Hydrology

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

Flood risk is expected to increase across Ireland while increases in the frequency of drought conditions is also expected.

The analysis of river flows is complex and subject to large variability and as a result it is difficult to extract signals of climate change.
An analysis of river flows over a period of more than 50 years of data (1972-2017) indicates an increase in river flows across most of the country. An analysis of a shorter period from 1992 suggests an increase in drought conditions, particularly in the east of the country.

Projected changes in temperature and precipitation will affect hydrological response. Due to the uncertainties associated with projected changes in precipitation, projected changes in hydrological response remain subject to a high level of uncertainty.
The response of individual catchments will be determined by individual catchment characteristics (e.g. groundwater versus surface water dominated catchments). For example, summer reductions for groundwater dominated catchments are not as severe as those projected for surface water dominated catchments.
Using impact models (conceptual runoff models), a robust signal of increasing seasonality in hydrological regimes is evident with increases in winter and spring streamflow likely and a decrease in summer. A 20% increase in the amount of water flowing through rivers are expected for the majority of catchment by mid-late century while for summer decreases of over 40% (those with little groundwater storage in particular) have been simulated for the end of the century.
Projected increases in winter flows coupled with likely increases in extreme precipitation events are likely to lead to an increased flood risk. However, catchment response time will be critical in determining the changing nature of extremes and those catchment with fast response times are likely to be most at risk.