/hydrologic karst model incorporates urban drainage software to simulate open channel and pressurised flow within the conduits, with flooding on the land surface represented by storage nodes with the same stage volume properties of the physical turlough basins. The lowland karst limestone catchment is located on the west coast of Ireland and is characterised by a well-developed conduit-dominated karst 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 ecosystems 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 depth and duration of flooding is of extreme importance, both from an ecological perspective in terms of wetland species distribution and for extreme flooding in terms of the disruption to homes, transport links and agricultural land inundated by flood waters. The seasonality of annual flooding is also predicted to shift later in the flooding season, which could have consequences in terms of ecology and land use in the catchment. The investigation of increasing mean sea levels, however, showed that anticipated rises would have very little impact on groundwater flooding due to the marginal impact on ebb tide outflow volumes. Overall, this study highlights the relative 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 studying the impact of climate change in lowland karst systems by coupling karst hydrogeological models with the output from high-resolution climate simulations.

Review of the Ecosystem Services of Temperate Wetlands and Their Valuation Tools

“…Recent modelling of a network of 15 turloughs in this area linked to a proposed flood alleviation scheme by Morrissey et al (2020) [70], who found that should the optimal flood alleviation schemes be implemented, there would be an impact on turlough ecosystems, though the further elevated areas might actually benefit from the flooding reduction that killed trees in past flooding events, therefore underscoring the complexity of flooding in such areas. In addition, further modelling [71], has shown that climate change is expected to exacerbate flood risk through increased winter rainfall.…”

Deciphering the water balance of poljes: example of Planinsko Polje (Slovenia)

“…Therefore, it is crucial to continue improving our understanding on how poljes are functioning in order to provide long term adaptation and resilience to what might happen within the next decades. Such response should include an appropriate flood forecast that would be used to implement worst-case scenarios and a land-use management policy specific to these regions (Morrissey et al, 2021;Ravbar et al, 2021).…”

Assessment of Climate Change Impact on the Annual Maximum Flood in an Urban River in Dublin, Ireland

“…Uncertainties associated with climate change are linked to changing dynamics of precipitation which range from variations in changes in the amount, intensity, and frequency of precipitation [24]. Hydroclimatic approaches, therefore, need to be used to study catchment runoff responses due to varying precipitation patterns in order to understand the magnitude, intensity, and frequency of extreme flood events [25,26].…”