Increasing seasonality in hydrological regimes is expected with decreased summer and increased winter flows likely.

Summary of Change

Flood risk will increase due to a combination of higher river flows and increases in extreme precipitation events. This is referred to as “combination events” and are likely to play a greater role in climatic events in the future. One example of this is high tides coupled with fluvial and pluvial events especially in the lower reaches of the Lee and Lower Harbour. This would have specific effects in settlements such Cork City and its environs.

Groundwater flooding, which is the emergence of groundwater at the surface away from river channels and watercourses, under conditions where the ‘normal’ ranges of groundwater level and flow are exceeded. This is likely to be exacerbated in areas along the estuary where ground water is subject to tidal influence.

Climate Risks Identified

Pluvial, or surface-water flooding, which results from rainfall-generated overland flow, which may occur during or immediately after intense rainfall events and before the runoff enters a watercourse or drainage system. This was evident in Douglas in 2012 and Freemount in August 1997.

Fluvial or river flooding, which occurs when excessive rainfall causes a river to exceed its capacity. This was evident in Cork City environs with the River Lee exceeding capacity in 2000 and 2014 and elsewhere in the County, the River Bandon in 2015 and River Blackwater in 2008.

Observed Throughout Ireland, annual average rainfall amounts have increased, by roughly 5 %, relative to the 1961-1990 baseline period with this increase observed across all seasons. However, spatially, rainfall intensity and amounts vary with no clear direction of change yet apparent [34]. Severe rainfall events have had significant local effects in County Cork, such as 55mm 1-day record measured in Baile Bhuirne in November 2009 and 58mm 1-day record measured in Bandon in June 2012.

Projected Precipitation projections are less certain than those for temperature and when examined on an individual basis, climate models indicate differing temporal and spatial patterns. However, the projections provide a robust indication of increased seasonality with wetter winters and drier summers likely [35] [36] [37] [38]. For spatial variations, there is a level of disagreement between individual climate models and as a result spatial details are not deemed reliable [38]. As global temperatures increase, the hydrological cycle is expected to become more intense and will result in more extreme precipitation events [4]. For Ireland, projected changes in the frequency of very wet days (>20mm of precipitation) indicate a marked increase for winter (approximately 20%) [38].